A Citizen's Band (CB) Radio Installation Primer, by C.G.

Monday, Jun 2, 2008

Citizen Band (CB) radio requires no FCC license to operate so it is a good choice for local communication. If cell phones fail to work for whatever reason, it may be the best method for remote communication since its range is better than FRS and GMRS. When I installed my first CB in a vehicle, I was happy just to get it in and be able to transmit to my buddy who lived the next block over. I’ve matured since then and my tolerance for white noise is less than what it used to be. I’ve learned over the years how to properly set up a radio system and I’m normally left with a CB that has few problems. So, I’m writing this to help those of you that use Citizen's Band radio in your vehicles, but may be plagued with noise, weak signals, or are just generally unhappy with your radios performance. At worst, this article should give you a jumpstart in your quest for a 1:1 standing wave ratio.

The basic components of a radio system are simple: power, radio, antenna feed line, and antenna. If all function properly, the radio shouldn’t give you any problems. But for vehicle use, with all those wires and working parts, problems do arise. I’ll talk about each of the above mentioned components and other aspects of radio communication you may need to know for a proper set up. Please keep in mind, these pages are not entirely comprehensive about CB installation or uses and may not answer all your questions… it’s written based upon my experiences in radio communication and quite frankly, I haven’t experienced it all, yet. But with that said, here goes:

Antenna
The two most important things to consider when mounting an antenna are grounding and positioning; when both of these things are considered and handled properly, you should receive a decent Standing Wave Ratio (SWR) reading (more about that, later). The best way to ground an antenna is to drill holes for the mounting bracket into a metal portion of your vehicle. If you’re concerned about resale value and don’t want to drill, look into mobile mounting units that require no drilling from a supplier like HRO (Ham Radio Outlet); they sell units for doors, trunks, rain channels, etc.
An antenna mounted in the middle of a metal roof will get the best signal because it is surrounded by a reflective surface. However, you may have a problem grounding the antenna without causing a leaking problem in your roof (but that would of course mean you won’t be asked to drive that often so it has its upside). You should mount the antenna where you will get the best SWR without sacrificing clearance or risking damage to the antenna or mount… or getting while driving in a rainstorm. I recommend a pickup bed immediately behind the cab, a lower quarter panel, or the lid of a trunk. If you mount your antenna in any of these locations, you should get be able to clear the roof line of your vehicle by about 6” to 1’ with a 36” antenna and transmit decently.

Two other things to consider are antenna quality and length. First, quality. Simply put, the two best brands of antenna on the market are Firestick and K40; I would recommend both of these two brands for a mobile unit. Second, the length of your antenna is a matter of preference quite honestly, although I will admit that longer antennas generally transmit and receive better. The reason it is more a matter of preference than performance is clearance. A 6-foot antenna mounted on a roof is going to have some clearance issues with your garage, trees, etc.; but if you choose to mount your antenna on a bumper, then a 6-foot model would probably be fine. I use a three foot antenna on my pickup and can transmit about five miles on the regular 40 CB channels. Just another issue to keep in mind when you purchase your setup.

Feed line
The Feed line is the length of coaxial ("coax") cable from the radio to the antenna. There are subtle differences in coax Feed line based upon insulation, grade of cable, etc. Generally speaking, the better the Feed line, the better it will transmit your signal, so buy quality coaxial cable. When buying the necessary mounting supplies, you need to make sure it is all matched for impedance. Almost all CB radios will have a 50 ohm impedance jack for the antenna input and most coax sold for CB radios is as well--but it doesn’t hurt to ask before you buy.

Much has been said about the length of the Feed line for a CB radio. Some people say that 18’ is the proper length, some people say 17’ is the proper length. To be honest, impedance match is the most important thing. But I cut my coax to 17’4” staying in practice with radio theory that the Feed line should be a factor of the wavelength that you will transmit on (I won’t bore you with the calculation with MHz and inches). 17’4” is probably much more than you will need, but will allow for an antenna choke if you need it. Be sure to buy Feed line that already has PL259 connectors already installed if you’re not familiar with the installation process. But FYI, it’s not difficult to learn if you’re familiar with soldering; any radio technician at Ham radio Outlet (HRO) can explain the process.

Radio and Installation
First, let me bash on the handheld units a bit. CB transmission is essentially line of sight transmission and anything that blocks the line of sight is going to weaken the signal. A handheld CB is for use outside of a vehicle… using it inside a vehicle you get minimal transmission distance because the signal bounces off the metal components of the vehicle, and even with a soft top jeep, the signal still needs to pass through a barrier and as a result it’s weakened. So if you’re using a handheld and wonder why you can’t hear much, there’s the reason. I will admit that I have a portable unit, a Midland 75-820, that is a handheld unit with a separate magnetic base antenna for use while in a vehicle. It’s performance is adequate but not optimal. Frankly, the Midland setup has two major problems, 1) engine noise which can be caused by the rotation of the alternator feeding back through the electrical system (a problem more prevalent on older vehicles but still present on many today) because the ground for everything is through the cigarette lighter… and 2) the limited volume the unit puts out with such a small speaker (an operator in a loud truck or topless jeep may have problems using this CB when driving on the highway). I use this unit only as a backup unit or in a second vehicle that doesn’t have a hard wired setup.

I currently use a Cobra 18WXST II. It is a reasonably priced unit from a quality manufacturer. Regardless of what you buy, most quality units will have an internal noise filter, scanning feature, and NOAA weather bands, but be sure to buy the unit best suited for your needs. If you’re interested in SSB transmitting or extended range, you may want to get a better unit; I recommend the Cobra 148GTL. [JWR Adds: That is also one of my favorite models. Its proven design remained essentially unchanged for many years, making it readily adaptable for out-of-band transmission by licensed ham radio operators that can transmit in the 10 Meter band (which is adjacent to Citizens Band.)]

Now, it sounds as though it should be common sense but be sure to mount the unit where it will be easy to use and not an obstruction while using the vehicle (the dash board is probably a bad choice as is the foot well near the pedals). I recommend bolting the unit to the center console or using a RAM mount somewhere on the transmission hump.

Cleanliness of installation should be considered too. Do you want coax cable on the floor of your back seat or run under the carpet? Do you want to run the wires out an existing hole in the chassis or drill a new one? I normally run the power line through the dash and directly to the battery; this eliminates some noise you can receive when tapping into an existing hot [12 VDC energized] line or fuse (more on that later). Be sure to use a fuse for your radio before hooking it up or you may soon be buying a new radio. The coaxial cable I normally run under the carpet or floor mats to the rear of the cabin and drill a small hole (if necessary) near the mount.

SWR
Now that the system is set up, lets learn how to optimize its transmission capability. The first thing we need to address is SWR. Essentially, a SWR meter measures how well your equipment will transmit and receive on the specific frequency you intend to use. If you have everything grounded properly, your equipment is impedance matched, and you have a decent antenna mounted in the correct location, the SWR should be ok. An SWR reading of 1:1 is optimal but a reading of 1.5:1 is excellent, a reading of 2:1 is considered good (actually great for most applications), but anything higher than 3:1, well, you pretty much wasted your time with the installation. Getting the best SWR on your specific rig is a matter of trial and error… in my experience, you can’t go wrong if you ground everything well and place the antenna on top of a metal roof or mount it where at least a portion of the antenna clears the roof line.

An SWR meter can be purchased at any Radio Shack or electronic supply house. Most come complete with directions and are pretty easy to use, even for a novice. If you’re unhappy with the SWR you get from your setup initially, don’t worry, you can improve it by tuning your antenna. All antennas are tunable, but some are tuned easier than others. Some need to be cut and some need to be bent to retard the oscillation on the part past the bend. The K40, for example, is one of the easier ones; it has a small whip that sticks out the top on the antenna and is moved up and down using a supplied Allen key; by adjusting the length of the whip, you can receive a better SWR reading.

Noise Elimination
Even if you are happy with the SWR you get on your system, you may still have problems with noise (one doesn’t necessarily effect the other) so lets learn how to eliminate that noise.
Most radios come with an internal noise filter… a button or toggle switch on the face of the radio that eliminates much of the squelch noise from the radio output. The problem with this feature is that it also makes distant transmissions difficult to hear. If you want to (or need to) address the problem further, know that noise on a CB unit (while the engine is running) is normally caused by two things… 1) noise coming through the hotline of the radio or 2) noise being picked up by the antenna.
(Note: You need to remember, a CB picks up 27 MHz radio waves and an engine or other vibrations can cause interference and distortion of those radio waves. Power windows or seats can cause feedback… that’s normally caused by the electrical motor. An older engine can create oscillation heard on a CB… chances are it’s the points spinning in the distributor. So noise isn’t necessarily just an electrical hotline problem… you need to eliminate both possibilities mentioned above.)

A few simple tests can isolate the source of the noise.
1. Hook the radio up to the battery directly or better yet, a separate battery not hooked into the truck’s electrical system. This will bypass and eliminate any noise caused by the alternator or firing of the cylinders. If you still get noise, it’s coming in through the antenna.
2. Disconnect the Feed line from the antenna or the Feed line from the radio. This will eliminate any noise being received on the antenna. If you still get the noise, it’s coming from the power/ground lines.
I’ve had both types of problems (both on the same rig once)… so here are the fixes I used to eliminate most (not all) of the noise.

Antenna Noise
To eliminate noise caused by the antenna receiving unwanted signals, put in an “antenna choke.” Disclaimer time: I have an idea why this fix works but I’m not sure and I haven’t gotten a straight answer from anyone on the matter… so do me a favor and don’t ask because all I can tell you is that it does work to eliminate noise coming in through the antenna. Take about 6 feet of the Feed line and wrap it into 6 or 8 loops (kind of like wrapping up an electrical cord or piece of rope but about the diameter of a coffee can) then tape the loops together.
If an antenna choke doesn’t successfully eliminate all noise, there are other methods to try. Try changing the location of your antenna to a spot on the vehicle where it is shielded from the engine. Radio waves are line of sight reception and sometimes simply hiding the antenna from the constant oscillation of the engine can do the trick. Another method is to try using shorter or longer lengths of coax… but that is an expensive exercise in trial and error… try the other methods first.

Hot Wire Noise
First off, try attaching the hot wire(s) for the radio directly to the battery of the vehicle. Much of the noise picked up through the hot wire comes from the alternator feeding current into the system.
This method should work, but if not, try installing an external noise filter onto the hot wire and ground wire of your CB. They are small cylinders (about the size of a bicycle handle) and can be picked up at Radio Shack or other electronics stores. Simply attach the hot wire(s) from the radio to the red wire of the filter, then the red wire on the other side of the filter to a power source. Attach the ground wire from the radio to the black wire on the filter, then the black wire on the other side of the filter to a chassis ground.

These techniques should help you set up a radio properly, even if you run into difficulties. It may take some time and trouble shooting on your part but you’ll be left with minimal noise and decent reception/transmission capabilities. The cost shouldn’t be too bad either. It all can be done for under $150 with new equipment. But if your budget allows, spend more [for the best equipment available].


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