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Fabricating CB Antennas 
Citizens Band frequencies are at the top end of the high-frequency band, or stated another way, just below the bottom end of the VHF band. Here is where base-loaded CB antennas usually work well. A mobile antenna should be placed in the middle of the vehicle roof to make best use of the ground plane. The longer the CB whip, the better the performance. The more you load an antenna, the shorter it gets, and the lower the radiation resistance. Lower radiation resistance means less signal output and input. Select the tallest antenna possible and put it as high as possible.
You might also consider a phased two CB antenna system to give an additional
3dB of gain. You can purchase "co-phase" coaxial cable assemblies, or make your
own using a coaxial cable T-connector and two equal lengths of RG8AU coax. Make
sure that each side of your co-phased coaxial cable feed lines are identical
in length, down to a fraction of an inch, but be sure to avoid a precise half-wavelength
on 11 meters for your phasing harness. Mount the antennas on either side of
your vehicle. The best performance will be to the front and rear of the vehicle,
with slight nulls to each side of the vehicle.
The easiest way to get the strongest signal out on Citizens Band is to use
an unloaded whip CB antenna. You may purchase these stainless steel or fiberglass
whips at any CB Radio store. Mount the whip as high on your vehicle as possible.
Because it has no loading coils, it will offer unity gain without loss whereas
you might expect a loss of 1 to 2dB from a loaded CB antenna.
On VHF and UHF mobile radio bands, the whips are so short that they may be
phased vertically in a collinear array to achieve increased gain on transmit
and receive. Why send half your signal into the sky when it can do more good
down close to the horizon? You can spot a VHF or UHF collinear high-gain antenna
by the loading coils in the center of the whip.
For VHF operation, a 5/8-wavelength CB antenna offers a low take-off angle
and may achieve increased gain of approximately 3dB over a conventional 18"
spike on the roof. You can spot these antennas easily by a single yard-long
whip and a gray or stainless steel loading coil at the base.
For UHF operation at 400-500 MHz, a popular mobile CB Antenna is the collinear
halfwave-over-halfwave whip. It's about 20" tall with a sealed phasing coil
in the center, and offers increased gain over a little 611 spike. A car with
one installed on the roof usually will still fit into a residential garage.
There are lots of CB antennas out on the market today, all kinds of different
shapes and sizes. Because of this competitive market, companies are always trying
to put out a better product for a cheaper price. Commercially-made CB antennas
are usually easy to put up and maintain. However, you might want to try your
hand at making an antenna. You can make an one out of readily-available parts
that will work as well or better than some commercially-made CB Antennas.
You will need an SWR meter to check out the Antenna after building it.
This CB antenna consists of a driven element and four radial wires that act
as a ground. The driven element receives the transmit energy from the rig.
104" (264 cm.) [I 02' (259 cm.)] piece of aluminum pipe or conduit
¾" - 1" diameter
Two U-bolts, same size as pipe
One sheet metal screw
One J-hook
Four "egg" ceramic insulators
408" (10.22 m.)[400'"(10.2 m.)] of 16 gauge wire
Rope, enough to guy the ground radial, depending on the height of the antenna
A couple of two-by-fours
Electrical tape
Silicone sealer to cover coax connection
The inside conductor of the coax is connected to the aluminum pipe by means
of a screw into the bottom of the pipe. See the detail drawing on this page.
Coat this connection with sealer or cover it with tape to protect it from corrosion.
All vertical antennas need to be grounded in some way. A mobile CB antenna
uses the car body as the ground. On this CB Antenna, the four radial wires are
used as the ground. This is called the ground plane of the antenna.
The braided wire which forms the outside conductor of the coax is soldered
to all four radial wires. The wires must be exactly 264 cm (104') long [259
cm(102") long] (¼ wavelength).
Remember that the inner conductor and outer braid of the coax must not touch
each other, nor can the radials come in contact with the driven element. The
radials slope down at about a 45 degree angle in different directions, and are
tied to the insulators. Rope or nylon cord is then tied to the insulators and
used to hold the radials out. They can be attached to anywhere convenient; trees,
a fence, house, etc.
If you are short on room for such a radial system, you can use 104" (radials)
and 102" (driven elements) pieces of aluminum tubing, or suspend the wires on
PVC pipe, bamboo, or 1" x 2"' wooden sticks. It's a must to check the SWR when
done. It should be lower than 2, and ideally lower than 1.5 or 1.3.
A ¼ wave ground plane CB antenna made from wire can be suspended from a tree.
We have talked to stations over 40 miles away using this antenna up about 30
feet high, running a mobile rig for a base.
For a quickie CB antenna, a vertical dipole (1/2) wave can be made right from
the coax itself You take your coax and very carefully, without nicking the braided
shield, strip 102 inches of the outer insulation jacket off one end. After removing
the outer jacket, start bunching the shield down the coax from the end. Now,
where the outer jacket and the shield meet, separate the braided shield enough
to get the inner conductor out through the hole in the braid. Pull all of the
inner conductor through and stretch it and the braid out. Be careful not to
skin any of the insulation off the inner conductor. Now attach an antenna insulator
to the end of the inner conductor. Measure the braided shield. Cut it off at
about 106" and attach an antenna insulator to the end. The total length of the
inner and outer conductor should be about 17 feet (1/2 wave). You can haul it
up to any height you want with a string or rope attached to the insulator on
the center conductor. It's a good idea to coat the end of the coax cable where
it separates with some kind of waterproof sealer. This keeps water from seeping
into the coax, which could cause a high SWR.
Just attach a coax connector on the end of the coax going to your transceiver
and you are on the air. The SWR should be 1.5 or better, if cut to the proper
length. It'll get out about as good as a ¼ wave ground plane CB radio antenna
if you get it up high and in the clear. Do not hoist this antenna up next to
a metal pole, because the metal will interfere with the antenna's operation
and cause a high SWR.
A mobile CB antenna can be used as a base antenna by mounting it on the top
of a metal pipe. The metal pipe serves as ground connection for the antenna,
taking the place of the body of the vehicle. Remember to run a separate ground
wire to a proper grounding rod for lightning protection.
This is an easy antenna to build and find the parts for. If you follow these
instructions and have it come out looking like these pictures, it should have
a very low SWR and appreciable gain.
You can use any number of pieces of aluminum pipe so long as they are ridged
and fairly thick-walled so as not to become bent and broken in a strong wind.
The pieces should be gradually smaller, one being able to fit inside the next.
Cut two 2' grooves with a hacksaw down the outer pieces of aluminum and put
a hose clamp around them. Now adjust the antenna to 22 ½ feet (6.85 meters)
and tighten the hose clamps down to hold it all together. This 22 ½-foot vertical
element can now be mounted with two U-bolts on to the 2" x 6' board. This board
should be treated or painted to protect it from the weather.
Put a bolt through the piece of wood a few inches below the vertical element.
Here you should fasten one end of the 6 foot (183 centimeters) piece of copper
wire or tubing, the outside braid of the coax and each of the 104" (264 cm)[102"
(259 cm)] long, stranded wires. These are called the ground radials and should
be tied off with string (not wire) at a 45 degree angle away from the bolt.
The ground radials and the braid from the coax can be soldered together or can
be crimped together with a crimp connector that fits the bolt. The other end
of the 6' copper wire is bent and fastened to the vertical element. The end
of the center wire of the coax is then twisted onto this in such a way that
it ca be slid up or down along the copper wire and soldered after adjustment.
The SWR of this CB antenna is adjusted by sliding this connection. You do this
by keying your rig up on channel 20 and sliding this connection up or down until
you have the lowest SWR. In our experience, an SWR of 1:1 or 1 was easily reached
on channel 20 with a low SWR throughout the 27 MHz band.
Be sure to cover the end of the coax real well with a moisture proofing sealing
compound so no moisture can get in it.
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.
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
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.
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.
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.
