CB radio - coaxial cable length

I bought an 18ft and just have the extra zip-tied in a bundle under the dash.  Didnt do the figure-8 or anything, works fine with little SWR.  When I purchased mine I just grabbed the best cable they had.  All were 18footers so I didn't consider length, just quality.

Where are you mounting your antenna that you can get away with 3ft of cable?

The suburban has a plastic overhead "console" with storage space in it. . . and already had a hole in the roof (between driver/pass seat) for an antenna. So I am going to attach the CB radio bracket to the plastic overhead console, just above the rearview mirror. The challenge (well, one of several) was to remove the metal bracket that the plastic overhead console bolts to . . . because there was surface rust on the underside of the roof sheet metal. The metal bracket was attached with metal rivets that were a lot tougher than they looked and were a bit of a bitch to drill out.

So I got the bracket off, cleaned off all the rust, then primed and spray-painted the metal. Now I want to install the antenna and antenna holder. Then I will need to reinstall the metal bracket with rivets. It's a lot easier to reach/work with the antenna holder with the metal bracket removed. So here we are.

It's gonna suck if I get it all put back together with the 3-foot coaxial cable, then learn that the SWR is too high such that I have to take it apart and mess with reconnecting a coaxial cable to the antenna in the 1 inch of space that exists between the metal bracket and the roof sheetmetal . . .

Definitely go with the 18 foot coax, figure 8 or spread out the excess to keep the swr down. Get quality coax and run an antenna that has an adjustable tip for the swr

Remember to have a good ground as well. Don't wind your cable up but like Dale said spread it out if you can in a figure 8.

Here's a nice response I got from the guy who runs howtocbradio.com:

There are 'some' benefits to having a length of cable that matches the wavelength of the antenna/frequency your operating on (physics is a constant 🙂 ) , but there's also problems with having too much coax hanging around.   Taking that extra coax and coiling it in a certain way will change a SWR reading to a desirable level until you move or recoil the coax, giving a different reading all together.   The only time I've worried about the amount of coax between rig and antenna is when its going to be a stupidly long length.   Go with the 3 foot if it falls into the way you want your setup to run and only consider using a longer length if your SWR is impossible to get down to an acceptable level. A properly constructed CB antenna should match well enough no matter what length of coax you use.   I hope this helps and if you have any more questions you can use this email address.   All the best   Carl

At the meeting tonight someone asked about tuning their CB antenna. The below link has a video that explains the process and I have an SWR meter if you want to borrow it.

https://www.rightchannelradios.com/blogs/installation-guides/18330687-cb-antenna-tuning-instructions

I am a Radio Station Engineer with a lot of experience with CB radio on the HF and UHF frequencies. I am also a Radio Amateur and I have been involved with radio for most of my life. That amounts to over 50 years.

I am saying this so you understand I have extensive experience with cabling of antennas from low power rigs right up to many kilowatts.

The length of coax to use in =any= installation, if it is done properly, is the minimum practical length.
So, if you need a Metre (3ft to some) length then make it a little longer for practicality and go with that.

Why ?
Simple. If you have a 50 ohm output connected to a 50 ohm cable which is in turn connected to a 50 ohm antenna then you make it as short as is practical because everything is matched and you will get maximum power into the load (antenna).
I'm trying to make this really simple but believe me, the 18' length is a furphy - it was a dream explanation by people who didn't understand how things =really= work. ie. Transmission Theory.

In an installation where something is wrong, the longer cable "hides the problem" - ie. It doesn't fix it, it just makes you think it is better when it is definitely not and all it does is introduce more loss which degrades performance.

And another thing, a low SWR/VSWR does not necessarily mean it works better ! Think about this - a dummy load of the correct impedance has a 1:1 VSWR. You simply cannot do better ! And yet you can't use it except as a test load for your equipment (And it is exceptionally handy for testing coax !)
I can make an antenna that has a near perfect VSWR and it's performance can be dismal (at best). SWR/VSWR means naff-all.

That's it in a nutshell folks.

Make sure your ground at the antenna base is very good (it's the most common error) during vehicle installations. If you hang an antenna off anything and it doesn't have enough metal under it to act as an effective ground plane, the receiving AND transmitting performance will be degraded.

Use the shortest practical length of coax.
Tune the antenna if you need to but honestly, I have extremely rarely ever needed to do this if it is a quality antenna and installed correctly.

At the Radio Station, we don't adjust the coax length, or any transmission cable length except to make it as short as possible .... And we are talking =real= power here, not a few watts or a few hundred watts.
We want the lowest loss and everything as best matched as possible to minimise transmission losses.

ChrisM
Head Radio Station Engineer
Queensland
Australia

Do it right and have fun !

Though an older post, than you Chris for posting this!  This is great information.