together a CB
you are putting
together a system for your Jeep, whether on a
budget or not, plan on buying the best antenna system (coax, mount,
antenna stud and antenna) that you can find and then go buy a radio.
All radios are pretty much the same, with the
exception of bells and
whistles that do little to improve the performance of your system. The
manufacturing of CB radios is FCC mandated...so the final output power
is regulated by law to a maximum of 4 watts. Any wattage that is
advertised as higher is audio output, meaning what you hear through the
speaker has more power, not what you send. For basic communications,
anything beyond a volume, squelch, RF gain and maybe a mic gain control
is an extra feature you can do without.
See this article for more information
on choosing a CB radio
There is nothing wrong with having all of the
extra features, but
not at the cost of the antenna system
. It is a bad trade off. The
best radio with a crappy antenna system will NEVER outperform a
cheap radio with a good antenna system. If anyone tries to tell you
otherwise...run away. Now, it isn't always just the antenna that is
bad. Too often you get a piece of junk coax. Think of junk coax as
trying to wash your Jeep with a hose that is full of holes. You can't
see RF energy pouring out, or interference pouring into a piece of bad
coax, but that is what you can often end up with.
Another part to watch for is the stud mount.
The majority of problems
in an electrical or electrical-mechanical device will involve poor
connections that cause opens, shorts or high resistance. The stud mount
is an electrical-mechanical device that must support the antenna and
act as a bridge between the antenna and the coaxial feed to the radio.
There are plenty of cheap ones out there. They are made of aluminum, or
they use non-stainless steel washers (they'll corrode), or they have
cheap plastic insulators (that crack or collapse).
When you shop for the antenna system, shop
smart and you will only need
to do it once. Give the majority of your time and money to the antenna
system and you will be on the right track. Before selecting an antenna,
you should be aware of the different types available...prior to that it
helps to understand what SWR is.
(standing wave ratio)
is a term every Jeeper with a CB should know.
SWR (measured with an SWR meter) shows you how well your coax, antenna
mount, ground plane and antenna match the output of your CB radio. It
is a ratio of maximum voltage or current (the CB radio) to minimum
voltage or current (everything from the coaxial connector at the radios
output to the tip of the antenna). Generally speaking, the lower the
SWR the better. Defective or inferior components, bad installations and
antennas not tuned to the specific location on the Jeep increases the
SWR. You should try to achieve a ratio below 2:1 on all channels. See this article for
additional SWR details
Before setting SWR, it helps to know some of
problems that can be
encountered and why they occur. If you take the time to read the
information compiled here you will go into your install with knowledge
that could save you a lot of time, effort and possibly, money.
Unlike receive-only antennas (AM/FM radio, TV,
scanner), antennas that
transmit require tuning. While antenna manufacturers can supply you
with an antenna that is pre-tuned to the general frequency of the
intended equipment, they cannot promise you perfect tuning "out of the
box". There are six needed components for a CB radio installation:
- CB radio
- power feed
- coaxial cable
- antenna mount
- ground plane or counterpoise (For most
installations that we do
as Jeepers, the mobile antenna will use the vehicle's body as
counterpoise...meaning that while the antenna is the radiating unit,
the Jeep is the reflecting unit. All transmit antennas need a
reflective unit...a.k.a. counterpoise or ground plane)
Even if the
manufacturer supplies you with an
entire kit (coax, mount
and antenna), this will leave you without the counterpoise
requirement. There is an exception to this general rule; antenna
systems that use the coax cable as a counterpoise. These
no-ground-plane kits are generally marketed to owners of fiberglass
vehicles. However, what follows is specific to installations that DO
NOT use coaxial counterpoise antennas.
people believe that
SWR only involves the antenna but that is not
accurate. When you place an SWR meter between the radio and the antenna
it does not determine one component from another. A defective
connector, bad coaxial cable, untuned antenna, etc. may all return the
same results on the meter. Even how the antenna is mounted will play a
big part in the resulting SWR readings. For instance, if the antenna is
mounted on a Jeep in a way that interferes with its ability to radiate
applied energy into free space, you will get a higher than desired SWR.
Location is important.
It isn't always practical to mount the antenna
in the optimum position
on any vehicle. When you set aside performance in favor of convenience,
you will need to settle for what you can get. Regardless of location,
tune your system/antenna. When tuned properly, the antenna will give
you the best performance you can expect from an antenna mounted in any
given location. Most of all, remember that untested installations can
cost you big bucks. Checking your CB antenna system for continuity,
shorts and opens is a MUST and should always precede checking SWR.
Operating transmitting radios when the SWR is over 3:1, or with
opens/shorts can damage the radios circuits.
CB radios only
transmitted on one channel, it would be much easier
to setup antennas. Most CB's have 40 channels, but mobile antennas can
only be made to resonate at one specific frequency or channel. For
example, on a 40 channel CB, channel 19 is the center frequency (27.185
MHz). If the antenna is tuned to be resonant on channel 19, the further
away from that channel you are, the higher the SWR will be. This is
also known as "Center frequency dip". CB antennas are therefore made to
resonate at a frequency in the middle of the available band (channel 19
on CB) and are made broad-banded enough to keep the off-frequency
related SWR at the two extreme ends of the band (Channel's 1 & 40)
This important, because it needs to be taken
into account when
measuring and setting SWR. Essentially, you will need to take 3
readings: At channels 1, 19 and 40. With these three readings you can
determine all kinds of things about the system...including whether the
antenna is electrically long or short. More on actually taking SWR
reading and adjusting all this later. (If you communicate on one or two
adjacent channels anywhere within the band, you can tune your antenna
to achieve optimum performance on those channels. Most people, however,
prefer to use the entire bandwidth when tuning.)
CB antennas are
tunable in one way or another. Antennas that have a
tuning device (usually mechanical), are referred to as a "tunable
antenna". Because of this, lots of people think the following types of
antennas are not tunable and so they make no attempt to have the
tuners), can be tuned by
removing wire from the top (to fix a electrically long condition) or
the coils at the top of the antenna can be separated and spaced further
apart (to fix an electrically short condition). In addition, parts that
increase the physical length of the antennas (springs, quick
disconnects, etc.) can be added.
antennas (which come in straight or helical
wire configurations) that are electrically too long can have the cap
removed and the top can be cut off with a hacksaw. If the SWR test
shows that it is electrically short, the addition of a spring or quick
disconnect (or both) is the only way to correct it.
have a set screw (or two) just below the area
that the whip is inserted into the loading coil. By loosening up the
set screw(s) you are able to slide the whip up or down as required to
are some basic
rules to follow when choosing a CB antenna to
install on your Jeep. Before you even consider buying the antenna,
mount, etc. figure out where it will be mounted on the Jeep and take
the following points into account.
antennas perform better than center loaded
antennas, center loaded antennas perform better than base loaded
- I'm not going to get into a discussion of what
loading a CB antenna means, you can go here
for more info.
- At least two-thirds of the antenna
should be above a vehicles
roof line for optimum performance.
- Taller antennas perform better than
- Antennas mounted higher perform
better than if mounted lower
perform better when mounted as close to center as possible on metal
vehicles - this is neither practical nor even possible on most
Jeeps...so we are already at a disadvantage
length of the antenna should be determined by the likelihood of it
hitting of overhead objects as well as the type and strength of the
antenna mount itself
The bandwidth of
the antenna should always meet or exceed the needs of a 40 channel CB.
you've used the
previous criteria to figure out where you're going to mount you're
antenna, how long it needs to be, etc., you are ready to start
shopping. One other thing to note: If the antenna/mount combination is
available in a kit form, you will normally save money by purchasing it
as a kit. Just make sure that the components are all of high quality.