WF7A
09-07-2008, 06:07 AM
Howdy, all:
I've been asked to submit a three-part article for an ultralight pilot magazine about radios and thought I'd best get your opinions to see if it's near the mark or not. I've included the rough draft below so I'd really appreciate your input. Remember, these guys aren't radio savvy so I have to keep things simple.
Thanks!
Rich
pee ess: Some of the formatting was lost when I dumped the text in here from MS-Word. Sorry!
----------------------------------
While taking some PPG flight training recently, I had the opportunity to use what many PPC and PPG pilots use for communication between other pilots in the air and on the ground, FRS radio transceivers. I quickly came to the conclusion after a few radio exchanges with my instructor that although FRS radios are inexpensive and easy to use, they…well…suck: They have very limited range and are prone to interference from other FRS radio users and PPG electrical systems. With radios being such a critical link to flight safety and for flying with our buddies, it’s amazing how little pilots know about them. What this series of articles will do is not only educate you with a little radio theory, radio choices and usage, but also how to build simple yet very effective antennas for both air and ground use to extend your radio’s range well beyond what you’re used to…which can save your skin some day when the chips—and you—are down!
Radios 101
“I tell ya, I get no respect, not even from my parents. When I was a child they gave me one walkie-talkie as a birthday present.” —Rodney Dangerfield
Simply put, a radio transceiver’s job is two-fold: to convert sound waves (or digital data) into radio waves and back again. But when you think about it, your radio is really two systems: the radio transceiver itself and its antenna. Let’s talk about the radio, first.
The radios we typically use are either channel-specific or operate over a range—or band—of frequencies…but which channel or band should we use? The easy answer is “That depends.” If you want to communicate with other general aviation pilots then an aviation band (“avband”) radio is the best choice; CB users, a CB transceiver; amateur radio (“ham”) operators, HF, VHF, and/or UHF radios, and of course the ubiquitous FRS radios. The real question is, “Which one would be best?”
Again, that depends.
If you never plan to chat with general aviation aircraft or controls towers then you obviously don’t need an avband radio; CB radios are notoriously subject to interference, both natural and man-made, and require long antennas to get any distance with them. That leaves ham radio transceivers, with a 2-meter VHF model your best bet. Here’s why:
·affordability: a basic 2-meter radio, sans unnecessary bells and whistles, costs around $150 for either a handheld one or a mobile one for a vehicle or base station use;
·access to repeaters: Repeaters dramatically extend the range of a radio, especially from the ground, by rebroadcasting your signals over a great distance—a BIG plus if you’re down somewhere that’s ringed by mountains or hills that block radio waves;
·ease of use: You’ll need to obtain an amateur radio license to use the radios but it’s easy to get one: no Morse code knowledge is required and the Theory test is a simple multiple-choice exam. You’ll need to learn a little elementary radio theory and good operating practices, but it’s relatively easy stuff;
·lots of accessories are available, and
·a support network: Hams are dedicated to public service so if you need help because you’re hurt or stranded somewhere, a fellow ham will be happy to help you out.
If there’s any “con” to using a ham radio it’s that you have to ID with your callsign every ten minutes while engaged in a conversation, and when you initiate and end a conversation—a minor inconvenience at most. To learn more about obtaining a ham radio license, go to www.arrl.org (http://www.arrl.org/) or www.fcc.gov (http://www.fcc.gov/). For which model radios are winners or losers, check out the radio review sections submitted by ham radio operators at www.eham.com (http://www.eham.com/) and www.qrz.com (http://www.qrz.com/).
Antennas 101
Antennas are probably the least understood component of a radio system—you just take it for granted it does its thing by collecting or broadcasting radio waves, which it does, but depending on its construction it can either be very efficient or just a shade above useless. Assuming a good conductor is being used—e.g., aluminum, copper, steel, or brass—in its construction, a key factor in determining antenna performance is how long it is so we need to determine that, first; it’s based on a radio frequency’s wavelength.
As an analogy, a radio wave is like an ocean wave in that it has crests (peaks) and troughs and that there’s a distance (wavelength) between one crest of one wave and the next. (See Figure 1.) Like the Speed ¸ Time = Distance formula we use for flying, we use the same formula for determining wavelength, or the Distance part of the aforementioned equation, by substituting Time with Frequency.
In free space, radio waves travel at the speed of light (approximately 300 million meters per second). So, there’s our speed. Next, we need the waves’ frequency, or how many times (cycles) it repeats itself in one second, by convention called Hertz (Hz). For example, the FRS radio frequency range is from 462.5625 MHz (Channel 1) to 467.7125 MHz (Channel 14); that means for Channel 1 there are 462,562,500 cycles per second and Channel 14, 467,712,500. (The “M” in MHz means “multiply by 1 million.”)
Let’s take the middle of the frequency road[1] (http://forums.qrz.com/#_ftn1), FRS Channel 7 (462.7125 MHz), and find its wavelength. After canceling like values in the fractions (millions), the calculation can be reduced to 300 ¸ 462.7125 = 0.648 m (25.5 in.); if you were to cut a piece of wire that long it would represent its physical and electrical wavelength.[2] (http://forums.qrz.com/#_ftn2) In real world antenna design, the wire, or conductor, can be longer or shorter than its electrical wavelength; generally, an antenna physically longer than its electrical wavelength is more effective a radio wave radiator/collector; shorter is less effective.
Without getting technical here, you can discard half of a full wavelength antenna yet still have an efficient radiator half a wavelength long, so let’s cut our full-wavelength antenna in half from the previous example, leaving us with 32.4 cm (12.75 in.) It doesn’t take a genius to see that the antenna on all U.S.A. FRS radios isn’t 12.75 in long. So, what gives? Can’t the manufacturer’s antenna engineers perform simple math? Are the manufacturers so cheap that they’re short-changing us in wire?
There are a couple of reasons why an FRS antenna is so short and fixed in place:
·the FCC (Federal Communications Commission) wanted to limit an FRS radio’s range—that’s why you can’t buy a longer antenna for them. A shorter antenna means reduced range, and
·ergonomics: It would be all too easy to break a longer antenna through carelessness.
However, there’s a not-so-obvious result of an antenna being shortened well below its electrical wavelength: you’re going to take a big hit in antenna efficiency. How much? I’m glad you’re sitting down. The FRS antenna is only about 4 cm (1.5 in.) long. With a paltry maximum 500 mW to begin with (that’s half of one Watt, about 1/8th the power of a common bathroom nightlight), its typical antenna efficiency is about 1%–10%, or 5 mW–50 mW. In practical usage, that means about half a mile range in open land or as little as 100 yards indoors…and that’s if you’re lucky.[3] (http://forums.qrz.com/#_ftn3) FRS radios don’t look so attractive now, do they?
Let’s examine the 2-meter ham radio: it has a frequency range of 144 MHz–148 MHz. Taking the middle-of-the-road 146 MHz, its wavelength is 2.05 meters (hence a “2-meter” radio), or 6.7 feet. (In comparison, an avband radio—which has a usable (voice-only) frequency range of 118 MHz -136 MHz, or a center frequency of 127 MHz, is a little longer: 2.36 meters, or 7.75 feet.) Aside from having an average of 5W[4] (http://forums.qrz.com/#_ftn4) power available, you now have many antenna options available to you that you didn’t have with the FRS radios. To find out what they are, you’ll need to read Part 2 of this article in the next issue. :)
[1] (http://forums.qrz.com/#_ftnref1) It’s standard practice to design an antenna for the middle of the frequency range of its intended use; that’s because as you transmit or receive above or below its designed, or resonant, frequency, its performance begins to suffer.
[2] (http://forums.qrz.com/#_ftnref2) Just for fun: The wavelength of a 60 Hz signal coming out of an electrical outlet in your home is 5,000,000 meters, or 3,109 statute miles between peaks; that’s Seattle to Tampa in one second! In contrast, a GigaHertz—a common unit used in computer microprocessor speed—is one billion cycles per second; if you want to see how long its wavelength is, cut a wire 30 cm (11.8 in.) long.
[3] (http://forums.qrz.com/#_ftnref3) When you see something like “26-mile range!” on an FRS radio’s packaging, that’s the theoretical range based on mathematics, not an empirical measurement.
[4] (http://forums.qrz.com/#_ftnref4) Although 5W is ten times more powerful than the FRS’s 50mW, it doesn’t automatically mean it has a range ten times further; radiated energy is a function of logarithmic power increases, not exponential.
I've been asked to submit a three-part article for an ultralight pilot magazine about radios and thought I'd best get your opinions to see if it's near the mark or not. I've included the rough draft below so I'd really appreciate your input. Remember, these guys aren't radio savvy so I have to keep things simple.
Thanks!
Rich
pee ess: Some of the formatting was lost when I dumped the text in here from MS-Word. Sorry!
----------------------------------
While taking some PPG flight training recently, I had the opportunity to use what many PPC and PPG pilots use for communication between other pilots in the air and on the ground, FRS radio transceivers. I quickly came to the conclusion after a few radio exchanges with my instructor that although FRS radios are inexpensive and easy to use, they…well…suck: They have very limited range and are prone to interference from other FRS radio users and PPG electrical systems. With radios being such a critical link to flight safety and for flying with our buddies, it’s amazing how little pilots know about them. What this series of articles will do is not only educate you with a little radio theory, radio choices and usage, but also how to build simple yet very effective antennas for both air and ground use to extend your radio’s range well beyond what you’re used to…which can save your skin some day when the chips—and you—are down!
Radios 101
“I tell ya, I get no respect, not even from my parents. When I was a child they gave me one walkie-talkie as a birthday present.” —Rodney Dangerfield
Simply put, a radio transceiver’s job is two-fold: to convert sound waves (or digital data) into radio waves and back again. But when you think about it, your radio is really two systems: the radio transceiver itself and its antenna. Let’s talk about the radio, first.
The radios we typically use are either channel-specific or operate over a range—or band—of frequencies…but which channel or band should we use? The easy answer is “That depends.” If you want to communicate with other general aviation pilots then an aviation band (“avband”) radio is the best choice; CB users, a CB transceiver; amateur radio (“ham”) operators, HF, VHF, and/or UHF radios, and of course the ubiquitous FRS radios. The real question is, “Which one would be best?”
Again, that depends.
If you never plan to chat with general aviation aircraft or controls towers then you obviously don’t need an avband radio; CB radios are notoriously subject to interference, both natural and man-made, and require long antennas to get any distance with them. That leaves ham radio transceivers, with a 2-meter VHF model your best bet. Here’s why:
·affordability: a basic 2-meter radio, sans unnecessary bells and whistles, costs around $150 for either a handheld one or a mobile one for a vehicle or base station use;
·access to repeaters: Repeaters dramatically extend the range of a radio, especially from the ground, by rebroadcasting your signals over a great distance—a BIG plus if you’re down somewhere that’s ringed by mountains or hills that block radio waves;
·ease of use: You’ll need to obtain an amateur radio license to use the radios but it’s easy to get one: no Morse code knowledge is required and the Theory test is a simple multiple-choice exam. You’ll need to learn a little elementary radio theory and good operating practices, but it’s relatively easy stuff;
·lots of accessories are available, and
·a support network: Hams are dedicated to public service so if you need help because you’re hurt or stranded somewhere, a fellow ham will be happy to help you out.
If there’s any “con” to using a ham radio it’s that you have to ID with your callsign every ten minutes while engaged in a conversation, and when you initiate and end a conversation—a minor inconvenience at most. To learn more about obtaining a ham radio license, go to www.arrl.org (http://www.arrl.org/) or www.fcc.gov (http://www.fcc.gov/). For which model radios are winners or losers, check out the radio review sections submitted by ham radio operators at www.eham.com (http://www.eham.com/) and www.qrz.com (http://www.qrz.com/).
Antennas 101
Antennas are probably the least understood component of a radio system—you just take it for granted it does its thing by collecting or broadcasting radio waves, which it does, but depending on its construction it can either be very efficient or just a shade above useless. Assuming a good conductor is being used—e.g., aluminum, copper, steel, or brass—in its construction, a key factor in determining antenna performance is how long it is so we need to determine that, first; it’s based on a radio frequency’s wavelength.
As an analogy, a radio wave is like an ocean wave in that it has crests (peaks) and troughs and that there’s a distance (wavelength) between one crest of one wave and the next. (See Figure 1.) Like the Speed ¸ Time = Distance formula we use for flying, we use the same formula for determining wavelength, or the Distance part of the aforementioned equation, by substituting Time with Frequency.
In free space, radio waves travel at the speed of light (approximately 300 million meters per second). So, there’s our speed. Next, we need the waves’ frequency, or how many times (cycles) it repeats itself in one second, by convention called Hertz (Hz). For example, the FRS radio frequency range is from 462.5625 MHz (Channel 1) to 467.7125 MHz (Channel 14); that means for Channel 1 there are 462,562,500 cycles per second and Channel 14, 467,712,500. (The “M” in MHz means “multiply by 1 million.”)
Let’s take the middle of the frequency road[1] (http://forums.qrz.com/#_ftn1), FRS Channel 7 (462.7125 MHz), and find its wavelength. After canceling like values in the fractions (millions), the calculation can be reduced to 300 ¸ 462.7125 = 0.648 m (25.5 in.); if you were to cut a piece of wire that long it would represent its physical and electrical wavelength.[2] (http://forums.qrz.com/#_ftn2) In real world antenna design, the wire, or conductor, can be longer or shorter than its electrical wavelength; generally, an antenna physically longer than its electrical wavelength is more effective a radio wave radiator/collector; shorter is less effective.
Without getting technical here, you can discard half of a full wavelength antenna yet still have an efficient radiator half a wavelength long, so let’s cut our full-wavelength antenna in half from the previous example, leaving us with 32.4 cm (12.75 in.) It doesn’t take a genius to see that the antenna on all U.S.A. FRS radios isn’t 12.75 in long. So, what gives? Can’t the manufacturer’s antenna engineers perform simple math? Are the manufacturers so cheap that they’re short-changing us in wire?
There are a couple of reasons why an FRS antenna is so short and fixed in place:
·the FCC (Federal Communications Commission) wanted to limit an FRS radio’s range—that’s why you can’t buy a longer antenna for them. A shorter antenna means reduced range, and
·ergonomics: It would be all too easy to break a longer antenna through carelessness.
However, there’s a not-so-obvious result of an antenna being shortened well below its electrical wavelength: you’re going to take a big hit in antenna efficiency. How much? I’m glad you’re sitting down. The FRS antenna is only about 4 cm (1.5 in.) long. With a paltry maximum 500 mW to begin with (that’s half of one Watt, about 1/8th the power of a common bathroom nightlight), its typical antenna efficiency is about 1%–10%, or 5 mW–50 mW. In practical usage, that means about half a mile range in open land or as little as 100 yards indoors…and that’s if you’re lucky.[3] (http://forums.qrz.com/#_ftn3) FRS radios don’t look so attractive now, do they?
Let’s examine the 2-meter ham radio: it has a frequency range of 144 MHz–148 MHz. Taking the middle-of-the-road 146 MHz, its wavelength is 2.05 meters (hence a “2-meter” radio), or 6.7 feet. (In comparison, an avband radio—which has a usable (voice-only) frequency range of 118 MHz -136 MHz, or a center frequency of 127 MHz, is a little longer: 2.36 meters, or 7.75 feet.) Aside from having an average of 5W[4] (http://forums.qrz.com/#_ftn4) power available, you now have many antenna options available to you that you didn’t have with the FRS radios. To find out what they are, you’ll need to read Part 2 of this article in the next issue. :)
[1] (http://forums.qrz.com/#_ftnref1) It’s standard practice to design an antenna for the middle of the frequency range of its intended use; that’s because as you transmit or receive above or below its designed, or resonant, frequency, its performance begins to suffer.
[2] (http://forums.qrz.com/#_ftnref2) Just for fun: The wavelength of a 60 Hz signal coming out of an electrical outlet in your home is 5,000,000 meters, or 3,109 statute miles between peaks; that’s Seattle to Tampa in one second! In contrast, a GigaHertz—a common unit used in computer microprocessor speed—is one billion cycles per second; if you want to see how long its wavelength is, cut a wire 30 cm (11.8 in.) long.
[3] (http://forums.qrz.com/#_ftnref3) When you see something like “26-mile range!” on an FRS radio’s packaging, that’s the theoretical range based on mathematics, not an empirical measurement.
[4] (http://forums.qrz.com/#_ftnref4) Although 5W is ten times more powerful than the FRS’s 50mW, it doesn’t automatically mean it has a range ten times further; radiated energy is a function of logarithmic power increases, not exponential.