September 30, 2009 Educational Radio Net, PSRG 71st Session
The digital computer is ubiquitous. These computers are everywhere. Kids have their own and, more than likely, so do the grandparents. Most users are very proficient with the keyboard and blaze through the games, documents, spreadsheets, and whatnot without even a thought of what is going on inside that mysterious box called a computer. I am willing to bet that not one in ten users can define a "bit" and I will further wager that not one in 100 users has a good grasp of computer arithmetic or how the rational coding of bits makes their computer tick.
My task tonight is to lead you down that magic path and explore the idea of the "bit" and how it can be used to represent numbers or events. We will then extend the bit notion into nibbles, bytes, and words. Some of the net participants tonight are likely to be expert in this bit world so, if you quality, think of ways to help me clarify the notion when I break for questions or comments.
Let’s start with our very familiar decimal number system and dissect it in a way that I bet few of you have done. We will concern ourselves only with integers so no fractions are allowed in our discussion. Integers are the numbers 1, 2, 3, etc. that have no fractional part. You may call them whole numbers if you please. Integers can be precisely defined but that would muddy the water a bit so we will dispense with such formalism in favor of simplicity. We will start with the integers 1 through 9 and include the notion of nothingness as in zero.
When we think of the decimal integers we must consider the ordering. For example after nothingness as in zero we think of 1, then 2, then 3, etc. in order through 9. Our standard notion of 9 is that it is ‘bigger’ than 8 and 8 is ‘bigger’ than 7 or 6 or 5, etc. In the following discussion throw ordering out the door. We will not be interested in ordering. In fact we will not even use numbers rather we will choose a collection of identical marbles and call then symbols. So, zero (or nothingness) plus 1 through 9 equals 10 symbols which we represent with 10 marbles.
Unfortunately this forum of ours does not include a chalkboard so we must create a virtual chalkboard in your mind. If it helps then close your eyes and imagine the following: in your mind arrange 6 boxes in a 2 row x 3 column array. Each of the boxes in the top row has 10 identically sized marbles and the row of lower boxes have ‘nothing’ or zero marbles. Just so we do not get marbles in the wrong boxes lets choose black marbles for the rightmost box, brown marbles for the center box, and red marbles for the leftmost box.
Ok, lets do something useful with this scheme. Assume that you are sitting on the back porch looking toward the Cascades and you want to tally lightning strikes. When the first strike occurs you move a black marble from the top right box into the box below. At the next strike you repeat the previous operation and move another black marble from the top right box into the box below. As you notice more and more lightning strikes you move black marbles until you have no more black marbles in the top right box. At this point you have used all of your marbles, so to speak, and you indicate this fact by moving a brown marble into the middle box below then move all of the ‘used’ black marbles back into the top right storage box.
The lightning strikes continue and you move black marbles, one by one, into the lower box until you again run out of marbles. At this point you move a brown marble from the top box into the box below and reload the top box with the black marbles. Eventually you will run out of brown marbles in the top center box so you will move a red marble from the top left box to the box below and reload the top boxes with appropriate black and brown marbles.
The point of this mental exercise is to illustrate that you can tally objects with symbols and that every time you exhaust, or cycle through, your symbol set you just indicate this fact by incrementing the symbol set to the left. You can choose as many symbols as you please. In this example, based on the decimal system with 10 symbols, each box to the left is weighted or "heavier" by 10 with respect to its neighbor to the right. As a result, this 10 symbol scheme goes units, tens, hundreds, thousands, etc. so is very convenient for us mortals. Once you know the weighting you can easily figure out how many lightning strikes you tallied by counting the symbols in each weighted box.
In the interest of time let me assert that you can use a set of 12, or 9 or 8 or 7, etc. symbols and the scheme holds true. Now lets examine the case where we have reduced the set to two symbols. Thinking for a moment you realize that "bi" means two as in binary star or binocular. Could the binary number system be as simple as accounting for just two symbols? The answer is, of course, yes. The beauty of using two symbols in numerical computing is that transistors are very good switches and can be used to represent the two binary states perfectly. A SPST switch normally has two states such that it is either on or off. Open or closed. It is a trivial exercise to arrange a circuit with a mechanical switch such that one switch position results in +5 volts and the other position results in zero volts. The symbols associated with a two state switch are zero and one as in 0 or 1.
Now, in a fashion similar to the decimal box exercise above let’s arrange 8 binary boxes side by side in a row. We know that the state of each of these "binary" boxes can be represented by either a 0 or a 1. Assume that the rightmost box is the, so called, least significant box and that all boxes are in the 0 state. Visually the boxes look like 0000 0000. Now, bump the rightmost box to the 1 state and the visual presentation goes to 0000 0001. Well, the rightmost box has now used all of its symbols so to tally the next event it must return to 0 and the box to the left is bumped from 0 to 1 as in 0000 0010. If you carry this process forward you will eventually achieve 1111 1111 and the next event will change all positions back to 0000 0000. The weighting goes by 2 rather than 10 as in the decimal case so each position to the right is ½ of its left neighbor or each position is twice its neighbor to the right. The sequence is 256, 128, 64, 32, 16, 8, 4, 2, 1. These 8 boxes represent a byte and each of the positions is a binary digit or bit. Two sets of 8 boxes as in 2 bytes or 16 bits represents a binary "word". Half a byte as in 4 bits is a nibble (or nybble to some).
The total number of distinct combinations of 8 bits from 0000 0000 to 1111 1111 is 256 and goes as 2^8. A binary word composed of 16 bits can assume 2^16 or 65,536 distinct combinations. Recall that we are limiting ourselves to positive integers so we are only able to handle numbers up to 65,536. There are schemes to handle signed integers such as 2’s complement arithmetic and to be completely flexible there are floating point schemes which look a lot like scientific notation.
Four binary bits can assume 16 distinct combinations and is the basis of the hexadecimal number system which has symbols 0 through 9 plus A, B, C, D, E, and F. Four binary bits are also used for BCD or binary coded decimal notation by throwing away the six unused states.
How would one go about doing math operations on a computer? Well, microprocessors are very good and quick at adding or subtracting but clumsy when multiplying or dividing. Early microprocessors required many operations or, so called, clock cycles to produce numerical products and it was common to have a math coprocessor standing by to do the heavy lifting. For example, if you want to multiply a number by 10 in the decimal system you just move the decimal point one position to the right. In the binary system you would shift left (x2), shift left again (x4), shift left again (x8), and then add twice to achieve the 10x product. Clearly, there is a lot of time consuming overhead doing math in this fashion. Contemporary microprocessors are constructed with onboard and dedicated numerical processors with slick routines and which unburden the main unit.
If you look at the schematic of any computer one thing will pop out immediately. There are lots of parallel paths connecting the various semiconductor packages. These parallel wire structures are called busses and might be as wide as 16 bits… possibly more… for memory addressing as an example. There is likely a data buss as well. One line generally represents the buss with breakouts at the ends. Each wire handles one bit of data on the data buss.
In summary, the intent of this presentation is to show that symbols can be used to tally events and that recycling symbols will work in any number system. Starting with the familiar decimal number system and showing that symbol manipulation leads handily to the very simple two state, or binary, number system. A bit is a two state binary digit, a nibble is four associated bits, a byte is 2 associated nibbles or 8 bits, and a word is 2 bytes of 16 associated bits. Modern computers are said to have 32 bit words and, in some cases, 64 bit words.
This concludes the set up discussion for bits, nibbles, bytes, and words. Are there any questions or comments with regard to tonight's discussion topic?
This is N7KC for the Wednesday night Educational Radio Net
Wednesday, September 30, 2009
Wednesday, September 23, 2009
Phase Shift Keying, Bob, No. 70
Tonight I am continuing with my series on Spread Spectrum Radio. I am going to discuss Phase Shift Keying (PSK), which is the form of modulation used by Direct Sequence Spread Spectrum (DSSS) Radio.
Spread Spectrum Radio Review
Let's have a short review of spread spectrum. The two main kinds in use in ham radio are Frequency Hopping and Direct Sequence. Frequency hopping is relatively easy to understand. Your carrier, rather than being on a fixed frequency, jumps from one frequency to another. As long as the equipment receiving makes the same jumps you will be able to transmit the signal and prevent interference on any one frequency from causing a problem. This can be used for analog or digital transmission but is most commonly used for digital. Note that you must have a pattern of frequency changes that is known to both parties in order to allow the receiver to follow the transmission.
In the other method, Direct Sequence, you only transmit digital information. In fact the name "Direct Sequence" comes from the 11 digit sequence of ones and zeros that is used to modulate the carrier. If your data bit is a zero then you send the sequence normally. If your data bit is a one then you send a one where the sequence has a zero and send a zero where the sequence has a one. For example 101 would turn into 010. I mentioned that the carrier is modulated by this sequence but I didn't say how. It is modulated using Phase Shift Keying.
Phase Shift Keying (PSK)
So, what exactly is phase shift keying? It is a way of changing the phase of a carrier to transmit a digital signal. In essence what you are doing with PSK is phase hopping. In the simplest example called Binary Phase Shift Keying (BPSK) you hop 180 degrees out of phase to transmit a certain piece of digital data. So the signal is either in it's "normal" phase or in it's 180 degree out phase which is to say, inverted. Note that the frequency of the carrier isn't changed but when you change the phase and modulate the carrier you create side-band emissions. The faster you modulate the signal, the wider the side-bands. In addition to BPSK there is Quadrature PSK (QPSK) where the phase can be one of four values, 0, 90, 180 or -90. There is also 8PSK using 8 phase angles and so on. The general term is Multiple Phase Shift Keying (MPSK).
Differential Phase Shift Keying (DPSK)
Basic BPSK has the signal at normal 0 phase to represent a digital zero and at 180 degrees out to represent a digital 1. A commonly used variation on this is called Differential Binary Phase Shift Keying (DBPSK) and instead of a 1 being 180 degrees out of phase, a 1 always changes the phase while a 0 always keeps the phase the same. This way you don't need a reference signal to know which is 0 degrees and which is 180 degrees.
PSK-31
If you want a very narrow signal you are limited to a slow digital transfer rate. This is the case with PSK-31. The 31 comes from the 31.25 bits per second data rate which generates 31.25Hz sidebands. This is pretty much the opposite of spread spectrum. The whole point of PSK-31 was to use such a small slice of the band that you could actually fit many PSK-31 channels in the space of a typical SSB voice bandwidth.
PSK for Spread Spectrum
With spread spectrum you want a very wide bandwidth; by definition, one that is much wider than necessary to convey the information. By encoding each bit of data with the 11 bit sequence used in DSSS you now modulate the signal 11 times for each bit transferred. So for a 1 Mbit/sec transmission, you modulate at 11 MHz. This achieves the spread spectrum you are looking for. This modulation is encoded using DBPSK and a suppressed carrier.
Spread Spectrum Radio Review
Let's have a short review of spread spectrum. The two main kinds in use in ham radio are Frequency Hopping and Direct Sequence. Frequency hopping is relatively easy to understand. Your carrier, rather than being on a fixed frequency, jumps from one frequency to another. As long as the equipment receiving makes the same jumps you will be able to transmit the signal and prevent interference on any one frequency from causing a problem. This can be used for analog or digital transmission but is most commonly used for digital. Note that you must have a pattern of frequency changes that is known to both parties in order to allow the receiver to follow the transmission.
In the other method, Direct Sequence, you only transmit digital information. In fact the name "Direct Sequence" comes from the 11 digit sequence of ones and zeros that is used to modulate the carrier. If your data bit is a zero then you send the sequence normally. If your data bit is a one then you send a one where the sequence has a zero and send a zero where the sequence has a one. For example 101 would turn into 010. I mentioned that the carrier is modulated by this sequence but I didn't say how. It is modulated using Phase Shift Keying.
Phase Shift Keying (PSK)
So, what exactly is phase shift keying? It is a way of changing the phase of a carrier to transmit a digital signal. In essence what you are doing with PSK is phase hopping. In the simplest example called Binary Phase Shift Keying (BPSK) you hop 180 degrees out of phase to transmit a certain piece of digital data. So the signal is either in it's "normal" phase or in it's 180 degree out phase which is to say, inverted. Note that the frequency of the carrier isn't changed but when you change the phase and modulate the carrier you create side-band emissions. The faster you modulate the signal, the wider the side-bands. In addition to BPSK there is Quadrature PSK (QPSK) where the phase can be one of four values, 0, 90, 180 or -90. There is also 8PSK using 8 phase angles and so on. The general term is Multiple Phase Shift Keying (MPSK).
Differential Phase Shift Keying (DPSK)
Basic BPSK has the signal at normal 0 phase to represent a digital zero and at 180 degrees out to represent a digital 1. A commonly used variation on this is called Differential Binary Phase Shift Keying (DBPSK) and instead of a 1 being 180 degrees out of phase, a 1 always changes the phase while a 0 always keeps the phase the same. This way you don't need a reference signal to know which is 0 degrees and which is 180 degrees.
PSK-31
If you want a very narrow signal you are limited to a slow digital transfer rate. This is the case with PSK-31. The 31 comes from the 31.25 bits per second data rate which generates 31.25Hz sidebands. This is pretty much the opposite of spread spectrum. The whole point of PSK-31 was to use such a small slice of the band that you could actually fit many PSK-31 channels in the space of a typical SSB voice bandwidth.
PSK for Spread Spectrum
With spread spectrum you want a very wide bandwidth; by definition, one that is much wider than necessary to convey the information. By encoding each bit of data with the 11 bit sequence used in DSSS you now modulate the signal 11 times for each bit transferred. So for a 1 Mbit/sec transmission, you modulate at 11 MHz. This achieves the spread spectrum you are looking for. This modulation is encoded using DBPSK and a suppressed carrier.
Wednesday, September 16, 2009
THE VACUUM DIODE EXPOSED, Lee Bond N7KC
September 16, 2009 Educational Radio Net, PSRG 69th Session
What a digital summer we experienced at the hands of Curt Black, WR5J! Curt pulled all the stops on a summers survey of free software downloads for your computer which, more or less, turned your radio into an analytical tool. As impressive as this tour was, one must ultimately realize that the most complex task that your computer performs is based on tiny packets of electrons or "charge" being directed here and there by the software commands. Elemental electrons in motion, or moving electric "charge", is the bottom line idea in electrical theory and all electrical devices including radio equipment.
Let's review what we know about "charge". We know that it enjoys the symbol Q in the literature. We also know that it is an assembly of electrons and can be as few a one electron. We know that a collection of electrons numbering 6.14 x 10^18 is known as a Coulomb of charge. We know that charge will move under the influence of an electric field. We know that the original notion, or conventional notion, of charge was based on the erroneous idea that charge carried a positive sign hence moved in the direction of an applied electric field. Modern theory has reversed the original positive charge idea since electrons are negative entities and, in fact, move counter to the direction of any applied electric field. We know that charge can be motionless as in static charge. We know that an electrical current is charge in motion. It would seem that we know a lot about charge.
The study of charge is best represented by the science of Physics with Physical Chemistry running a close second. The study of charge as it applies to the vacuum tube would come under the heading of Classical Newtonian Physics in contrast to the study of charge in semiconductor materials which would come under the heading of Modern Quantum Physics. In my view the vacuum tube represents the most elegant device for demonstrating the behavior of electrical charge influenced by an electric field. Lucky me to be raised in the heyday of the vacuum tube. As late as 1963 the US Navy destroyer to which I was assigned had a single piece of transmitting equipment that had modern solid state diodes in the circuitry. The selenium rectifier preceded germanium devices and modern silicon devices and required no heater but it is a stretch to include it as more than a rudimentary solid state device. The solid state transistor with all its ramifications is a relative newcomer to the field of electronics. Modern radio equipment's are solid state for the most part and only the old timers can relate stories of warming their hands in the glow of those magnificent glass bottles.
No one has actually seen an electron. These entities are very, very tiny and to image them requires wavelengths small in comparison to the size of an electron. The one common instance of, more or less, stationary electrons occurs in the lattice structure of many crystals and x-ray crystallography has demonstrated diffraction images suggesting that these things are real. The fact that we can manipulate these tiny guys to the degree that we can is testimony to the very clever work of early scientists.
We know that conductors have an abundance of so called "free" electrons. This is in contrast to tightly "bound" electrons which are not available to contribute to electric current flow. For example the neutral copper atom has 29 electrons associated with the nucleus in 4, so called, shells with the innermost shell containing 2 electrons followed by the next shell containing 8 electrons followed by the next shell containing 18 electrons followed by the outermost shell with a single, so called, valence electron. The three inner shells are tightly bound to the atomic nucleus but the outer single electron is easily forced out of place and can contribute to the electric current bumping along a copper wire. Most metals are conductors to varying degrees with silver, copper, and gold at the top. A copper atom missing its valence electron is known as a copper ion.
I think we now have enough information to appreciate how a two terminal vacuum diode works so let's move on to some apparatus to demonstrate the effect. Forget the little glass bottle for the moment. We are going to use a laboratory bell jar and good quality vacuum pump as a part of our apparatus. Everyone has seen the "bell" jar on a stand with a mechanical vacuum pump attached. For our purposes the bell jar stand needs some electrical penetrations so that we can supply potentials to the bell jar innards. The first of the two inside devices is the filament or heater which also serves as a cathode. There are several schemes for heaters so let me select the one known as the directly heated filament cathode. This will be a tungsten wire section which will glow a bright red to orange when filament voltage is applied. Adjacent to the filament-cathode wire we will position a "plate" of flat metal such that it does not touch the filament. This metallic plate is, in fact, called the "plate" electrode in vacuum tube terminology and serves as the anode. Note that the plate may be cylindrical and surround the filament in real world devices.
Our demonstration diode is complete. We have a filament (cathode) and plate (anode) plus a means of producing a good vacuum so on goes the bell jar but someone forgot to start the vacuum pump. Not realizing that a good vacuum is missing we switch on the filament voltage and sure enough the filament starts to light. Then there is a bright flash as the oxygen in the bell jar contributes to the destruction of the filament. Oops. Off with the jar and we install another filament wire. Ok, this time we turn on the pump and let it run until it chortles. Now when we flip the switch for the filament the wire glows a cheery orange. The chortling pump indicates that the internal vacuum (or pressure) is in the 1 to 10 micron range and suitable for our demonstration. The low internal pressure means that atoms of oxygen and nitrogen are scarce and will not interfere with the electronic process that we are interested in observing.
Let's think about the filament voltage for a moment. I did not mention it but the source of the filament voltage is a battery. Traditionally the battery used for filament power is known as the "A" battery.
So, here is our situation... we have a nicely glowing filament with an unconnected plate nearby and both are within a reasonably good vacuum. The glowing filament is probably heated to 800 degrees F or thereabouts and the thermal energy of the filament has caused lightly bound electrons to break free and form a cloud in the immediate vicinity of the filament-cathode. The thermal energy for breakaway is known as the work function and metals vary in this regard. Some substances such as barium offer very low work functions and are used in cooler, indirectly heated, cathode structures.
Our cloud of electrons is negatively charged. If we cause the nearby plate element to become positively charged with respect to the filament-cathode then the electrons will move toward the plate anode and, since moving electrons constitute electrical current, we can measure a plate current if we insert some current measuring device in series with the plate. With regard to the plate, the battery traditionally used to supply plate voltage is known as the "B" battery hence follows the term B+ for the plate positive voltage supply.
There is a third battery associated with vacuum tubes which is known as the "C" battery however it is not relevant here since we are using a two terminal device or diode and the C battery is only relevant in triode structures and beyond for grid biasing.
At this point we have demonstrated that electrons will traverse a vacuum if the plate is positive with respect to the source of electrons. If the plate is negative relative to the source then the electrons are repelled and no plate current will flow. Herein lies the secret of the rectifying diode. If the plate is alternately positive then negative with respect to the cathode as would happen if connected to alternating mains then plate current only flows on positive excursions of plate voltage. Bi-directional current from AC mains becomes unidirectional current in the plate circuit. A single diode offers half wave rectification and a dual diode (or two individual diodes) offers full wave rectification.
The high vacuum in the bell jar or little glass bottle performs two functions. First the pumping process removes virtually all oxygen so the filament suffers no oxidation. Secondly, the high vacuum is synonymous with low pressure both which equate to few residual gas particles present to hinder electron flow from cathode to plate anode. In reality small glass bottles with high internal temperatures will out gas damaging particles which will poison the vacuum so special devices known as "getters" are used internally to trap these vacuum destroyers.
Special attention must be given to the metal leads going through the little glass tube envelopes. If the glass and wire conductors do not expand and contract in the same manner with extreme changes in temperature then the seal will be broken and the tube will be rendered useless in short order. Special wire alloys which match the glass thermal characteristics are used to avoid this problem.
In summary, the physics and mathematics associated with the classic vacuum tube is elegant and a fun pursuit for the very curious. The concept of electronic charge flow within a triode vacuum tube is easily grasped and directly applicable to field effect transistors. The natural extension from diode to triode by introducing a control grid between cathode and plate made possible amplification and the rest is history.
This concludes the set up discussion for the Vacuum Diode. Are there any questions or comments with regard to tonight's discussion topic?
This is N7KC for the Wednesday night Educational Radio Net
What a digital summer we experienced at the hands of Curt Black, WR5J! Curt pulled all the stops on a summers survey of free software downloads for your computer which, more or less, turned your radio into an analytical tool. As impressive as this tour was, one must ultimately realize that the most complex task that your computer performs is based on tiny packets of electrons or "charge" being directed here and there by the software commands. Elemental electrons in motion, or moving electric "charge", is the bottom line idea in electrical theory and all electrical devices including radio equipment.
Let's review what we know about "charge". We know that it enjoys the symbol Q in the literature. We also know that it is an assembly of electrons and can be as few a one electron. We know that a collection of electrons numbering 6.14 x 10^18 is known as a Coulomb of charge. We know that charge will move under the influence of an electric field. We know that the original notion, or conventional notion, of charge was based on the erroneous idea that charge carried a positive sign hence moved in the direction of an applied electric field. Modern theory has reversed the original positive charge idea since electrons are negative entities and, in fact, move counter to the direction of any applied electric field. We know that charge can be motionless as in static charge. We know that an electrical current is charge in motion. It would seem that we know a lot about charge.
The study of charge is best represented by the science of Physics with Physical Chemistry running a close second. The study of charge as it applies to the vacuum tube would come under the heading of Classical Newtonian Physics in contrast to the study of charge in semiconductor materials which would come under the heading of Modern Quantum Physics. In my view the vacuum tube represents the most elegant device for demonstrating the behavior of electrical charge influenced by an electric field. Lucky me to be raised in the heyday of the vacuum tube. As late as 1963 the US Navy destroyer to which I was assigned had a single piece of transmitting equipment that had modern solid state diodes in the circuitry. The selenium rectifier preceded germanium devices and modern silicon devices and required no heater but it is a stretch to include it as more than a rudimentary solid state device. The solid state transistor with all its ramifications is a relative newcomer to the field of electronics. Modern radio equipment's are solid state for the most part and only the old timers can relate stories of warming their hands in the glow of those magnificent glass bottles.
No one has actually seen an electron. These entities are very, very tiny and to image them requires wavelengths small in comparison to the size of an electron. The one common instance of, more or less, stationary electrons occurs in the lattice structure of many crystals and x-ray crystallography has demonstrated diffraction images suggesting that these things are real. The fact that we can manipulate these tiny guys to the degree that we can is testimony to the very clever work of early scientists.
We know that conductors have an abundance of so called "free" electrons. This is in contrast to tightly "bound" electrons which are not available to contribute to electric current flow. For example the neutral copper atom has 29 electrons associated with the nucleus in 4, so called, shells with the innermost shell containing 2 electrons followed by the next shell containing 8 electrons followed by the next shell containing 18 electrons followed by the outermost shell with a single, so called, valence electron. The three inner shells are tightly bound to the atomic nucleus but the outer single electron is easily forced out of place and can contribute to the electric current bumping along a copper wire. Most metals are conductors to varying degrees with silver, copper, and gold at the top. A copper atom missing its valence electron is known as a copper ion.
I think we now have enough information to appreciate how a two terminal vacuum diode works so let's move on to some apparatus to demonstrate the effect. Forget the little glass bottle for the moment. We are going to use a laboratory bell jar and good quality vacuum pump as a part of our apparatus. Everyone has seen the "bell" jar on a stand with a mechanical vacuum pump attached. For our purposes the bell jar stand needs some electrical penetrations so that we can supply potentials to the bell jar innards. The first of the two inside devices is the filament or heater which also serves as a cathode. There are several schemes for heaters so let me select the one known as the directly heated filament cathode. This will be a tungsten wire section which will glow a bright red to orange when filament voltage is applied. Adjacent to the filament-cathode wire we will position a "plate" of flat metal such that it does not touch the filament. This metallic plate is, in fact, called the "plate" electrode in vacuum tube terminology and serves as the anode. Note that the plate may be cylindrical and surround the filament in real world devices.
Our demonstration diode is complete. We have a filament (cathode) and plate (anode) plus a means of producing a good vacuum so on goes the bell jar but someone forgot to start the vacuum pump. Not realizing that a good vacuum is missing we switch on the filament voltage and sure enough the filament starts to light. Then there is a bright flash as the oxygen in the bell jar contributes to the destruction of the filament. Oops. Off with the jar and we install another filament wire. Ok, this time we turn on the pump and let it run until it chortles. Now when we flip the switch for the filament the wire glows a cheery orange. The chortling pump indicates that the internal vacuum (or pressure) is in the 1 to 10 micron range and suitable for our demonstration. The low internal pressure means that atoms of oxygen and nitrogen are scarce and will not interfere with the electronic process that we are interested in observing.
Let's think about the filament voltage for a moment. I did not mention it but the source of the filament voltage is a battery. Traditionally the battery used for filament power is known as the "A" battery.
So, here is our situation... we have a nicely glowing filament with an unconnected plate nearby and both are within a reasonably good vacuum. The glowing filament is probably heated to 800 degrees F or thereabouts and the thermal energy of the filament has caused lightly bound electrons to break free and form a cloud in the immediate vicinity of the filament-cathode. The thermal energy for breakaway is known as the work function and metals vary in this regard. Some substances such as barium offer very low work functions and are used in cooler, indirectly heated, cathode structures.
Our cloud of electrons is negatively charged. If we cause the nearby plate element to become positively charged with respect to the filament-cathode then the electrons will move toward the plate anode and, since moving electrons constitute electrical current, we can measure a plate current if we insert some current measuring device in series with the plate. With regard to the plate, the battery traditionally used to supply plate voltage is known as the "B" battery hence follows the term B+ for the plate positive voltage supply.
There is a third battery associated with vacuum tubes which is known as the "C" battery however it is not relevant here since we are using a two terminal device or diode and the C battery is only relevant in triode structures and beyond for grid biasing.
At this point we have demonstrated that electrons will traverse a vacuum if the plate is positive with respect to the source of electrons. If the plate is negative relative to the source then the electrons are repelled and no plate current will flow. Herein lies the secret of the rectifying diode. If the plate is alternately positive then negative with respect to the cathode as would happen if connected to alternating mains then plate current only flows on positive excursions of plate voltage. Bi-directional current from AC mains becomes unidirectional current in the plate circuit. A single diode offers half wave rectification and a dual diode (or two individual diodes) offers full wave rectification.
The high vacuum in the bell jar or little glass bottle performs two functions. First the pumping process removes virtually all oxygen so the filament suffers no oxidation. Secondly, the high vacuum is synonymous with low pressure both which equate to few residual gas particles present to hinder electron flow from cathode to plate anode. In reality small glass bottles with high internal temperatures will out gas damaging particles which will poison the vacuum so special devices known as "getters" are used internally to trap these vacuum destroyers.
Special attention must be given to the metal leads going through the little glass tube envelopes. If the glass and wire conductors do not expand and contract in the same manner with extreme changes in temperature then the seal will be broken and the tube will be rendered useless in short order. Special wire alloys which match the glass thermal characteristics are used to avoid this problem.
In summary, the physics and mathematics associated with the classic vacuum tube is elegant and a fun pursuit for the very curious. The concept of electronic charge flow within a triode vacuum tube is easily grasped and directly applicable to field effect transistors. The natural extension from diode to triode by introducing a control grid between cathode and plate made possible amplification and the rest is history.
This concludes the set up discussion for the Vacuum Diode. Are there any questions or comments with regard to tonight's discussion topic?
This is N7KC for the Wednesday night Educational Radio Net
Wednesday, September 9, 2009
Winlink 2000, Boone Barker KC7RK, no. 68
The Winlink 2000 System: E-Mail by Radio for Radio Amateurs
Boone Barker, KC7RK
Introduction
This paper provides a brief introduction to the Winlink 2000 system—what it is and how it works, and how to become a user.
To start, here are a couple of defining quotes from the Winlink web site at www.winlink.org .
“Winlink 2000 (WL2K) is a worldwide system of volunteer resources supporting e-mail by radio, with non-commercial links to internet e-mail.”
“To use the Winlink 2000 system, you must hold an Amateur Radio license or be a member of a supported organization or agency. Use of the system and all software is free of charge for those who qualify.”
So Winlink is global, with access around the world. It is developed and supported entirely by volunteers. It is free. The system provides e-mail services to licensed Radio Amateurs without access to the internet such as mariners at sea or expeditions in remote areas.
In addition, a growing number of government agencies and organizations have included WL2K in their emergency communication plans. Winlink 2000 can provide user -to-user e-mail services in a familiar format from inside a disaster area, using only a radio to connect to the outside world.
Elements of Winlink 2000
At the heart of the WL2K system are five mirror image, redundant Common Message Server (CMS) hubs. They are located in San Diego (USA), Wein (Austria), Perth (Australia), Halifax (Canada), and Washington DC (USA). With this redundancy, the system will remain operational even if large segments of the internet are down.
Connected to the five CMS sites are a multitude of Radio Message Server (RMS) nodes, like spokes on a wheel. Traffic flows between the CMS hubs and the internet e-mail recipient, and between the end users and the RMS gateways.
As an aside, the term “PMBO” (for a participating mailbox) is being phased out, but still shows up in Winlink writings.
The radio network has both RMS HF stations and RMS VHF/UHF Packet stations.
RMS HF stations form a controlled and frequency-coordinated global network of Winlink stations. The HF stations all use Pactor, a digital ARQ mode that transfers text files and graphics quickly and error-free. Pactor 2 and 3, the faster modes, are only available on TNC’s produced by SCS in Germany. The WL2K Development Team is working on WINMOR, a new HF transmission protocol that will be freely distributed. It will complement, not replace Pactor; RMS HF stations will be able to handle both modes.
RMS VHF/UHF Packet stations are also part of the network, providing automated messaging capability using AX.25 packet radio in combination with the WL2K Common Message Servers. Although limited in range, RMS Packet stations are widely available in the United States and a few other countries. RMS Packet can provide regular local access to Winlink, or a temporary emergency portal for radio e-mail users, or for fixed installation at unattended remote locations where it can provide radio e-mail communications to the “last mile.”
The locations of public and emcomm RMS stations are shown in maps on the Winlink web site. Related status tables list station call sign, with frequency and mode and grid locator. Note that information about frequencies used by RMS HF emcomm stations is limited to authorized sysops and users.
WL2K Client Software
Paclink is a Winlink 2000 radio e-mail client that links to common e-mail programs such as Outlook Express and Mozilla Thunderbird. Paclink adds telnet, VHF packet radio, HF Pactor radio and WINMOR HF radio channels for WL2K connectivity to compatible user e-mail client programs. Installation and configuration are relatively easy.
Airmail is the oldest and most widely used e-mail program for sending and receiving messages on the Winlink system. Airmail supports HF Pactor, VHF/UHF Packet, and telnet connections over any TCP/IP medium including the internet and high-speed radio media like D-Star. Airmail also has position reporting capability, and a very nice HF propagation prediction program. It can be linked to common e-mail programs such as Outlook Express. Installation and configuration are somewhat difficult, but a nice guide is available; just Google “INSTALLATION AND SETUP FOR WINLINK AIRMAIL”.
Airmail is a stand-alone e-mail program. The primary drawback of Airmail is that it only works with a short list of hardware modems. But it is well suited for WL2K HF connections using a Pactor modem. And the latest version of Airmail 3.3.081 can be used with AGW Packet Engine and a soundcard to make VHF/UHF packet connections, by installing AMPE software. See http://www.qsl.net/mararc/ampe.htm web site.
On the other hand, Paclink has to be linked with an e-mail program. But it works with a wide variety of hardware TNC’s and modems and with AGW Packet Engine. TNC initialization scripts can be modified by the user. Also, scripts can be used to connect through a digipeater or packet node. CMS Telnet is simple and easy on Paclink, to send and receive WL2K messages on an internet connection.
Both programs are free to download from the Winlink web site.
Other software
AGW Packet Engine (AGWPE) handles traffic between your TNC or soundcard and packet programs that are configured to use AGWPE. It is free to download from the SV2AGW.com web site. A lengthy tutorial for installation and configuration is located at http://www.kc2rlm.info/soundcardpacket .
Winlink 2000 RMS Packet gateways can also be accessed with regular packet software, to compose and send a message from the keyboard. Just connect to the RMS Packet node and read the greeting. Type H for help and then follow the instructions to compose a message. This is perhaps the easiest way to try out Winlink if you already have a packet setup.
Hardware
For telnet connection to a CMS, the only hardware needed is a computer with internet access. WL2K e-mail through RMS Packet stations requires a VHF radio, a compatible TNC or modem or soundcard, and necessary interface cables.
To connect with an RMS HF gateway on Pactor 1 requires that you have any one of the hardware TNC’s on setup lists in Airmail or Paclink. Pactor 2 or 3 requires that you have a Pactor TNC made by SCS . These cost $1,000 or more.
How do you get started?
First and obviously, you need an amateur radio license. With that, here is a suggested initial sequence.
Go to www.winlink.org, register on the web site, and download Paclink or Airmail—your choice. Install and configure the software for telnet to a CMS site. Compose a test message to your internet e-mail address. Send the message using the telnet connection. When that is successful, reply to your Winlink e-mail address.
Another option: if you already have an operational packet setup, use it to connect to a local RMS Packet node. The Winlink web site has a map that shows all of the active RMS Packet stations. Just zoom in on your local area and pick them out. Then go to the Reports tab on the Winlink Web site, scroll down to RMS Packet Status, and look up frequencies of those stations in the table. Sometimes these local nodes are not functioning. So if you don’t get a connection, try another station.
With your first radio or telnet e-mail you will be registered in the WL2K system. Your e-mail address will be [your call]@winlink.org.
You can use WL2K client software with packet and your TNC if it is listed in the setup for Paclink Packet TNC Channels or in Airmail VHF Packet Client Setup. Check out the TNC using a simple terminal program. Then try connecting to one of the local RMS Packet stations.
If you want to use a soundcard for packet, first download and install AGW Packet Engine. Create a new radioport for your soundcard. Then configure Paclink or Airmail to use AGWPE. Remember that Airmail requires that AMPE be running. There is a link to AGWPE is the Airmail TNC list but it is not functional.
You might also want to download AGWTerninal, and AGWMonitor from the SV2AGW web site. They are free. AGW Monitor lets you see all the traffic to and from your TNC/modem/soundcard, and AGWTerminal is a nice simple terminal program. AGWTracker is a simple APRS program, also nice. All require that AGWPE or Packet Engine Pro be running.
If an online course is to your liking, there is a “Winlink for Dummies” course that takes you through all the steps. It can be accessed through www/winlink.org/GetStarted.
Some recommendations
You should always format WL2K e-mail messages in plain text. HTML format adds unnecessary bytes to the message. Attachments should be made as small as possible.
Learn about the Winlink Whitelist and how to work with it. This is an anti-spam filter. E-mails to your Winlink e-mail address need to have //WL2K in the subject line or they will be rejected—unless they come from an e-mail account on your Whitelist. E-mail addresses on outgoing messages are automatically added to your Whitelist.
When you configure a radioport in AGWPE for SignaLink USB, select an unused printer port (LPT3) as your PTT port. It’s easy to hang up at this point in the setup.
Summary
Winlink 2000 has been used since 1999 by Radio Amateurs at sea and in the jungles to send e-mail messages by radio. As a result of experience in Katrina recovery operations and other disasters, Winlink has been included in operational plans of a growing number of emcomm organizations such as RACES and ARES units, Red Cross, MARS, Baptist Relief, and the Salvation Army.
Another defining quote from the Winlink web site:
“The WL2K mission is to provide, through a volunteer network, effective last resort communications in civil emergencies and personal communications in non-emergency conditions.”
As a Radio Amateur, you may already have experience with packet radio—that’s all you need to access Winlink by radio. Another simple start involves connecting by telnet over the internet. And if you are already a Winlink user, you might consider becoming the sysop for your own RMS Packet station. Software and guidelines are on the web site.
So have fun setting up Winlink and trying it out. It might well be very useful in an emergency, to you and to your community.
September 9, 2009
Boone Barker, KC7RK
Introduction
This paper provides a brief introduction to the Winlink 2000 system—what it is and how it works, and how to become a user.
To start, here are a couple of defining quotes from the Winlink web site at www.winlink.org .
“Winlink 2000 (WL2K) is a worldwide system of volunteer resources supporting e-mail by radio, with non-commercial links to internet e-mail.”
“To use the Winlink 2000 system, you must hold an Amateur Radio license or be a member of a supported organization or agency. Use of the system and all software is free of charge for those who qualify.”
So Winlink is global, with access around the world. It is developed and supported entirely by volunteers. It is free. The system provides e-mail services to licensed Radio Amateurs without access to the internet such as mariners at sea or expeditions in remote areas.
In addition, a growing number of government agencies and organizations have included WL2K in their emergency communication plans. Winlink 2000 can provide user -to-user e-mail services in a familiar format from inside a disaster area, using only a radio to connect to the outside world.
Elements of Winlink 2000
At the heart of the WL2K system are five mirror image, redundant Common Message Server (CMS) hubs. They are located in San Diego (USA), Wein (Austria), Perth (Australia), Halifax (Canada), and Washington DC (USA). With this redundancy, the system will remain operational even if large segments of the internet are down.
Connected to the five CMS sites are a multitude of Radio Message Server (RMS) nodes, like spokes on a wheel. Traffic flows between the CMS hubs and the internet e-mail recipient, and between the end users and the RMS gateways.
As an aside, the term “PMBO” (for a participating mailbox) is being phased out, but still shows up in Winlink writings.
The radio network has both RMS HF stations and RMS VHF/UHF Packet stations.
RMS HF stations form a controlled and frequency-coordinated global network of Winlink stations. The HF stations all use Pactor, a digital ARQ mode that transfers text files and graphics quickly and error-free. Pactor 2 and 3, the faster modes, are only available on TNC’s produced by SCS in Germany. The WL2K Development Team is working on WINMOR, a new HF transmission protocol that will be freely distributed. It will complement, not replace Pactor; RMS HF stations will be able to handle both modes.
RMS VHF/UHF Packet stations are also part of the network, providing automated messaging capability using AX.25 packet radio in combination with the WL2K Common Message Servers. Although limited in range, RMS Packet stations are widely available in the United States and a few other countries. RMS Packet can provide regular local access to Winlink, or a temporary emergency portal for radio e-mail users, or for fixed installation at unattended remote locations where it can provide radio e-mail communications to the “last mile.”
The locations of public and emcomm RMS stations are shown in maps on the Winlink web site. Related status tables list station call sign, with frequency and mode and grid locator. Note that information about frequencies used by RMS HF emcomm stations is limited to authorized sysops and users.
WL2K Client Software
Paclink is a Winlink 2000 radio e-mail client that links to common e-mail programs such as Outlook Express and Mozilla Thunderbird. Paclink adds telnet, VHF packet radio, HF Pactor radio and WINMOR HF radio channels for WL2K connectivity to compatible user e-mail client programs. Installation and configuration are relatively easy.
Airmail is the oldest and most widely used e-mail program for sending and receiving messages on the Winlink system. Airmail supports HF Pactor, VHF/UHF Packet, and telnet connections over any TCP/IP medium including the internet and high-speed radio media like D-Star. Airmail also has position reporting capability, and a very nice HF propagation prediction program. It can be linked to common e-mail programs such as Outlook Express. Installation and configuration are somewhat difficult, but a nice guide is available; just Google “INSTALLATION AND SETUP FOR WINLINK AIRMAIL”.
Airmail is a stand-alone e-mail program. The primary drawback of Airmail is that it only works with a short list of hardware modems. But it is well suited for WL2K HF connections using a Pactor modem. And the latest version of Airmail 3.3.081 can be used with AGW Packet Engine and a soundcard to make VHF/UHF packet connections, by installing AMPE software. See http://www.qsl.net/mararc/ampe.htm web site.
On the other hand, Paclink has to be linked with an e-mail program. But it works with a wide variety of hardware TNC’s and modems and with AGW Packet Engine. TNC initialization scripts can be modified by the user. Also, scripts can be used to connect through a digipeater or packet node. CMS Telnet is simple and easy on Paclink, to send and receive WL2K messages on an internet connection.
Both programs are free to download from the Winlink web site.
Other software
AGW Packet Engine (AGWPE) handles traffic between your TNC or soundcard and packet programs that are configured to use AGWPE. It is free to download from the SV2AGW.com web site. A lengthy tutorial for installation and configuration is located at http://www.kc2rlm.info/soundcardpacket .
Winlink 2000 RMS Packet gateways can also be accessed with regular packet software, to compose and send a message from the keyboard. Just connect to the RMS Packet node and read the greeting. Type H for help and then follow the instructions to compose a message. This is perhaps the easiest way to try out Winlink if you already have a packet setup.
Hardware
For telnet connection to a CMS, the only hardware needed is a computer with internet access. WL2K e-mail through RMS Packet stations requires a VHF radio, a compatible TNC or modem or soundcard, and necessary interface cables.
To connect with an RMS HF gateway on Pactor 1 requires that you have any one of the hardware TNC’s on setup lists in Airmail or Paclink. Pactor 2 or 3 requires that you have a Pactor TNC made by SCS . These cost $1,000 or more.
How do you get started?
First and obviously, you need an amateur radio license. With that, here is a suggested initial sequence.
Go to www.winlink.org, register on the web site, and download Paclink or Airmail—your choice. Install and configure the software for telnet to a CMS site. Compose a test message to your internet e-mail address. Send the message using the telnet connection. When that is successful, reply to your Winlink e-mail address.
Another option: if you already have an operational packet setup, use it to connect to a local RMS Packet node. The Winlink web site has a map that shows all of the active RMS Packet stations. Just zoom in on your local area and pick them out. Then go to the Reports tab on the Winlink Web site, scroll down to RMS Packet Status, and look up frequencies of those stations in the table. Sometimes these local nodes are not functioning. So if you don’t get a connection, try another station.
With your first radio or telnet e-mail you will be registered in the WL2K system. Your e-mail address will be [your call]@winlink.org.
You can use WL2K client software with packet and your TNC if it is listed in the setup for Paclink Packet TNC Channels or in Airmail VHF Packet Client Setup. Check out the TNC using a simple terminal program. Then try connecting to one of the local RMS Packet stations.
If you want to use a soundcard for packet, first download and install AGW Packet Engine. Create a new radioport for your soundcard. Then configure Paclink or Airmail to use AGWPE. Remember that Airmail requires that AMPE be running. There is a link to AGWPE is the Airmail TNC list but it is not functional.
You might also want to download AGWTerninal, and AGWMonitor from the SV2AGW web site. They are free. AGW Monitor lets you see all the traffic to and from your TNC/modem/soundcard, and AGWTerminal is a nice simple terminal program. AGWTracker is a simple APRS program, also nice. All require that AGWPE or Packet Engine Pro be running.
If an online course is to your liking, there is a “Winlink for Dummies” course that takes you through all the steps. It can be accessed through www/winlink.org/GetStarted.
Some recommendations
You should always format WL2K e-mail messages in plain text. HTML format adds unnecessary bytes to the message. Attachments should be made as small as possible.
Learn about the Winlink Whitelist and how to work with it. This is an anti-spam filter. E-mails to your Winlink e-mail address need to have //WL2K in the subject line or they will be rejected—unless they come from an e-mail account on your Whitelist. E-mail addresses on outgoing messages are automatically added to your Whitelist.
When you configure a radioport in AGWPE for SignaLink USB, select an unused printer port (LPT3) as your PTT port. It’s easy to hang up at this point in the setup.
Summary
Winlink 2000 has been used since 1999 by Radio Amateurs at sea and in the jungles to send e-mail messages by radio. As a result of experience in Katrina recovery operations and other disasters, Winlink has been included in operational plans of a growing number of emcomm organizations such as RACES and ARES units, Red Cross, MARS, Baptist Relief, and the Salvation Army.
Another defining quote from the Winlink web site:
“The WL2K mission is to provide, through a volunteer network, effective last resort communications in civil emergencies and personal communications in non-emergency conditions.”
As a Radio Amateur, you may already have experience with packet radio—that’s all you need to access Winlink by radio. Another simple start involves connecting by telnet over the internet. And if you are already a Winlink user, you might consider becoming the sysop for your own RMS Packet station. Software and guidelines are on the web site.
So have fun setting up Winlink and trying it out. It might well be very useful in an emergency, to you and to your community.
September 9, 2009
Tuesday, September 1, 2009
Spread Spectrum Communications, Bob, no. 67
Tonight's topic, spread spectrum communications, may seem to be the stuff of spy fiction and ultra-expensive military hardware, but you have almost certainly used spread spectrum whether you know it or not and you probably have the sophisticated spread spectrum radio gear right in your own house. I'm talking about wireless networking gear, also known as WiFi. More on that later.
WHAT IS SPREAD SPECTRUM?
According to the ARRL Handbook, spread spectrum is defined as using an RF bandwidth much larger than needed to carry the signal, and where the bandwidth of the signal is independent of the modulation by the signal. It is a form of radio transmission that makes use of a wide bandwidth to avoid interference by noise or other signals. You can imagine that if you are transmitting a simple AM signal over 100 frequencies at the same time then someone transmititng on any one of those frequencies will only contribute one percent toward the final recombined signal. This would be fine until you had someone else also transmitting an AM signal on the same 100 frequencies. Then you would be back to a big interference problem. Partly in order to allow hams to use the same frequency range, there are more sophisticated ways to use those multiple frequencies. We will discuss those in a moment.
SPREAD SPECTRUM TRADE-OFFS
In general, spread spectrum transmissions offer three big advantages:
HISTORY OF SPREAD SPECTRUM
In a sense you could say that spread spectrum began with the earliest radio transmitters. Spark gap transmitters created CW signals that covered a very broad spectrum. You could charitably say that this signal could get through interfering signals but really, it was more of an interfering signal.
Early experiments with intentional spread spectrum began in the late 20's but it was World War II and the military that really pushed the technology forward. Unfortunately, because spread spectrum is still used by the military, much of the history is still kept secret.
SPREAD SPECTRUM IN HAM RADIO
In 1981, a group called the Amateur Radio Research and Development Corporation (AMRAD) began experimentation with spread spectrum. In 1989 an idea was put forth to use the Wireless LAN (WLAN) devices in ham radio, and in 1999 the FCC relaxed their rules about hams using spread spectrum. This relaxation opened the door for hams to use equipment already being made for WLAN.
Analog signals can be carried over spread spectrum transmissions, but nearly all spread spectrum use today is with digital signals and that is what we will discuss.
COMMON TYPES
Frequency Hopping Spread Spectrum (FHSS)
As the name implies, the transmitting frequency hops around in a pre-arranged pattern. In the 802.11 spec, there are 3 sets of 26 such patterns using 75 frequencies. By some clever hopping algorithms you can have 802.11 devices using different sequences, or channels, on the same 75 frequencies without interfering with each other. Because there are only 78 sequences, a receiving device could discover the channel being used by the various transmitters and sync up with one.
Direct-Sequence Spread Spectrum (DSSS)
In this method, a pseudo-random code is used to modulate the signal and drive a phase modulator using phase shift keying. I have to admit this it getting into the fringes of what I know so I am going to leave it at that.
Note that by using a pseudo-random code that is not generally known it would be possible to securely encrypt a signal with DSSS. Of course we are not allowed to do that in amateur radio and we avoid that pitfall by using published codes as can be found on the ARRL web site.
Orthogonal Frequency Division Modulation (OFDM)
This method is more like what you may think when you think of spread spectrum. In this mode, the signal is transmitted on 52 carrier frequencies simultaneously. Four of these are called pilot carriers and they help provide the synchronization. The other 48 each transmit independent bit streams so at any given time, 48 bits are being transmitted at once. The reason it is called orthogonal is that the frequencies and modulation patterns are chosen so that each frequency falls in the null of the neighboring frequencies.
THE FUTURE
Since this mode is so new and underutilized in ham radio, I'm going to do something I don't normally do and that is predict the future of spread spectrum. It is here to stay until something better comes along and, though it may not happen, I wouldn't be surprised to see it adopted in the low bands eventually. I know some of the new digital modes use it to some degree and I can see the FCC, being the pragmatists they are, expanding the use of it as the technology allows.
I want to acknowledge two primary sources for tonights lesson. The ARRL Handbook, a wealth of all things Ham; and Spread Spectrum Scene which I barely scratched the surface of.
WHAT IS SPREAD SPECTRUM?
According to the ARRL Handbook, spread spectrum is defined as using an RF bandwidth much larger than needed to carry the signal, and where the bandwidth of the signal is independent of the modulation by the signal. It is a form of radio transmission that makes use of a wide bandwidth to avoid interference by noise or other signals. You can imagine that if you are transmitting a simple AM signal over 100 frequencies at the same time then someone transmititng on any one of those frequencies will only contribute one percent toward the final recombined signal. This would be fine until you had someone else also transmitting an AM signal on the same 100 frequencies. Then you would be back to a big interference problem. Partly in order to allow hams to use the same frequency range, there are more sophisticated ways to use those multiple frequencies. We will discuss those in a moment.
SPREAD SPECTRUM TRADE-OFFS
In general, spread spectrum transmissions offer three big advantages:
- Relative Immunity to Interference
As described above, unless someone else is using the very same spread spectrum technique and is synchronized with you, you likely won't notice the interference - Security
As we will see, there are sophisticated ways to encrypt a signal. This is why it is still valuable to the military. - Lower Power Density
By spreading the signal over a range of frequencies, the power at any given frequency is so low it can be below the noise floor and unnoticed.
HISTORY OF SPREAD SPECTRUM
In a sense you could say that spread spectrum began with the earliest radio transmitters. Spark gap transmitters created CW signals that covered a very broad spectrum. You could charitably say that this signal could get through interfering signals but really, it was more of an interfering signal.
Early experiments with intentional spread spectrum began in the late 20's but it was World War II and the military that really pushed the technology forward. Unfortunately, because spread spectrum is still used by the military, much of the history is still kept secret.
SPREAD SPECTRUM IN HAM RADIO
In 1981, a group called the Amateur Radio Research and Development Corporation (AMRAD) began experimentation with spread spectrum. In 1989 an idea was put forth to use the Wireless LAN (WLAN) devices in ham radio, and in 1999 the FCC relaxed their rules about hams using spread spectrum. This relaxation opened the door for hams to use equipment already being made for WLAN.
Analog signals can be carried over spread spectrum transmissions, but nearly all spread spectrum use today is with digital signals and that is what we will discuss.
COMMON TYPES
Frequency Hopping Spread Spectrum (FHSS)
As the name implies, the transmitting frequency hops around in a pre-arranged pattern. In the 802.11 spec, there are 3 sets of 26 such patterns using 75 frequencies. By some clever hopping algorithms you can have 802.11 devices using different sequences, or channels, on the same 75 frequencies without interfering with each other. Because there are only 78 sequences, a receiving device could discover the channel being used by the various transmitters and sync up with one.
Direct-Sequence Spread Spectrum (DSSS)
In this method, a pseudo-random code is used to modulate the signal and drive a phase modulator using phase shift keying. I have to admit this it getting into the fringes of what I know so I am going to leave it at that.
Note that by using a pseudo-random code that is not generally known it would be possible to securely encrypt a signal with DSSS. Of course we are not allowed to do that in amateur radio and we avoid that pitfall by using published codes as can be found on the ARRL web site.
Orthogonal Frequency Division Modulation (OFDM)
This method is more like what you may think when you think of spread spectrum. In this mode, the signal is transmitted on 52 carrier frequencies simultaneously. Four of these are called pilot carriers and they help provide the synchronization. The other 48 each transmit independent bit streams so at any given time, 48 bits are being transmitted at once. The reason it is called orthogonal is that the frequencies and modulation patterns are chosen so that each frequency falls in the null of the neighboring frequencies.
THE FUTURE
Since this mode is so new and underutilized in ham radio, I'm going to do something I don't normally do and that is predict the future of spread spectrum. It is here to stay until something better comes along and, though it may not happen, I wouldn't be surprised to see it adopted in the low bands eventually. I know some of the new digital modes use it to some degree and I can see the FCC, being the pragmatists they are, expanding the use of it as the technology allows.
I want to acknowledge two primary sources for tonights lesson. The ARRL Handbook, a wealth of all things Ham; and Spread Spectrum Scene which I barely scratched the surface of.
Tuesday, August 25, 2009
Reminder - Educational Radio Net Wednesday night 8:00pm and Last Summer of Digital Fun Post
Reminder - Educational Radio Net Wednesday night 8:00pm PSRG 146.96
For the new folks on this WA-DIGITAL list, the Summer of Digital Fun Series
finishes up this Wednesday on the PSRG machine, 146.96 (-600 kHz offset, 103.5
tone)in Seattle.
All are welcome.
Make no mistake, the Educational Radio Nets will continue and the Digital Series
will also continue, but for things digital, probably once or so per month as we
keep exercising with these amazing modes.
I was tempted to talk about the Automatic Position Reporting System, APRS - a
tasty flavor of packet radio. Just eavesdrop on 144.39 for a sense of how
popular this mode is. However, it seems the last couple of weeks have seriously
challenged the group which has been winnowed down to just a few players. I hope
folks will pursue APRS on their own or contact me off list for any help they
might need with that system - it is really a blast. For lots of help including
a well developed Elmering program, check out http://www.nwaprs.info/ or just
look at the cool maps at http://aprs.fi/
So, for this last Summer Session we'll have more digital fun with a recap of
what we've done through the summer. Please begin the net with FLDIGI up and
running with acoustic coupling between your radio and the computer.
The best way to enjoy the Educational Radio Net is to have your software set up
and running as the net starts at 8:00.
If you have an interface, hook it up to your two-meter rig, otherwise use
acoustic coupling with a microphone feeding shack audio into your computer and
the rig audio softly coming out of a speaker in the room with you fairly close
to the mic.
If this is your first session, no problem. Pull the software off the WA-DIGITAL
files section and install it. Tune in and we'll go over set up of the software
during the session. The software is on the WA-DIGITAL yahoo group. If you are
using VISTA, please load the version FLDIGI 3.11.4-WinV. When the update went
to 3.12.4 for all windows systems, something bad happened, and VISTA stopped
working. There are Linux and Mac versions of the software as well - just Google
NBEMS or go to http://www.w1hkj.com/ .
Posts 2 and 3 go into setting up for FLDIGI. The first part of Post #4
describes the set up for acoustic coupling. IF you are set up for acoustic
coupling, you should see a difference in the waterfall as you open and close the
squelch on the rig you are using to monitor the PSRG machine. If you don't, go
to the CONFIGURATION menu and the AUDIO tab, then devices to point the software
to the audio source.
We will start out tonight with a blast of MT-63 preceded with an RS-ID to
automatically switch your software to the correct mode and frequency, so get
ready to receive on the output of the PSRG machine, 146.96. Remember to setup
FLDIGI with menu item CONFIGURATION, then under the ID tab to check the box next
to "TRANSMIT MODE RSID" and "RSID SEARCHES ENTIRE PASSBAND" Finally on the main
receive screen, be sure and check the little box up in the upper right corner of
the screen labeled "RS-ID" so that a green light is visible indicating you are
ready to switch modes and frequency when the signal is received. This feature
has to be turned on each time you want to use it - mostly to keep from being
wrenched out of an ongoing QSO by receiving another RS-ID.
If you have trouble with copy during the net, you might check the input of the
repeater to see if that is better for you. Several folks sent messages last week
suggesting that.
See you on the Net.
Hopefully this will be just the beginning of some great digital adventures.
I would like to suggest we continue using the WA-DIGITAL mail reflector to
schedule digital QSOs with other folks, also don't forget
http://www.obriensweb.com/sked/ to set up SKEDS or WSPRNET.ORG to monitor your
received whisperings.
Also, please consider joining the Pennsylvania NBEMS group via Echolink on a
local repeater or in the privacy of your home computer. The Pittsburgh hams have
been having a net using about 50% voice and 50% MT-63. We may join them by
Echolink by connecting to W3YJ-R (node 177325) at 5:00pm Sunday evenings (8:00pm
Eastern Time).
After the 5:00pm net I would like to suggest we retire to the SEA machine on
145.010 simplex. (just "Connect SEA" and then type "TALK" to join the group and
//ex to leave (the instructions come up when you join.)
As the fall comes on, I would like to suggest we dive into some of the major
pieces of software available and checkout all that they are capable of - I'm
thinking of MULTIPSK which does way more than just PSK, and HAM RADIO DELUXE -
HRD with D780 for digital modes - a beautiful piece of software.
Our continuing thanks to the PSRG for the use of the repeater for this net and
so many others that enhance our radio community.
vy 73 de WR5J
Curt Black
black@nwfirst.com
As a reminder, here is what we covered this summer:
Blog Post - #1 Intro to Digital Communication, Software and Modes Wednesday,
June 3, 2009
Blog Post - #2 Intro to FLDIGI – Install, Setup and Mode Selection, Wednesday,
June 10, 2009
Blog Post - #3 Using FLDIGI – Starting with PSK-31 and Transmitting a Good
Signal Wednesday, June 24
Blog Post - #4 More FLDIGI – RTTY, the WRAP Utility and RS-ID, Wednesday July 1,
2009
Blog Post - #5 WSPR – Weak Signal Propagation Reporter, Wednesday July 8, 2009
Blog Post - #6 MMSSTV/EasyPAL, Slow Scan Image Transmission, Wednesday July 15,
2009
Blog Post - #7 Digital SSTV (week 2) EasyPAL, Wednesday July 22, 2009
Blog Post - #8 WSJT-JT65A – Terrestrial HF, Wednesday July 29, 2009
Blog Post - #9 WSJT-HS-Meteor Scatter, Wednesday August 5, 2009
Blog Post - #10 Packet Radio Using Flex32, Wednesday August 12, 2009
Blog Post - #11 Packet Radio Using AGW Packet Engine, Wednesday August 19,
2009
Blog Post - #12 WINDRM – Digital Voice and HRD/DM780, Wednesday August 26, 2009
OK - we didn't really do WINDRM - take a look at the blog post and you will see
why - we still might give it a try, but it is the same modulation approach used
by EasyPAL and that didn't fly very far through the PSRG machine - However, we
did very well with an after-net on the 444.550 WW7SEA machine - as in perfect
copy and 22dB S/N ratios. We've got to find out what that is about...
For the new folks on this WA-DIGITAL list, the Summer of Digital Fun Series
finishes up this Wednesday on the PSRG machine, 146.96 (-600 kHz offset, 103.5
tone)in Seattle.
All are welcome.
Make no mistake, the Educational Radio Nets will continue and the Digital Series
will also continue, but for things digital, probably once or so per month as we
keep exercising with these amazing modes.
I was tempted to talk about the Automatic Position Reporting System, APRS - a
tasty flavor of packet radio. Just eavesdrop on 144.39 for a sense of how
popular this mode is. However, it seems the last couple of weeks have seriously
challenged the group which has been winnowed down to just a few players. I hope
folks will pursue APRS on their own or contact me off list for any help they
might need with that system - it is really a blast. For lots of help including
a well developed Elmering program, check out http://www.nwaprs.info/ or just
look at the cool maps at http://aprs.fi/
So, for this last Summer Session we'll have more digital fun with a recap of
what we've done through the summer. Please begin the net with FLDIGI up and
running with acoustic coupling between your radio and the computer.
The best way to enjoy the Educational Radio Net is to have your software set up
and running as the net starts at 8:00.
If you have an interface, hook it up to your two-meter rig, otherwise use
acoustic coupling with a microphone feeding shack audio into your computer and
the rig audio softly coming out of a speaker in the room with you fairly close
to the mic.
If this is your first session, no problem. Pull the software off the WA-DIGITAL
files section and install it. Tune in and we'll go over set up of the software
during the session. The software is on the WA-DIGITAL yahoo group. If you are
using VISTA, please load the version FLDIGI 3.11.4-WinV. When the update went
to 3.12.4 for all windows systems, something bad happened, and VISTA stopped
working. There are Linux and Mac versions of the software as well - just Google
NBEMS or go to http://www.w1hkj.com/ .
Posts 2 and 3 go into setting up for FLDIGI. The first part of Post #4
describes the set up for acoustic coupling. IF you are set up for acoustic
coupling, you should see a difference in the waterfall as you open and close the
squelch on the rig you are using to monitor the PSRG machine. If you don't, go
to the CONFIGURATION menu and the AUDIO tab, then devices to point the software
to the audio source.
We will start out tonight with a blast of MT-63 preceded with an RS-ID to
automatically switch your software to the correct mode and frequency, so get
ready to receive on the output of the PSRG machine, 146.96. Remember to setup
FLDIGI with menu item CONFIGURATION, then under the ID tab to check the box next
to "TRANSMIT MODE RSID" and "RSID SEARCHES ENTIRE PASSBAND" Finally on the main
receive screen, be sure and check the little box up in the upper right corner of
the screen labeled "RS-ID" so that a green light is visible indicating you are
ready to switch modes and frequency when the signal is received. This feature
has to be turned on each time you want to use it - mostly to keep from being
wrenched out of an ongoing QSO by receiving another RS-ID.
If you have trouble with copy during the net, you might check the input of the
repeater to see if that is better for you. Several folks sent messages last week
suggesting that.
See you on the Net.
Hopefully this will be just the beginning of some great digital adventures.
I would like to suggest we continue using the WA-DIGITAL mail reflector to
schedule digital QSOs with other folks, also don't forget
http://www.obriensweb.com/sked/ to set up SKEDS or WSPRNET.ORG to monitor your
received whisperings.
Also, please consider joining the Pennsylvania NBEMS group via Echolink on a
local repeater or in the privacy of your home computer. The Pittsburgh hams have
been having a net using about 50% voice and 50% MT-63. We may join them by
Echolink by connecting to W3YJ-R (node 177325) at 5:00pm Sunday evenings (8:00pm
Eastern Time).
After the 5:00pm net I would like to suggest we retire to the SEA machine on
145.010 simplex. (just "Connect SEA" and then type "TALK" to join the group and
//ex to leave (the instructions come up when you join.)
As the fall comes on, I would like to suggest we dive into some of the major
pieces of software available and checkout all that they are capable of - I'm
thinking of MULTIPSK which does way more than just PSK, and HAM RADIO DELUXE -
HRD with D780 for digital modes - a beautiful piece of software.
Our continuing thanks to the PSRG for the use of the repeater for this net and
so many others that enhance our radio community.
vy 73 de WR5J
Curt Black
black@nwfirst.com
As a reminder, here is what we covered this summer:
Blog Post - #1 Intro to Digital Communication, Software and Modes Wednesday,
June 3, 2009
Blog Post - #2 Intro to FLDIGI – Install, Setup and Mode Selection, Wednesday,
June 10, 2009
Blog Post - #3 Using FLDIGI – Starting with PSK-31 and Transmitting a Good
Signal Wednesday, June 24
Blog Post - #4 More FLDIGI – RTTY, the WRAP Utility and RS-ID, Wednesday July 1,
2009
Blog Post - #5 WSPR – Weak Signal Propagation Reporter, Wednesday July 8, 2009
Blog Post - #6 MMSSTV/EasyPAL, Slow Scan Image Transmission, Wednesday July 15,
2009
Blog Post - #7 Digital SSTV (week 2) EasyPAL, Wednesday July 22, 2009
Blog Post - #8 WSJT-JT65A – Terrestrial HF, Wednesday July 29, 2009
Blog Post - #9 WSJT-HS-Meteor Scatter, Wednesday August 5, 2009
Blog Post - #10 Packet Radio Using Flex32, Wednesday August 12, 2009
Blog Post - #11 Packet Radio Using AGW Packet Engine, Wednesday August 19,
2009
Blog Post - #12 WINDRM – Digital Voice and HRD/DM780, Wednesday August 26, 2009
OK - we didn't really do WINDRM - take a look at the blog post and you will see
why - we still might give it a try, but it is the same modulation approach used
by EasyPAL and that didn't fly very far through the PSRG machine - However, we
did very well with an after-net on the 444.550 WW7SEA machine - as in perfect
copy and 22dB S/N ratios. We've got to find out what that is about...
Blog-Post-12 – WinDRM—Digital Data and Voice Using Digital Radio Mondiale
Blog Post 12 – WinDRM—Digital Data and Voice Using Digital Radio Mondiale on the Han Bands
Wednesday August 26, 2009
This is Curt Black, WR5J, with the Educational Radio Net –
Please standby for a WinDRM Digital QST
OK, we are out of time for the Summer of Digital Fun, but I had prepared some material for this mode, so here is what I have so far.
The problem with these digital voice modes is the loss of the use of a proprietary codec - here is a recent message from Mel Whitten:
Curt,
The MELP codec is no longer available because it was brought to
The attention of one of the IP holders that we were using it. I
don't think the IP holder would really "care" because of the way
we were using MELP, but when confronted by this "person" in writing..
then the IP holder had to defend his property. Thus, we are left
with LPC-10, which does not sound "too bad" and could be used to
demonstrate capability.
… 14.236 is calling/net freq for digital voice. Some stations may be
heard around noon central time. Nets are still run (summer time thy're
not as frequent) on Sat and Sun on the times given on the web site.
keep in mind, that you may find FDMDV, AOR's DV and WinDRM on these frequencies. FDMDV suffered the most from the loss of MELP and does not sound very good with the lower bit rate LPC-10 but it has "instant" sync and simple to use. With MELP, FDMDV was a real winner. Work continues to find a replacement, but this is very difficult. There are no "legal" problems with any DV using MELP or SPEEX codecs. They are both open source. DV is about dead and probably will remain that way until a MELP equivalent codec is found or some new technology is found. AOR's DV is not robust enough to cope with current poor band conditions do to low sun spot activity. It does work very good with at least S9 signals and no QRM. Excellent voice quality but so -was- WinDRM with MELP.
Channelization for DV would be optimum. QRM is a real problem from SSB. FCC rules say DV must operate in the Voice sub-bands. . .
<<
The software is on the Yahoo WA-DIGITAL files section http://groups.yahoo.com/group/wa-digital/files/
It sounds like the loss of the Codec may have delt a fatal blow – but here is the installation and use information for those who might want to experiment – 73 de WR5J
http://n1su.com/windrm/download.html
WinDRM Docs – Release 1.3 was developed by Cesco, HB9TLK from a relatively new broadcast standard called Digital Radio Mondiale (DRM) and it’s open source
encoder/decoder named Dream (http://drm.sourceforge.net/). DRM is based on a proven
data communications technology called Coded Orthogonal Frequency Division
Multiplexing (COFDM) with Quadrature Amplitude Modulation (QAM). COFDM uses
many parallel narrow band sub-carriers instead of just one single wide band carrier for
transporting the data. As a result, WinDRM provides an efficient and robust method to
exchange information over HF including Digital Voice using open source CODECs.
WinDRM utilizes Forward Error Correction (FEC) and an Automatic-Repeat-Request
(ARQ) mode to ensure error free data transfers. WinDRM runs efficiently under
Windows operating system 2000 and XP. No modifications are required for modern SSB
HF ham transceivers. Current releases of WinDRM software may be found at
www.n1su.com/windrm. Other digital HF data/picture transfer software such as Digtrx,
EasyPal and HamPAL share the same core ham-DRM standard and therefore are
compatible with WinDRM. WinDRM is not compatible with all newer encoding methods
now being used by HamPal. WinDRM is not compatible with AOR’s ARD 9000/9800
fast radio modem.
The WinDRM GUI (graphic user interface)
Five “State” Radio Buttons - (enabled under program control during receive ) as follows:
Input/Output
IO – Enabled: Sound card is linked and passing data to the processor. Disabled:
Indicates sound card is not compatible and/or PC’s processor is too slow. If not enabled,
WinDRM
2
WinDRM will not decode data. Note: IO should always be enabled during receive and
transmit.
Frequency Acquisition
Freq – Enabled: The three FAC reference carriers/pilots (3 higher intensity vertical lines
in the waterfall displays) have been found. These correlate with the DC Offset frequency
(normally 350Hz) which is graphically shown as a blue vertical line.
Time Synchronization Acquisition
Time – Enabled: Timing acquisition is done. This indicates the search for the beginning
of the OFDM symbol has been completed. Disabled: No synchronization, (usually
caused by poor SNR) distortion of the transmitted signal and/or receive band pass is too
narrow. Note: False indications (flickering) can be caused by AWGN (atmospheric
noise) and generally, may be ignored.
Frame Synchronization
Frame - Enabled: Frame synchronization is completed and the start of a DRM frame
(400ms) has been found. The Receiver is in synchronization with the transmitting station.
Disabled: Lost frequency synchronization due to poor SNR or change in frequency (avoid
“tuning” once in sync). Note: False indications (flickering) can be caused by AWGN
(atmospheric noise) and generally, may be ignored.
Fast Access Channel
FAC – Enabled: Receiver is in the tracking mode, has received a good Cyclic
Redundancy Check (8-bit CRC) and is in synchronization with the WinDRM transmitting
station. FAC is a separate logical channel and modulated with 4-Amplitude Quadrature
Modulation (4QAM). FAC provides bandwidth spectrum occupancy (2.3/2.5khz), call
sign and other DRM transmit parameters for the WinDRM receiver. Time, Frame and
FAC always precede (must be enabled) MSC channel data. Disabled: Caused by lost
sync, failed CRC, QRM, change in frequency and/or distortion of the transmitted signal.
FAC provides the data for the receiving WinDRM station to set it up to automatically
receive data for file transfer or digital voice (no intervention required by the receive end
operator).
Main Service Channel
MSC - Enabled: Indicates actual audio and data bits are being decoded for voice, text
message and/or images. MSC may be modulated using 4QAM, 16QAM or 64QAM (see
MSC). The larger the QAM rate the higher spectral efficiency but with lower
performance (less robust in presence of errors caused by poor propagation or
QRM/QRN). Robustness is improved through interleaving of the MSC symbols. This
provides time diversity so that a burst of errors is spread across up to several frames
minimizing the destructive effects on the received data. Like FAC, MSC enabled
indicates the Cyclic Redundancy Check (CRC) has been acknowledged and good data
has been received (Info’s data for MSC will increment after the CRC has been
computed). Disabled: Disruptions (dropouts), text message not received, or missed
3
block/segment/packet image data. QRM/QSB/QRN and weak signals can cause MSC to
fail or “flicker” during reception. A minimum SNR of 7dB generally ensures MSC will
remain enabled. Note: All these radio buttons must be enabled (from decoded
transmitted data) before the file/picture or voice data will be received.
Files: (download from: www.n1su.com/windrm/ )
The .wav files must be created using Digtrx or similar program. For docs on how to
create these files, go to http://www.kiva.net/~djones/index.htm . Note: These wave files
are not necessary to execute/use WinDRM. WinDRM stores files/pictures with errors in
the Corrupt folder. Good, error free Files/pictures are stored in the Pictures folder.
Mixer.bin contains data for the sound card’s mixer settings. Settings.txt file stores user
settings such as com port, call sign, etc. User files/pictures to be sent may be stored in
any directory for transmission, but are normally kept in the WinDRM directory for quick
access. Note: Digtrx creates 16bit 8000Hz sample rate wave files. WinDRM requires
16 bit 48000Hz wave file format. Use a freeware program like Audacity
(http://audacity.sourceforge.net/) to convert the wave files from 8000Hz to 48000Hz
mono.
Other files are created by WinDRM include:
bsr.bin
bsr0.bin
bsrreq.bin
bsrreq0.bin
RX_Log.txt
4
Known specs and definitions:
TX Data rate
MSC transmit data rate in bits-per-second (bps) is shown in the SNR box when
transmitting. For the DRM TX “Default” setting this is 2617bps. The Mode box will
display B/S/16/0/2.5 for this setting (see “Mode” for explanation of this data). The
CODECs (Linear Predictive Coding, SPEEX and Mixed-Excitation Linear Predictive)
require at least 2400bps. For data, WinDRM offers a “Speed” mode at a higher bit rate
of 4362bps and a “Robust” slower bit rate mode of 997bps. By changing these DRM TX
settings, the MSC protection, Coding, Bandwidth, and Interleave may be carefully chosen
to match the transceiver filters and current band conditions. For HF, a good starting point
is the default TX DRM setting. For poor band conditions, try the robust mode. Refer to
the specs found at: http://www.qslnet.de/member/hb9tlk/drm_h.html
Modulation and Forward Error Correction
Carriers are modulated using 4QAM, 16 or 64 in the MSC. The QAM constellation size
is selected by the user under the DRM TX settings. QAM4 is set by WinDRM for FAC
since it is the most robust. OFDM/QAM modulated carriers would appear to be
overlapping within their spectrum. However, once they are synchronized at the receiver,
they no longer over lap (now orthogonal/unique) and can then be demodulated. QAM
has both fixed amplitude and phase modulation. Forward Error Protection (FEC) is
provided by Reed Solomon (RS) code. By definition, RS has the ability “…to produce at
the sender ‘n’ blocks of encoded data from ‘k’ blocks of source data in such a way that
any subset of k encoded blocks suffices at the receiver to reconstruct the source data.”
This gives DRM the ability to “repair itself on the fly” by accurately rebuilding the audio
or file data as it was originally coded at the transmitter. If this can’t be done, then
WinDRM keeps track of the errors (bad data segments) in the file and with the BSR, the
data can be replaced with error free data using either the manual request (user
intervention required) or automated using the ARQ feature in a point to point QSO.
PC requirements
Windows OS, 2000 or XP. 700mHz minimum processor speed with 1.2GHz or higher to
ensure smooth operation. Avoid executing other programs while WinDRM is decoding or
transmitting. For testing/experimenting, 2+ GHz PCs can run two instances (i.e. A to B)
of WinDRM in a back-to-back mode (connect sound card line out/speaker to line in/mic
and carefully set levels or use Virtual Audio Cables VAC. Instance A may then be used
to transmit pictures to instance B. If VAC is available (a separate program), DV may
5
also be demonstrated since VAC take care of exchanging data between each instance of
WinDRM allowing microphone voice input to the sound card.
Status of received data in the Info box for images (RX Pics)
The “Info” box during receive provides a status of the data being decoded as it is
received. These counters are shown in three sets of one to three digits separated with a
forward slash (/). The first set is the number of memory segments (size) in the file. The
second set shows the number of good segments decoded. The last set shows the segment
number of the last segment decoded.
The first set of numbers represents what WinDRM “knows about” at the start of the
transmission and will change because the program begins assembling the data before the
total is known. If a segment is received in error (CRC failure), a following instance
provides the opportunity to receive it again. If received OK, the counter will increment.
After all the data is received, the segment counts will all agree indicating the file has been
received error free. If a picture was received, it will open up in Irfanview or the
viewer/program associated with the file’s extension. Note: The segment size increases
with the constellation size (4 thru 64) of the QAM since it is possible to transmit more
bits per symbol in the higher order constellations.
Status of received data in the Info box for voice (RX)
While receiving voice, the Info block displays 1 to 100% representing the quality of the
decoded data. The quality is determined by the number of good frames of data received
*versus bad since the last synchronization. Drop outs (speech loss) may be experienced
with 70 percent or less. With SNRs of 12 or higher, expect a quality number near 100
percent (no dropouts).
6
Status of transmitted data in the Info box for files ( TX Pics)
After transmitting the lead in sync data, the Info box provides the status of the file as it is
being sent. The counter consists of two sets of numbers separated by a forward slash (/).
First set shows the instance being sent while the second set shows the percentage (1 to
100 percent) of the total segments sent. The number of instances the file will be sent is
shown in the “Select File” window. A choice of 1 to 3 may be selected but additional
instances can be sent by adding the file in the Select File window more than once.
Status of transmitted data in the Info box for voice (TX)
No data is shown in the Info box during voice transmission except during the lead in sync
period.
Info box during “lead in” transmission
In both picture and voice transmissions, lead in sync data is sent to the receiving station
for setting up the timing and other OFDM carrier information. This lead in maybe
lengthened to provide more set up (sync) time at the receive end by selecting long lead in
under the Select Files window. While the lead in is being sent (up to several seconds),
the Info box will increment various numbers indicating this data is being transmitted and
the actual file data has not started. Some of this data includes determining the size of the
file and packetizing data prior to be sent.
Text Message data
Up to 128 ASCII characters (including spacing) may be transmitted. Greater than 128
will be truncated at the receive window. Text messages may not be sent with data
(file/picture transmissions). Text messages may be added or changed during TX. The
data rate is only 80bps, but the message is continuously transmitted during the voice
transmission. In receive, the text message window remains open at the end of the
transmission. This message window may be closed at any time but will re-open while
7
data is being received. Text messages may only be sent and received with Digital Voice
transmissions.
Transmit and Receive parameters (and transceiver setup)
For optimum performance, the OFDM carriers must fit within the band pass of the
receiver and transmitter. The default 350 Hz DC Offset was chosen to ensure the 2.5Khz
wide OFDM signal is inside both the transmit and receive audio band pass. The 350Hz is
an offset from DC (0 hertz) and where the carriers of the OFDM begin. The timing
(OFDM searches for this) locks on and starts all it’s shifting up in frequency from the DC
offset for all 57 carriers. This offset can be changed but it must chosen so the spectrum
will fit within the TX and RX band passes. If the DC is moved too much from 350, all
the OFDM carriers may not fit within these band passes. Although it is not important to
be exactly on the transmitting stations frequency, modern transceivers should allow the
receiving station to be within 100hz of this offset frequency. Too far off frequency may
result in lowering SNR if OFDM carriers fall outside the receiver’s band pass. If any
tuning of the frequency is made during receive, the signal is phase shifted and attenuated.
The orthogonality of the OFDM symbols may also be destroyed and this causes ICI
(inter-carrier-interference). This will immediately stop decoding data. Click on “Reset”
to re-sync the data if any tuning must be done to bring all carriers within the band pass of
the receiver. When the WinDRM users talk on SSB, carefully tune to their SSB
frequency. This will ensure you are on the frequency being used for DRM data also. Be
sure the receiver’s band pass is at least set to at least 2.5 kHz FLAT band pass with no
DSP and/or audio processing. For most receivers, setting AGC to Fast (or OFF) will
improve SNR. For transmit, minimize distortion by turning off compression, EQ (or DSP
filtering within the band pass) and avoid any ALC action. For 100 watt rigs, set power to
approximately 15 watts average power. This mode works best with very linear
transmitters and amplifiers. All commercial DRM transmitters are Class A. OFDM has a
rather high crest factor caused by the mathematical FFT operation applied to the
transmitted signal. The peak power is much higher (7-9 dB) than the average power read
on a conventional wattmeter. Experience has found that operating out of the linear region
of your transceiver and/or amplifier may result in a 3 to 4 dB lower SNR at the receiving
station. For a detailed explanation of how to set the power out of your transmitter, go to:
http://www.tima.com/~djones/DRM_power.htm WinDRM’s Shifted Power Spectrum
Density (Shifted PSD) in the absence of multi-path/QRM, will display a “Flat top” signal
across the entire bandwidth of the received signal. Ask the receiving station to comment
on your transmitted signal using this display. If it is not “flat”, then either the transmitter
or the receiving station’s is not set up properly which can degrade performance.
CODEC
Select under DRM TX Settings, “CODEC” (voice) or “DATA” (files/pics) being
transmitted will be displayed. Under program control (FAC data), the receiving station
will automatically decode and display the mode of transmission being sent (LPC,
SPEEX, or Data).
SNR
8
Signal-to-Noise-Ratio is an estimated value that indicates the quality and strength of the
received signal. Experience has found, near error free data may be decoded with a SNR
greater than 7.0 dB. The higher the number, the better the signal is being received. An
SNR of 10 or better usually ensures error free copy. QRN, QRM, transmit distortion and
propagation problems caused by multi-path cancellation lower the SNR. Transmitters
and amplifiers operating out of their linear region (trying to run too much power!), failure
to turn off compression or DSP/EQ and too narrow band pass all degrade SNR. Under
ideal band conditions, SNR will rise to 25db or greater when both the transmitting and
receiving stations are set up properly. Note: SNR is determined from the carriers
between the low (725Hz) and high (1850Hz) reference pilot carriers only.
DC
Refers to the frequency offset from 0 Hz to the start of OFDM carriers. Default is set at
350Hz. This is an arbitrary number chosen to ensure both the 2.3 and 2.5 kHz signal BW
“fits” within the bandpass of the receiving station. This may be confirmed by observing
the shifted PSD, transfer function displays or the moving waterfall displays. The accuracy
of the receiving station’s tuning for the COFDM signal is dependent upon this factor
which will allow a 100-125Hz tuning error without affecting the decoding process. It is
important to note however, that once sync is obtained, no further “tuning” of the signal
should be attempted. A blue vertical line indicates the location of DC offset. Values of 50
to 5000 Hz are valid entries but 350 Hz is normally used.
Mode
Displays the DRM TX settings. The default is:
B (DRM Mode B) S (Short Interleave) 16 (Main Service Channel 16 Quadrature
Amplitude Modulation) 0 (Protection level) 2.5 (2.5 kHz Bandwidth). Most stations
use 2.5kHz since additional carriers are available with this wider BW giving better
receive performance. TX DRM modes are selected to correlate with the quality of the
signal (as affected by propagation, signal strength, QRN, etc) available at the receive end.
These modes affect the transmission speed and robustness of the received signal. For
more info, see “DRM TX Settings” later in this doc.
9
Setup
Any com port 1 through 8 may be selected for control of the transmitter’s PTT using
conventional RS232C data terminal ready (DTR) line. For most applications, a standard
RS232C cable is used to connect the PC’s com port to the sound card interface
(RigBlaster or equivalent). In addition, the DTR or ready to send (RTS) line may be
used to mute the receiver’s speaker while receiving data. Implementation of this feature
may be found at KB4YZ’s web site. (http://www.kiva.net/~djones/index.htm ) WinDRM
may be started and the PTT controlled in the “Remote” (PTT on CTS or PTT on DSR)
mode using the com port’s CTS or DSR line. This Remote mode will allow the use of
external switching from the PTT switch on a microphone or a PTT foot switch. To avoid
a possible ground loop, an optical isolator or a relay should be used to assert (apply a
positive +5 to 12vdc) to either the DSR or CTS line. Note: Due to some ambiguity
between Windows OS and WinDRM, the CTS and DSR are reversed (CTS is pin 6 and
DSR is pin 8 in the 9 pin Sub-D PC’s com port connector). Use of a pull-down resistor
on these pins will help ensure no false PTTs. For com port protection, a current-limiting
resistor may be used in series with the positive voltage applied to the DSR or CTS pin.
This Remote feature is not saved in WinDRM’s user’s settings file therefore when used,
it must be checked each time the program is executed. TX voice may also be activated
using the keyboard’s spacebar. With “TX Voice” in focus (as show in above display),
taping the spacebar will put WinDRM in transmit (activating PTT) and pushing it again
will return WinDRM to receive (a toggle function). To un-focus TX voice and avoid
placing WinDRM in transmit while using the keyboard for other functions, push the
keyboard’s “Tab” key. Spacebar PTT will not function while in the “Remote” mode.
10
Setup
Call sign
Up to 8 number/letters may be entered. “NOCALL” is the default.
11
Setup
Display
Receive Spectrum
The Spectrum’s display is approximately 2.5 kHz wide in the horizontal while the
vertical shows the amplitude in dB (no scales are shown for any of the displays). The
shape of the signal is rectangular (flat top) and represents the 2.3 or 2.5 KHz band width
of the received signal. This display may be used to set the audio input level of the sound
card. Too much input will over-drive the sound card (line input should always be used
when available) and may cause distortion and low SNR. Carefully adjust the line input
level and the receiver audio until the top of the COFDM spectrum averages
approximately half way up in the display window. Although there is normally good
dynamic range in most sound cards, the goal is obtain the highest SNR reading. After
sync has been obtained, a blue vertical line will appear in the spectrum. This blue line
shows where the timing for acquiring the COFDM signal has started (the DC offset
frequency) which is normally 350Hz. This line may pop up intermittently as it will
“false” on random noise and should be ignored when no valid COFDM signal is being
received. The three reference pilot carriers are easily seen in the display with frequencies
of 725, 1475 and 1850Hz.
12
Receive Waterfalls
Three waterfalls are available, Moving, Static, and Flicker reduced. The COFDM
spectrum will be displayed with an even intensity level across its 2.3 or 2.5 KHz
bandwidth. Within the waterfall, three FAC reference (or pilot carriers) of higher
intensity can be seen. These stand out because they have higher gain (transmitted at
twice the power). These FAC pilots are modulated with known fixed phases and
amplitude which optimize DRM’s performance for initial synchronization, duration and
reliability. They are used to calculate the initial coarse frequency offset of the received
DRM signal. This is the first part of the COFDM sync process and must occur before the
received DRM signal can be decoded. The high-lighted red markers at the top of the
waterfall display indicate where the FAC reference carriers are located when the
transmitter and receiver DC offsets match. The moving waterfall sweeps from top to
bottom with the red marker’s indicating the position of reference carriers remaining fixed
at the top of the display. The moving waterfall adds a visual method to monitor the
health of the decoded signal in the form of a vertical line on each side of the waterfall
spectrum. During the decoding process, the green vertical lines indicate data is being
received without errors and red lines indicate errors. These green/red indicators move
with the spectrum instantly showing when and where the data errors occurred. The
horizontal line across the top of this display indicates the bandwidth of the COFDM
signal. The signal in the waterfall should fully extend the width of this line. The Flicker
reduced waterfall is a modified moving waterfall designed to reduce “flicker” from some
types of fast LCD or laptop displays. Note: The waterfall display shown above depicts
the effects of multi-path cancellation as shown by the darkened (“notches”) areas. The
carriers in this area are being attenuated due to these phenomena. The two bright lines (on
the bottom left, just before the start of data) is unwanted noise (probably caused by a
ground loop between the transceiver and the PC soundcard) on the Speaker Out audio
line to the transceiver’s Mic input. Every effort should be made to eliminate this type of
interference when connecting audio cables between the PC and the transceiver. To
minimize ground loop and/or RFI problems associated with sound cards and the
13
transceiver, refer to these informative papers found at:
http://audiosystemsgroup.com/SAC0305Ferrites.pdf
and http://audiosystemsgroup.com/Ferrites-Ham.pdf
Important: It can not be emphasized enough that common mode noise (i.e. ground
loops – ac currents) must be eliminated or risk the high probability that unwanted noise
will be heard in the speaker at the receiving station while decoding digital voice. When
this noise is present, it is directly proportional to the TX microphone (mixer) level input
and will reduce the favorable experience expected of this mode. Only the decoded voice
should be heard from the PC speakers.
Input Level (receive)
This display graphically shows the received audio. Sound card (recording) Line Input
may be set to approximate the level as shown in the display above.
14
Shifted PSD (receive)
This display plots the “estimated Power Spectrum Density (PSD) of the input signal”.
The X axis measures the PSD of 0 to 50dB while the Y axis is frequency from 0 to 12
KHz. Here the incoming DC frequency (350 Hz) is mixed with 5650 Hz to give a 6 KHz
(the blue vertical line is correctly shown in DRM mode B only). The peak on the left is
the mirror image (5650 – 350 = 5300 Hz) and is partially suppressed by the WinDRM’s
internal IF filter. If a peak is displayed between the signal and the mirror signal, a
50/60Hz noise could be in the transmitted audio from ground loop. The three peaks seen
at the top of the waveform are the pilot carriers for sync and have twice the power. Any
roll off or dips in the waveform indicate the carriers in these areas have a loss of power
caused by QSB and/or attenuation in the band pass of the transmitter or receiver. If the
transmitter or receiver does not allow the 2.3/2.5khz wide (350 to 2850Hz) DRM signal
to pass without attenuation, this waveform will roll off on either end. Up to 10dB or
more SNR can be lost because careful attention has not been taken to properly set up the
transmitter, receiver and soundcard for the “flat top” OFDM spectrum.
15
Transfer Function ( receive)
This plot shows the “squared magnitude of the channel estimation at each sub carrier”.
The green line is the transfer function (TF in dB) while the blue line shows the phase
distortion of the channel (Group Delay in ms). Optimum signals will yield a flat response
and display even/flat lines across the width of the display.
Impulse Response (receive)
This plot shows the “estimated Impulse Response (IR) of the channel based on the
channel estimation”. This pulse is used in determining the HF channel’s frequency and
phase characteristics so the signal may be restored as close as possible to what it looks
like at the transmitter. The time delay of the shortest path is taken as the zero reference
for the estimated pulse response.
16
Fast Access Channel (FAC) Phase (receive)
This plot shows the 4 QAM rectangular constellation. For more info on QAM see above
info under FAC radio button and this URL:
http://en.wikipedia.org/wiki/Quadrature_amplitude_modulation
.
Main Service Channel (MSC) (receive)
This plot shows the various constellations for a 4 through 64 QAM logical channel that
provides the voice and file data. High SNR keeps the points in a close (tight)
constellation but some scattering is expected on HF where the Reed-Solomon error
17
correction coding is applied. QAM varies the amplitude and phase of each one of the
carriers (for 16 QAM and up). Then, through frequency multiplexing (adding these
carriers together across the 2.3/2.5 kHz BW) the OFDM is created. 16QAM is shown
here.
Setup
CODEC
Either Linear Predictive Coding (LPC) or SPEEX open source CODECs may be selected
for digital voice. LPC is the default. All three require 2.5 kHz/2400bps minimum data
(default
CODECs, see: http://www.otolith.com/otolith/olt/lpc.html and http://www.speex.org/.
Robust DV is not “easy” to do on HF and may never meet everyone’s needs. A couple of
seconds delay is required for sync before voice can be decoded therefore fast break-ins
are not currently possible. And, DV is not as robust as SSB.
18
Setup
Text Message
Edit TX Text Message (voice mode only)
Selecting “Edit TX Text Message” will open up a window to enter text.
Up to 128 ASCII characters (including spacing) may be transmitted. Greater than 128
will be truncated in the receive window. Text messages can not be sent with data
(file/picture transmissions). Text messages may be sent, changed or deleted during a
voice transmission. The data rate is only 80bps, but the message is continuously
transmitted during the voice transmission. This may be used to send your QTH and
station info and will remain open after the DV transmission has been completed.
Allow RX Text Message (default)
Default provides a window for receiving the transmitted messages. This text message
window remains open for further review after the transmission has ended. (For more info,
see previous “Edit TX Text Message” description)
19
Setup
Save Received Files
Checked (default) indicates files received without errors will be saved in the sub-folder of
WinDRM named “Pictures”. If a file is missing segments, it will be saved in the
“Corrupted” subfolder. Both of these folders are initially created by WinDRM.exe.
20
Show Received Files
Checked (default) indicates error-free files will automatically be displayed (when
associated with a viewer such as Irfanview). Irfanview is the “viewer of choice” and may
be downloaded free at www.irfanview.com Irfanview requires a plug-in and must be
associated with the image file extensions (.jpg, jp2 etc) to display pictures. In Irfanview,
go to Options>Set File Associations>Extensions then select “Images Only” or just check
the extensions you wish Irfanview to display. Note: Received files and pictures will be
saved in the Pictures or Corrupt folders even if no viewer has been configured. Note:
Plug file name is typically named irfanview_plugins_xxx.exe (xxx = version).
Show Only First Instance
Checked (default) indicates only a single instance of an error-free file will be displayed
when received multiple times.
21
Soundcard
Opening the mixer will display the sound card’s “Recording” and “Playback” sliders for
Audio in and out. These are associated as follows:
RX Input = Mixer Recording Line-In (connect to receiver’s speaker)
TX Output = Mixer Playback Master Volume (connect to transmitter’s microphone input)
Voice input = Mixer Recording Mic-In (connect PC microphone to soundcard)
Voice output = Mixer Playback Master Volume (connect to amplified PC speakers)
22
For Digital Voice using a single sound card, inputs are switched under program control
(receive line-in switched to mic-in for transmit). Adjust mixer sliders for proper input
and output levels. Start with the “sliders” approximately one-third up. Only the
RECORDING microphone should be enabled. For transmit, PLAYBACK Master
Volume and Wave Out must be selected. Use the Master Volume for the coarse
adjustment and Wave out as the fine adjustment. Note: Uncheck/deselect all other
inputs/outputs. For decoded Digital Voice, Mixer Playback Master Volume must be
manually switched between the PC’s amplified speakers for receive and the transmitter’s
mic input for transmit. If two sound cards are available, set up one card for Receive and
the other for Transmit. Then, no manual switching will be required. Note: For ease of
setup/use, two sound cards are highly recommended Digital Voice. It is very easy to add
a second sound card especially if it is a USB. A low cost “USB 2.0 to Audio Adapter
w/Microphone Jack” card for (under $10) may be found at www.geeks.com. This is a
thumbnail size card (p/n HE-280B) and requires no additional drivers for XP. Just plug
it in, XP finds and installs the drivers and WinDRM will display both cards under
“Soundcard”. USB headsets may also be used (i.e. Logitech 250/350) For further help
with the Soundcard Mixer, see http://www.sagebrush.com/mixtech.htm
DRM TX Settings
Mode A/B/E (A = Ground wave B = Single to multi hops E = NVIS Multi-hops)
MSC Protection (
BandWidth (2.3Khz – 2.5Khz)
Interleave (Short 400ms – fast QSB Long 2sec – Slow QSB)
MSC Coding (4/16/64 Quadrature Amplitude Modulation)
DC Offset (50-350-5000Hz)
Clicking the Default button will result in the following
23
Mode MSC Protection Bandwidth Interleave MSC Coding DC offset
B Normal 2.5 Short 16QAM 350
Robust lowers the transmission BPS by changing 16QAM to 4QAM. Speed raises the
transmission BPS by changing Mode to A, MSC protection to Low and Interleave to
Long 2 seconds. Long interleave requires additional sync time. Voice requires 2.5kHz
bandwidth for the 2400 bps CODECs. 64QAM on a HF channel requires a higher SNR
and minimum multi-path to perform well. MSC Protection A, B and E provides different
levels of forward error protection (FEC) to protect the MSC from the detrimental effects
of QSB/QRM/QRN. B is higher than A with E (known as D in DRM) for Near Vertical
Incidence Skywave (NVIS) transmission where the signal is transmitted with a very high
angle of radiation short path propagation. In practice, however the extra protection for
this mode appears to have limited results. In DRM, Mode A is used for ground wave
propagation where Mode B for single hop/multiple hop propagation. The default mode
“B” on HF has shown to have the best overall performance. Mode E has been shown to
be the most robust in the presence of multipath and weaker signal levels.
Note: A BSR request may be made using different (larger to smaller QAM constellation)
the request through lower SNRs. However, the originating station responding to this
request must send the response to this request (“Send bad segment report”) in the same
DRM RX Settings
Default settings are:
24
Freq. Acq. Sens. Search Window Size Auto Reset
60 350 Enabled
Higher settings increase sensitivity for weak signals but with higher probability of false
sync. Fast Auto Reset has shown to be effective in providing faster sync recover under
poor signal conditions. These settings work well in the default mode, however this is a
good area for hams to experiment and find what settings are best under varying
signal/band conditions.
BSR (Bad Segment Report – automated)
BSR provides a procedure to repair (sometimes called a “fix”) a defective file or picture.
Normally, a defective file or picture is caused when the received station does not receive
all the memory segments error free (segment failed CRC check). Depending upon how
many segments were not received, the picture may not be displayed using the SPA (Show
Picture Anyway) or will appear unclear/blurry. When this happens, clicking on the
“BSR” button will open a window and show the number of segments “missing”. The
received station may then send a BSR “Request” to the sending station and request these
missing segments be resent so the file (picture) may be repaired and displayed. This is the
manual method and requires user intervention. The “automated” BSR completely
automates this procedure for P2P (point to point) transfer of files. Auto Open BSR
request, TX ARQ and RX ARQ must be checked to initiate this procedure. Note:
WinDRM does not look for activity on the frequency. The procedure simply relies on
timing between the tx to rx and rx to tx change-overs and does not “listen” on the channel
for other activity. Therefore, users should maintain control of the station while this
automated BSR is being executed, i.e. “attended” operation. Upon a successful Auto
ARQ exchange, the sending station will send “Good Copy” to the receive station’s
waterfall. Note: Up to 30 additional segments are sent in with the receiver’s BSR. These
“additional” segments are sent to ensure the receiving station is in sync. Up to four
multiple BSRs windows may be open at one time. There requests may be transmitted one
25
at a time or all can be transmitted by clicking on the “BSR send” button while any one of
these request are being made (during transmission).
Load last RX file
When selected, the last error free file received will be loaded in the “Select Files”
window. This is normally used when the entire file is to be re-sent.
Auto open BSR request
Automatically opens up the BSR window when a defective file is received. This must be
checked to initiate the automated BSR procedure.
TX ARQ
Automates the “send” request for the BSR
RX ARQ
Automates the “receive” request for BSR Note: For auto BSR, both transmit and receive
stations must have Auto open BSR Request, TX ARQ and RX ARQ checked.
BSR (button)
Bad Segment Report
When a picture is received with segments missing, a left click on this button will display
the number of segments. Press “OK” to request these segments be re-sent.
26
SPA (button)
Show Picture Anyway
Left click on this button will attempt to associate and display the last received picture
even if it the file is incomplete. If there is enough data for the picture to partially
assemble the picture, it will be displayed. Dependent up on the amount of missing data
(memory segments) and preference of the received station, the user may then click on the
BSR button to show the number of segments missing. Now, the BSR the request can be
made to resend the missing data. The picture above is an example of a picture displayed
using the SPA with missing segments.
Picture shown “repaired” after receiving the missing 35 segments using the BSR request
procedure. Note: This entire procedure may be automated when the “Auto Open BSR,”
“TX ARQ” and “RX ARQ” checked.
27
Example of the transmitting station’s responding to a BSR request. Note: This is not the
data used in the previous repaired picture.
G (button – works with Windows XP only)
Good (good picture received)
Left click on G will transmit a pre-recorded wave file displaying “GOOD” in
the received station’s waterfall. Filename: g.wav
B (button – works with Windows XP only)
BAD (bad picture received)
Left click on B will transmit a pre-recorded wave file displaying “BAD” in
the received station’s waterfall. Filename: b.wav
28
ID (button – works with Windows XP only) Left click on ID will transmit a pre-recorded
wave file displaying the transmitting station’s call sign in the received station’s waterfall.
Filename: id.wav
For help in creating these wave files, go to KB4YZ’s web site:
http://www.kiva.net/~djones/index.htm
TUNE (button)
Left click on TUNE will transmit a pre-recorded wave file for setting the proper output
level of the transmitter. Three reference pilot (sync) carriers will be displayed in the
received station’s waterfall. From left to right, A=1850Hz, B=1475Hz and C=725Hz.
With a properly adjust transmitter (good linearity – not overdriven!), the receiving station
will only see these 3 carriers. Any others displayed (at the receiving station) are products
of inter-modulation distortion which will degrade performance. See KB4YZ’s WinDRM
tuning file at http://www.tima.com/~djones/drmtune.htm. Non-linearity can cause
spectral re-growth of unwanted carriers. Driving the typical transceiver and/or power
amplifier too hard will cause this spectral regrowth (unwanted carriers). Yes it is just as
bad as it sounds and it should be avoided. Drive 100w transceivers to only 20w max
average and a typical 1kw amps to 200w average power. For the adverse effects caused
by non linear transmissions, see http://www.tima.com/~djones/DRM_power.htm
29
TX Pic (button)
Left click opens a window to add or remove files for transmission. Radio buttons enable
from 1 to 3 instances of the file be transmitted. Additional instances of the same file may
be sent by adding the file multiple times in the Select Files window. Long Leadin
increases the time for sync data at the beginning of the transmission. This is used in the
presence of weaker signal conditions or QRM to help ensure the sync is made at the
receiving station prior to sending the file data. Return button closes and returns to the
opening WinDRM display. TX button starts transmission of sync data followed by the
file data.
30
TX Voice (button)
Left click starts a voice transmission (or if in focus, tap the spacebar). The microphone
must be connected to the soundcard’s “MIC” input. The display graphically shows the
transmit microphone level (sound card’s microphone input). Adjust the mixer’s Record
slider while speaking across the PC microphone. Best results will be found when the
microphone input level is kept rather low while speaking in a loud tone of voice. Keep
the average level so peaks fill approximately 50-75% of the display. Speaking too loud
will cause the display to turn red. Some PC electret microphones have poor non-linear
response and may sound “basey” yet tend to accentuate the highs which cause high peaks
and distortion in this application. Experiment in this area to find the best microphone and
level for the highest speech quality The audio filter may help the intelligence of the
speech in some conditions. SPEEX sounds like it adds more fidelity to the speech (when
compared to LPC) but at the same time, it is a bit muffled and tends to “flat top” the input
easier. This is an area where a well chosen microphone (such as a one from Heil Sound)
will improve the voice quality. The input impedance of most sound cards microphone is
approximately 2500 ohms. This impedance may vary but should be a consideration when
choosing a microphone. The TX button name changes to “RX” while transmitting.
“Echo” of the decoded voice may be caused by some combinations of PC and soundcard.
This may be a soundcard latency problem related to the timing and transfer of data or a
ground loop. Changing sound cards may correct this problem. Known “good” low cost
sound cards include M-Audio, and Sound Blaster Audigy series. When retuning to
Receive, the button label will momentarily display “Wait” (for approximately 2 seconds)
while the transmit buffer empties. If the “Remote” feature is activated (PTT on DSR or
PTT CTS checked under Setup>
display Remote.
Note: A very small low cost (less than $10 USD) USB sound card by C-Media (HE-
280B has shown to perform very well with WinDRM. It may be found at
www.geeks.com Or use a USB headset such as the Logitec model 250 or 350.
31
RESET (button)
Reset re-starts the sync process in receive. Normally, this button is rarely needed.
About
Info
32
About
Help
33
Typical connections between PC, interface and radio
See “
available com port 1 thru 8 may be used for all functions (PTT, Spacebar PTT, Remote
PTT and Transceiver Speaker Mute).
Further DRM technical info and software may be found at:
http://www.drmrx.org/, (DREAM 1.10.6cvs or later) and www.drmradio.co.uk
------------------------------------------ -------------- ------------------------------------------
updated 23-Jul-2008
© copyright 2005-2008 by Mel Whitten, KØPFX – mel@melwhitten.com
Suggested Frequencies: (Warning – most of these are from web pages dated two or more years ago…things look bad)
80 Meters:
3.606 net, 7pm CST, usually daily except Saturdays
40 Meters:
7.130 2230Z net
7.096 EU
7.169.33, 7.170, 7.173, 7.177, 7.286, 7.291 (USB)
20 Meters:
14.255 EU
Monday-Friday daily net at 11AM Eastern time - 14.236
Saturday/Sunday net at 1900 UTC - 14.236
14.236 is most popular AOR frequency
17 Meters:
18.1625
15 Meters:
21.370
Sorry, many dead links on the AOR and FDMDV pages – especially the on-line finder for skeds
http://n1su.com/aor-ard-9800.html
http://n1su.com/fdmdv/download.html
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