Fishing Pole Ear--A Homemade Mobile CB Antenna

[myhelipad]

While the next project won't necessarily save you any money, you might
want to give it a try if you are interested in understanding more
about how fiberglass whip antennas do their thing. We have talked 30
miles mobile-to-base on one of these home brew fishing pole antennas
using a $20 barefoot rig.

Antenna Parts

One 7-foot fiberglass fishing pole with hollow base One piece of
steel rod 4 to 6 inches long-right diameter to slip into base of pole
One ¼" x 1" machine bolt (threads to match mount) 12 feet of enamel
#18 gauge wire Some good epoxy glue


Antenna Mount Parts

One 114' x 21/z" bolt and nut (same threads as bolt on base)

One longer-than-usual ¼" nut

Two plastic insulating washers

Three metal 5/8" diameter washers

One large terminal lug


First you've got to get yourself a fishing pole, 6 to 9 feet long. If
you already have an old one lying around, you can clip off the line
loops and cut the handle off.

We did some shopping and found that a finished fishing pole as long as
we wanted was at least as expensive as a newly-manufactured CB
antenna. But then we discovered a sporting goods store that sold
unfinished fiberglass poles 7-feet long for $6. The kind we found was
a black hollow tapered pole with about a 1/8" inside diameter at the
base.

The next step is to hook something to the pole so you can screw it to
a mount on your vehicle. The way we did it was to get a piece of scrap
steel rod near the inside of the base of the hollow pole. (If the pole
is not hollow you will have to figure out another way of hooking to
it.)

Grind a slight taper to match inside taper of the fishing pole. Braze
bolt to rod. Use 1/4" x 1" steel bolt. Epoxy the steel rod inside the
base of the fishing pole.

There are many commercially made CB antenna mounts that you can buy at
electronic parts stores that could be used to hold your fishing pole
ear. If you elect to buy one of these mounts, get one with a spring so
that if the pole encounters a stray tree branch, it can bend instead
of break! If you are going to use this antenna with a store bought
mount, the threads on the bolt on the bottom of the antenna should
mate with the hole in the top of the mount's spring.
Tuning the Fishing Pole Ear

Now it's time to get into the electrical part of the antenna. The
fishing pole is not the antenna; it's just a prop that holds the wire
up. So we need to wind a wire around the fishing pole in such a way
that will make it tune the 27 MHz CB band

If your antenna is shorter than 9 feet long, you can tune it by
winding a coil around the pole. On our 7-foot ear, we found that it
was necessary to make a coil of four turns ¼" apart about 2'- 3' up
from the base of the pole. Tightly wrap the wire in a spiral up from
the base of the pole. Make the distance between windings as wide as
possible below and above the coil. If you follow these particular
dimensions you should be close to being tuned up. To really make the
ear a perfect match, however, you'll need to use an SWR meter to check
the SWR. You may have to modify the coil spacings or add or subtract a
turn from the coil to get it just right.

Different lengths of CB Antennas will also work, but different coil
windings will be necessary, so if you have a different length pole
you'll have to use a meter to tune it up. You just have to dive right
in and try different numbers of coil windings. The longer the pole,
the less center coil windings; the shorter, the more windings
necessary. It takes some playing around and trial and error.

We used enamel coated wire, the kind used in motor windings,
generators, transformers, etc. It's best to use enamel-coated wire so
that the coil turns can't possibly short to each other.

At the bottom, wrap the wire around the 1/4" bolt. Be sure to scrape
the enamel coating off the wire and clean the bolt for good contact.
Solder that wire to the bolt or use a nut to hold the wire onto the
bolt so that it makes a good electrical connection.

We covered some CB antennas we made with a thin coat of fiberglass
(which you can tint any color you want). They looked pretty good but
the fiberglass chipped off some of the antenna tips because they were
mounted fairly high up and got tangled in the trees. You can prevent
chipping by putting some shrink tubing over the tip. Shrink tubing
would be another possible way to hold the wire on the fishing pole.
It's available at most electronics shops.

Building a Fishing Pole Antenna Mount

If you are really adventurous, you can also build your antenna mount.
The main point to understand when making an antenna mount is that the
radiating element is not supposed to ground out to the body of the
vehicle. This means that the bolt the antenna hooks to must be
insulated from the metal body of the vehicle.

Your homemade mount must use good insulating washers, because if the
bolt shorts to the vehicle body it could possibly blow out your rig's
final RF power transistor.

One source of home brew insulating washers is the main output
terminals of junk alternators or generators. The washers should be
made out of some type of plastic. The best kind of insulating washer
has a shoulder around its hole. You drill a hole in the vehicle body,
big enough to allow the shoulder to fit through. This holds the bolt
away from the metal body.

If you can't find a plastic washer with a shoulder, it is possible to
use two flat plastic washers with a little piece of plastic tubing in
place of the shoulder. Make sure the plastic is tough enough to not
get cut by the edge of the hole in the vehicle body.

Your base CB antenna system may be put up 20 feet higher than the
highest point of the building or tree on which it is mounted; however,
the highest point of the antenna must not be more than 60 feet above
the ground. There are additional restrictions on an antenna system
located near an airport. Consult FCC Laws Part 95, Subpart D for your
particular situation.