CB Antennas for RV's
Compliments of Firestik® Antenna Company Technical Support Team
Copyright © 1996 Firestik® Antenna Company
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Unlike receive only antennas (AM/FM, Scanner, or TV), CB antennas require some type of ground plane to operate properly. What is ground plane? Ground plane, often times referred to as counterpoise, is the means by which the ground wave of your transmission moves outward from your antenna. Without ground wave, the performance of your CB will be, at best, disappointing. Copper and steel are excellent materials for ground plane. Fiberglass and thin aluminum sheets are not. Without getting too deeply into the boring technical aspects of antennas, there are a handful of basic concepts that will help the RV'er sort through the sometimes confusing problems encountered with CB. The scope of this article is to help you get the most from your CB set-up. One of the biggest mistakes that an RV'er can make is to fall into the "pick out the radio and stick on an antenna" frame of mind. With the exception of the "bells and whistles" (weather channels, PA capability, one button emergency channel, etc.), all CB radios are pretty much the same insofar as performance is concerned. The FCC limits the output transmitter power to a maximum of 4 watts. Aside from some low powered handhelds, every manufacture designs their radios to put out the maximum power. If you set aside the extras, your biggest concern will be where to mount the radio. Beyond that, you need only think about where to tap into the vehicles 12 volt system. If you find that you are getting unwanted noise (buzzing, popping, whining), run your radio power leads straight to one of the vehicles batteries. This will by-pass all of the other circuits that could cause unwanted interference. Enough said on radios. Fiberglass and aluminum RV's are communication nightmares for most CB users, especially those who think that any antenna will do the trick. With the most common antennas on the market, the best you can hope for is to have a grounded metal mirror arm or luggage rack to mount your antenna bracket to. If you don't have that, you had better run a chassis ground wire to the antenna mounting bracket. Even that may not help. The fact is, the antenna and its feedline are the most critical parts of the CB system. They can be down right nasty if not handled properly. So, what should you do when you own one of those problem vehicles? Your choices are few. If you feel adventuresome, you could remove the entire headliner, cover the inside of the roof with copper or steel screening (artificial ground plane) and ground it to your vehicle chassis and antenna mount. Or, you could install co-phased (dual) antennas, if you can do so in a manner that allows at least two-thirds of both antennas to be within clear, unobstructed view of one another. The co-phase options works very well because the transmission pattern is strongest towards the front and rear of the vehicle. This is usually advantageous to travelers as most of their communications will take place along their direction of travel. Finally, if you want to be a one antenna operation, your only intelligent choice is a "no ground plane" antenna. The "no ground plane" term is actually misleading. As stated before, you need a ground plane if you want your antenna to work as intended. The term "no ground plane" refers to the fact that your vehicle doesn't need to supply the ground plane. It is built into the coaxial cable. The idea isn't new. Anyone who has ever owned a boat and used a CB or marine band radio has undoubtedly used a "no ground plane" antenna. The design works great on boats and RV's alike. There are, however, a few rules that need to be followed with "no ground plane" antennas. They are:
On the subject of SWR. SWR stands for "standing wave ratio". This measurement relates to the efficiency, or inefficiency, of the signal delivery system (the antenna, coaxial cable, connectors and ground plane). The easiest way to explain SWR might be to have you visualize 100 people running for the exit after somebody shouted "fire"! If the hall way is cluttered and/or the doorway too small, some of them are not going to get out in time. In transmitters, if the SWR is too high, those who can't make it down the hall and out the door quick enough head back to the transmitter. The more that arrive back, the hotter it gets in the transmitters final output circuit. If too many come back, the "finals" will burn out and your radio will need repaired. Setting SWR is important. That includes antennas that are pre-tuned at the factory. Why? Because they are pre-tuned on a test bench ... not on your vehicle. If you drive a test bench, you might be okay. Otherwise, understand that antennas are sensitive to their surroundings. If you tune your antenna on the left mirror then move it to the right mirror, chances are you will need to re-tune the antenna at the new location. If you want the best performance from your CB, get a good antenna and adjust the SWR after the antenna has been mounted on the vehicle in its final location. Firestik Antenna Company manufactures a line of "no ground plane" antennas that were specifically designed for boats, RV's, or any other installation where ground plane deficiency is a problem (bikes, back packs, golf carts, whatever). |
Updated: 2023.12.05