CB Antenna Coax Length

[D'Animal]

So I'm installing a CB in my tow rig and bought the Co-Phased (Dual) antennas. I mounted one on each of the senior RV mirror arms.

I read the directions and have a few questions.

Directions Say:

Antennas should be mounted 8ft - 9ft apart.

• That would be one on the front bumper and dang near on on the rear bumper. How critical is this?

For optimum performance the antennas use 18' of Coax per side. Excess Coax must not be coiled. The coiling of the cable creates a "Choke" within the coax.

• Since each antenna is about 4 ft from the CB, how critical is this?

The prefered method is randomly stuffing the coax to hide it.

• Any ideas on where to stuff 12' of Coax and not coil it?

 

[LCSODIVER]

well by placing one at the rear and one at the front, you will have directional gain to the sides of the vehicle but "nulls" to the front and rear. they are really meant to go on the outside mirrors of a big rig. so as far apart side to side is you best bet. As for the coax length, that is a huge misnomer in the CB crowd. just keep the coax equal lengths from the antennas to the T where they join and use what you need to get it to the radio. but yes coiling the coax can form a choke. If you do change out the coax or make your own just make sure to use 50 ohm coax such as RG-58 or RG-8x NOT the RG-6 75 ohm coax used for tv applications. Good luck, Bob KC7GTQ

 

[D'Animal]

Thanks


The rest of my rigs use Fire Stick antennas and the coax is 5' long. No problems but also they have about a 2 mile range.

I found I needed a longer range while in the mountains of Utah on my way back from Cruise Moab.

I was going to just cut off the extra coax and attatch to the antennas.

If I do this and keep both of the wires the same length, will I have a problem?

 

[LCSODIVER]

you shouldn't have any problems, just make sure that they are equal. and it would be a good idea to get a SWR meter and test/tune them once installed.

 

[Kofoed]

x2 on what LCSO said. The side-to-side spacing whould be 1/4 wave length apart--9 feet. The narrower they are together, the less directional the signal is. All that extra coax makes a pain to keep from getting kinked and the cheap sh!t they sell in the kit introduces losses--which may not mean anything trying to talk 2 miles down the road

 

[D'Animal]

Does anybody make a good connector that after I cut the coax to length, it will still work good?

 

[FJ40_owner]

Does anybody make a good connector that after I cut the coax to length, it will still work good?

Dan, you need to get off that CB stuff. I could talk from Placerville to Visalia on my home ham 2 meter station. You and I know you cannot do that on CB. But back to your question-s

The coupler you need for your coax to radio connection part number is a "PL-259" You need to identify the coax you are using as the inner sleeve may be needed for RG-58 type coax.

Installing an antenna on the front and rear bumper is called Phasing. The reason truckers install them on their mirrors is to act as a directional antenna. The get gain front to back. They need to be spaced an exact lenght apart.

You need to properly ground the shield of your antennas as well.

The CB itself should be powered directly from your battery, both pos and neg. (Fused)

I see no reason you cannot cut the coax to any lenght, unless they plan on it being a counterpoise.

You could do better with GMRS or FRS radios and junk the CB.

PM me if you like.

 

[BenMara]

Exposing the 18' CB Coax Myth

 

[D'Animal]

Thank

Exposing the 18' CB Coax Myth

That was a very good and easy to understand article.

 

[slickrock]

Dan, I have seen duals closer together than 8 feet. It is myth. If you put one on each mirror, you will get a figure 8 type plain for reception. Get a dual phase coax jumper and I'll get it tuned for you.