Don't Forget, meetings have moved to our new location @ Mark and Monica's Family Pizza, 4751 Manzanita Ave., Carmichael, CA 95608!
10:46 am
Club Member
April 10, 2015
Offline
hi guys:
I am working on the CB/antenna setup in my suburban. I know a little bit about radios, and have read internet forums re: the great debate about the coaxial cable length. Many "experts" (including some who legitimately are experts) recommend an 18-foot coaxial cable to optimize signal, because it is one half the length of a CB radio wave (which is 36 feet long).
I understand that a cable that is of poor quality or that is too short can cause a high Standing Wave Ratio ("SWR"), which, without getting into the technical details, would cause your radio to not work well (poor reception and transmission).
The distance between my radio and my antenna will be very short, such that a 3-foot cable would be more than adequate. I understand (reading various Internet forums and such) that a 3-foot cable simply is not adequate and would cause a high SWR, and that it would be better to use a 9-foot cable and place/wrap the excess into a figure 8 configuration (to avoid or minimize SWR) and tuck it away. I was wondering if anyone here could provide any details on that. It sure would be easy to use a 3-foot cable, but I want to get this right now and not have to mess with it ever again.
Buck & Katie
2:03 pm
Club Trailmaster
March 13, 2015
Offline
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?
2:30 pm
Club Member
April 10, 2015
Offline
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 . . .
Buck & Katie
3:23 pm
Club Member
March 5, 2015
Offline
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
Dale Clement
5:46 pm
Club Member
February 26, 2014
Offline
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.
6:29 pm
Club Member
April 10, 2015
Offline
Here's a nice response I got from the guy who runs howtocbradio.com:
Buck & Katie
10:26 pm
Club Member
July 14, 2016
Offline
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.
Jeff and Kathy Root
9:57 pm
March 23, 2025
Offline
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 !
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