CB Ant. Tips
"Phantom" Antenna Tips
Every industry has its bottom dwellers. We can not protect you
from them. Consumers who make decisions based strictly on price, or on what someone says
instead of what they can do, will often fall prey to the bottom dwellers.
Beware of information from "experts" (real or
self-proclaimed). There is antenna theory and there is antenna reality. We have yet to see
a vehicle that simulates a lab. While theory is a good starting place...experience is
invaluable when it comes to real problems. The knowledge gained from the best book on
theory will not necessarily produce the best antenna design.
Some "experts" may "claim" 5/8 wave mobile
antennas are not possible because they would need to be 23 feet high. They are wrong!
Physical length and ground wave performance are not the same. If you ever hear someone
make that claim, ask them how a handheld CB can have a 1/4 wave antenna 8 inches long and
mobile 1/4 wave antennas can be anywhere from 12-60 inches long in spite of the fact that
a physical 1/4 wave is 108 inches.
Never key up or attempt to operate your CB without a working
antenna or "dummy load" (non-radiating antenna simulating device) connected to
the radios antenna jack, unless you have extra money to buy another radio, or know a good
All mobile and base transmitting antennas need counter-poise,
more commonly called ground plane. The antenna is the reactive unit, the ground plane is
the reflective unit. Neither is more important than the other. In mobile installations
with standard antenna systems, the vehicle metal (body, frame, etc.) acts as the ground
plane. In "no-ground-plane" systems, the coax shield is used for counterpoise.
Most, but not all, manufacturers pre-tune their mobile antennas
on a test bench. To protect your radio's circuitry and achieve optimum performance, mobile
transmitting antennas (CB, cell phone, amateur, etc.) need to be tuned on the vehicle.
Before transmitting, you should check your antenna system for
shorts or opens. If you have continuity between the center pin of the connector and the
outer threaded housing, you may have a short. Don't transmit! If you do not find
continuity between the center pin of the coax and the antenna base, you have an open. Fix
it. (See "Testing Continuity") Exceptions: Some base loaded antennas use a
center tap design and there will be continuity from ground to center conductor. Also,
Firestik "No Ground Plane" antenna kits will have coaxial center pin to ground
SWR that pegs the needle on all channels almost always indicates
a short in your antenna system. Do not attempt to tune the antenna until the short is
fixed. Operating with high SWR will probably damage your CB's internal circuits.
Make sure that the antenna you are using is the right antenna for
your application. Don't use a TV antenna or an AM/FM antenna for your CB. Do not operate
your CB without an antenna or dummy load.
Transmitting antennas are sensitive to objects in their
"near field of radiation." Tune your antennas in an open area. Never tune inside
or next to a building, near or under trees, near or under power lines, and never with a
person holding or standing next to the antenna. Try to simulate normal operating
If you mount two or more antennas close to each other, you will
alter the transmission patterns of each one. The affect may be either positive or
negative. We recommend that a minimum of 12" exist between your CB antenna and other
types of antennas.
Your radio cannot tell one component from another. As far as the
radio is concerned, the coax, stud mount, mounting bracket, antenna and vehicle is ONE
unit. Don't be too quick to fault your antenna until you are sure that all of the other
components have been given equal consideration.
Of all antennas returned to Firestik for warranty service, 75%
show no signs of being tuned to the vehicle. All antennas should be checked prior to use.
Most will require some adjustment. Less than 3% of all returned antennas have actual
performance causing problems. Of those, half of the problems are user or installer
created. High SWR and other performance problems are 20 times more likely to be caused by
bad coax, bad connections, shorted mounts, poor installation location or faulty test
In almost every instance, once you get the same SWR reading on
channels 1 and 40, further antenna tuning will not improve the readings. If the SWR is
still over 2:1, you have other problems to conquer. Exception: There are rare occasions
when the ground plane is so small or large that the system is way out of phase (especially
with high-performance antennas). If you have high SWR on all channels and have confirmed
that you have no opens or shorts in the feedline, try making a small tuning adjustment in
the antenna. There are times when the SWR will drop equally across all channels under
unusual ground plane conditions. If you find this to be the case, carefully adjust the
SWR that is high on all channels (over 2:1 but not pegging the
needle) after the antenna has been tuned normally indicates a ground plane or coax cable
The doors, mirrors, spare tire racks, luggage racks, etc. on many
vehicles are insulated from a good ground with nylon or rubber bushings. This also stands
true for fiberglass vehicles. Make sure that your antenna mount is grounded, even if it
entails running a ground wire to the vehicle chassis. Bad hard ground at the mount
generally equates to less than optimum performance. Exception: No ground plane antenna
kits do not require a grounded mount.
If you are hearing whining noises from your radio while your
vehicle is running, it is probably due to "dirty power" being supplied to the
radio. Under dash power may be more convenient, but the "cleanest" power will be
found by running the radio's power leads straight to the battery.
You can never buy coax cable that is too good for your system.
Never compromise quality for cost when purchasing coax. Your best bet is to stick with
coax that has a stranded center conductor and 90% or higher shielding.
Most manufacturers of high performance antennas recommend a
specific length of coax cable. If your antenna manufacturer suggests a specific length,
give priority to that recommendation.
If your ground plane is good, your mount grounded and, your
antenna favorably located, coax length rarely becomes an issue. But, if one or more
mismatches occur, you may find high SWR. This can often be corrected by using 18 feet
lengths of high quality coax.
Excess coax between your radio and antenna mount should never be
wound into a circular coil of less than 12" in diameter. Doing so can cause system
problems. Your best option for handling excess coax is to serpentine the cable into a 12
to 18 inch yarn-like skein. Secure the skein in the center with a wire tie and tuck it
Single antenna installations require coax with approximately 50
ohm's of resistance (RG-58/U, RG-58 A/U or RG-8X). Dual antenna installations require the
use of 72 ohm cable (RG-59/U or RG-59 A/U).
Coaxial cables with foam (polyfoam) center conductor insulation
should be your last choice for use on mobile (vehicle) installations. Even though it will
work initially, it has limited life and does not stand up to the conditions encountered in
the mobile environment. Choose coax with polyvinyl insulation when doing mobile installs.
Coax cables should never be cut and spliced together like common
electrical wire. Line losses will occur.
Coaxial cable with holes in the outer insulation, severe bends,
or door, trunk or hood caused pinches will cause performance problems. Treat your coax
If you live in an area where rain and/or sleet is common, wipe
your antenna down with a rag that has been coated with WD-40, Armor-All, Pledge, light
oil, etc. This trick prevents ice build up that can overload and cause your antenna to
break. In an emergency use butter, cooking oil or anything else that will repel water.
When tuning your antenna(s), make sure that you do so with the
vehicle doors, hood and trunk closed. If left open, they can cause inaccurate SWR
readings. Try to simulate actual operating conditions.
Mobile antennas, for best performance, should have no less than
60% of their overall length above the vehicles roof line. For co-phased antennas to
perform optimally, the space between the top 60% of the two antennas needs to be
Remember, all transmitting antennas need ground plane
(counterpoise). Base antennas, much like "no ground plane" antennas, build it
in. Do not use mobile antennas for base station applications unless you know how to build
your own ground plane.
If you are installing a single antenna on one side or the other
of your vehicle, best on-the-road performance will be realized if the antenna is on the
passenger side of the vehicle.
Co-phased (dual) antenna installations create a radiation pattern
that favors communication directly in front and back of the vehicle. This is why co-phase
systems are popular with people who do a lot of highway driving. Co-phase antennas must be
center or top loaded. Top loaded antennas are the best.
Some people believe that co-phased antennas must be separated by
a minimum of nine (9) feet. We have successfully used co-phase antenna systems with
spacing as little as four (4) feet. Space alters the pattern and not always negatively.
Each vehicle will be different.
Co-phase antennas can improve performance on vehicles that lack
good ground plane characteristics (fiberglass motorhomes, trucks, etc.). Instead of using
available metal to reflect the radiated energy, the antennas use each others field.
When tuning co-phased antennas (dual), it is best to adjust both
antennas an equal amount to maintain equality in their individual resonant frequency.
On a co-phase system, if you try to tune each antenna
independently using RG-58 type coax and then connect them to the co-phasing harness, you
will almost always find that they will appear electrically short as a set. We recommend
that you first assemble the entire system. Take all measurements and make all adjustments
with both antennas in place.
If you are experiencing SWR that is high across the entire band
and have eliminated shorts, opens, groundless mounts and coax as potential problems,
suspect lack of ground plane. Try adding a spring or quick disconnect to the antenna base.
In some cases, the repositioning of the antenna relevant to available ground plane will
solve the problem.
One of the greatest benefits of the FS series (patented tunable
tip) antenna is noted when there is lack of available ground plane. If the tuning screw
reaches its "maximum out" position before satisfactory SWR is realized, a common
1/4-20 threaded bolt or screw of a longer length can be used to replace the supplied
tuning screw. If the vinyl cap is too short to remain in place, the user can disregard it
or clip a hole in the top for the longer screw to pass through.
In rare instances, like antennas mounted in the middle of a metal
van roof, excess ground plane can cause a problem. This usually shows up as high SWR
across the band. In these cases, a tunable tip antenna may not be the best choice. The
reason being, the antenna is too long and the tunable tip cannot adjust down far enough
(see line 40). If you suspect this, an antenna that wire can be removed from will usually
fit the bill (i.e. KW or RP series).
There may be situations when a tunable tip will bottom out before
optimum tuning is achieved. If this happens, try removing the knurled jam nut and finger
tighten the tuning screw against the o-ring. If still too long, remove the tuning screw
altogether. If total removal causes the antenna to go short, cut the tuning screw in half
and re-insert it into the tuning extender and re-test. The following items on the FS
Series "tunable tip" antennas, when removed, will have an effect on SWR (in
order from least effect to most effect). O-ring, jam nut, tuning screw mass (cutting off
length), vinyl cap, tuning screw complete.
The vinyl cap on any "tunable tip" Firestik antennas is
optional. However, your antenna needs to be tuned as it will be used . . . with or without
Magnetic mounts should be used in temporary situations only. If
you leave them in the same spot for a long period, the paint will not age like that of the
uncovered areas and/or moisture will be trapped between the mount and vehicle causing rust
or discoloration. Periodically lift the magnet and gently clean off the underside of the
magnet and the vehicle surface.
It is a bad idea to use magnetic mounts and amplifiers together.
Magnetic mounts rely on capacitance grounding. This situation can literally cause the
paint under the mount to bubble or discolor due to excessive heat build up.
On wire-wound antennas that require wire removal for tuning
purposes, best overall performance will be achieved by keeping the loose end of the wire
pressed down tightly against the wire coil. If you use power amplification on top loaded
antennas and do not process the end of the wire load so it can dissipate its heat into
other adjacent coils, you can melt the tip of the antenna.
Generally speaking, center loaded antennas perform better than
base loaded antennas, and top loaded antennas perform better than all. For any given
antenna design (base, center or top loaded), the taller the antenna the better. With
length comes a wider bandwidth (lower SWR over more channels), more power handling
capability and overall performance increases.
When ultimate mobile performance is desired, function should be
given precedence over mounting location convenience and appearance.
Don't confuse SWR with overall performance. You should seek SWR
of 2:1 or lower on channel 1 and 40, but keep in mind that best performance may not be
found at the lowest SWR readings. For the most part, if you get your SWR below 2:1, on
both ends of the band, don't be overly concerned about using meter tricking procedures
that bleed off energy.
The SWR meters built into CB radios are okay for general
readings, but are rarely sensitive and/or accurate enough for fine tuning of antennas. Use
them mostly to indicate serious high SWR problems only.
Firestik has tested literally hundreds of SWR meters. A large
percentage of these have shown to be off by 0.3 to 0.7 when compared to a piece of
certified equipment. There is no standard among production meters. However, unless a unit
is defective, most will indicate the most serious problems that you might encounter
Aside from cost, the type of wire used in or on antennas (copper,
silver, aluminum, gold, tinned, etc.) has negligible effect on antenna performance. The
antenna must be designed to resonate with the wire type and gauge chosen by the designer.
However, larger wire gauges will normally increase the bandwidth and heat dissipation
abilities of the antenna.
Copper is 55% better than aluminum, 27% better than gold and 578%
better than tin insofar as conductivity is concerned. Silver will conduct AC/DC current
less than 2.5% more efficiently than copper, but the cost to performance is generally
unjustified and any gain, insofar as RF transmission is concerned, is negligible.
If devices other than an SWR meter are going to be used between
the CB radio and antenna, always tune the antenna system first without that device in
line. If SWR is high with the other device in line, you will know where the problem is.
In "no ground plane" systems, it is best to choose a
system that terminates the coaxial ground at the radio end of the cable. These systems are
far less reactive to cable routing errors and will almost always outperform systems that
are terminated at the antenna base or antenna end of the coax.
Cables and antennas from standard & no-ground plane kits are
not interchangeable. The "No Ground Plane" antennas from Firestik have a yellow
band near the base.
Wire wound antennas with a plastic outer coating will greatly
reduce audible RF static when compared to metal whip antennas.
If you leave your antenna on your vehicle permanently, remove the
rubber o-ring that is found on the threaded base of some antennas. Tighten permanent
antennas with a wrench. Add a lock washer if you want.
If you use mirror mounts and often find yourself in areas with
overhead obstructions, tighten the bolts just enough to keep the antenna vertical at
highway speeds. If the antenna contacts something overhead, the mount will rotate on the
mirror arm and protect your antenna.
If you use long antennas and find that they bend too far back at
highway speeds, tilt them forward if possible. When under a wind load, they will end up in
a relatively vertical position.
On antennas that are topped off with a vinyl tip, make sure that
you take your SWR measurements with the tip in place. If you tune your antenna with the
tip off and then reinstall the tip, your SWR will change.
Without advocating the use of power amplifiers or unauthorized
channels, take note that the Firestik II tunable tip antennas have a fairly large metal
tip that broadens the bandwidth and dissipates a considerable amount of heat.
It is illegal to use power amplifiers with CB radios. It is
illegal to "tweak" the radios internal circuits to increase output power. The
transmitter power of a legal, FCC certified CB radio is 4 watts AM.
If having one antenna for CB/AM/FM is appealing, use a CB antenna
and a splitter that allows it to be connected to your AM/FM radio. Devices that let you
use your AM/FM antenna for CB use will leave you disappointed.
On a budget? Buy a cheap radio and a good antenna. Aside from
added bells and whistles, all CB's are FCC regulated to transmit no more than 4 watts of
power. A good antenna on an inexpensive radio will almost always outperform a bad antenna
on an expensive radio.
Beware of the wire wound mobile antennas mentioned in ads that
claim them to be "full-wave" or "wave and a half". At best, you are
being deceived by the misleading association of wire length to actual performance
characteristics. Wire length, for all intents and purposes, is irrelevant. With
"very" few exceptions, antennas must function as a 1/4 wave or 5/8 wave to be
useful on mobile installations. For example, Firestik and Firestik II antennas between 2
foot and 5 foot have a radiation pattern similar to a 5/8 wave reference antenna. However,
wire lengths range from 20 feet to 32 feet (0.6 to 0.9 of a full wave length). If wire
length was relevant, each antenna would need 22.5 feet of wire.