## Wednesday, June 25, 2008

### Antennas 2, The Ground Plane Vertical (Bob, Week 6)

This week we introduce the other most common type of antenna. It goes by many names but they all essentially refer to the same thing. Here are some of the names:
• Vertical
• Ground Plane
• Quarter-Wave Ground Plane
• Monopole
Not all vertical antennas are a quarter-wave of course and they are not even all ground plane antennas, but the names above usually refer to the quarter-wave ground plane antenna and that's what we will discuss today.

HOW DOES IT WORK?
Let's recall the dipole from last week. That antenna is center-fed and is 1/2 wavelength long overall. So each radiating half of the antenna is 1/4 wavelength. Further, this is a balanced antenna where each side is being fed a voltage and allows a current to flow. The voltage and current is opposite going to each half.

The quarter-wave ground plane antenna is one half of that dipole and the ground plane acts like a mirror to electrically give the appearance of the other side of the dipole. Most people have seen at least a photograph, if not in person, where a mountain is reflected off of a very still lake or pond. It appears that there is a mountain exactly like the real one but directly below it and upside-down. The same idea applies to the ground plane antenna. The ground plane is the still pond and the vertical monopole is the mountain. To a receiving antenna it looks electrically like a vertical dipole with the bottom half of the dipole being the reflection.

What make this antenna work the way it does is the ground plane so let's talk a bit more about that. The ground plane acts as a reflector but it doesn't have to be mirror smooth. In fact it doesn't even have to be solid. A typical ground plane is 3 or 4 wires extending more or less horizontally from the base of the vertical element. Because of the size of wavelengths we are dealing with this is sufficient to give the "mirror" effect. Also it's important to note although it may seem obvious that the ground plane is actually kept at ground potential. That means no voltage and no driven current. (There probably is induced current but I haven't studied up on this and I'll leave it for another time.) It also means that this is an unbalanced antenna. Unlike the dipole where we are driving the two elements in equal and opposite directions, with this antenna we are only driving the vertical element and not driving the ground plane.

WHAT DO YOU MEAN "MORE OR LESS HORIZONTAL"?
I didn't say that because we don't care if it's horizontal or not. Although it's true that the ground plane will work even when the elements are not exactly horizontal. But we do care what the angle is because changing this angle changes the feedpoint impedance. This allows us to create an antenna that closely matches the standard 50 Ohm impedance of the unbalanced coax feedline used by amateurs. It turns out that if the ground plane itself is up at least one-half wavelength off the ground (earth, the ground you are standing on) then a horizontal ground plane has an impedance of 22 Ohms. If you tilt the ground plane elements down 45 degrees, the antenna will have an impedance very close to 50 Ohms.

A SIMPLE HOMEMADE QUARTER-WAVE GROUND PLANE
By putting together the elements described above you can make a simple home-made ground plane antenna for 144 MHz out of nothing more than a female UHF connector and some heavy solid copper wire. This was my second homemade antenna (a wire dipole was the first) and I got some very good reports reaching a long distance on low power. You get a UHF connector designed to be attached to a flat plate. It will have a square plate attached with four holes, one at each corner. You simply solder the vertical element which is a measured length of wire to the center conductor of the connector and make small loops on the end of the four ground plane wires, use screws and nuts to hold them in place and solder them as well. The plans are in the ARRL Handbook and the Antenna book and must be online somewhere. I will look for a link and add it.

As promised here is just the first link that came up when I googled. There are doubtless many more.
2 Meter Ground Plane Project

## Wednesday, June 18, 2008

### Antennas 1, The Dipole (Bob, Week 5)

This week we begin an open-ended series on Antennas. Antennas are the one part of our hobby left where it is common and worthwhile to build your own gear. It's true that you can still build your own radio, amplifier, power supply, etc. and many do, but with the advent of modern electronics this is now much less common than it used to be. But antennas haven't changed too much over the years. There have certainly been some new and effective designs but the basic function and design is still as valid today as it was in the very early days of radio.

Today I start with the Dipole, also known as the Half-Wave Dipole since the length of the antenna is roughly one-half wavelength of your operating frequency. More on why it is only "roughly" one-half wavelength later. The dipole is good for illustrating some of the antenna basics and is a good and effective do-it-yourself antenna if you have the space and can get it high enough off the ground.

So, what is it? and why half-wave? A dipole at it's simplest is a long straight conductor that is broken at the middle into two separate halves. Each half is connected at the center by one of the two conductors of your feedline. Because of this way of connecting your feedline to the antenna we say that a dipole is a center fed antenna. As the RF current passes from the feedline to the antenna it is stopped by the endpoints of the antenna. So the current at the endpoints is zero and it is at a maximum at the feedline connection. The reason a half wave is chosen is so that the antenna will be resonant.

RESONANCE
Resonance could be an entire topic on it's own and maybe someday it will be but I'm not prepared to go into it in depth today. Instead I will give you a musical analogy. When you blow across the top of a pop bottle you hear a tone of a given frequency. Let's not worry about harmonics just now. The reason you hear the tone you do is because the bottle is resonant at that frequency. When you blow across it, the sound you make isn't of any given frequency. That sound travels down to the bottom of the bottle and back up again in a certain time and reinforces the sound you made. The time it takes to go down and back determines the frequency of resonance. In a similar way, the resonant frequency will depend on how long it takes a radio wave to travel the length of the wire antenna and be reflected back. It turns out that the distance to do that is one-quarter wave. Since you have two of these quarter-wave pieces, end to end, you get a half-wave antenna.

WHY 'ROUGHLY' HALF-WAVE?
When we talk about a wave-length we are talking about how far the wave would travel in the time it takes to go through one cycle. In general when we talk about the speed of radio waves we say that it is the same as the speed of light. But inside a wire it is not. It is actually a bit slower so we have to apply a factor to the calculation. So in effect the antenna is a half-wave long but it is a half-wave at the speed it travels in the wire.

BALANCED OR UNBALANCED?
I will fill this in more later...

## Tuesday, June 17, 2008

### IMPEDANCE SERIES PART 4, Lee week 5

June 18, 2008 Educational Radio Net, PSRG 5th session

Much like any radio talk show I will "set up" the topic and then allow time at the end for questions or comments. Truth be known this subject is a mathematical adventure but, given that we do not have a "white" board for graphic illustration, I will attempt to convey fundamental ideas verbally.

This session is the 4th in the impedance series. Given that impedance is the combination of reactance and resistance and, further, that reactance is an alternating current phenomenon it is clear that we must have some elemental definitions under our belts to fully appreciate the subject. This multi-part series is an attempt to elevate participants, in narrative fashion, to an intuitive level of electrical understanding without using any serious mathematics.

In part 1, I developed the idea of electrical current consisting of moving charge and defined the ampere as 1 coulomb of charge moving past a fixed point in 1 second. One coulomb was defined as a collection of charge numbering 6.24 x 10^18 electrons.

In part 2, I continued with the notion of mechanical "work" and considered objects at different "potential" levels in a gravitational field. The concept of "voltage", also known as electrical potential difference, and the relationship of voltage to current follows closely with the idea of a mechanical weight being moved between different levels. In both cases work is being done and energy is being manipulated in various ways.

In part 3, I capitalized on Bob’s lightning series to review electrical current in the context of a charged cloud redistributing charge in the form of lightning where modest amounts of charge make a large impression if moved rapidly.

In part 4, this edition, I will return to the notion of potential difference and end with a definition of voltage.

Where are we going with these discussions you might ask? Once we have the notions of electrical current and voltage well in hand I will introduce the notion of "power" in both the mechanical and electrical context. After the power discussion I will introduce the physical property of materials called resistance and then merge the voltage, current, and resistance trio into the workhorse notion of Ohm’s Law. Subsequent parts of the series will introduce AC, or alternating current, and DC, or direct current, followed by capacitance and inductance, then reactance, and, finally, I will introduce impedance as the combination of resistance and reactance. All discussion material will be reviewed continually and be available on the blog.

So… let’s take a look at the notion of electrical potential difference. Remember in part 2 we talked about a box on the floor and considered the mechanical work involved in moving the box from the floor to a table top . In this example the Earth’s gravitational field resisted the elevation change of the box. Recall that the box, if falling from the table top to floor, simply gave up the work done when initially moved from floor to table top. Additionally, while on the floor the box had some potential to fall into the basement. So, clearly, one could measure the difference in potential work required in moving between basement and floor and table top. Given that work and energy are identically the same we can make the claim that the energy stored as a result of the box moving from floor to table top is just the difference in potential energy (or work) between these two levels. What are the units of energy? In the physical sciences the common term used is joule. Less common is the erg. Watt-hour meters also measure energy and are commonly found at the electrical entrance to your home. In subsequent parts of this series we will discuss the relationship between energy, power, and time in detail.

You will not be surprised to learn that charge in an electric field behaves much like a box in a gravitational field. Electric fields are produced by charge separation. For example, the lightning associated cloud, or charge separated cloud, in proximity to the Earth’s surface creates a very significant electric field with respect to the Earth's surface. The bottom line is that charge in an electric field gets pushed around. One of the early investigators of these sort of phenomenon was a fellow by the name of Coulomb and the assemblage of charge in the amount of 6.24 x 10^18 electrons bears his name. Coulomb studied the force of attraction or repulsion between two charges and formulated the equation known as Coulomb’s Law which shows the force to be directly related to the charge magnitudes and inversely related to the separation distance squared. Coulomb’s Law is very similar to the universal gravitational law wherein the attraction force is directly related to the objects mass and inversely related to the separation distance squared. In both laws the force drops off very rapidly with separation distance.

Now, let’s consider charge in an electric field. Suppose the field is directed to the right as in points to the right. A positive charge… also know as "conventional" charge… in this field will move in the direction of this field or to the right. If you choose to push the charge in the opposite direction then you must supply energy or, in mechanical terms, do work on the charge to make it move. Now we can define the volt in terms of the work done in moving charge from point A to point B. If you move 1 coulomb of charge in an electric field such that 1 joule of work is done then the potential difference between points A and B is defined as 1 volt. Another way to state this is that 1 joule is required to push 1 coulomb through a potential difference of 1 volt.

Let’s look at the practical ramifications of this definition. Take a D cell for example where common knowledge says that the available voltage is 1.5 volts. Placing both voltmeter probes on the positive terminal shows zero volts or no potential for doing any work. However, placing one probe on the positive terminal and the other on the negative terminal shows 1.5 volt difference and indicates that the battery can do some work. The battery potential difference of 1.5 volts can push some charge through an external circuit and do some useful work. A D cell can do more work than a AA cell since there is more active material available inside the battery to maintain the terminal voltage.

In summary, gravitational fields and electrical fields behave much the same mathematically. In both cases work is done when moving objects against these fields. Relative or "net" work is the difference in potential work at different locations. Net work in the amount of 1 joule is required to move 1 coulomb through a potential difference of 1 volt.

This concludes the set up discussion of electrical potential difference or more simply voltage. Are there any questions related to the concept of voltage?

## Wednesday, June 11, 2008

### IMPEDANCE SERIES PART 3, Lee week 4

June 11, 2008 Educational Radio Net, PSRG 4th session

Much like any radio talk show I will "set up" the topic and then allow time at the end for questions or comments. Truth be known this subject is a mathematical adventure but, given that we do not have a "white" board for graphic illustration, I will attempt to convey simple ideas verbally.

This session is the 3rd in the impedance series. Given that impedance is the combination of reactance and resistance and, further, that reactance is an alternating current phenomenon it is clear that we must have some fundamental definitions under our belts to fully appreciate the subject. This multi-session series is an attempt to elevate participants, in narrative fashion, to an intuitive level of electrical understanding without using any serious mathematics.

In part 1 we developed the idea of electrical current consisting of moving charge and defined the ampere as 1 coulomb of charge moving past a fixed point in 1 second. One coulomb was defined as a collection of charge numbering 6.24 x 10^18 electrons.

In part 2 we continued with the notion of mechanical "work" and considered objects at different "potential" levels in a gravitational field. The concept of "voltage", also known as electrical potential difference, and the relationship of voltage to current follows closely with the idea of a mechanical weight being moved between different levels. In both cases work is being done and energy is being manipulated in various ways.

In part 3, tonight's session, I had intended to continue with the voltage idea however the discussion of lightning phenomenon last week has presented a fine opportunity for reviewing moving charge so I will seize the moment and rehash moving charge in the context of lightning. Never fear... voltage will be dealt with next week.

So... consider a cloud. The average cloud consisting of water vapor is electrically neutral, more or less, so sticking probes here and there throughout the cloud would show no significant "potential difference" or voltage. Now consider the Earth under the cloud. Pretty much electrical neutral or tending toward a slight negative charge.

There are times, however, when the cloud is experiencing severe temperature differences and turbulence which can lead to a process of charge separation. The process of charge separation is actually electrical "work" being done in the cloud. Negative charge, or electrons, migrate to the cloud bottom known as the N-region and positive charge, that left over after the separation process, migrates to the cloud top per some rule of nature where it resides as the P-region. The cloud has been transformed by mother nature from a neutral blob of water vapor to a polarized, or charge separated blob. Texas A&M meteorology experts believe that the separated charge in the cloud can amount to around 40 coulombs in both the negative and positive regions.
See http://www.met.tamu.edu/class/Metr304/Severedir/LightningDir/lightning-stu.html

Now let us consider the Earth below that polarized cloud. We have not talked about it but everyone knows that opposites attract and that likes repel. The same holds true for charge... charge of opposite sign, + and -, experience some force of attraction whereas charge of like sign, ++ or --, repel one another. Since the Earth is nearest the bottom of the cloud and the cloud bottom is negatively charged, any free negative charge moves away from the immediate vicinity of the cloud. As a result the Earth surface becomes polarized below the polarized cloud. The cloud is said to have induced the opposite charge on the ground.

There are other examples of charge separation. Consider what happens when you shuffle your feet on the carpet on a dry day and then approach a door knob. Ouch for sure. Shuffling your feet over certain carpets causes a separation of charge on your body and the discharge spark between finger and door knob is just a miniature lightning strike. Excess charge on your body and clothing is looking for a lower potential object with which to neutralize itself.

Another example is laboratory demonstrations of charge separation. Rubbing fur across a rubber rod will cause the rubber rod to become negatively charged whereas rubbing silk on a glass rod will cause the glass rod to become positively charged. Separating charge by rubbing or friction is called the Triboelectric effect.

One more bit of information figures into our discussion. Charge distribution. Let me assert without proof that charge distribution goes inversely as the radius of the charged object. Take an egg for example... it has a pointy end and a not so pointy end. Since the pointy end radius of curvature is smaller than the not so pointy end radius, the pointy end will accumulate more charge than the blunt end. If the pointy end of the egg were similar to the point of a needle then the bulk of the charge on the egg would be found at the needle point. Such large concentrations of charge are associated with large potentials and tend to produce corona discharge which is sometimes called St. Elmo's Fire. Many times you can even hear the sizzle during a thunder storm. Given that your finger is more pointy than the rest of your body there will be a charge concentration at your finger tip and get your attention when discharged to a door knob.

Back to lightning. The surface of the earth under storm clouds certainly has pointy irregularities such as transmission towers or church steeples or some such so the induced charge is not distributed uniformly. Even the ocean may have large waves with pointy tips. In like manner the polarized cloud bottom may have features which tend to concentrate charge at points. Since pointed objects have large charge accumulations and large charge accumulations go hand in hand with high potentials there is the strong possibility of corona discharge from both the Earth and cloud. High speed cameras have shown that corona discharges called "leaders" are produced from the Earth upwards and from the cloud downwards. When two leaders touch then a low impedance... that Z word again... path or circuit is established which provides an easy path for charge transfer.

Now we can finish the review of charge and the transfer thereof.

Texas A&M folks also believe that the average lightning strike involves about 25 coulombs of charge transfer. Recall that 1 coulomb per second equals 1 ampere. Consider that a 120 volt, 120 watt incandescent house lamp requires 1 ampere to operate. So, the average lightning strike charge of 25 coulombs, if transferred in 1 second would operate 25 of the 120 watt lamps for 1 second. Suppose that the 25 coulombs were transferred in 1/10 second. Then the current climbs to 10 times 25 amperes or 250 amperes. Suppose that the lightning discharge lasted only 1 millisecond... then the current would be 1000 times 25 amperes or 25,000 amperes. Since the average strike lasts a bit less than 1 microsecond... 1 millionth of a second... we can say that the current or moving charge is at least 25 mega amperes. The point here is that small amounts of charge, if moved rapidly, represent huge amounts of current flow which can instantly and explosively boil the sap in trees or blow roots right out of the ground.

In summary, we can see that neutral objects... clouds or people or laboratory rods... can suffer charge separation and become polarized which may lead to lightning strikes or mild shocks when reaching for a door knob. Additionally, small amounts of charge can produce enormous electrical currents if moved very quickly and cause serious damage to people and things including sensitive electronic equipment. Finally, the distribution of charge on any object depends on surface irregularities.

This concludes the set up discussion of charge in motion as in lightning strikes. Are there any questions related to the concept of moving charge?

## Tuesday, June 10, 2008

### Lightning Protection 2 (Bob, Week 4)

June 11, 2008

This second part will cover commercial products and techniques for protecting your equipment from lightning damage even if they are still plugged in.

Review
First the good news. Lightning strikes are comparatively rare here and up and down the West Coast compared to just about anywhere else in the United States.

But...
Lightning can damage your equipment even if it doesn't strike your antenna. It can come in through the power lines, the phone lines, weather station connections and even the ground.

The easiest and best way to protect your equipment is to disconnect it from any lines that connect outside your house. But if you want to be able to keep it plugged in there are products that can help prevent damage. They aren't foolproof but considering the low incidence of lightning strikes you can expect near you it may be all you need.

The General Idea
What you want to do to protect your equipment is to have any electrical spikes caused by the lightning to pass directly to ground without coming into your equipment. I am going to present a few products and techniques but these are by no means comprehensive or definitive. In other words, don't accept this as the best information. I hope to give a good start and expect you to do your homework for your set up.

The first thing you need is a good ground. This should be, the same as your RF ground. A good ground makes as much contact with the earth (dirt) as you can practically make. One good way to make a ground is to have several copper rods spaced several feet apart connected by a heavy copper strap. Another benefit to living in this area is that our soil is mostly clay after you get below the first few inches of topsoil. This is bad for gardeners but good for grounding. Clay has the lowest resistance (technically resistivity) of the common soil types.

Inside the shack, for lightning protection it is very important to have a single point to ground all of your equipment. In the RF ground segment I talked about using a copper strap or pipe. I still think these will serve but an even better solution is a large copper plate that you can directly attach your lightning protection equipment to. Whatever you use, you must then have a low impedance path to ground. The idea is to have the easiest path for the lightning or surge to take be directly to the earth outside your shack. A good choice for the connection between your single point ground and the earth is a 1 1/2 inch flat copper strap. You could even go with a wider strap for lower impedance and better protection.

Connected directly to the single point ground should be your lightning/surge protection equipment.

I am by no means an expert and this is a subject open to great debate so take my recommendations as just one opinion based on reading some of the more recent articles.

For AC power protection you have two options, one is to protect your entire house at the circuit breaker. According to a recent QST article, you can do that using MOV's for about \$500. Another way would be to have the protection only for your gear by having a surge protector on the one power line that powers your gear. Powerstrips with built in surge protectors won't do much against a direct or near lightning strike.

For the COAX coming in, a poplular choice is one of the Polyphaser products. The B50 series are appropriate for amateur radio. These are gas tube devices and are said to be better than the spark gap type for newer equipment. The idea is that the old separate component and tube gear was much more resistant to surge damage so a spark-gap protection device would be sufficient. But with today's gear you need something that will redirect the energy to ground allowing less to get through to your sensitive gear.

Don't forget your other connections outside the shack: phone lines, gps, weather station, etc. All will need to be protected or disconnected to ensure the safety of your gear.

Polyphaser's Ham Section

Lightning Protection for the Amateur Radio Station -- Part 1 QST June 2002
Lightning Protection for the Amateur Radio Station -- Part 2 QST July 2002
Lightning Protection for the Amateur Radio Station -- Part 3 QST August 2002

Polyphaser Technical Article for Ham Radio
- lengthy and informative article considering they want to sell you their products.

Here is a great link that I found with lots of good information. I am adding it particularly at Lee's request because it shows relative resistivities of different soil types.
OH5IY's Lightning Protection Page

### ARRL FREQUENCY MEASURING TEST, Lee week 1

May 21, 2008 Educational Radio Net, PSRG 1st session

Topic notes: Frequency measuring tests
FMT of 5/21/08
Early transmitting equipment, quartz crystal control
LM series frequency meters
100 Khz crystal calibrators (Kenwood TS-820, etc.)
WWV, WWVH, WWVB, GPS, CHU, etc.
WWV website, etc.

See: http://tf.nist.gov/stations/wwv.html

### IMPEDANCE SERIES PART 2, Lee week 3

June 4, 2008 Educational Radio Net, PSRG 3rd session

One of the topic suggestions from Dave, KE7RJI, was impedance and antenna matching. This is a great topic but one of enormous scope and complexity. After some thought I felt it appropriate to serialize the topic and spread it over several weeks so that we can deal with the component subjects in more detail. To this end we must all speak the same language so a discussion and review of elemental concepts is essential so that we can use them for building blocks. My intent is not to "whip" you into engineers but rather give you the tools to listen to engineers and have a good intuitive understanding of just what is going on.

Impedance is one of the corner stones of electrical theory in general and radio systems in particular. To really grasp the significance of the symbol "Z" requires at least some understanding of the big three circuit elements... resistance, inductance, and capacitance plus some understanding of electrical current and voltage. Last week we started the narrative by discussing the most elemental idea in electrical physics... that of "charge", both moving and stationary. This week we will review "charge" and add the notion of "voltage". In the weeks following we will address the circuit elements in turn and then review and, finally, merge them together into some coherent structure.

Much like any radio talk show I will "set up" the topic and then allow time at the end for questions or comments. Truth be known this subject is a mathematical adventure but, given that we do not have a "white" board for graphic illustration, I will attempt to convey simple ideas verbally.

So, lets get started with the review of "charge".

In the formative years of electrical theory it was understood that something clearly moved when influenced by electrical forces. That hypothetical "something" was given the name "charge" and considered to be positive due to the direction it would move when in the presence of some motive force provided by a, so called, electric field. Modern electrical theory has shown that charge is an electron and, in fact, the elemental electronic charge is negative. So, from a historical perspective, the early and assumed positive charge became known as "conventional" theory in contrast to the now better understood "electron" theory of charge composition.

The electron is very tiny and is normally attached to some atom... helium or hydrogen or some metal such as copper for example. When agitated by forces yet to be discussed the electron can break free of the "mother" atom and become a free electron in contrast to being a "bound" electron before agitation. One free electron bumping along a wire would be impossible to locate or measure without some fancy laboratory instruments however large numbers of moving electrons are readily detected by nanoamp, microamp, milliamp, and just plain ammeters.

There are some very important definitions which are associated with charge.

First. Charge is identically the charge of an electron and is assigned the symbol Q.

Second... the coulomb. This is simply a fixed number of electrons. In fact 1 coulomb is defined as an assemblage of 6.24 x 10^18 electrons and is assigned the symbol C.

Third... the ampere. The ampere is charge in motion and which constitutes electrical current. One "ampere" is defined as 1 coulomb moving past a point in 1 second and enjoys the electrical symbol "I". In the sciences, something per time is known as a "rate" so electrical current... charge in motion... is an example of rate. Other examples are miles/hour, feet/second, apples/minute, coulombs/second, speed, etc.

So, there you have it... a coulomb, with symbol C, is just a known quantity of charge... in a bag for example... and electrical current is just a known quantity of charge moving past a fixed point. A coulomb sitting around doing nothing is electrostatic charge whereas a coulomb marching down a wire is electrodynamic charge and which is the same as electrical current and is measured in amperes.

This concludes the review of charge, moving charge known as electrical current, and the definition of the ampere.

Let's move on to the notion of voltage.

First we need to understand a few things about "work". If you have a box on the floor next to a table and you pick up that box and place on a table then you have done some work. You have moved a box vertically through a gravitational field to do this work. If the box had been in the basement and you moved it to the upstairs table then you would have done more work than just moving it from the upstairs floor to the table. Had you been on the Moon and done the same box moving exercise over the same distances then you would have done less work since the Moon's gravitational field is not as strong as the Earth's. Had you used a lighter box, then you would have done less work on either the Moon or Earth. So, apparently, the amount of work done seems to be related to the "heaviness" of the box, the strength of the gravitational field, and the distance moved.

Now, suppose the box falls from the table to the floor. If you did some work moving the box from floor to table then the box must have also done some work moving from table to floor. In effect the falling box reversed your previous work effort. Apparently the box had some "potential" for doing work while sitting on the table. In like fashion, while sitting on the floor, the box has some potential to fall to the basement. The box actually has the potential to fall to the center of the Earth.

Now we have the ability to define how much work is done in these circumstances. The work you do in moving the box from floor to table is the difference in the two potentials of box on floor and box on table. This is a sneaky way of introducing the notion of potential difference which we can relate directly to voltage potential difference in later segments of this series. Let me just state that "work" and energy are identically the same. We will soon find out that moving electric charge, also known as electrical current, behaves pretty much the same in an electric field as does the moving box in a gravitational field and that voltage is really a measure of electrical potential difference or the ability to do some work.

This concludes the introduction to the concept of voltage. We will develop this voltage notion further and offer a formal definition in the next segment of this series.

### IMPEDANCE SERIES PART 1, Lee week 2

May 28, 2008 Educational Radio Net, PSRG 2nd session

One of the topic suggestions offered during last weeks edition was impedance and antenna matching. This was (and is) a great topic but one of enormous scope and complexity. After some thought I felt it appropriate to more or less serialize the topic and spread it over several weeks so that we can deal with the subject in more detail.

Impedance is, certainly, one of the corner stones of electrical theory in general and radio systems in particular. To really grasp the significance of the symbol "Z" requires at least some understanding of the big three circuit elements... resistance, inductance, and capacitance. Additionally, some understanding of electrical current and voltage relationships is necessary to get the big picture. So, this week lets start the narrative by discussing the most elemental idea in electrical physics... that of "charge", both moving and stationary. In the weeks following we will address the circuit elements in turn and then merge them together into some coherent structure.

Much like any radio talk show I will "set up" the topic and then allow time at the end for questions or comments. Truth be known this subject is a mathematical adventure but, given that we do not have a "white" board for graphic illustration, I will attempt to convey simple ideas verbally.

So, lets get started with the concept of "charge".

In the formative years of electrical theory it was understood that something clearly moved when influenced by electrical forces. That hypothetical "something" was given the name "charge" and considered to be positive due to the direction it would move when in the presence of some motive force. Modern electrical theory has shown that charge is an electron and, in fact, the elemental electronic charge is negative. So, from a historical perspective, the early and assumed positive charge became known as "conventional" in contrast to the now better understood "electron" theory of charge composition.

The electron is very tiny and is normally attached to some atom... helium or hydrogen for example. When agitated by forces yet to be discussed the electron can break free of the "mother" atom and become a free electron in contrast to being a "bound" electron before agitation. One free electron bumping along a wire would be impossible to locate or measure without some fancy laboratory instruments however large numbers of moving electrons are readily detected by nanoamp, microamp, milliamp, and just plain ampmeters. There are some very important definitions which are associated with charge.

First... the coulomb. This is simply a fixed number of electrons. In fact 1 coulomb is an assemblage of 6.24 x 10^18 electrons.

Second... the ampere. This is defined as 1 coulomb of charge moving past a point in 1 second and is assigned the electrical symbol "I". In physics, something per time is known as a "rate". Good examples are miles/hour, feet/second, apples/minute, coulombs/second, etc.

So, there you have it... a coulomb, with symbol Q, is just a known quantity of charge... in a bag for example... and electrical current is just a known quantity of charge moving past a fixed point. A coulomb sitting around doing nothing is electrostatic charge whereas a coulomb marching down a wire is electrodynamic charge.

This concludes the first in a series of elementary ideas and basic definitions.

## Saturday, June 7, 2008

### Lightning Protection 1 (Bob, Week 3)

June 4, 2008

Here are my notes for this topic:

My Topic: Grounding continued, Lightning protection

3 or 4 types of Ground

1. DC Ground or Case Ground
2. RF Ground
3. Ground Plane for a Ground Plane Antenna
4. Lightning Protection Ground

Tonight I will be discussing lightning protection and grounding for that.

Just how common is it?

What happens in a thunderstorm?

Anatomy of a lightning strike.

How might I be affected?

How can I protect myself?
• disconnect all equipment from all outside sources
• put lightning protection on any outside source

### Grounding (Bob, Week 2)

May 28, 2008

Here are my notes for this topic:

My Topic: Ground

3 or 4 types of Ground

1. DC Ground
2. RF Ground
3. Ground Plane for a Ground Plane Antenna
4. Lightning Protection Ground

Tonight I will be discussing the first two, which specifically relate to grounding the radio equipment in your shack.

The topic of Antennas is one that can, and will, fill several lessons and the ground plane antenna, a very useful and common type of antenna will be covered in another lesson.

Likewise, lightning protection is a topic that deserves it’s own separate lesson which will be done another Wednesday.

So, let’s talk about what makes a good ground for your equipment.

Low Impedance – regular wire is not so good
copper flashing
braided copper wire
can use the braid from coax
Don’t Daisy Chain
Buss Bar – Copper Pipe is good
connect each piece to the buss bar
Grounding Rod outside
cold water pipe

### CQ - Avoiding Interference (Bob, Week 1)

May 21, 2008

Here are my notes for this topic:

My Topic:
For my topic I have chosen a question from the General exam question pool. You can get the question pools online from the National Conference of Volunteer Examiner Coordinators web site. That is www.ncvec.org.

G2B12 (A)
What is a practical way to avoid harmful interference when selecting a frequency to call CQ using phone?
A. Ask if the frequency is in use, say your callsign, and listen for a response
B. Keep your CQ to less than 2 minutes in length to avoid interference to contacts
that may be in progress
C. Listen for 2 minutes before calling CQ to avoid interference to contacts that may
be in progress
D. Call CQ at low power first and if there is no indication of interference, increase
power as necessary

Why is A the correct answer?

What are some of the situations where the frequency could be in use but you wouldn’t know it?
1. Two people are talking to each other but you can only hear one side and the side you can’t hear is talking.
2. There is a net and you can’t hear most of the people but one or more can hear you.

So, why ask instead of waiting and listening and then calling CQ.
What is wrong with starting at low power?
What is wrong with a short CQ?

## Wednesday, June 4, 2008

### Introducing the Educational Radio Net

This blog is intended to support the Educational Radio Net (ERN). The ERN is an amateur radio net that takes place Wednesdays at 8:00PM on the 2 meter repeater of the Puget Sound Repeater Group, 146.96MHz -600, with a tone of 103.5.

The purpose of this net is to help our fellow amateur radio operators learn theory, gain practical knowledge, and generally benefit from the experience of the more seasoned operators.

Your hosts are Bob Helling, K9PQ, and Lee Bond, N7KC.