CB Antennas?

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The second advantage of co-phased antennas is there ability to perform where there is little reflective ground plane for the single antenna to radiate its energy from. For instance, on fiberglass vehicles or those with light aluminum sheeting over a non-metallic frame. In those situations a co-phase set-up allows the antennas to use each other's radiation field to direct the combined energy across the horizon. In order to be effective at least 2/3's of each antenna must have unobstructed line-of-sight to the other antenna.

There’s no magic antenna that works better than another, it’s all about size.
They need to be a quarter wavelength (or half wave or full wave, but that’s huge at 27 MHz).
A 1/4 wave CB antenna is 9 feet long. The way shorter antennas are able to tune and resonate like a full 9 foot 1/4 wave is by coiling up the length of it.
If you look at a short antenna like a Firestick, you’ll see it’s a fiberglass pole with a wire spiral wrapped up it’s length.
That’s called continuous loading.
Other short CB antennas have a coil at the base or in the center about halfway up. It looks like a cylindrical lump, but there’s a coil of wire making up the rest of the required length of the antenna inside it. That’s “base loaded” or “center loaded”.
The coil just allows it to tune and resonate correctly for the frequency it’s being used for.
The shorter the antenna, even if it’s loaded correctly, the worse it works. The longer the better.

They also need a groundplane. The metal car body they’re mounted on acts as the groundplane.
Electrically, it mirrors the antenna to make it behave as if it were a full half-wave antenna. Without it, the radiation pattern is upward toward the sky.
It needs the groundplane to lower the pattern so it’s stronger in a more line of sight pattern where it’s more useable.
Note, a groundplane isn’t a “ground”, totally different thing.
The radiation pattern becomes directional toward the mass of the groundplane.
If you mount the antenna at the front of the vehicle, it will be more directional and strong toward the rear of the vehicle, following where the groundplane is.
Ideally you’d use a 9 foot whip on the top and center of the vehicle, but obviously that has practical problems.
You want it as high as possible, as long as possible and as centrally located as possible, and you compromise down from there as needed.

You also need to tune it with an SWR meter.
Standing Wave Ratio. That’s the amount of power that just bounces back at the radio rather than efficiently resonating and radiating out from the antenna. Most CB antennas have a set screw and a fine height adjustment to allow this. You want the reading on the SWR meter as low as possible. 1.5 to 1 or less is great.

BradW wrote:
On our old lance I mounted two 2' firestik antennas on the top of the ladder.. Since they "saw" each other, they used each other as a ground plane. That setup worked very well.

A groundplane is an entirely different thing. It’s effect is to lower the radiation pattern from mostly skyward to more line of sight.
Two antennas near each other affect the radiation pattern differently, they make it more directional. They really need to be about 9 feet apart, a quarter wavelength.
The reason you saw that on trucks in the CB heyday with twin antennas on the mirrors, which are about 8 feet apart, is they make the radiation pattern like a figure-8 as viewed from above. They’re directional to the front and rear, and much less to the sides.
The idea was to concentrate the signal up and down the highway and minimize interference from the sides.
Your ladder was acting as the groundplane.
The reason they works well was how high up they were. You’d probably do better with a single one.

BradW wrote:
https://youtu.be/H_s4kA2LEh8

Similar to this mount. I added two additional screws and a spring.

Mk, yeah I can see why you might not trust it. Its thinner than the mount I have and would likely be more prone to bending.

I generally use our cb when we are traveling with others who have cb radios. I only switch to 19 when there is a wreck/traffic back up or I'm just bored.

Swearing doesn't bother me on 19. What does piss me off is the racist insults aimed at people out working hard just trying to earn a living.

I removed mine after hearing the amount of swearing and very rude language. So glad it's gone, Just like avoiding a place where it more important for some individuals to throw others under the bus and click about it.

https://youtu.be/H_s4kA2LEh8

Similar to this mount. I added two additional screws and a spring.

BradW wrote:

Supercharged111 wrote:


A fender mount can't handle a 5 footer?

I have a fender gap mount on our jeep jk. I would not trust it to handle a 5' antenna.

What's the anchor points like on yours? Mine has five screws that anchor it into the body and its been successfully holding the 5' firestiks without a spring for sixteen years, including having a dolt like me smacking the antenna into tree branches and a low hanging drive thru.

If your hood area is aluminum or plastic, then yeah, that makes total sense, but if its half way decent sheet metal one like that should stay put.

Supercharged111 wrote:


A fender mount can't handle a 5 footer?

I have a fender gap mount on our jeep jk. I would not trust it to handle a 5' antenna.