Hi All,
Lee and I have decided to take the summer off. We thought it would mean that there would be no Educational Radio Net until the fall but we were fortunate enough to have Curt Black, WR5J step in and offer to run several sessions on various topics. I will let Curt fill in the details in his own post.
I want to thank you all for checking in and participating in this net and ask that you do the same for Curt. Lee and I will still be checking in and enjoying Curt's lessons.
73,
Bob
K9PQ
Tuesday, June 2, 2009
Wednesday, May 27, 2009
Morse Code text session #9 052709
QST DE W7VHY = N7KC@comcast.net = A new study shows that an 18 month mission to Mars would expose astronauts to more space radiation than NASA shielding technology can handle. AR DE W7VHY SK
Amateur Television by Lee Bond, N7KC
May 27, 2009 Educational Radio Net, PSRG 53rd Session
Television is ubiquitous… vision at a distance receiving equipment surrounds us completely. In today’s world television is a very mature technology however, if you were born before 1950, you can very likely remember when there was no television. I remember vividly the moment that I first viewed a television set as a youngster and it changed my life in the sense that I wanted to be a part of something very exciting. I was raised in a very small rural Ohio farming village and, while delivering papers late one evening, I peeked through the front door of a house rumored to have a television. This strange box was the talk of the town, the only one in the town, and the only external evidence of something going on in that house was the strange antenna structure attached to the chimney. Looking through the front door I could see a large wooden box labeled RCA and I was instantly captivated by the moving images on the small screen. From that moment in 1951 and forward I was intent on becoming an electrical engineer specializing in television technology.
The early wooden box TV’s were very expensive devices and only the well to do enjoyed the early television experience. The Chicago Worlds Fair in 1933-34 demonstrated a device for electronically reproducing a moving image and one or two of my older family members had actually seen this device. RCA, Dumont, and Zenith… among others… had worked hard in those eighteen years between 1933 and 1951 to produce these first consumer television sets. They were, of course, black and white sets which operated with vacuum tubes since any solid state device was years away in development. Bulky and deep chassis units with point to point wiring. A three dimensional wonderland when you stop to think about it.
Without doubt there were amateur radio operators who salivated at the thought of transmitting images via the ham bands but generating the images for transmission was also a very expensive proposition. There were no small battery operated camcorders or inexpensive security cameras as we know today rather still images were generated by flying spot scanner and enormous studio cameras were required to produce moving video signals. Video recorders using two inch tape eventually enabled storage of video images but, for the most part, the early programs were live events filled with memorable errors.
Technology does march on and changes came rapidly. The physical size of television components started to shrink and performance was better and better. Mass production resulted in falling prices and, eventually, low voltage solid state devices replaced the vacuum tube. Well to do amateurs could actually afford quality video equipment.
Let me preface this next part by saying that I am not going to present a detailed account of how the various slow scan and fast scan signals are developed. Any ARRL Handbook has excellent sections which are easily read. I will just hit the high points and direct the listener to these other sources.
Amateur efforts at transmitting images can be broken into two parts. Slow scan television and fast scan television. The NTSC fast scan video standard developed in the late 40’s and early 50’s remained intact until updated by color television requirements many years later. A consequence of NTSC fast scan video is the requirement of about 4.5 Mhz of data bandwidth for a high quality display and, given that the signal is transmitted as a double sideband amplitude modulated signal with the lower sideband passed through a vestigial filter the actual bandwidth required is about six Mhz. Clearly, transmitting fast scan NTSC based video in the high frequency amateur bands is out of the question. The only region with available bandwidth is UHF and up in the 70 cm wavelengths and shorter.
Enter slow scan image transmission. If you have a non moving image such as a photographic slide it is possible to sequentially sample the slide in a line by line fashion and develop an analog signal which can modulate some carrier wave and be passed to a remote receiving device where the modulation is undone… so to speak… and reconstruct the original image. The scheme uses audio frequencies which fit within the normal voice audio range of the average amateur radio transmit/receive system. The penalty for using low data rates is time. A complete image might consist of 120 or 240 lines and take several tens of seconds to transmit. So, moving images are out. A number of schemes for processing and transmitting slow scan images have evolved over the years and today’s schemes are very robust and yield excellent results with minimal equipment. Digital cameras, computers, and scan converters can be combined to make slow scan color television an exciting pursuit and within the budget of most radio enthusiasts. Listen around 14.230 Mhz to hear the characteristic warble of slow scan signals.
In contrast to slow scan techniques, fast scan television based upon the NTSC video standard has changed very little over the years. The idea is to process sequential images so fast that the persistence of the eye renders them continuous in appearance. The frame rate in analog fast scan television is 30 frames per second for black and white and about 29.94 frames per second for color. Both black & white and color frames consist of 525 lines of information which are divided into two fields each containing 262.5 lines. Bright scenes at 30 frames per second tend to flicker so the two interlaced fields double the flicker rate and flicker is generally unnoticeable to the average eye. The huge bandwidth requirement for fast scan techniques is a result of large amounts of information processed in a short amount of time.
Today’s market offers a plethora of fine video equipment perfectly suited to the amateur radio operator. Ebay is loaded with excellent video cameras from the security sector and a couple of manufacturers offer wide band video transmitters. Receiving fast scan video is as simple as capturing the radio signal and down converting it to a standard channel which is available on your home analog television set.
Analog television, especially color television, based on the NTSC standard was the first technology triumph of the 20th century in my view. Television changed our society in ways we never imagined. The digital computer is important but the television came first.
In summary, slow scan television is used principally for narrow band still image transmission in contrast to fast scan television which is associated with wide bandwidth high quality moving image transmission.
This concludes the set up discussion for Amateur Television. Are there any questions or comments with regard to tonight's discussion topic?
This is N7KC for the Wednesday night Educational Radio Net
Television is ubiquitous… vision at a distance receiving equipment surrounds us completely. In today’s world television is a very mature technology however, if you were born before 1950, you can very likely remember when there was no television. I remember vividly the moment that I first viewed a television set as a youngster and it changed my life in the sense that I wanted to be a part of something very exciting. I was raised in a very small rural Ohio farming village and, while delivering papers late one evening, I peeked through the front door of a house rumored to have a television. This strange box was the talk of the town, the only one in the town, and the only external evidence of something going on in that house was the strange antenna structure attached to the chimney. Looking through the front door I could see a large wooden box labeled RCA and I was instantly captivated by the moving images on the small screen. From that moment in 1951 and forward I was intent on becoming an electrical engineer specializing in television technology.
The early wooden box TV’s were very expensive devices and only the well to do enjoyed the early television experience. The Chicago Worlds Fair in 1933-34 demonstrated a device for electronically reproducing a moving image and one or two of my older family members had actually seen this device. RCA, Dumont, and Zenith… among others… had worked hard in those eighteen years between 1933 and 1951 to produce these first consumer television sets. They were, of course, black and white sets which operated with vacuum tubes since any solid state device was years away in development. Bulky and deep chassis units with point to point wiring. A three dimensional wonderland when you stop to think about it.
Without doubt there were amateur radio operators who salivated at the thought of transmitting images via the ham bands but generating the images for transmission was also a very expensive proposition. There were no small battery operated camcorders or inexpensive security cameras as we know today rather still images were generated by flying spot scanner and enormous studio cameras were required to produce moving video signals. Video recorders using two inch tape eventually enabled storage of video images but, for the most part, the early programs were live events filled with memorable errors.
Technology does march on and changes came rapidly. The physical size of television components started to shrink and performance was better and better. Mass production resulted in falling prices and, eventually, low voltage solid state devices replaced the vacuum tube. Well to do amateurs could actually afford quality video equipment.
Let me preface this next part by saying that I am not going to present a detailed account of how the various slow scan and fast scan signals are developed. Any ARRL Handbook has excellent sections which are easily read. I will just hit the high points and direct the listener to these other sources.
Amateur efforts at transmitting images can be broken into two parts. Slow scan television and fast scan television. The NTSC fast scan video standard developed in the late 40’s and early 50’s remained intact until updated by color television requirements many years later. A consequence of NTSC fast scan video is the requirement of about 4.5 Mhz of data bandwidth for a high quality display and, given that the signal is transmitted as a double sideband amplitude modulated signal with the lower sideband passed through a vestigial filter the actual bandwidth required is about six Mhz. Clearly, transmitting fast scan NTSC based video in the high frequency amateur bands is out of the question. The only region with available bandwidth is UHF and up in the 70 cm wavelengths and shorter.
Enter slow scan image transmission. If you have a non moving image such as a photographic slide it is possible to sequentially sample the slide in a line by line fashion and develop an analog signal which can modulate some carrier wave and be passed to a remote receiving device where the modulation is undone… so to speak… and reconstruct the original image. The scheme uses audio frequencies which fit within the normal voice audio range of the average amateur radio transmit/receive system. The penalty for using low data rates is time. A complete image might consist of 120 or 240 lines and take several tens of seconds to transmit. So, moving images are out. A number of schemes for processing and transmitting slow scan images have evolved over the years and today’s schemes are very robust and yield excellent results with minimal equipment. Digital cameras, computers, and scan converters can be combined to make slow scan color television an exciting pursuit and within the budget of most radio enthusiasts. Listen around 14.230 Mhz to hear the characteristic warble of slow scan signals.
In contrast to slow scan techniques, fast scan television based upon the NTSC video standard has changed very little over the years. The idea is to process sequential images so fast that the persistence of the eye renders them continuous in appearance. The frame rate in analog fast scan television is 30 frames per second for black and white and about 29.94 frames per second for color. Both black & white and color frames consist of 525 lines of information which are divided into two fields each containing 262.5 lines. Bright scenes at 30 frames per second tend to flicker so the two interlaced fields double the flicker rate and flicker is generally unnoticeable to the average eye. The huge bandwidth requirement for fast scan techniques is a result of large amounts of information processed in a short amount of time.
Today’s market offers a plethora of fine video equipment perfectly suited to the amateur radio operator. Ebay is loaded with excellent video cameras from the security sector and a couple of manufacturers offer wide band video transmitters. Receiving fast scan video is as simple as capturing the radio signal and down converting it to a standard channel which is available on your home analog television set.
Analog television, especially color television, based on the NTSC standard was the first technology triumph of the 20th century in my view. Television changed our society in ways we never imagined. The digital computer is important but the television came first.
In summary, slow scan television is used principally for narrow band still image transmission in contrast to fast scan television which is associated with wide bandwidth high quality moving image transmission.
This concludes the set up discussion for Amateur Television. Are there any questions or comments with regard to tonight's discussion topic?
This is N7KC for the Wednesday night Educational Radio Net
Wednesday, May 20, 2009
Morse Code text session #8 052009
QST DE W7VHY = N7KC@comcast.net = Sunspot group 1017 is fading rapidly and probably will be gone by the end of the day. AR DE W7VHY SK
DSP 1: Introduction to Digital Signal Processing for Ham Radio, Bob, no. 52
Tonight is the first of what will be a multi-part session on Digital Signal Processing (DSP). Unlike Lee's impedance series we won't be building a set of concepts leading to DSP. DSP isn't a single concept; rather it is a catch-all term for several distinct and only loosely related methods. My approach to teaching DSP will be to break it down by how it is used in Ham Radio rather than by theoretical construct.
Also, DSP is used in many fields today besides Ham Radio but we will limit our discussions to Ham Radio. Of course, if you have knowledge you would like to share about non-Ham uses of DSP, you are welcome to share it but I won't be going into non-Ham uses myself.
Let's start with a very basic idea of what DSP is. First of all, the signal that is being processed, usually starts out analog and ends up analog. Whether it is the analog audio signal received by your microphone that ends up as an analog radio wave transmission, or an analog radio wave reception that ends up as an analog audio wave coming out of the speaker, it is still analog at both ends and digital only in the processing circuitry. The exception to this is the ever growing list of digital modes that start off as digital information, in the form of characters, are converted to analog for radio transmission, and end up as characters again.
Once you are representing the signal digitally you can do your digital processing. Probably the most well known use is to create better filters than you can with analog circuits. Other uses are to create displays showing signals on a frequency line so that you can tune to the signal you want, or even just point and click in some cases. Less well known but equally important is that DSP is used to convert the audio signal from your microphone to the SSB, AM or FM that is sent out. Probably the ultimate use of DSP is the Software Defined Radio. I will go into these uses in detail in subsequent sessions.
Right now I am going to go into more detail on the conversion between Analog and Digital. As I said earlier, in order to do digital signal processing, you must convert the signal from analog to digital, then do your processing, then convert it back to analog again. These steps are known as Analog to Digital Conversion (ADC) and Digital to Analog Conversion (DAC). The same abbreviations are used for the circuits that perform the steps. Usually these circuits are combined into a single Integrated Circuit, or chip, so you will commonly hear about an ADC or a DAC chip. These conversions are done by the time-slice method. In this method, voltage measurements are taken of the analog wave at regular time intervals. You will need several measurements per wavelength in order to accurately describe the analog signal. The rule of thumb for for a simple sine wave is that the frequency of taking voltage measurements should be at least twice as high as the frequency of the wave you are measuring. Keep in mind that complex waveforms can be thought of as the sum of sine waves of different frequencies and amplitudes. So to accurately represent a complex waveform your sample frequency must be at least twice as high as the highest frequency sine wave that is a component of your waveform. Typically when the voltage is measured it is stored as a 16 bit binary value. Allowing for positive and negative that gives 32,768 voltage levels from the smallest measurable above zero to the maximum. This affects the dynamic range of your system, that is, how much difference you can have between the smallest and largest amplitudes. In Software Defined Radios where a PC is an integral part of the radio, you can use floating point processing to greatly increase the number of voltage levels represented and thus increase dynamic range at least for internal processing. Ultimately it must be converted back to analog through a DAC which will probably be only 16 bit.
As we continue on and go into more detail about digital signal processing, keep in mind that for voice communication we always start with an analog audio signal, have an analog wave traveling through space and end with an analog audio signal on the other end. It is only the processing internal to the sending radio and receiving radio that works in digital.
Also, DSP is used in many fields today besides Ham Radio but we will limit our discussions to Ham Radio. Of course, if you have knowledge you would like to share about non-Ham uses of DSP, you are welcome to share it but I won't be going into non-Ham uses myself.
Let's start with a very basic idea of what DSP is. First of all, the signal that is being processed, usually starts out analog and ends up analog. Whether it is the analog audio signal received by your microphone that ends up as an analog radio wave transmission, or an analog radio wave reception that ends up as an analog audio wave coming out of the speaker, it is still analog at both ends and digital only in the processing circuitry. The exception to this is the ever growing list of digital modes that start off as digital information, in the form of characters, are converted to analog for radio transmission, and end up as characters again.
Once you are representing the signal digitally you can do your digital processing. Probably the most well known use is to create better filters than you can with analog circuits. Other uses are to create displays showing signals on a frequency line so that you can tune to the signal you want, or even just point and click in some cases. Less well known but equally important is that DSP is used to convert the audio signal from your microphone to the SSB, AM or FM that is sent out. Probably the ultimate use of DSP is the Software Defined Radio. I will go into these uses in detail in subsequent sessions.
Right now I am going to go into more detail on the conversion between Analog and Digital. As I said earlier, in order to do digital signal processing, you must convert the signal from analog to digital, then do your processing, then convert it back to analog again. These steps are known as Analog to Digital Conversion (ADC) and Digital to Analog Conversion (DAC). The same abbreviations are used for the circuits that perform the steps. Usually these circuits are combined into a single Integrated Circuit, or chip, so you will commonly hear about an ADC or a DAC chip. These conversions are done by the time-slice method. In this method, voltage measurements are taken of the analog wave at regular time intervals. You will need several measurements per wavelength in order to accurately describe the analog signal. The rule of thumb for for a simple sine wave is that the frequency of taking voltage measurements should be at least twice as high as the frequency of the wave you are measuring. Keep in mind that complex waveforms can be thought of as the sum of sine waves of different frequencies and amplitudes. So to accurately represent a complex waveform your sample frequency must be at least twice as high as the highest frequency sine wave that is a component of your waveform. Typically when the voltage is measured it is stored as a 16 bit binary value. Allowing for positive and negative that gives 32,768 voltage levels from the smallest measurable above zero to the maximum. This affects the dynamic range of your system, that is, how much difference you can have between the smallest and largest amplitudes. In Software Defined Radios where a PC is an integral part of the radio, you can use floating point processing to greatly increase the number of voltage levels represented and thus increase dynamic range at least for internal processing. Ultimately it must be converted back to analog through a DAC which will probably be only 16 bit.
As we continue on and go into more detail about digital signal processing, keep in mind that for voice communication we always start with an analog audio signal, have an analog wave traveling through space and end with an analog audio signal on the other end. It is only the processing internal to the sending radio and receiving radio that works in digital.
Wednesday, May 13, 2009
Morse Code text session #7 051309
QST DE W7VHY = Today, astronomers are monitoring an enormous patch of seething magnetism churning through the suns surface in a splash of bright, white froth. AR DE W7VHY SK
COAXIAL CABLE, Jim Hadlock, K7WA, no. 51
COAXIAL CABLE
May 13, 2009 – Educational Radio Net
Jim Hadlock K7WA
Introduction:
Coaxial cable transmission line is commonly used to connect our transceivers to antennas. It is used for other purposes as well, such as Matching Sections, Baluns, Traps, and Stubs. Sooner or later, each of us will probably need to add coax to our home or mobile radio systems. Tonight’s session will cover the different types of coax and the criteria to consider when deciding what cable is best for a given situation. In the spirit of amateur radio, I am going to try to avoid using manufacturer and distributor names on the air, see the Educational Radio Blog for more information on specific products and suppliers.
Coaxial type cable was first used for transatlantic telegraph cable communication in the late 1800’s. These early cables were composed of a central conductor encased in a cylindrical insulating material, and were considered coaxial because the seawater that surrounded them completed their return circuits. Later developments led in 1929 to a patented design by two engineers who worked for AT&T for a coaxial cable system intended for transmission of television signals. During World War II the military accelerated the development and production of flexible, solid-dielectric coax. It was at this time that coax acquired its now-familiar RG/U (Radio Guide Utility) numbers. After the war, amateur radio operators began using the readily available surplus coaxial cable for their antenna feedline systems.
Coaxial cable consists of an inner conductor with an insulated covering (dielectric), which is then covered with a braided wire or foil sheathing (shield). The sheathing is covered with a flexible outer jacket. Although coax has greater loss than twin-lead or open-wire transmission lines, it has some important advantages: it can be buried underground, run inside a metal mast or taped to a tower without harmful effects. In addition, our modern radios are designed for unbalanced coaxial cable transmission line.
Specifications:
Looking at a table of transmission line characteristics (ARRL Handbook (2005): Nominal Characteristics of Commonly Used Transmission Lines (Table 21.1) page 21.2-21.3) we see several characteristics specified for each type of cable:
Applications:
Consider the following factors when selecting coaxial cable:
Power
Highest frequency (HF, VHF, UHF)
Length
Loss (determined by frequency, cable type, and length)
Weight
Flexibility
Environment
Coaxial Cable Types (50 Ohm Impedance):
RG-174 used for internal connections -
RG-58 comes with commercial antennas (high loss) -
RG-8X low power HF, short VHF feedlines -
RG-8 higher power or VHF/UHF feedlines -
RG-213 high power HF, short VHF feedlines -
Heliax and Hardline long feedlines at VHF or UHF -
Examples: (remember, 3 dB is 50% power loss!)
Example 1: 144/440 mHz J-Pole 50 ft feedline: 100 ft feedline
RG-58 4.5 dB loss 9.7 dB loss
RG-8X 3.35 dB loss 6.7 dB loss
RG-213 2.35 dB loss 4.7 dB loss
RG-8 1.35 dB loss 2.7 dB loss
Example 2: HF Antenna (below 50 mHz)
RG-58 2.9 dB loss
RG-8X 1.5 dB loss
RG-213 1.3 dB loss
RG-8 0.8 dB loss
Connectors and Adaptors:
UHF (PL-259 type), most common general use -
Type N, low loss, used at VHF and UHF -
BNC, used on Hand-held radios and test equipment -
Conclusions:
Use the best coaxial cable and connectors for the requirements -
Used coaxial cable may not be a bargain -
Mostly, you get what you pay for -
References:
ARRL Handbook (2005): Nominal Characteristics of Commonly Used Transmission Lines (Table 21.1) page 21.2-21.3, also see the ARRL Antenna Book and other references
The Wireman, Inc. (coaxial cable, antenna wire, connectors, etc.), www.thewireman.com
Radioware (Amphenol PL-259 connectors, coaxial cable, etc), www.radio-ware.com
The Pacific Northwest VHF Society “Noise Floor” newsletter (Winter 2008 and Summer 2008) contains a two-part article on attaching Type N connectors to coax – must reading for anyone who wants to attach their own connnectors!: http://www.pnwvhfs.org/articles/noisefloor/noisefloor.htm
May 13, 2009 – Educational Radio Net
Jim Hadlock K7WA
Introduction:
Coaxial cable transmission line is commonly used to connect our transceivers to antennas. It is used for other purposes as well, such as Matching Sections, Baluns, Traps, and Stubs. Sooner or later, each of us will probably need to add coax to our home or mobile radio systems. Tonight’s session will cover the different types of coax and the criteria to consider when deciding what cable is best for a given situation. In the spirit of amateur radio, I am going to try to avoid using manufacturer and distributor names on the air, see the Educational Radio Blog for more information on specific products and suppliers.
Coaxial type cable was first used for transatlantic telegraph cable communication in the late 1800’s. These early cables were composed of a central conductor encased in a cylindrical insulating material, and were considered coaxial because the seawater that surrounded them completed their return circuits. Later developments led in 1929 to a patented design by two engineers who worked for AT&T for a coaxial cable system intended for transmission of television signals. During World War II the military accelerated the development and production of flexible, solid-dielectric coax. It was at this time that coax acquired its now-familiar RG/U (Radio Guide Utility) numbers. After the war, amateur radio operators began using the readily available surplus coaxial cable for their antenna feedline systems.
Coaxial cable consists of an inner conductor with an insulated covering (dielectric), which is then covered with a braided wire or foil sheathing (shield). The sheathing is covered with a flexible outer jacket. Although coax has greater loss than twin-lead or open-wire transmission lines, it has some important advantages: it can be buried underground, run inside a metal mast or taped to a tower without harmful effects. In addition, our modern radios are designed for unbalanced coaxial cable transmission line.
Specifications:
Looking at a table of transmission line characteristics (ARRL Handbook (2005): Nominal Characteristics of Commonly Used Transmission Lines (Table 21.1) page 21.2-21.3) we see several characteristics specified for each type of cable:
RG or TypeNumber General type or Family-
Part Number Manufacturer’s part number-
Impedance 50 and 75 ohm are most common,
determined by the size and spacing
of the two conductors, and the
dielectric material between them -
Velocity Factor rate of rf propagation in the cable
compared to free space -
Capacitance two parallel conductors have capacitance -
Center Conductor AWG center conductor size and construction -
Dielectric Type dielectric material -
Shield Type shield construction -
Jacket Material jacket construction -
Jacket Outer Diameter dimension of the outer jacket -
Maximum Voltage (RMS) maximum voltage rating -
Matched Loss loss in decibels for different frequencies -
Power Handling Capability recommended maximum power -
Applications:
Consider the following factors when selecting coaxial cable:
Power
Highest frequency (HF, VHF, UHF)
Length
Loss (determined by frequency, cable type, and length)
Weight
Flexibility
Environment
Coaxial Cable Types (50 Ohm Impedance):
RG-174 used for internal connections -
RG-58 comes with commercial antennas (high loss) -
RG-8X low power HF, short VHF feedlines -
RG-8 higher power or VHF/UHF feedlines -
RG-213 high power HF, short VHF feedlines -
Heliax and Hardline long feedlines at VHF or UHF -
Examples: (remember, 3 dB is 50% power loss!)
Example 1: 144/440 mHz J-Pole 50 ft feedline: 100 ft feedline
RG-58 4.5 dB loss 9.7 dB loss
RG-8X 3.35 dB loss 6.7 dB loss
RG-213 2.35 dB loss 4.7 dB loss
RG-8 1.35 dB loss 2.7 dB loss
Example 2: HF Antenna (below 50 mHz)
RG-58 2.9 dB loss
RG-8X 1.5 dB loss
RG-213 1.3 dB loss
RG-8 0.8 dB loss
Connectors and Adaptors:
UHF (PL-259 type), most common general use -
Type N, low loss, used at VHF and UHF -
BNC, used on Hand-held radios and test equipment -
Conclusions:
Use the best coaxial cable and connectors for the requirements -
Used coaxial cable may not be a bargain -
Mostly, you get what you pay for -
References:
ARRL Handbook (2005): Nominal Characteristics of Commonly Used Transmission Lines (Table 21.1) page 21.2-21.3, also see the ARRL Antenna Book and other references
The Wireman, Inc. (coaxial cable, antenna wire, connectors, etc.), www.thewireman.com
Radioware (Amphenol PL-259 connectors, coaxial cable, etc), www.radio-ware.com
The Pacific Northwest VHF Society “Noise Floor” newsletter (Winter 2008 and Summer 2008) contains a two-part article on attaching Type N connectors to coax – must reading for anyone who wants to attach their own connnectors!: http://www.pnwvhfs.org/articles/noisefloor/noisefloor.htm
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