Radio Antennas Primer
Peanut Butter
Full Time Jeeper
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- 1979 Jeep CJ7 TH400 Automatic 258 I6 Quadratrac Amc 20 rear & Dana 30 front, 32 x 11.5 x 15 tires. Currently a Complete Custom Rebuild in progress.
Also I own a 2001 Jeep Cherokee, White, all stock with 4.0L. automatic, and police package. Best part of that is it came with leather seats! This package also has the NP242 Transfer Case, 8.25 rear end, and trailer towing package.
Awhile back I did a radio primer: http://www.jeep-cj.com/forums/f49/two-way-radio-basics-21511/
This time I'll cover antennas as this comes up a lot.
Any radio emits RF energy from the rear antenna connection. This is basically a form of electricity. The RF travels through the center section of the coax cable to the antenna. From the antenna the RF energy radiates away from the antenna. This energy is then received by another radio or just dissipates into thin air (actually it is absorbed by other objects).
So let's start with the coax. For mobile use the coax cable is usually RG-58 or something similar. This coax cable has a stranded wire center instead of a solid copper wire. This allows the coax to bend easily around corners and can be hidden behind plastic covers. A solid center coax will allow the RF signal to travel better from end to end, however in a vehicle this solid center can break in two very easily. Coax also has a wire shield wrapped around it to prevent the RF energy from escaping. The better the shield the less energy escapes. So the best coax used is called hardline. It has a solid copper center and copper tubing as the shield. The ends of the coax have a connector on them that screws into the radio and attaches to the antenna. Not all connectors are created equal. Just like the coax some keep the RF energy from escaping better than others. You'll usually find the better connectors as you go up in frequency.
As for antennas, there are volumes and volumes of books written on the design of the best antenna. Almost all antennas compromise in some way. Especially with a mobile antenna. The best antenna is exactly one wavelength long for the frequency being used. This is fine with most VHF radios as that length ranges from 18 to 25 inches, UHF from 3 to 9 inches. For a CB it is 102 inches. Everything else is a multiple of the wavelength. So for a fiberglass CB antenna that is about 4 feet in length, there is a wire wrapped around the inside of the antenna that is around 102 inches long. Just keep in mind that the higher in frequency you go the shorter the antenna needed. So the lower in frequency you go the longer the antenna that is needed. This is also true of the ground that is needed. For a VHF antenna that would be about an 18 inch square piece of metal. Kind of like the length of the wire needed to make the antenna.
Placement of the antenna. This is important because of the ground it needs as already mentioned. A full wavelength VHF antenna (about 18 inches) mounted in the center of a vehicle (usually the top of the roof) provides the best all around radiation of the RF energy. It will radiate out in a circle around the vehicle. Now let's move that antenna to the rear fender of the vehicle. The RF energy now radiates in an oval from the side of the vehicle the antenna is on towards the opposite side. When trying to communicate over long distances this can make a big difference. So if you are only interested in short range communication this is not a factor. If your trying to talk a very long distance you may need to point your vehicle in a different direction based on where your antenna is.
No matter where you decide to put your antenna, it must be grounded to a large piece of metal, unless it is a marine antenna designed for a fiberglass boat.
Generally speaking the bigger the antenna, the higher it is mounted, and the better it is grounded the better it will communicate with other radios.
Google is a really good resource for information on different type of antennas, different types of coax, and different types of connectors.
One last thing about power. More power - More Better. But a wise man once told me that you can have the best, highest priced radio in the world, but if you don't have a good antenna, you're not going to talk to anybody. It's always best to know the limits of your radio, and get the type of radio that you need for the communication you require.
Sorry one other thing. FRS, MURS, and CB radios do not require a license to use. ALL OTHER RADIOS REQUIRE A LICENSE TO OPERATE! Violating this law can result in fines in the $10,000+ range and jail time. Don't think being out in the middle of nowhere will protect you. It's just not worth it. Rugged Radios is one of the biggest violator of this policy. Just because they sell you a radio doesn't mean you have the privilege of using it without a license. The opposite is actually true, most all of their radios require you get a license.
Please feel free to ask questions, if not myself there are others on this forum with quite a bit of radio experience and knowledge.
This time I'll cover antennas as this comes up a lot.
Any radio emits RF energy from the rear antenna connection. This is basically a form of electricity. The RF travels through the center section of the coax cable to the antenna. From the antenna the RF energy radiates away from the antenna. This energy is then received by another radio or just dissipates into thin air (actually it is absorbed by other objects).
So let's start with the coax. For mobile use the coax cable is usually RG-58 or something similar. This coax cable has a stranded wire center instead of a solid copper wire. This allows the coax to bend easily around corners and can be hidden behind plastic covers. A solid center coax will allow the RF signal to travel better from end to end, however in a vehicle this solid center can break in two very easily. Coax also has a wire shield wrapped around it to prevent the RF energy from escaping. The better the shield the less energy escapes. So the best coax used is called hardline. It has a solid copper center and copper tubing as the shield. The ends of the coax have a connector on them that screws into the radio and attaches to the antenna. Not all connectors are created equal. Just like the coax some keep the RF energy from escaping better than others. You'll usually find the better connectors as you go up in frequency.
As for antennas, there are volumes and volumes of books written on the design of the best antenna. Almost all antennas compromise in some way. Especially with a mobile antenna. The best antenna is exactly one wavelength long for the frequency being used. This is fine with most VHF radios as that length ranges from 18 to 25 inches, UHF from 3 to 9 inches. For a CB it is 102 inches. Everything else is a multiple of the wavelength. So for a fiberglass CB antenna that is about 4 feet in length, there is a wire wrapped around the inside of the antenna that is around 102 inches long. Just keep in mind that the higher in frequency you go the shorter the antenna needed. So the lower in frequency you go the longer the antenna that is needed. This is also true of the ground that is needed. For a VHF antenna that would be about an 18 inch square piece of metal. Kind of like the length of the wire needed to make the antenna.
Placement of the antenna. This is important because of the ground it needs as already mentioned. A full wavelength VHF antenna (about 18 inches) mounted in the center of a vehicle (usually the top of the roof) provides the best all around radiation of the RF energy. It will radiate out in a circle around the vehicle. Now let's move that antenna to the rear fender of the vehicle. The RF energy now radiates in an oval from the side of the vehicle the antenna is on towards the opposite side. When trying to communicate over long distances this can make a big difference. So if you are only interested in short range communication this is not a factor. If your trying to talk a very long distance you may need to point your vehicle in a different direction based on where your antenna is.
No matter where you decide to put your antenna, it must be grounded to a large piece of metal, unless it is a marine antenna designed for a fiberglass boat.
Generally speaking the bigger the antenna, the higher it is mounted, and the better it is grounded the better it will communicate with other radios.
Google is a really good resource for information on different type of antennas, different types of coax, and different types of connectors.
One last thing about power. More power - More Better. But a wise man once told me that you can have the best, highest priced radio in the world, but if you don't have a good antenna, you're not going to talk to anybody. It's always best to know the limits of your radio, and get the type of radio that you need for the communication you require.
Sorry one other thing. FRS, MURS, and CB radios do not require a license to use. ALL OTHER RADIOS REQUIRE A LICENSE TO OPERATE! Violating this law can result in fines in the $10,000+ range and jail time. Don't think being out in the middle of nowhere will protect you. It's just not worth it. Rugged Radios is one of the biggest violator of this policy. Just because they sell you a radio doesn't mean you have the privilege of using it without a license. The opposite is actually true, most all of their radios require you get a license.
Please feel free to ask questions, if not myself there are others on this forum with quite a bit of radio experience and knowledge.