By: Tim Mulverhill
We've all been on the trail when someone has had a problem with their CB - either they weren't hearing a reply, weren't getting out with their message, or were muffled, garbled, or swamped with static. I know I've played `relay the message' on a number of runs. As a professional in the wireless communications field and someone who recently decided to replace my cheapo communications gear with a quality setup, I thought my experience might help some of the others looking to be heard.Our club relies on CB communications equipment (Commo gear to you veterans). This equipment is limited in power output and frequency by the FCC. These factors combine to limit the effective range of these units, so to squeeze the most performance out of a CB we need to make sure all of the parts of the system are optimized and installed correctly.
For background, CB radios are limited to 4.0 watts of power output by the FCC. Yes, there are illegal ways to increase power output. The problem is that while people may be able to hear you farther away, they won't be able to talk back to you. A setup like this is called an alligator - all mouth and no ears. I won't be discussing linear amplifiers or other methods of increasing power output.
The CB frequency range runs from 26.965 MHz to 27.405 MHz. This is a low frequency range that allows for decent penetration of objects like cars and buildings. Cell phones operate in the 750 - 850 MHz range and PCS type phones in the 1900 - 2100 MHz range, normally operating at 0.6 watts of power. The higher the frequency, the harder it is for the signal to penetrate obstructions at the same power level.
The ideal antenna length would be equal to one full wavelength, which would be 432'' or 36'. As this is impractical on a vehicle, wavelength 108'/9' whips became common. Steel whip antennas are available in this length but are prohibited by NE4Wi club rules. These antennas can be a safety hazard to bystanders as they tend to `whip' around and cause injuries. They are also subject to `blowing over' in a vehicle's slipstream from a vertical position that also affects antenna performance.
Outside of a full wavelength antenna, the 5/8 wave, or 5' wound antenna becomes the next best option. These are available with a fiberglass mast, which eliminates the hazards and drawbacks of the steel whip. Antennas with a wound wire covered in a plastic sheathing greatly reduce audible RF static over metal whips. A longer antenna = better performance. I have settled on the 5' length for my own installation.
*Wiping the outside of the antenna down with WD-40 in the winter months will keep ice and snow from accumulating on the mast and reducing it's RF performance and wind resistance.
Quality coaxial cable should be used for the installation. The coax becomes an extension of the antenna and needs to be in tune with the frequency range used. The ideal coax length will be a multiple of a wavelength, or 9'. If you can use a 9' cable, you're in luck. If you need longer, use an 18' cable and deal with the extra cable. Extra cable should not be tightly coiled - this can act as a `choke'. Serpentine extra cable like a skein of yarn 10-14'' long and tie in the center with a wire tie, or simply stuff it out of the way if you have carpet or moldings. Sharp bends are to be avoided. RF energy is different than electricity - think of a coax line as a garden hose, kinks that would slow the flow of water will have a similar effect on your radio signal.
CB Radios follow the same general rule as other products - you get what you pay for. The radios in our rigs have a harder life than one mounted in an 18-wheeler or the family car. They are bounced around, hit, exposed to water and dust. I've managed to kill two cheapie Radio Shack units in the last 4 years. When I bought them I was primarily interested in their low price and small size. My new setup includes a larger, more expensive Cobra unit that is more robust. The delicate plug-in type microphone, which is prone to damage on my earlier radios, has now been replaced by a screw-in connection, which is far sturdier and resistant to the elements. Outside of durability and other features, all radios are the same - limited by the 4 watt power restriction set by the FCC. One brand will not be more powerful than another. Keep in mind that a cheap radio with a good antenna system will always outperform an expensive radio with a poor antenna system.
Handheld Radios - Are good for spectators/spotters on the trail, but come up short as a primary vehicle radio. All of the signal blocking materials that make an external antenna necessary will work to defeat a handheld radio. The short antenna works against optimal communications and must be held as near vertical as possible (that goes for cell phones, too). If you are planning to use a handheld, there are adapters that will allow you to connect the antenna mount to a regular RG-58 coax for an external antenna installation. I have seen situations where a handheld can't reach farther than two car lengths from a sealed vehicle or can only listen to a conversation and not reply.
Antenna mounts are another critical area when installing a CB. A quality mount will be sturdy enough to hold the antenna in place (especially when tree branches are hitting it). The mount acts as a bridge between the antenna and the coaxial cable and should have quality hardware - stainless steel washers & studs, nylon insulators instead of plastic. Rusted components will cause problems with the signal. Mounts should use a split lock washer instead of a star type.
There are a number of ways to mount an antenna to a trail rig: TJ's can mount to the stock spare tire carrier behind the spare, and a number of aftermarket products put the mounts behind the taillights (Turbo City), on the windshield brackets (Sun), on the bumper, or under the hood (Firestik). YJ's frequently mount to the spare tire stop. Cherokees use bumper mounts, roof mounts, or magnetic antenna mounts.
When choosing a mounting location keep a few basics in mind:
Magnetic Mounts do not offer the same performance as a standard mount but are often used for temporary installations. These should be located in the center of a roof or hood.
Connections are a critical area - any corrosion or moisture in your connections can cause problems. Fill all coax connections with dielectric grease (the same stuff used on spark plug boots). This will help seal out contaminants and maintain a healthy connection. Also, wrap the coax connection with self-vulcanizing tape or seal with liquid electrical tape. These connections are at the antenna to antenna mount, antenna mount to coax, any coax to coax connections, and coax to radio. One corroded connection can compromise the entire installation.
Dual antenna installations - using two antennas can increase radio performance. Having an antenna on either side of a vehicle will keep the vehicle from obstructing any of the signal. Dual antenna setups can also act as an artificial ground plane when properly installed. If you've ever been at a traffic light and had the radio station fade out, but come back in as you pulled up a few feet, the two antenna system allows you to be in two places at once. This is one of the reasons cell phone facilities have 3 or 4 antennas facing a given direction. When installing a dual antenna system, RG-59 cable is used instead of the RG-58 for a single antenna.
SWR (Standing Wave Ratio) - When all of the equipment is installed it is time to tune the system. An SWR meter is used to do this and is vital to optimizing the components you've worked hard to assemble and properly install. SWR measures the power coming out of the radio compared to the power leaving the antenna. A high SWR reading will expose a bad connection, coax line, antenna mount or antenna. Operating a radio with an SWR reading over 3:1 can damage the radio. Also, a CB should never be operated without an antenna hooked up as damage can result.
In testing, the SWR meter is placed in the RF circuit at the radio so the entire coax and antenna can be tested together. The specifics on testing and adjusting can be found at the website listed at the end of this article.
RF Signals are blocked by a number of materials - Steel vehicle bodies and auto glass reduce signal strength significantly. This is why CB's require an external antenna to pipe the signal into the vehicle. Mounting an antenna where it will be blocked by these materials will defeat the antenna's performance. Fiberglass and canvas tops offer less resistance to RF energy than steel and safety glass. Some tinted glass is especially resistant to RF penetration and will simply reflect a signal.
My install includes the previously mentioned Cobra CB, connected to a heavy-duty 18' coax, which is split to two antennas mounted on my spare tire carrier. The antenna mounts are 2''x 2'' box tube cut diagonally, and mounted with the flat surface up. These are welded to opposite ends of the tire carrier for maximum separation, about 3.5'. The antennas are both 5/8-wave fiberglass whips and join the coax through heavy-duty mounts using stainless hardware. All connections are sealed and taped. To prevent a sharp bend when attaching to the radio, a 90-degree fitting was used to keep the line straight. The improvement over the old setup has been huge.
A note on components - use quality parts when possible. Radio Shack is convenient and inexpensive, but some of the components are lacking. Their coax has less insulation (and damage resistance) than other manufacturers, their mounts are light duty. I've snapped a number of their antennas and destroyed two of their CB's.
I have used their 90 degree fitting, self vulcanizing tape, and other cable routing accessories in my install, but that is it. K40 and Firestik warranty their antennas against breakage and use stainless steel components in their mounts. which was used as a reference for this article.
Other Options - Aside from CB's there are licensed channels (Ham/Shortwave) that can reach around the world. This equipment requires passing FCC tests and posessing a current license. This is a better option for emergency purposes as the range is greater and emergency services monitor certain channels. The cost is greater, strict radio procedure must be adhered to, and there are few others in our group that you would be able to communicate with.
FRS Radio - Family Radio Service Radios, like the Motorola Talkabout, have become popular in recent years. These channels are similar to the Citizens Band and are used in convenient, hand-sized radios. Better FRS radios have a number of channels to choose from, which is important if other FRS users are in the area. I had a set of the Radio Shack FRS radios that had only one pre-set channel. Anytime I attempted to use it there were other FRS users with the same radio or channel cluttering the airwaves. Again, if using FRS, everyone else you want to reach must have FRS also.
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