Lots of folks get concerned when mounting CB antennas on fiberglass sided
RVs. They have been told that they need to buy the more expensive, but
less efficient no ground antennas commonly found on boats. While spending
extra money is a prerogative we all have, there is no need to do this for your
CB antenna. When mounting a CB antenna on your fiberglass rig, simply make
sure that mount is anchored at least by one screw into a metal member of the
framework of your rig. It really doesn't matter that your rig has a fiberglass
skin as long as you can get the ground side of the antenna mount connected to
some piece of metal in your rigs framework.
For example, on our Discovery, I have the CB antenna mounted at the seam
between the drivers sidewall and the front cap. This seam sits on
one of the steel/aluminum framing members that make up the sidewall of the
rig. It makes a great ground connection for a CB antenna (or any
other antenna for that matter). Two of the screws that hold the antenna
mount are screwed directly into this metal frame member. In most rigs,these
metal frame members are bonded together creating a wonderful
ground for the antenna to work against.
To understand why this is important, one has to remember that every antenna
wants to have one side of the mechanical structure grounded. Of
course, in an RV one normally doesn't actually get a ground connection, but the
frame rails and side structure/roof metal sections act as a
pretty good ground for the antenna system. On a fiberglass boat, there is
normally no metal structure to ground to, so the antennas are built with a coil
of wire in the bottom to act as ground. Others may use the
coax shield as the antenna ground although this is less than desirable.
In either case, these antennas are at best, a compromise for a good ground
connection on your rig.
Folks will tell you that the length of the coax is important, but unless you are
co phasing a pair of antennas (more on this later) the length of
the coax should be the distance between your radio and the antenna! Yes, there
are advantages to having the coax a specific length for the
specific frequency you are operating on. These advantages deal with the
type of coax, the type of center conductor and the velocity factor of
said coax. All of this is really unimportant in our application.
After all, the bottom frequency (Channel 1) of the CB band is almost 2
megahertz from the top of the band (channel 40). Cutting the coax to be
the appropriate length for one channel makes it not correct for the other
39. Just make it long enough to get from the radio to the
antenna.
Many folks get concerned over the type of antenna to use. Probably the
most efficient mobile CB antenna is the quarter wave whip. This antenna
is over 8 feet long and unless you bumper mount it, will be too tall for your
rig. Therefore, one needs to compromise and use a physically
shortened antenna. Most of us use either a 4 foot wire wound antenna or a
base loaded whip. All fiberglass 4 foot antennas consist of a piece
of wire wound around a fiberglass stick and normally covered with a hard
vinyl/plastic coating. Base loaded antennas consist of a coil of wire
and a whip, usually less than 4 feet tall. The coils in both of these
antennas make the physically short antennas the correct electrical length to
operate on the CB band. It doesn't matter what the brand name
is as long as they are mechanically sound. They all work the same way and
no manufacturer can change the laws of radio propagation or
electrical properties of antennas. None of the little chunks of metal that
you see on some CB antennas does any good. Placing the antenna in
a 45 degree slant as you see on some trucks today actually will degradethe
signal, since you are now changing the polarization of the antenna.
All of us who run mobile radios on CB or FRS or most of the Ham radio bands, use
vertical polarization. For short range communications like CB, the
polarization of the antennas should be the same. If you turn
the CB antenna horizontal to the ground, the polarization becomes horizontal and
the signal is degraded greatly to someone close by with
vertical polarization. While I cannot tell you the exact polarization of a 45
degree angle on an antenna, it certainly is not purely vertical.
Keep your antenna straight up.
Many folks like to use two antennas like the truckers do. This is ok on
a big motorhome as one needs to get the antennas a quarter wave apart,
or about 8 feet, for them to work properly. In addition, they need a
phasing harness of coax measured exactly the right length for the radio
waves to reach the antennas in the correct phase or they just don't work. The
problem with co-phased antennas is that they make your signal directional.
Picture a figure 8. Co-phased antennas make the signal stronger in the
lobes that go forward and back from the antennas like the figure eight.
Side lobes are less effective and your transmit and
receive signals will be much less in these directions. All of this is
really nice if you are traveling across west Texas in a straight line and the
folks you want to communicate with are either directly in front
or directly behind you. If you are in hill country with curves and you
want to talk to Billy Bob who has rounded the curve and is now in the weak part
of the figure 8, your signal will not be as good as it would
be with a single antenna that radiates in a basic circle around itself.
The best place to mount your antenna is in the center of your coaches roof, but
this isn't practical for most of us. The next choice would be either on
the driver side high on the coach or on your ladder. If your
ladder is on the driver side, great, if it is on the curb side, it is still ok,
but not as desirable. Why? most of the low limbs and signs live on
the curb side of the road. Antennas mounted high on your rig on
the curb side have a very short life span.
The bottom line is, keep your installation simple, get the antenna up as high as
you can without violating the law ( I believe it is 13 feet 1 inch, but I would
keep it below that anyway) and ground your antenna to the rigs metal frame
members.
As far as a radio, it is the least important part of your CB system. I
use a $35 radio I bought at Wal-Mart although I really like the Cobra that has
all the controls in the microphone. The ability to change to
channel 9 and 19 with the push of a button on the mike is a good feature.
I generally leave my CB on channel 13 to talk to other RVs but do switch to 19
to see why I am waiting in a 5 mile backup on some
road.
Of course, if you really want to communicate, get your amateur radio license
and talk to the world. If you want good road information however, get on
channel 19 and ask the truckers. Besides, you will learn some really creative
ways to use the English language.
John Veach
Amateur Radio station KE4D and fulltime Rver
