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].