Q Jean-Pierre, VE2GDA, asks, “I log all of my contact times using UTC, but the question of which date to use is not always clear. Suppose I log a contact that was made at a 2230 local time on June 4. The UTC time will be local time plus four hours, so I log it at 0230 UTC. But does the date become June 5, or does it remain June 4?”
A Many hams are often confused about this point. The simple answer is that the date must match the time. In your example, the “UTC date” would be June 5. It may have indeed been June 4 according to your local time, but for UTC it is after midnight and, henceforth, the next day (June 5).
From QST October 2000
Saturday, July 31, 2010
I own a Bell SVGA monitor that has been giving me fits. It generates interference that just happens to fall on several of my “favorite” frequencies.
Q I own a Packard Bell SVGA monitor that has been giving me fits. It generates interference that just happens to fall on several of my “favorite” frequencies. I’ve tried every RFI suppression technique known—short of installing the monitor in a copper cage. Do you have any other tips?
A I’d suggest that you try changing your display settings. Going to a higher or lower resolution display may at least shift the interference away from your favorite frequencies. Frankly, you may want to consider shopping for a new monitor. You may discover that other brands offer better shielding. If you can get your hands on a portable shortwave receiver, take it to the computer stores and use it to check the various monitors. Obviously you want to find the monitor that generates the least amount of interference, if any at all, on the frequencies or bands you use most often.
From QST October 2000
A I’d suggest that you try changing your display settings. Going to a higher or lower resolution display may at least shift the interference away from your favorite frequencies. Frankly, you may want to consider shopping for a new monitor. You may discover that other brands offer better shielding. If you can get your hands on a portable shortwave receiver, take it to the computer stores and use it to check the various monitors. Obviously you want to find the monitor that generates the least amount of interference, if any at all, on the frequencies or bands you use most often.
From QST October 2000
How do lightning trackers work?
Q How do lightning trackers work? Is this something that a ham could do at home?
A A single-site lightning tracker detects the low frequency radio signals produced by lightning’s electrical discharge. These signals are the cracklings you hear on AM radios when thunderstorms are nearby. Lightning signals travel for hundreds of miles and can be detected by directional low-frequency antennas. Specialized software plots the approximate direction of each strike and analyzes the signal strength to calculate the distance. The results are typically plotted on a map display. More sophisticated systems combine strike data from several receiver sites to create more accurate position plots.
Yes, you can set up a lightning tracker at home. The Boltek
Corporation, among others, makes a lightning tracking system based on a receiver board that plugs into your PC. The directional LF antenna can be installed outdoors or in your attic. The entire system costs about $500. Contact the Boltek Corporation, 2316 Delaware Ave, Buffalo, NY 14216; tel 905-734- 8045; http://www.boltek.com.
The Boltek lightning tracker in action.
From QST October 2000
A A single-site lightning tracker detects the low frequency radio signals produced by lightning’s electrical discharge. These signals are the cracklings you hear on AM radios when thunderstorms are nearby. Lightning signals travel for hundreds of miles and can be detected by directional low-frequency antennas. Specialized software plots the approximate direction of each strike and analyzes the signal strength to calculate the distance. The results are typically plotted on a map display. More sophisticated systems combine strike data from several receiver sites to create more accurate position plots.
Yes, you can set up a lightning tracker at home. The Boltek
Corporation, among others, makes a lightning tracking system based on a receiver board that plugs into your PC. The directional LF antenna can be installed outdoors or in your attic. The entire system costs about $500. Contact the Boltek Corporation, 2316 Delaware Ave, Buffalo, NY 14216; tel 905-734- 8045; http://www.boltek.com.
The Boltek lightning tracker in action.
From QST October 2000
How old does a radio have to be before it is considered “collectible?” Can an FM transceiver from the ’70s be considered “vintage? ...
Q How old does a radio have to be before it is considered “collectible?” Can an FM transceiver from the ’70s be considered “vintage?”
A The answer depends on who you ask. Some radio collectors strictly adhere to the 50-year rule. That is, a radio must be at least 50 years old to be considered an antique. Others are more generous. For example, many collectors covet Ten-Tec Power Mite QRP transceivers from the early ’70s. The Heathkit HW-series QRP transceivers from the same period are often in high demand. Among the FM rigs, Drake TR-22s are often considered collectible as are the early Clegg and Regency transceivers. As always, “collectible” is in the eye of the beholder.
The Clegg FM-27B was among the first synthesized 2-meter FM amateur transceivers and is now considered collectible by some hams. This advertisement appeared in the February 1974 QST.
From QST October 2000
A The answer depends on who you ask. Some radio collectors strictly adhere to the 50-year rule. That is, a radio must be at least 50 years old to be considered an antique. Others are more generous. For example, many collectors covet Ten-Tec Power Mite QRP transceivers from the early ’70s. The Heathkit HW-series QRP transceivers from the same period are often in high demand. Among the FM rigs, Drake TR-22s are often considered collectible as are the early Clegg and Regency transceivers. As always, “collectible” is in the eye of the beholder.
The Clegg FM-27B was among the first synthesized 2-meter FM amateur transceivers and is now considered collectible by some hams. This advertisement appeared in the February 1974 QST.
From QST October 2000
Can Direct TV dishes be used on the amateur microwave bands?...
Q Tom, KF6DRI, asks, “Direct TV has changed over from Primestar and left me the old 24-inch Primestar dish. Can these dishes be used on the amateur microwave bands?”
A Yes, your Primestar 24-inch dish should work just fine on 1296 MHz and higher microwave bands up to at least 10 GHz. In chapter 1 of the UHF/Microwave Projects Manual, Paul Wade, W1GHZ, describes how to design a feed for these types of offset dishes. Paul also has a microwave Web site at http://www.w1ghz.cx.
From QST October 2000
A Yes, your Primestar 24-inch dish should work just fine on 1296 MHz and higher microwave bands up to at least 10 GHz. In chapter 1 of the UHF/Microwave Projects Manual, Paul Wade, W1GHZ, describes how to design a feed for these types of offset dishes. Paul also has a microwave Web site at http://www.w1ghz.cx.
From QST October 2000
Twice this year I have been transmitting at the full legal limit and my TV set has ‘popped off ...
Q Ron, N9RC, asks, “I have a 1994 RCA 35-inch console TV fed by cable. Twice this year I have been transmitting at the full legal limit and my TV set has ‘popped off.’ According to my TV repairman, the horizontal circuit has ‘shorted.’ (Apparently the horizontal transformer failed.) He says he has seen this happen in another case when a ham was transmitting at the house.
“This costs $400 per incident! I never had the problem until this year, but we have added a few VCR cables that I have now belatedly removed. I’ll be adding common mode chokes to these cables and elsewhere. I can’t afford for this to keep happening! Is there a fix?”
A Ouch! This sort of problem is rare, but it can happen. RF energy is usually picked up on any wiring connected to the TV (TV sets do not make good antennas, but wires do), then gets conducted onto the chassis of the TV, into its power supply and into its circuitry. In this case, it looks like the horizontal circuitry is particularly sensitive. There are a few things I’d suggest, although to find out if they work does entail some degree of risk.
First, the greater the separation between your transmit antenna and the TV and any wires connected to it (ie, ac, cable, antenna, speaker, etc.), the lower the RF energy will be. So, raising the height of your antenna or locating it farther away from the house could be helpful. In this case, do not use end-fed wires—only antennas fed with coaxial cable. If you have any problems with RF in the shack, correct the underlying transmit antenna problem.
Adding common-mode chokes to all of the wires connected to
the TV may also help keep the RF energy from getting into the set. You can make a common-mode choke with an F-240-43 ferrite core, wrapping about 10 turns of wire (coax, speaker, etc.) onto the core, just where it enters the TV set. For smaller wires, you can use an F-140-43 size core. You will have to treat the cable or antenna lead, the ac wiring and anything else connected to the TV. You may also want to add an ac line filter to the TV.
Some companies have developed service bulletins to deal with RFI problems, although this is generally the exception. Contact RCA and see if they have any info for you.
From QST October 2000
“This costs $400 per incident! I never had the problem until this year, but we have added a few VCR cables that I have now belatedly removed. I’ll be adding common mode chokes to these cables and elsewhere. I can’t afford for this to keep happening! Is there a fix?”
A Ouch! This sort of problem is rare, but it can happen. RF energy is usually picked up on any wiring connected to the TV (TV sets do not make good antennas, but wires do), then gets conducted onto the chassis of the TV, into its power supply and into its circuitry. In this case, it looks like the horizontal circuitry is particularly sensitive. There are a few things I’d suggest, although to find out if they work does entail some degree of risk.
First, the greater the separation between your transmit antenna and the TV and any wires connected to it (ie, ac, cable, antenna, speaker, etc.), the lower the RF energy will be. So, raising the height of your antenna or locating it farther away from the house could be helpful. In this case, do not use end-fed wires—only antennas fed with coaxial cable. If you have any problems with RF in the shack, correct the underlying transmit antenna problem.
Adding common-mode chokes to all of the wires connected to
the TV may also help keep the RF energy from getting into the set. You can make a common-mode choke with an F-240-43 ferrite core, wrapping about 10 turns of wire (coax, speaker, etc.) onto the core, just where it enters the TV set. For smaller wires, you can use an F-140-43 size core. You will have to treat the cable or antenna lead, the ac wiring and anything else connected to the TV. You may also want to add an ac line filter to the TV.
Some companies have developed service bulletins to deal with RFI problems, although this is generally the exception. Contact RCA and see if they have any info for you.
From QST October 2000
What are the rules governing the use of a ham transceiver outside the amateur bands? ...
Q Steve, N6PHX, asks, “What are the rules governing the use of a ham transceiver outside the amateur bands? Can one use an amateur transceiver on CB, for example?”
A You can only use radios that have been FCC certified for use in the service for which they are intended. That makes it illegal to use a ham transceiver on CB, for example, because a ham rig is not FCC certified for use as a CB radio.
From QST September 2000
A You can only use radios that have been FCC certified for use in the service for which they are intended. That makes it illegal to use a ham transceiver on CB, for example, because a ham rig is not FCC certified for use as a CB radio.
From QST September 2000
Recently I tuned through some PACTOR signals, but all I could copy were call signs being sent repeatedly ...
Q Les, W2QHS, asks, “Recently I tuned through some PACTOR signals, but all I could copy were call signs being sent repeatedly. Were these stations attempting to link to BBSs? Is it possible to have just a casual conversation with a PACTOR station?”
A The PACTOR signals you’ve seen are indeed stations attempting to establish connections, often to automated BBSs or Internet e-mail gateways that are part of the Winlink2000 network. Winlink2000 in particular has become popular among sailing enthusiasts and others who wish to exchange e-mail from remote locations. It is certainly possible to enjoy casual keyboard-to-keyboard PACTOR QSOs, but these tend to be the exception rather than the rule.
For “live” HF digital conversations, most amateurs have chosen PSK31 or RTTY. You should be able to find someone to chat with on either mode on 20 meters between 14.070 and 14.099 MHz at just about any time. PSK31 predominates between 14.070 and 14.073 MHz, but in recent months activity has expanded to 15 meters (21.070 MHz) and 10 meters (28.120 MHz).
From QST September 2000
A The PACTOR signals you’ve seen are indeed stations attempting to establish connections, often to automated BBSs or Internet e-mail gateways that are part of the Winlink2000 network. Winlink2000 in particular has become popular among sailing enthusiasts and others who wish to exchange e-mail from remote locations. It is certainly possible to enjoy casual keyboard-to-keyboard PACTOR QSOs, but these tend to be the exception rather than the rule.
For “live” HF digital conversations, most amateurs have chosen PSK31 or RTTY. You should be able to find someone to chat with on either mode on 20 meters between 14.070 and 14.099 MHz at just about any time. PSK31 predominates between 14.070 and 14.073 MHz, but in recent months activity has expanded to 15 meters (21.070 MHz) and 10 meters (28.120 MHz).
From QST September 2000
Can you tell me how one figures the spacing for the matching section of a J antenna? ...
Q Howard, KK7KL, asks, “Can you tell me how one figures the spacing for the matching section of a J antenna? Is there a rule of thumb? Any assistance you could pass along would be greatly appreciated.”
A The J pole is an interesting antenna. It is essentially an endfed half-wavelength antenna, and the transmission line is used as a transmission-line transformer to transform the high feedpoint impedance to 50 Ω for your radio. The relationship between all of the elements is complex. The high impedance of the end-fed radiator is determined by its length and diameter and, to a smaller degree, the presence of nearby dielectric insulators.
The impedance of the matching section is determined by its conductor diameter and spacing. This is not very critical in most J pole designs. The transmission line transformer is usually cut to a quarter wavelength, shorted at one end. It is then tapped at the point that corresponds to an impedance of 50 Ω. Minor variations in the length of the radiating element and the transmission-line transformer can be compensated for by either changing the length of one or both elements slightly, or by changing the tap point on the transformer.
Most J poles are either designed by trial and error, or by
modeling them on a computer. You can start with the half-quarter wavelength dimensions (don’t forget the approximately 0.97 velocity factor on the transmission line section), then adjust the tap point and length of the radiating element. If you have access to an impedance bridge, such as the MFJ-259B or Autek VHF Analyst, you can adjust the tap position for 50 Ω resistive and the length of the radiating element to get the reactance down to zero.
Of course, there is nothing magical about the half-/quarter wavelength combination. I recently modeled a J pole whose dimensions are much shorter than the norm, and it, too, gives 50 Ω at the feed point.
From QST September 2000
A The J pole is an interesting antenna. It is essentially an endfed half-wavelength antenna, and the transmission line is used as a transmission-line transformer to transform the high feedpoint impedance to 50 Ω for your radio. The relationship between all of the elements is complex. The high impedance of the end-fed radiator is determined by its length and diameter and, to a smaller degree, the presence of nearby dielectric insulators.
The impedance of the matching section is determined by its conductor diameter and spacing. This is not very critical in most J pole designs. The transmission line transformer is usually cut to a quarter wavelength, shorted at one end. It is then tapped at the point that corresponds to an impedance of 50 Ω. Minor variations in the length of the radiating element and the transmission-line transformer can be compensated for by either changing the length of one or both elements slightly, or by changing the tap point on the transformer.
Most J poles are either designed by trial and error, or by
modeling them on a computer. You can start with the half-quarter wavelength dimensions (don’t forget the approximately 0.97 velocity factor on the transmission line section), then adjust the tap point and length of the radiating element. If you have access to an impedance bridge, such as the MFJ-259B or Autek VHF Analyst, you can adjust the tap position for 50 Ω resistive and the length of the radiating element to get the reactance down to zero.
Of course, there is nothing magical about the half-/quarter wavelength combination. I recently modeled a J pole whose dimensions are much shorter than the norm, and it, too, gives 50 Ω at the feed point.
From QST September 2000
Since I can’t connect to a ground rod, should I still connect the grounds of all of my equipment together? ...
Q Michael, KD5BBC, asks, “I live in a second-floor apartment, so attaching a ground wire to a ground rod is out of the question. Since I can’t connect to a ground rod, should I still connect the grounds of all of my equipment together? I don’t seem to have a problem with RF feedback in the shack, and transmitting on 40 through 10 meters with 100 W doesn’t seem to affect either my computer on the other side of the room or my TV in the next room. I have what appears to be an active ground on the 3-plug electrical line (according to the tester I bought at RadioShack). Should I try to ground to that, or would that also be asking for problems?”
A Yes, absolutely connect all the equipment in the shack together and then to the ground on the wall socket. A good way to accomplish this is to check that the screw holding the cover in place is grounded. You can do this by first turning off the circuit breaker to the plug and measuring between the screw and the ground plug with an ohmmeter. Then strip the braid off some old coax to make a nice flexible ground strap between your station and the screw. That takes care of the safety ground. You’ll still need an RF ground, which often takes the form of a counterpoise wire. See my answer to W6RLF earlier in this column.
Also, check out “Antennas and Grounds for Apartments” on the TIS Web page at: http://www.arrl.org/tis/ under Antennas/Grounding.
From QST September 2000
A Yes, absolutely connect all the equipment in the shack together and then to the ground on the wall socket. A good way to accomplish this is to check that the screw holding the cover in place is grounded. You can do this by first turning off the circuit breaker to the plug and measuring between the screw and the ground plug with an ohmmeter. Then strip the braid off some old coax to make a nice flexible ground strap between your station and the screw. That takes care of the safety ground. You’ll still need an RF ground, which often takes the form of a counterpoise wire. See my answer to W6RLF earlier in this column.
Also, check out “Antennas and Grounds for Apartments” on the TIS Web page at: http://www.arrl.org/tis/ under Antennas/Grounding.
From QST September 2000
I’m attempting to run PSK31 with the DigiPan software, but I can’t seem to get the waterfall display to function properly ...
Q Dennis, AA0A, asks, “I’m attempting to run PSK31 with the DigiPan software, but I can’t seem to get the waterfall display to function properly. I know that audio is getting to the sound card from my transceiver (I can even record the audio using Windows Sound Recorder). Any ideas?”
A This sounds like a display problem of some sort. Are you
using the 256-color display mode? Check your Windows
display properties under SETTINGS—CONTROL PANEL—
DISPLAY. Make sure the SETTINGS are either 256-color or
“High Color.” See Figure 3.
Update: Success! I was running under the lowest color mode—16 colors. I changed the display setting to 256 colors and everything is working!—AA0A
Figure 3—To change your display color settings in Windows, you need to access the DISPLAY window in CONTROL PANEL.
From QST September 2000
A This sounds like a display problem of some sort. Are you
using the 256-color display mode? Check your Windows
display properties under SETTINGS—CONTROL PANEL—
DISPLAY. Make sure the SETTINGS are either 256-color or
“High Color.” See Figure 3.
Update: Success! I was running under the lowest color mode—16 colors. I changed the display setting to 256 colors and everything is working!—AA0A
Figure 3—To change your display color settings in Windows, you need to access the DISPLAY window in CONTROL PANEL.
From QST September 2000
I have a question concerning the MFJ Artificial Ground. I’m using a 100-foot longwire antenna fed with an MFJ tuner...
Q Paul Brenner, W6RLF, asks, “I have a question concerning the MFJ Artificial Ground. I’m using a 100-foot longwire antenna fed with an MFJ tuner. I have about 5 feet of tinned copper braid going to a six-foot copper rod ground just under the window where the tuner is located. The performance of the long wire on 40 meters seems just so-so, although it’s a decent length (3/4 wavelength) on 40. If I add the MFJ Artificial Ground to improve my RF grounding, will that help the performance of my antenna system?”
A It would seem unlikely to be of much help. The MFJ Artificial Ground (see Figure 2) does a fine job taming RF in the shack. It is also an excellent “counterpoise tuner” for hams who are using end-fed wire antennas in apartment situations without a short access path to an outdoor ground or radial system, but this isn’t your problem.
Have you considered improving your antenna system? At
3/4 wavelength on 40 meters, it is technically not a long wire but a random wire (“… the power gain of a long-wire antenna as compared to a half-wave dipole is not considerable until the antenna is really long [its length measured in wavelengths]”—ARRL Antenna Book, 18th edition). Try adding as much wire as possible to your antenna; it can run in just about any direction. Get your antenna as high in the air as possible. In addition, attach some 33-foot radial wires to your ground rod. Begin with 4 or 5 wires, either lying on top of the soil or buried underneath. My guess is that you’ll see an improvement in your antenna performance.
Figure 2—The MFJ-934 Artificial Ground
From QST September 2000
A It would seem unlikely to be of much help. The MFJ Artificial Ground (see Figure 2) does a fine job taming RF in the shack. It is also an excellent “counterpoise tuner” for hams who are using end-fed wire antennas in apartment situations without a short access path to an outdoor ground or radial system, but this isn’t your problem.
Have you considered improving your antenna system? At
3/4 wavelength on 40 meters, it is technically not a long wire but a random wire (“… the power gain of a long-wire antenna as compared to a half-wave dipole is not considerable until the antenna is really long [its length measured in wavelengths]”—ARRL Antenna Book, 18th edition). Try adding as much wire as possible to your antenna; it can run in just about any direction. Get your antenna as high in the air as possible. In addition, attach some 33-foot radial wires to your ground rod. Begin with 4 or 5 wires, either lying on top of the soil or buried underneath. My guess is that you’ll see an improvement in your antenna performance.
Figure 2—The MFJ-934 Artificial Ground
From QST September 2000
I have a problem when I transmit on HF...
Q Arnold, AA3HO, asks, “I have a problem when I transmit on HF. When my wife is on the Web my transmissions apparently garble the incoming and outgoing data, preventing her from reaching her desired sites. The computer does not lock up, and the dial-up connection isn’t lost. What tips can you give me to locate and fix the problem?”
A There is a whole chapter in the ARRL RFI Book (http://www.arrl.org/catalog/6834/) on computers—I can’t reproduce it all for you here. It covers interference both ways—to and from computers.
Here is a plan of action. The book points out that many of the same fixes for RFI to computers are those for RFI from computers. These may be found in an article on the TIS Web site: http://www.arrl.org/tis/. Click on RFI/EMI in the menu, then choose “Computer Interference.” Try those fixes.
Also, from personal experience, make sure everything is grounded. All of your ham equipment should be grounded together. Ground your computer; a strap made from discarded coax cable shield running from a screw on the computer’s metal case to ground works nicely. A good ground point for the computer is the little screw on the cover plate of your wall power socket. Test this by shutting off the circuit breaker to that plug and use an ohmmeter between the screw and the ground wire hole. At the very least, make sure your PC is attached to your station ground.
Incidentally, the problem may not be the computer at all and may be your external modem, if that’s what you use. Use the same techniques on it if possible.
Finally, make sure you have no RF coming back into the shack from the antenna. If, per chance, you are using an end fed random or long wire antenna, you may have to try another type. For balanced antennas, such as dipoles, consider adding a 1:1 balun at the feed point.
From QST September 2000
A There is a whole chapter in the ARRL RFI Book (http://www.arrl.org/catalog/6834/) on computers—I can’t reproduce it all for you here. It covers interference both ways—to and from computers.
Here is a plan of action. The book points out that many of the same fixes for RFI to computers are those for RFI from computers. These may be found in an article on the TIS Web site: http://www.arrl.org/tis/. Click on RFI/EMI in the menu, then choose “Computer Interference.” Try those fixes.
Also, from personal experience, make sure everything is grounded. All of your ham equipment should be grounded together. Ground your computer; a strap made from discarded coax cable shield running from a screw on the computer’s metal case to ground works nicely. A good ground point for the computer is the little screw on the cover plate of your wall power socket. Test this by shutting off the circuit breaker to that plug and use an ohmmeter between the screw and the ground wire hole. At the very least, make sure your PC is attached to your station ground.
Incidentally, the problem may not be the computer at all and may be your external modem, if that’s what you use. Use the same techniques on it if possible.
Finally, make sure you have no RF coming back into the shack from the antenna. If, per chance, you are using an end fed random or long wire antenna, you may have to try another type. For balanced antennas, such as dipoles, consider adding a 1:1 balun at the feed point.
From QST September 2000
Friday, July 30, 2010
What is the meaning of ‘DIN’, the infamous multi-pin plug? ...
Q Roger Brackney, K6ZTK, asks, “What is the meaning of ‘DIN’, the infamous multi-pin plug?”
A DIN is an acronym for Deutsche IndustriNorm, the standards- setting organization for Germany. A DIN connector (see Figure 1) is a connector that conforms to one of the many standards defined by DIN. There are many types of DIN connectors in addition to the familiar multi-pin circular types.
Figure 1—The ubiquitous DIN connector
From QST September 2000
Quads antenna What are these?
Q I’m familiar with Yagi antennas, but I also hear occasional references to antenna designs known as quads. What are these?
A Like a Yagi antenna, a quad is directive. That is, it focuses your RF power in a particular direction. In terms of how they are put together, quads are different animals. They consist of two or more loops of wire, each supported by a bamboo or Fiberglass cross-arm assembly. The loops are a quarter wavelength per side (one full wavelength overall). One loop is driven and the other serves as a parasitic element—usually a reflector. A variation on the quad is called the delta loop. The electrical properties of both antennas are the same. Both antennas are shown in Figure 2. They differ mainly in their physical properties, one being of plumber’s delight construction, while the other uses insulating support members. One or more directors can be added to either antenna to obtain additional gain and directivity.
Figure 2—Typical quad and delta loop antenna designs. The 1/4 wavelength of 75-Ω coax acts as a matching transformer between the 100-Ω feed point impedance and the 50-Ω impedance of the station coax.
From QST August 2000
A Like a Yagi antenna, a quad is directive. That is, it focuses your RF power in a particular direction. In terms of how they are put together, quads are different animals. They consist of two or more loops of wire, each supported by a bamboo or Fiberglass cross-arm assembly. The loops are a quarter wavelength per side (one full wavelength overall). One loop is driven and the other serves as a parasitic element—usually a reflector. A variation on the quad is called the delta loop. The electrical properties of both antennas are the same. Both antennas are shown in Figure 2. They differ mainly in their physical properties, one being of plumber’s delight construction, while the other uses insulating support members. One or more directors can be added to either antenna to obtain additional gain and directivity.
Figure 2—Typical quad and delta loop antenna designs. The 1/4 wavelength of 75-Ω coax acts as a matching transformer between the 100-Ω feed point impedance and the 50-Ω impedance of the station coax.
From QST August 2000
Can I run the 450-Ω ladder line through the PVC pipe with no problems? ...
Q Woody, WD4NSB, asks, “I have a 45-foot pole in my front yard that has my 10-meter Yagi antenna mounted on it. All of my coaxial feed lines are routed to the pole through a PVC pipe buried under the ground. I have just put up a McCoy Dipole (nonresonant random length) and will be feeding it with 450-Ω ladder line from a tuner for operation on all bands (160- 10 meters). Can I run the 450-Ω ladder line through the PVC pipe with no problems? If I can’t run the 450-Ω ladder line directly in the pipe, can I make up a 100-Ω balanced line from two lengths of coax (using the center conductors as the feed line and grounding the braids)?”
A Running ladder-line underground through your PVC pipe is not a good idea. Other than very short lengths, or short points of contact, ladder line needs to be kept about 2 feet from any conductors. Running it through your pipe will place it just fractions of an inch away from ground, not to mention the other feed lines in the pipe, for a considerable distance.
Making a balanced line from two pieces of coax is also counterproductive in your situation. The reason for using ladder line in the first place is because of its low loss—this advantage is negated when using the coax balanced line.
If the feed line must go through the pipe to your dipole, my
advice would be to use parallel multiple dipoles fed together at a common feed point with good quality coax. You probably won’t need to use an antenna tuner. See Figure 5 on page 7-3 of the 18th edition of the ARRL Antenna Book.
From QST August 2000
A Running ladder-line underground through your PVC pipe is not a good idea. Other than very short lengths, or short points of contact, ladder line needs to be kept about 2 feet from any conductors. Running it through your pipe will place it just fractions of an inch away from ground, not to mention the other feed lines in the pipe, for a considerable distance.
Making a balanced line from two pieces of coax is also counterproductive in your situation. The reason for using ladder line in the first place is because of its low loss—this advantage is negated when using the coax balanced line.
If the feed line must go through the pipe to your dipole, my
advice would be to use parallel multiple dipoles fed together at a common feed point with good quality coax. You probably won’t need to use an antenna tuner. See Figure 5 on page 7-3 of the 18th edition of the ARRL Antenna Book.
From QST August 2000
Using 1750-Hz access tones vs. subaudible CTCSS access. Which of these systems do the European repeaters use? ...
Q I plan to vacation in Europe this fall and I’d like to try some 2-meter FM repeater operating. I’m a little confused, though, about using 1750-Hz access tones vs. subaudible CTCSS access. Which of these systems do the European repeaters use?
A They may use both. It’s standard practice in Europe to transmit a 1750-Hz tone to access a repeater. Virtually all European repeater systems are configured in this way. Many, however, include CTCSS access as well. This means that you must send the required 1750-Hz access tone and then include the necessary CTCSS tone during your transmission. Fortunately, most modern FM transceivers include the ability to transmit the 1750-Hz burst and CTCSS tones.
From QST August 2000
A They may use both. It’s standard practice in Europe to transmit a 1750-Hz tone to access a repeater. Virtually all European repeater systems are configured in this way. Many, however, include CTCSS access as well. This means that you must send the required 1750-Hz access tone and then include the necessary CTCSS tone during your transmission. Fortunately, most modern FM transceivers include the ability to transmit the 1750-Hz burst and CTCSS tones.
From QST August 2000
I need a quick refresher on the meaning of Q. Can you help? ...
Q I need a quick refresher on the meaning of Q. Can you help?
A Hmmm…I believe Q was the name of an omnipotent alien who appeared occasionally on Star Trek: The Next Generation. His “meaning” wasn’t always clear! But if you’re talking about the ratio of an electronic component’s ability to store energy to the sum total of all of its energy losses, I can help. That’s Q in a nutshell and it is expressed mathematically as:
Q=X/R
where:
Q = figure of merit or quality
X = XL (inductive reactance) for inductors and XC (capacitive reactance) for capacitors (in ohms), and R = the sum of all resistances associated with energy losses in
the component (in ohms).
The Q of capacitors is ordinarily high. Good quality ceramic capacitors and mica capacitors may have Q values of 1200 or more. Small ceramic trimmer capacitors may have Q values too small to ignore in some applications. Microwave capacitors typically have poor Q values (10 or less at 10 GHz).
Inductors are subject to many kinds of electrical energy losses including wire resistance, core losses and skin effect. As a result of inherent losses, inductor Q rarely, if ever, approaches capacitor Q in a circuit where both components work together.
From QST August 2000
A Hmmm…I believe Q was the name of an omnipotent alien who appeared occasionally on Star Trek: The Next Generation. His “meaning” wasn’t always clear! But if you’re talking about the ratio of an electronic component’s ability to store energy to the sum total of all of its energy losses, I can help. That’s Q in a nutshell and it is expressed mathematically as:
Q=X/R
where:
Q = figure of merit or quality
X = XL (inductive reactance) for inductors and XC (capacitive reactance) for capacitors (in ohms), and R = the sum of all resistances associated with energy losses in
the component (in ohms).
The Q of capacitors is ordinarily high. Good quality ceramic capacitors and mica capacitors may have Q values of 1200 or more. Small ceramic trimmer capacitors may have Q values too small to ignore in some applications. Microwave capacitors typically have poor Q values (10 or less at 10 GHz).
Inductors are subject to many kinds of electrical energy losses including wire resistance, core losses and skin effect. As a result of inherent losses, inductor Q rarely, if ever, approaches capacitor Q in a circuit where both components work together.
From QST August 2000
I’m just getting started in low-power (QRP) operating and I have two questions ...
Q Mark Schoonover, KA6WKE, asks, “I’m just getting started in low-power (QRP) operating and I have two questions. How do you establish an RF ground while out in the field? In the Army we pounded in ground rods for field operations. Most of my QRP will involve hiking to various sites and the thought of dragging along a ground rod and hammer is not too exciting.”
A Depending on the type of antenna system you use, grounding in the field may not be all that important. Many antennas, such as dipoles, Yagis, and so on, do not require ground connections for proper operation. Consider the space shuttle; it is nowhere near a ground, but it works just fine!
Other antennas do require grounds—end-fed wires, most verticals, etc. In those cases, you establish the best ground possible with a counterpoise, which can consist of one or more 1/4-wavelength wires connected to the “ground” point such as a short ground rod. Counterpoise radials work best if they are a few inches above the soil.
RF notwithstanding, don’t forget the role grounding plays in lightning protection. If you are truly in the field, however, you shouldn’t be anywhere near the antenna if lightning is about.
From QST August 2000
A Depending on the type of antenna system you use, grounding in the field may not be all that important. Many antennas, such as dipoles, Yagis, and so on, do not require ground connections for proper operation. Consider the space shuttle; it is nowhere near a ground, but it works just fine!
Other antennas do require grounds—end-fed wires, most verticals, etc. In those cases, you establish the best ground possible with a counterpoise, which can consist of one or more 1/4-wavelength wires connected to the “ground” point such as a short ground rod. Counterpoise radials work best if they are a few inches above the soil.
RF notwithstanding, don’t forget the role grounding plays in lightning protection. If you are truly in the field, however, you shouldn’t be anywhere near the antenna if lightning is about.
From QST August 2000
Tuesday, July 27, 2010
In the “PSK31 2000” article in the May 2000 QST ...
Q In the “PSK31 2000” article in the May 2000 QST, there is a single-transistor circuit that is used for transceiver keying via a computer COM port. I’ve seen this circuit used frequently for other switching applications, but some versions add a diode between the base of Q1 and ground. Why is this?
A Radio designer Dave Benson, NN1G, provides the answer: “The diode (D2) between the base of Q1 and ground acts as a ‘shunt diode’ (see Figure 1). The RTS or DTR pins on COM ports can drop to about -10 V in the ‘off’ state, which may be sufficient to get Q1 to go into reverse breakdown. The results could be a rig that is locked in transmit, or otherwise be erratic in its keying characteristics. Adding the shunt diode will prevent this from happening.”
Figure 1—A COM port switching circuit modified with the addition of a shunt diode (D2) between the base of transistor Q1 and ground.
From QST August 2000
A Radio designer Dave Benson, NN1G, provides the answer: “The diode (D2) between the base of Q1 and ground acts as a ‘shunt diode’ (see Figure 1). The RTS or DTR pins on COM ports can drop to about -10 V in the ‘off’ state, which may be sufficient to get Q1 to go into reverse breakdown. The results could be a rig that is locked in transmit, or otherwise be erratic in its keying characteristics. Adding the shunt diode will prevent this from happening.”
Figure 1—A COM port switching circuit modified with the addition of a shunt diode (D2) between the base of transistor Q1 and ground.
From QST August 2000
I’m having problems with RFI to my neighbor’s (and my own) telephone ...
Q Erik Iddings, KF4KRK, asks, “I’m having problems with RFI to my neighbor’s (and my own) telephone. One neighbor picked me up on a 900-MHz cordless phone. She said she could not understand anything but could tell I was on the air. My mother has picked me up on a corded telephone, again nothing legible. And my other neighbor picks me up on his 49-MHz cordless.
“I operate 6-meter SSB using an ICOM IC-706 MkII with 100 W PEP. My radio and tuner are properly grounded. I even made up a coax balun at the shack entry point hoping that would solve the problem. The interference is still there.
“One of my fellow ARES members is an engineer with the
telephone company. I called her the other day and told her
about the problem. She had the customer service manager and a line technician come out and install an RF suppresser on one neighbor’s incoming line. That didn’t work.
“I’m about to go out of my mind trying to figure this out. Unless I can get this RFI problem resolved, it looks like I’m going to have to give up operating on 6 meters unless all the neighbors are at work!”
A Start with the premise that the FCC rules require that spurious emissions (signals outside the ham bands) not cause interference with other radio services. This is your sole regulatory responsibility.
Now, those 900 MHz and 49 MHz cordless phones are regulated by Part 15. Part 15 says that these devices must not cause harmful interference and are not protected from interference from licensed users. The FCC’s material on interference also adds that non-radio devices (telephones, alarm systems, etc) that experience interference are “improperly functioning” as radio receivers. Although you may want to help your neighbors resolve these problems, the rules may help you put that into perspective. For RFI that is not caused by a rules violation, your help is simply neighborly and you should see yourself as a locator of solutions, not a provider of solutions.
For general info about RFI, info for your neighbor, info on telephone interference, info on Part 15, see http://www.arrl.org/tis/ and follow the TISPAGES and RFI links.
I will add that you can sometimes correct problems with cordless phones by filtering the base unit. Get a RadioShack telephone interference filter for the line and a Palomar F-140-43 ferrite core for the power supply lead (wind about 5 turns or so). If this doesn’t work, it is the RF end of the phone being overloaded. For the 49 MHz phone, it is rare that base-unit filtering works to suppress interference from a 6-meter signal. The wireless phones or their owner’s manuals should have a label that indicates that they are not protected from interference.
From QST August 2000
“I operate 6-meter SSB using an ICOM IC-706 MkII with 100 W PEP. My radio and tuner are properly grounded. I even made up a coax balun at the shack entry point hoping that would solve the problem. The interference is still there.
“One of my fellow ARES members is an engineer with the
telephone company. I called her the other day and told her
about the problem. She had the customer service manager and a line technician come out and install an RF suppresser on one neighbor’s incoming line. That didn’t work.
“I’m about to go out of my mind trying to figure this out. Unless I can get this RFI problem resolved, it looks like I’m going to have to give up operating on 6 meters unless all the neighbors are at work!”
A Start with the premise that the FCC rules require that spurious emissions (signals outside the ham bands) not cause interference with other radio services. This is your sole regulatory responsibility.
Now, those 900 MHz and 49 MHz cordless phones are regulated by Part 15. Part 15 says that these devices must not cause harmful interference and are not protected from interference from licensed users. The FCC’s material on interference also adds that non-radio devices (telephones, alarm systems, etc) that experience interference are “improperly functioning” as radio receivers. Although you may want to help your neighbors resolve these problems, the rules may help you put that into perspective. For RFI that is not caused by a rules violation, your help is simply neighborly and you should see yourself as a locator of solutions, not a provider of solutions.
For general info about RFI, info for your neighbor, info on telephone interference, info on Part 15, see http://www.arrl.org/tis/ and follow the TISPAGES and RFI links.
I will add that you can sometimes correct problems with cordless phones by filtering the base unit. Get a RadioShack telephone interference filter for the line and a Palomar F-140-43 ferrite core for the power supply lead (wind about 5 turns or so). If this doesn’t work, it is the RF end of the phone being overloaded. For the 49 MHz phone, it is rare that base-unit filtering works to suppress interference from a 6-meter signal. The wireless phones or their owner’s manuals should have a label that indicates that they are not protected from interference.
From QST August 2000
I would like to run my TNC and ICOM IC-737 transceiver ...
Q Arnie, N1SZS, asks, “I would like to run my TNC and ICOM IC-737 transceiver simultaneously utilizing software that controls both devices. How do I configure my computer’s two serial ports using Windows 98?”
A From the Windows START button, select Settings, then Control Panel, then double-click on System. Select the Device Manager tab, then click (once) on the “+” next to the Port item. You should see lines for both COM1 and COM2. Click on COM2, then click the Properties button. Next, click the Resources tab. If you need to change the settings shown, you will have to click on the “Use automatic settings” box to clear the check mark. Next, select the “Interrupt Request” line or “Input/ Output Range” line and click the “Change Settings” button to change the setting to whatever you need it to be.
From QST August 2000
A From the Windows START button, select Settings, then Control Panel, then double-click on System. Select the Device Manager tab, then click (once) on the “+” next to the Port item. You should see lines for both COM1 and COM2. Click on COM2, then click the Properties button. Next, click the Resources tab. If you need to change the settings shown, you will have to click on the “Use automatic settings” box to clear the check mark. Next, select the “Interrupt Request” line or “Input/ Output Range” line and click the “Change Settings” button to change the setting to whatever you need it to be.
From QST August 2000
Friday, July 23, 2010
I’d like to set up a 30-meter antenna in my back yard ...
Q I’d like to set up a 30-meter antenna in my back yard, but I’m really tight on space. I’ve been told that I can use a technique known as ‘linear loading’ to reduce the size of a dipole. Can you enlighten me?
A What you’ve heard is true—linear loading can significantly reduce the required lengths of resonant antennas. For example, it is easy to make a resonant antenna that is 30 to 40% shorter than an ordinary dipole for a given band. The shorter length comes from bending back some of the antenna wire. The increased self-coupling lowers the resonant frequency.
NN0F constructed a linear-loaded dipole using 25-feet of common 450-Ω ladder line and capacitive end hats (see Figure 1). The end hats are simply 6-foot lengths of stiff wire. Both conductors of the ladder line at each end are soldered to the hat wires. At the middle of the antenna (12 feet 6 inches from the ends) you cut through one of the ladder line conductors and attach your 50-Ω coaxial feed line. Cut through the other conductor as well, but leave it open. This antenna should provide a good match (no tuner required) and it fits easily within most back yards.
Figure 1—A two-wire linear-loaded antenna for 30 meters using 450-Ω ladder line.
From QST July 2000
A What you’ve heard is true—linear loading can significantly reduce the required lengths of resonant antennas. For example, it is easy to make a resonant antenna that is 30 to 40% shorter than an ordinary dipole for a given band. The shorter length comes from bending back some of the antenna wire. The increased self-coupling lowers the resonant frequency.
NN0F constructed a linear-loaded dipole using 25-feet of common 450-Ω ladder line and capacitive end hats (see Figure 1). The end hats are simply 6-foot lengths of stiff wire. Both conductors of the ladder line at each end are soldered to the hat wires. At the middle of the antenna (12 feet 6 inches from the ends) you cut through one of the ladder line conductors and attach your 50-Ω coaxial feed line. Cut through the other conductor as well, but leave it open. This antenna should provide a good match (no tuner required) and it fits easily within most back yards.
Figure 1—A two-wire linear-loaded antenna for 30 meters using 450-Ω ladder line.
From QST July 2000
I travel often on business and I am considering the idea of operating HF QRP from the various hotels where I stay...
Q Mike, AA9RH, asks, “ I travel often on business and I am considering the idea of operating HF QRP from the various hotels where I stay. However, most of my trips take me to large urban or suburban hotels which offer great height (say 20-30 stories), but definitely confine one to indoor operating. Is it possible to enjoy success from inside one of these large, sealed-up hotels?”
A The answer depends on how you define “success.” Doc has been able to make a few QRP contacts from hotel rooms using indoor antennas, but the antennas usually didn’t load well. In addition, they tended to pick up a lot of noise from hotel computers, TVs, hair dryers and so on.
Some hotel windows are not completely sealed; they can be opened slightly. If this is the case, you could discreetly drop a long, thin wire. With a good antenna tuner, and a 1/4-wavelength counterpoise wire on the floor, you may be able to load your “stealth antenna” and make some contacts.
If you are fortunate to have a room with a balcony, you might be able to put up a mobile whip and counterpoise. These are not the most efficient antennas, but they may do the job in a temporary hotel-room application.
From QST July 2000
A The answer depends on how you define “success.” Doc has been able to make a few QRP contacts from hotel rooms using indoor antennas, but the antennas usually didn’t load well. In addition, they tended to pick up a lot of noise from hotel computers, TVs, hair dryers and so on.
Some hotel windows are not completely sealed; they can be opened slightly. If this is the case, you could discreetly drop a long, thin wire. With a good antenna tuner, and a 1/4-wavelength counterpoise wire on the floor, you may be able to load your “stealth antenna” and make some contacts.
If you are fortunate to have a room with a balcony, you might be able to put up a mobile whip and counterpoise. These are not the most efficient antennas, but they may do the job in a temporary hotel-room application.
From QST July 2000
I live in a condo with neighbors on both sides. If I use it with my 150-W transmitter ...
Q Bernard, K8LIX, asks, “The Dovetron stealth antenna uses house wiring as part of the radiating system. I live in a condo with neighbors on both sides. If I use it with my 150-W transmitter, what kind of measurements will I have to make in order to satisfy the FCC RF safety requirements?”
A You can make the same calculations for this as for any antenna. Unless you and your neighbors are on the same circuit, you can probably safely assume that all of the wiring in your unit could be radiating. These types of antennas are not very efficient, so a calculation assuming 0-dBi gain is probably reasonable.
At 150 W, with a 40% duty factor and 67% on/off operating times, you have 40 W of average power for the purposes of the safety calculation. Your neighbors would need to be the following distances from any part of your residential electrical wiring:
28 MHz: 6.2 feet
14 MHz: 3.1 feet
7 MHz: 1.5 feet
Assuming the same conditions and 100% on/off time (in 6 minutes), you and your family would have to be:
28 MHz: 3.4 feet
14 MHz: 1.7 feet
7 MHz: 0.8 feet
From QST July 2000
A You can make the same calculations for this as for any antenna. Unless you and your neighbors are on the same circuit, you can probably safely assume that all of the wiring in your unit could be radiating. These types of antennas are not very efficient, so a calculation assuming 0-dBi gain is probably reasonable.
At 150 W, with a 40% duty factor and 67% on/off operating times, you have 40 W of average power for the purposes of the safety calculation. Your neighbors would need to be the following distances from any part of your residential electrical wiring:
28 MHz: 6.2 feet
14 MHz: 3.1 feet
7 MHz: 1.5 feet
Assuming the same conditions and 100% on/off time (in 6 minutes), you and your family would have to be:
28 MHz: 3.4 feet
14 MHz: 1.7 feet
7 MHz: 0.8 feet
From QST July 2000
I have a question about an HF/ VHF SWR/power meter I just purchased. I’m using an ADI AT600HP 2m/70cm hand-held transceiver ...
Q Andy, KB1ETK, asks, “I have a question about an HF/ VHF SWR/power meter I just purchased. I’m using an ADI AT600HP 2m/70cm hand-held transceiver. It generates 5 W output on the ‘high power’ setting when I use the 13.6-V battery. When I hook up my home-brew 1/4-wavelength vertical the meter measures an SWR of 1.3:1 and the RF power measurements are correct: 5 W on high, 2 W on medium, 400 mW on low. But when I attach the rubber duck antenna that came with the radio (with the SWR/power meter in between), my measured power output shoots up to close to 10 W on high, 6 W on medium, and 3 W on low. How is this possible?”
A The power reflected at the rubber ducky is re-reflected back down the coax from the transmitter to the antenna. When it reaches the antenna, the power again reflects and the cycle begins again. On each reflection, there is some power lost in the transmission line. However, the net effect is that both the forward and reflected powers will read higher than they actually are. The difference between the forward and reverse power readings is the actual net power. Thus, when the SWR is higher than 1:1, the forward power will rise, but so will the reflected power.
Here’s a good case in point. I used to own an HF QRP rig that did not reduce power for high SWRs. Its maximum output was 2W. When I had a schedule with a station very close by and didn’t have a tuner handy, I ran a random wire around the room and connected the rig directly to it. The SWR meter said I had 10W forward and 8W reflected. The difference between forward and reverse powers was 10 − 8 = 2 W, just what it should have been.
Rubber ducks are poor antennas in all respects save one— portability. I wouldn’t be overly concerned about the high SWR with your rubber duck. VHF/UHF equipment typically transmits into a 3:1 to 4:1 SWR without suffering ill effects. Further, a rubber duck uses the H-T (and the human body holding it) as its “ground plane.” Putting a piece of coax between the rubber ducky and the SWR meter doesn’t yield the same amount of groundplane area and the feed-point impedance of the rubber ducky will change from when it is used in a more traditional fashion connected directly to the H-T.
From QST July 2000
A The power reflected at the rubber ducky is re-reflected back down the coax from the transmitter to the antenna. When it reaches the antenna, the power again reflects and the cycle begins again. On each reflection, there is some power lost in the transmission line. However, the net effect is that both the forward and reflected powers will read higher than they actually are. The difference between the forward and reverse power readings is the actual net power. Thus, when the SWR is higher than 1:1, the forward power will rise, but so will the reflected power.
Here’s a good case in point. I used to own an HF QRP rig that did not reduce power for high SWRs. Its maximum output was 2W. When I had a schedule with a station very close by and didn’t have a tuner handy, I ran a random wire around the room and connected the rig directly to it. The SWR meter said I had 10W forward and 8W reflected. The difference between forward and reverse powers was 10 − 8 = 2 W, just what it should have been.
Rubber ducks are poor antennas in all respects save one— portability. I wouldn’t be overly concerned about the high SWR with your rubber duck. VHF/UHF equipment typically transmits into a 3:1 to 4:1 SWR without suffering ill effects. Further, a rubber duck uses the H-T (and the human body holding it) as its “ground plane.” Putting a piece of coax between the rubber ducky and the SWR meter doesn’t yield the same amount of groundplane area and the feed-point impedance of the rubber ducky will change from when it is used in a more traditional fashion connected directly to the H-T.
From QST July 2000
I’m curious about connecting two VHF antennas. Can you use a T connector to connect one feed line ...
Q Joe, NC4D, asks, “I’m curious about connecting two VHF antennas. Can you use a T connector to connect one feed line from a 6-meter beam, and another from a 2-meter beam, to a single piece of coax going back to the radio? Would this be any different than having multiple dipoles in parallel, all connected to the same feed line?”
A Parallel dipoles work as they do because the antennas that are nonresonant to the frequency of the transmitted signal provide a high impedance at the connection point while the antenna that is resonant provides a low (approximately 50 Ω) impedance.
A 6-meter beam may or may not offer sufficiently high impedance to 2-meter RF, and vice versa. Either way, you still have the issue of what happens in the coax. Coax that is terminated in its characteristic impedance will present the same impedance on the other end. Coax that is terminated in a high impedance will present a different impedance on the other end, dependent upon the length. Consider an open coax stub: the far end is about as high an impedance as you could want. If the coax is 1/2 wavelength (or a multiple thereof), the near end will also be a high impedance. However, if the coax is a 1/4 wavelength (or an odd multiple thereof), the near end will be a very low impedance. Lengths in between will give other impedance values.
So, to do what you describe, you would have to adjust the length of the coax going from the T to the 6-meter beam in such a way that it offers a high impedance to 2-meter RF. You’ll need to meet the opposite condition with the coax that runs between the T and the 2-meter beam. Perhaps an easier alternative would be to purchase a diplexer.
These matching/coupling devices are primarily designed to allow multiband VHF/UHF transceivers with single feed line ports to operate on several bands without changing antennas. Feed lines from each antenna connect to the diplexer, then a single coax feed line runs between the diplexer and the radio.
From QST July 2000
A Parallel dipoles work as they do because the antennas that are nonresonant to the frequency of the transmitted signal provide a high impedance at the connection point while the antenna that is resonant provides a low (approximately 50 Ω) impedance.
A 6-meter beam may or may not offer sufficiently high impedance to 2-meter RF, and vice versa. Either way, you still have the issue of what happens in the coax. Coax that is terminated in its characteristic impedance will present the same impedance on the other end. Coax that is terminated in a high impedance will present a different impedance on the other end, dependent upon the length. Consider an open coax stub: the far end is about as high an impedance as you could want. If the coax is 1/2 wavelength (or a multiple thereof), the near end will also be a high impedance. However, if the coax is a 1/4 wavelength (or an odd multiple thereof), the near end will be a very low impedance. Lengths in between will give other impedance values.
So, to do what you describe, you would have to adjust the length of the coax going from the T to the 6-meter beam in such a way that it offers a high impedance to 2-meter RF. You’ll need to meet the opposite condition with the coax that runs between the T and the 2-meter beam. Perhaps an easier alternative would be to purchase a diplexer.
These matching/coupling devices are primarily designed to allow multiband VHF/UHF transceivers with single feed line ports to operate on several bands without changing antennas. Feed lines from each antenna connect to the diplexer, then a single coax feed line runs between the diplexer and the radio.
From QST July 2000
I have a Yaesu FT-990 transceiver that I use with a Carolina Windom antenna...
Q John, KU4KZ, asks, “I have a Yaesu FT-990 transceiver that I use with a Carolina Windom antenna. Most of the time I use my antenna tuner, but the other day the tuner was accidentally in the bypass mode. I noticed that the tuner’s SWR meter was moving as I talked. It seemed to kick up as high as 2:1. I was running about 100 W output. When I brought the antenna tuner into the line, the needle did not move when I transmitted. Can you explain this?”
AYes, I believe I can. To answer your question, let’s briefly
discuss what an antenna tuner and an SWR meter do.
Part of the function of an SWR meter is to measure any power that is reflected back to your transceiver that’s caused by an impedance mismatch in the antenna system. Most modern rigs are designed to accommodate antenna impedances of 50 Ω. If the impedance at the antenna system input is anything other than 50 Ω, power will be reflected back to the radio. The reflected power needle on your SWR meter will indicate this power. If it reads zero, there is no measurable reflected power.
The job of the antenna tuner is to match the antenna system impedance to that of the transceiver. Note that an antenna tuner doesn’t “tune” anything—it matches two dissimilar impedances. The antenna tuner transforms whatever impedance exists at the end of your coax to 50 Ω for the radio. When impedances are matched there is no reflected power and, again, the reflected power needle will read zero.
So, when your antenna tuner was bypassed you were seeing
the result of having your transceiver connected directly to the
antenna system. The SWR meter indicated that reflected power was present as you spoke. (In SSB, power is generated only when you actually speak.) When you switched your tuner back in, the impedance mismatch was transformed to 50 Ω and the reflected power at the SWR meter dropped to zero.
By the way, don’t worry too much about harming your FT-990 this way. Like most transceivers, the FT-990 includes a foldback circuit that senses when there is too much reflected power getting into the radio. The foldback automatically reduces the output to a safe level.
From QST July 2000
AYes, I believe I can. To answer your question, let’s briefly
discuss what an antenna tuner and an SWR meter do.
Part of the function of an SWR meter is to measure any power that is reflected back to your transceiver that’s caused by an impedance mismatch in the antenna system. Most modern rigs are designed to accommodate antenna impedances of 50 Ω. If the impedance at the antenna system input is anything other than 50 Ω, power will be reflected back to the radio. The reflected power needle on your SWR meter will indicate this power. If it reads zero, there is no measurable reflected power.
The job of the antenna tuner is to match the antenna system impedance to that of the transceiver. Note that an antenna tuner doesn’t “tune” anything—it matches two dissimilar impedances. The antenna tuner transforms whatever impedance exists at the end of your coax to 50 Ω for the radio. When impedances are matched there is no reflected power and, again, the reflected power needle will read zero.
So, when your antenna tuner was bypassed you were seeing
the result of having your transceiver connected directly to the
antenna system. The SWR meter indicated that reflected power was present as you spoke. (In SSB, power is generated only when you actually speak.) When you switched your tuner back in, the impedance mismatch was transformed to 50 Ω and the reflected power at the SWR meter dropped to zero.
By the way, don’t worry too much about harming your FT-990 this way. Like most transceivers, the FT-990 includes a foldback circuit that senses when there is too much reflected power getting into the radio. The foldback automatically reduces the output to a safe level.
From QST July 2000
Is there a site on the Web where I can obtain pass predictions for Amateur Radio satellites?...
Q Is there a site on the Web where I can obtain pass predictions for Amateur Radio satellites?
A There is indeed. Point your browser to http://www.heavensabove. com/. This fascinating site is primarily devoted to observing objects in the night sky, but it tracks all kinds of satellites, too. It can provide a 24-hour listing of passes for various Amateur Radio satellites.
You can obtain a 24-hour list of Amateur Radio satellite passes for your location on the Web at Heavens Above at: http://www.heavens-above.com/.
From QST July 2000
A There is indeed. Point your browser to http://www.heavensabove. com/. This fascinating site is primarily devoted to observing objects in the night sky, but it tracks all kinds of satellites, too. It can provide a 24-hour listing of passes for various Amateur Radio satellites.
You can obtain a 24-hour list of Amateur Radio satellite passes for your location on the Web at Heavens Above at: http://www.heavens-above.com/.
From QST July 2000
Whenever I send a QSL directly to a DX station I include an SASE and a dollar ...
Q N1AHT asks, “Whenever I send a QSL directly to a DX station I include an SASE and a dollar. Is this the correct procedure?”
A Including an SAE (Self-Addressed Envelope) is always a good idea, but not an SASE (Self-Addressed Stamped Envelope). A US stamp is of no use at all to a ham in another country. He has to put his country’s stamp on the return envelope. As for the dollar, opinions on this practice differ. Many US hams include “greenstamps” (US dollars) with their QSLs to pay for the return postage. One US dollar will pay for return airmail postage from most areas of the world. The exceptions appear to be France and Germany where $2 may be necessary, depending on the exchange rates at the time.
Sending US dollars is an expensive way to QSL, but the advantage is that you will probably have your coveted card much sooner. Going through the QSL bureau system is more cost effective, but you could wait a year or longer to receive the card. It all boils down to how eager you are to have the confirmation in hand. Be advised that receiving foreign currency is illegal in a few countries. In addition, the postal workers in some countries have become remarkably adept at spotting Amateur Radio correspondence. They know these envelopes could contain money and are not above stealing the contents.
The alternative to the greenstamp is the IRC—International Reply Coupon. By international agreement, these are each valued at one unit of air mail postage at the destination. You’ll find IRCs at your local post office.
From QST July 2000
A Including an SAE (Self-Addressed Envelope) is always a good idea, but not an SASE (Self-Addressed Stamped Envelope). A US stamp is of no use at all to a ham in another country. He has to put his country’s stamp on the return envelope. As for the dollar, opinions on this practice differ. Many US hams include “greenstamps” (US dollars) with their QSLs to pay for the return postage. One US dollar will pay for return airmail postage from most areas of the world. The exceptions appear to be France and Germany where $2 may be necessary, depending on the exchange rates at the time.
Sending US dollars is an expensive way to QSL, but the advantage is that you will probably have your coveted card much sooner. Going through the QSL bureau system is more cost effective, but you could wait a year or longer to receive the card. It all boils down to how eager you are to have the confirmation in hand. Be advised that receiving foreign currency is illegal in a few countries. In addition, the postal workers in some countries have become remarkably adept at spotting Amateur Radio correspondence. They know these envelopes could contain money and are not above stealing the contents.
The alternative to the greenstamp is the IRC—International Reply Coupon. By international agreement, these are each valued at one unit of air mail postage at the destination. You’ll find IRCs at your local post office.
From QST July 2000
Saturday, July 17, 2010
How fast do electrons flow in copper wire?...
Q How fast do electrons flow in copper wire?
A It turns out that the electrons in copper travel quite slowly even though electricity travels at almost the speed of light. That’s because there are so many mobile electrons in copper (and other conductors) that even if those electrons move only an inch per second, they comprise a large electric current.
The fact that electricity itself travels at almost the speed of light just means that when you start the electrons moving at one end of a long wire, the electrons at the other end of the wire also begin moving almost immediately. But that doesn’t mean that an electron from your end of the wire actually reaches the far end any time soon. Instead, the electrons behave like water in a long hose. When you start the water moving at one end, it pushes on water in front of it, which pushes on water in front of it, and so on so that water at the far end begins to leave the hose. In a wire, the motion proceeds forward at the speed of light in the wire (actually the speed at which electromagnetic waves propagate along the wire), which is only slightly less than the speed of light in vacuum.
From QST June 2000
A It turns out that the electrons in copper travel quite slowly even though electricity travels at almost the speed of light. That’s because there are so many mobile electrons in copper (and other conductors) that even if those electrons move only an inch per second, they comprise a large electric current.
The fact that electricity itself travels at almost the speed of light just means that when you start the electrons moving at one end of a long wire, the electrons at the other end of the wire also begin moving almost immediately. But that doesn’t mean that an electron from your end of the wire actually reaches the far end any time soon. Instead, the electrons behave like water in a long hose. When you start the water moving at one end, it pushes on water in front of it, which pushes on water in front of it, and so on so that water at the far end begins to leave the hose. In a wire, the motion proceeds forward at the speed of light in the wire (actually the speed at which electromagnetic waves propagate along the wire), which is only slightly less than the speed of light in vacuum.
From QST June 2000
Our club is considering an APRS balloon project. The payload—a GPS receiver ...
Q Our club is considering an APRS (Automatic Position Reporting System) balloon project. The payload—a GPS receiver, packet TNC and 2-meter transmitter will total about 4 pounds. How much helium is the flight going to require?
A Your ordinary weather balloon, when filled with helium, is lighter than air and floats upward as descending air pushes it out of the way. Like a bubble in water, the helium goes up to make room for the air going down. The buoyant force that acts on the helium is equal to the weight of air that the helium displaces.
A cubic foot of air weighs about 0.078 pounds, so the upward buoyant force on a cubic foot of helium is about 0.078 pounds. A cubic foot of helium weighs only about 0.011 pounds. The difference between the upward buoyant force on the cubic foot of helium and the weight of the helium is the amount of extra weight that the helium can lift: about 0.067 pounds. Since your payload is going to weigh in at about 4 pounds, you’d need about 60 cubic feet (4 / 0.067) of helium. I’d recommend 100 cubic feet to provide a good rate of climb and to take into account other weight factors.
From QST June 2000
A Your ordinary weather balloon, when filled with helium, is lighter than air and floats upward as descending air pushes it out of the way. Like a bubble in water, the helium goes up to make room for the air going down. The buoyant force that acts on the helium is equal to the weight of air that the helium displaces.
A cubic foot of air weighs about 0.078 pounds, so the upward buoyant force on a cubic foot of helium is about 0.078 pounds. A cubic foot of helium weighs only about 0.011 pounds. The difference between the upward buoyant force on the cubic foot of helium and the weight of the helium is the amount of extra weight that the helium can lift: about 0.067 pounds. Since your payload is going to weigh in at about 4 pounds, you’d need about 60 cubic feet (4 / 0.067) of helium. I’d recommend 100 cubic feet to provide a good rate of climb and to take into account other weight factors.
From QST June 2000
I’ve been connecting to the Internet with my shack PC at 28.8 kbps...
Q I’ve been connecting to the Internet with my shack PC at 28.8 kbps. Just this week I received word that DSL will soon be available in my area and that it would greatly accelerate my Internet access. What can you tell me about DSL?
A DSL stands for stands for digital subscriber line, and it takes advantage of the fact that the total capacity of the telephone line coming into your home is vastly under-utilized. Simple voice communication uses only about 1% of the available bandwidth, leaving huge amounts of unused capacity that can support digital transmissions.
DSL uses your telephone line by skipping analog conversion. That is, there is no digital-to-analog conversation process like you see (and hear) in conventional modems. Instead, DSL keys digital data directly on the line. The result is mind-boggling speed—theoretically as high as 8 mbps (megabits, or millions of bits, per second), which is more than 250 times the rate you get at 28.8 kbps. And because the analog voice signal and digital DSL signals use different frequencies, they can be transmitted simultaneously. So not only do you get much higher transmission rates, you can leave your computer connected to the Internet 24 hours a day and still receive telephone calls—all over a single copper phone line.
Of course, there is a catch. (Isn’t there always?) DSL signals attenuate rapidly with distance. For most DSL technologies, the signal is only viable for 18,000 feet. In other words, if you don’t live within about 31/2 miles of your phone company’s central office, you can forget about DSL. That excludes something in excess of one-third of all homes in the United States.
DSL actually comes in a number of flavors. One of the most common is ADSL (asymmetric digital subscriber line). Most home and small office computer users download a lot of data off the Web, but send relatively little data in the other direction.
ADSL makes use of that by reserving more bandwidth for downstream data flow—from the Web to your computer—than upstream. With ADSL, downstream speeds of up to 6 mbps are possible (although 1.5 mbps is more typical); upstream tops out at 640 kbps. ADSL requires the installation of a voice/data splitter at your home. A slightly slower version, called DSL Lite, does the splitting at the phone company. Other varieties include HDSL (high bit-rate DSL) which carries equal amounts of data in both directions and has a maximum rate that is lower than ADSL; RADSL (rate-adaptive DSL), which analyzes the capacity of a customer’s phone line and adjusts the rate accordingly; and VDSL (very high data rate DSL), which can send data at an astonishing rate of 55 mbps, but only for about 1,000 feet.
From QST June 2000
A DSL stands for stands for digital subscriber line, and it takes advantage of the fact that the total capacity of the telephone line coming into your home is vastly under-utilized. Simple voice communication uses only about 1% of the available bandwidth, leaving huge amounts of unused capacity that can support digital transmissions.
DSL uses your telephone line by skipping analog conversion. That is, there is no digital-to-analog conversation process like you see (and hear) in conventional modems. Instead, DSL keys digital data directly on the line. The result is mind-boggling speed—theoretically as high as 8 mbps (megabits, or millions of bits, per second), which is more than 250 times the rate you get at 28.8 kbps. And because the analog voice signal and digital DSL signals use different frequencies, they can be transmitted simultaneously. So not only do you get much higher transmission rates, you can leave your computer connected to the Internet 24 hours a day and still receive telephone calls—all over a single copper phone line.
Of course, there is a catch. (Isn’t there always?) DSL signals attenuate rapidly with distance. For most DSL technologies, the signal is only viable for 18,000 feet. In other words, if you don’t live within about 31/2 miles of your phone company’s central office, you can forget about DSL. That excludes something in excess of one-third of all homes in the United States.
DSL actually comes in a number of flavors. One of the most common is ADSL (asymmetric digital subscriber line). Most home and small office computer users download a lot of data off the Web, but send relatively little data in the other direction.
ADSL makes use of that by reserving more bandwidth for downstream data flow—from the Web to your computer—than upstream. With ADSL, downstream speeds of up to 6 mbps are possible (although 1.5 mbps is more typical); upstream tops out at 640 kbps. ADSL requires the installation of a voice/data splitter at your home. A slightly slower version, called DSL Lite, does the splitting at the phone company. Other varieties include HDSL (high bit-rate DSL) which carries equal amounts of data in both directions and has a maximum rate that is lower than ADSL; RADSL (rate-adaptive DSL), which analyzes the capacity of a customer’s phone line and adjusts the rate accordingly; and VDSL (very high data rate DSL), which can send data at an astonishing rate of 55 mbps, but only for about 1,000 feet.
From QST June 2000
When I attempt to use my old Gonset linear amplifier with my ICOM IC-751 transceiver, there is a 3:1 SWR between the radio and the amp ...
Q Lionel, F5APZ, asks, “When I attempt to use my old Gonset linear amplifier with my ICOM IC-751 transceiver, there is a 3:1 SWR between the radio and the amp. Of course, this causes the 751 to fold back to only 50% output. What could be causing this?”
A My guess would be a problem with the amplifier-input circuit. A lot of older amps used tuned inputs that were switched as you changed bands. Over time, the values of the coils or capacitors can change, resulting in the input impedance changing. If you have the manual for the amp, take a look at the schematic. If the input circuit has adjustable coils or capacitors, you can try tweaking them for a better match. You could also use an antenna tuner between the rig and the amp, although you may still experience some power loss in the input circuit after the tuner. (Remember: An antenna tuner does not change the SWR at its output. See Figure 2.)
Although Gonset is long out of business, you might still be able to obtain a copy of the manual if you need one. To find a source for old equipment manuals, access the Web and go to the ARRL Technical Information Service page at: http://www.arrl.org/tis/ and click on the TISfind link.
Figure 2—An antenna tuner installed between a transceiver and amplifier will provide a 1:1 SWR for the transceiver to prevent power foldback. However, the tuner does nothing for the SWR between the tuner and the amplifier.
From QST June 2000
A My guess would be a problem with the amplifier-input circuit. A lot of older amps used tuned inputs that were switched as you changed bands. Over time, the values of the coils or capacitors can change, resulting in the input impedance changing. If you have the manual for the amp, take a look at the schematic. If the input circuit has adjustable coils or capacitors, you can try tweaking them for a better match. You could also use an antenna tuner between the rig and the amp, although you may still experience some power loss in the input circuit after the tuner. (Remember: An antenna tuner does not change the SWR at its output. See Figure 2.)
Although Gonset is long out of business, you might still be able to obtain a copy of the manual if you need one. To find a source for old equipment manuals, access the Web and go to the ARRL Technical Information Service page at: http://www.arrl.org/tis/ and click on the TISfind link.
Figure 2—An antenna tuner installed between a transceiver and amplifier will provide a 1:1 SWR for the transceiver to prevent power foldback. However, the tuner does nothing for the SWR between the tuner and the amplifier.
From QST June 2000
I’ve built a computer interface for use with my Kenwood transceiver. The interface works, but ..
Q Colin, VE1CSM, asks, “I’ve built a computer interface for use with my Kenwood transceiver. The interface works, but it seems to be generating interference. Can you help?
A Computer interfaces and their connecting cables are all potential sources of interference, both in terms of RF radiated from the cable and in terms of RF feedback into the devices the cables are connected to.
The fix for both involves two parts: proper shielding and common mode noise suppression via the use of ferrites. If you haven’t put the interface into a metal box, that’s the first thing you want to do. Second is that you would want to use a cable where all the signal-carrying conductors are enclosed in a foil (preferably) or high-density braid shield. A stranded braid wound around the outside of the other wires is not sufficient.
Even with all that, you may still have problems. The next step is the judicious application of Type 43 ferrite cores. To suppress common-mode signals (where the interfering signal is being picked up by the whole cable), you would take a suitable-size ferrite and wrap a number of turns of the cable around it. Donutshaped (toroid) cores are best in that they couple the energy back into the core, whereas rods tend to “leak” a little at the ends. As far as the number of turns goes, more is generally better, but there is a limit. If you wrap three turns around the ferrite and it helps, that’s great, but if it doesn’t, it usually means you need more turns. However, if you get a dozen turns around the ferrite and it doesn’t help, chances are two dozen turns won’t be any better.
From QST June 2000
A Computer interfaces and their connecting cables are all potential sources of interference, both in terms of RF radiated from the cable and in terms of RF feedback into the devices the cables are connected to.
The fix for both involves two parts: proper shielding and common mode noise suppression via the use of ferrites. If you haven’t put the interface into a metal box, that’s the first thing you want to do. Second is that you would want to use a cable where all the signal-carrying conductors are enclosed in a foil (preferably) or high-density braid shield. A stranded braid wound around the outside of the other wires is not sufficient.
Even with all that, you may still have problems. The next step is the judicious application of Type 43 ferrite cores. To suppress common-mode signals (where the interfering signal is being picked up by the whole cable), you would take a suitable-size ferrite and wrap a number of turns of the cable around it. Donutshaped (toroid) cores are best in that they couple the energy back into the core, whereas rods tend to “leak” a little at the ends. As far as the number of turns goes, more is generally better, but there is a limit. If you wrap three turns around the ferrite and it helps, that’s great, but if it doesn’t, it usually means you need more turns. However, if you get a dozen turns around the ferrite and it doesn’t help, chances are two dozen turns won’t be any better.
From QST June 2000
What is an iambic keyer or iambic keying?...
Q Frank Caputo, WA2AAW, asks, “What is an iambic keyer or iambic keying?”
A An iambic keyer is an electronic keyer that can be operated by a set of two paddles. By convention, for a right-handed person, the right paddle (index finger) produces continuous dits when depressed and the left paddle (the thumb) produces continuous dahs. The iambic part comes into play when the paddles are squeezed together (both thumb and index finger). This causes the iambic keyer to produce an alternating dit-dah-dit-dah.
From Webster’s dictionary: i·amb (ìıàmb´, ìıàm´) noun A metrical foot consisting of an unstressed syllable followed by a stressed syllable or a short syllable followed by a long syllable, as in delay.
From QST June 2000
A An iambic keyer is an electronic keyer that can be operated by a set of two paddles. By convention, for a right-handed person, the right paddle (index finger) produces continuous dits when depressed and the left paddle (the thumb) produces continuous dahs. The iambic part comes into play when the paddles are squeezed together (both thumb and index finger). This causes the iambic keyer to produce an alternating dit-dah-dit-dah.
From Webster’s dictionary: i·amb (ìıàmb´, ìıàm´) noun A metrical foot consisting of an unstressed syllable followed by a stressed syllable or a short syllable followed by a long syllable, as in delay.
From QST June 2000
For the last 20 years I’ve been feeding my antenna with a length of Belden RG-8U coax...
Q Gene, WA2FLN, asks, “For the last 20 years I’ve been feeding my antenna with a length of Belden RG-8U coax. If I place a dummy load at the antenna I still measure a 1:1 SWR in the shack, but I wonder whether I should replace the old feed line anyway. What do you think?”
A The conductors inside the cable have a tendency to oxidize over time and the dielectric may begin to absorb some moisture. All of this leads to increased loss, which will make your SWR look better than it actually is. I would consider 15-20 years to be the useful limit for coax, but it will vary quite a bit depending upon the environment and the materials used to make the coax.
If you really want to evaluate the condition of your coax, the best thing to do is to measure the RF power at the input of the cable, and at the dummy load on the other end. Subtract the input power from the power measured at the dummy load and you’ll know how much RF you’re losing in the cable. Compare the total loss to the specifications for your cable. This will tell you how much your 20- year-old coax has departed from its original pristine condition. For RG8U, the power loss in a 50-foot section at 14 MHz should be roughly 0.4 dB, which is about 9 W out of 100 W.
From QST June 2000
A The conductors inside the cable have a tendency to oxidize over time and the dielectric may begin to absorb some moisture. All of this leads to increased loss, which will make your SWR look better than it actually is. I would consider 15-20 years to be the useful limit for coax, but it will vary quite a bit depending upon the environment and the materials used to make the coax.
If you really want to evaluate the condition of your coax, the best thing to do is to measure the RF power at the input of the cable, and at the dummy load on the other end. Subtract the input power from the power measured at the dummy load and you’ll know how much RF you’re losing in the cable. Compare the total loss to the specifications for your cable. This will tell you how much your 20- year-old coax has departed from its original pristine condition. For RG8U, the power loss in a 50-foot section at 14 MHz should be roughly 0.4 dB, which is about 9 W out of 100 W.
From QST June 2000
What is the precise ratio of frequency (in hertz) to bandwidth (in meters)? ...
Q What is the precise ratio of frequency (in hertz) to bandwidth (in meters)? I have seen a six-digit figure floating around, but that may not be very exact. It’s likely that the ratio number could go on forever in precision, but can you give it to me in as many digits as possible?
A Is this sufficiently precise? 1 Hz = 299,792,458 meters You’ll find a terrific page on the Web for looking up constants at: http://physics.nist.gov/cuu/Constants/index.html.
From QST June 2000
A Is this sufficiently precise? 1 Hz = 299,792,458 meters You’ll find a terrific page on the Web for looking up constants at: http://physics.nist.gov/cuu/Constants/index.html.
From QST June 2000
I live in an apartment and I need to run a length of coax from my radio through a window to an outdoor antenna...
Q Tim, WD8OQX, asks, “I live in an apartment and I need to run a length of coax from my radio through a window to an outdoor antenna. The trick is that I need to do it without modifying or damaging the window. Do you have any ideas?”
A The Doctor was once faced with a similar problem while living in a condominium. My solution was the old open the window slightly and place a board there scheme.
See Figure 1. Cut a piece of 2 × 4 lumber so that it fits snugly into the lower sash. Drill a hole large enough to pass your coaxial cable. Pass the cable through the board and through the window.
Close the window onto the board and use another length of board between the top of the window and the upper frame to prevent the window from being opened from the outside. Connect the coax to your antenna, but leave enough slack in the cable to form a drip loop just outside the window. Finally, buy some packing foam material and use it to block any drafty gaps created by your new installation. When it’s time to move, the entire assembly can be torn down in minutes without damage to the window.
Figure 1—A narrow 2x4 with a properly drilled hole will pass a coaxial cable through a window without damaging or modifying the window itself.
From QST June 2000
A The Doctor was once faced with a similar problem while living in a condominium. My solution was the old open the window slightly and place a board there scheme.
See Figure 1. Cut a piece of 2 × 4 lumber so that it fits snugly into the lower sash. Drill a hole large enough to pass your coaxial cable. Pass the cable through the board and through the window.
Close the window onto the board and use another length of board between the top of the window and the upper frame to prevent the window from being opened from the outside. Connect the coax to your antenna, but leave enough slack in the cable to form a drip loop just outside the window. Finally, buy some packing foam material and use it to block any drafty gaps created by your new installation. When it’s time to move, the entire assembly can be torn down in minutes without damage to the window.
Figure 1—A narrow 2x4 with a properly drilled hole will pass a coaxial cable through a window without damaging or modifying the window itself.
From QST June 2000
Thursday, July 15, 2010
I just recently completed a modification of a RadioShack FM antenna for 2 meter use ...
Q John, KF6EOJ, asks, “I just recently completed a modification of a RadioShack FM antenna for 2 meter use, but I am a little confused about the issue of vertical vs. horizontal polarization. Two members of my local club say that for FM use I should use the antenna vertically polarized, which means modifying the antenna mounting holes, which I have already done. Is this true? I only have a FM H-T and I intend on using the antenna to increase my range.”
A When amateur 2-meter FM repeaters came along in the 70s they were used primarily for mobile communication. Horizontal mobile antennas proved cumbersome (remember the Halo?) and so vertical whips were the favored. Repeaters followed suit, using vertically polarized antennas as well. The penalty for a polarization mismatch (using horizontal polarization when the other station is using vertical, or vice versa) is a substantial signal loss.
So, the established custom among FM operators is to use vertically polarized antennas. If you want to communicate with other FM stations, choose vertical polarization. On the other hand, you should know that 2-meter SSB and CW operators use horizontal polarization—if you ever decide to give 2-meter DXing a try.
from QST May 2000
A When amateur 2-meter FM repeaters came along in the 70s they were used primarily for mobile communication. Horizontal mobile antennas proved cumbersome (remember the Halo?) and so vertical whips were the favored. Repeaters followed suit, using vertically polarized antennas as well. The penalty for a polarization mismatch (using horizontal polarization when the other station is using vertical, or vice versa) is a substantial signal loss.
So, the established custom among FM operators is to use vertically polarized antennas. If you want to communicate with other FM stations, choose vertical polarization. On the other hand, you should know that 2-meter SSB and CW operators use horizontal polarization—if you ever decide to give 2-meter DXing a try.
from QST May 2000
I put up a 10-meter quarter-wavelength ground plane antenna on my property in my subdivision...
Q Steve, N8UBR, asks, “I put up a 10-meter quarter-wavelength ground plane antenna on my property in my subdivision. When doing an RF safety evaluation for this system, is the distance measured from the main vertical radiator or the ground plane radials? (I plan to use 100 W.) The radials are currently above the ground, but will be buried in the spring when the ground thaws.”
A If I were doing your evaluation, I would consider radials that were within a few inches of the ground to be grounded and would do my calculations from the main antenna itself. If I had a ground-plane antenna with elevated radials, I would, to be conservative, consider them as an active part of the antenna system. The simple evaluation methods, such as the one found on the University of Texas Web page (see “The Doctor is IN,” February 2000), works very well for ground-mounted verticals. You can assume about 1 dBi of antenna gain and do use the ground-reflection factor.
Start with your 100 W output and adjust it for the operating mode and typical duty cycles.
100 W CW = 40 W
100 W SSB = 20 to 40 W, depending on speech processing,
use 30 W for average speech processing
100 W FM, RTTY, other digital = 100 W
Then, adjust it by the amount of time you might be transmitting continuously during the averaging time of 6 minutes for controlled exposure or 30 minutes of uncontrolled exposure. For “conversational” operating, you can use 100% for controlled exposure and about 67% for uncontrolled. If you wish, you can also make further adjustments for feed-line loss, but I will refer you to RF Exposure and You for more info on that.
For a 1-dBi-gain antenna on 28 MHz, this typically works out to:
Mode Controlled Distance (feet) Uncontrolled Distance (feet)
This all assumes 100 W, 1 dBi, 28 MHz, 10 minutes on, 10 minutes off, 10 minutes on and moderate speech processing for SSB. If you and your family are greater than 4.9 feet from the antenna and your neighbors are greater than 9 feet from the antenna, you can run 100W continuous duty (carrier) for an indefinite period.
The required distances are from your antenna to any point where people could actually be exposed. Most hams choose to control exposure in their backyard by instructing their families not to linger closer than the controlled distance to their antennas when they are on the air. You should also take some steps to ensure that no one can accidentally contact your antenna. Hams generally use their property line as the criterion for the uncontrolled distance because they have no way of knowing whether their neighbor might be spending time near the property line. With the above assumptions, if you operate SSB on 10 meters with 100 W and your antenna is located 4.9 feet from the property line, you are in compliance.
from QST May 2000
A If I were doing your evaluation, I would consider radials that were within a few inches of the ground to be grounded and would do my calculations from the main antenna itself. If I had a ground-plane antenna with elevated radials, I would, to be conservative, consider them as an active part of the antenna system. The simple evaluation methods, such as the one found on the University of Texas Web page (see “The Doctor is IN,” February 2000), works very well for ground-mounted verticals. You can assume about 1 dBi of antenna gain and do use the ground-reflection factor.
Start with your 100 W output and adjust it for the operating mode and typical duty cycles.
100 W CW = 40 W
100 W SSB = 20 to 40 W, depending on speech processing,
use 30 W for average speech processing
100 W FM, RTTY, other digital = 100 W
Then, adjust it by the amount of time you might be transmitting continuously during the averaging time of 6 minutes for controlled exposure or 30 minutes of uncontrolled exposure. For “conversational” operating, you can use 100% for controlled exposure and about 67% for uncontrolled. If you wish, you can also make further adjustments for feed-line loss, but I will refer you to RF Exposure and You for more info on that.
For a 1-dBi-gain antenna on 28 MHz, this typically works out to:
Mode Controlled Distance (feet) Uncontrolled Distance (feet)
This all assumes 100 W, 1 dBi, 28 MHz, 10 minutes on, 10 minutes off, 10 minutes on and moderate speech processing for SSB. If you and your family are greater than 4.9 feet from the antenna and your neighbors are greater than 9 feet from the antenna, you can run 100W continuous duty (carrier) for an indefinite period.
The required distances are from your antenna to any point where people could actually be exposed. Most hams choose to control exposure in their backyard by instructing their families not to linger closer than the controlled distance to their antennas when they are on the air. You should also take some steps to ensure that no one can accidentally contact your antenna. Hams generally use their property line as the criterion for the uncontrolled distance because they have no way of knowing whether their neighbor might be spending time near the property line. With the above assumptions, if you operate SSB on 10 meters with 100 W and your antenna is located 4.9 feet from the property line, you are in compliance.
from QST May 2000
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