CB antenna coax length

[alia176]

It's hard to argue against Firestick's FAQ but you can see where this came from:

http://www.firestik.com/FAQ.htm

Q Is the length of the coax cable important?
A We find that it is very important ... especially with high performance top-loaded antennas. Your safest bet is to use 18 feet (5.5 meters) coaxial leads on all of your CB installations.

Q I only needed 9 feet of coax to go from my radio to my antenna. How should I handle the excess?
A What ever you do, do not roll it into a small convenient coil. It will become an RF choke. If you cannot let it lie loose under a seat or in a headliner, wrap it into a yarn-like skein of about 12 to 16 inches, put a wire tie in the center and tuck it under your dash, seat, etc.

 

[george_tlc]

It's hard to argue against Firestick's FAQ but you can see where this came from:

http://www.firestik.com/FAQ.htm

Q Is the length of the coax cable important?
A We find that it is very important ... especially with high performance top-loaded antennas. Your safest bet is to use 18 feet (5.5 meters) coaxial leads on all of your CB installations.

Q I only needed 9 feet of coax to go from my radio to my antenna. How should I handle the excess?
A What ever you do, do not roll it into a small convenient coil. It will become an RF choke. If you cannot let it lie loose under a seat or in a headliner, wrap it into a yarn-like skein of about 12 to 16 inches, put a wire tie in the center and tuck it under your dash, seat, etc.

Yep, CB is special and needs special cable and lengths.

It is much more sensitive to cable length than our HAM stuff. Lucky for us that the HAM frequencies are not in the CB range otherwise we would need to bring along a lot of different cables (each cut to 1/2 wavelength). The CB frequency also strangely circumvents some laws of physics and its radio waves travel at the speed of light through the coax. This is fortunate otherwise the cable length would need to be changed depending on the type of coax in use rather than be able to just use 18' all the time. It would also mean that CB coax suppliers would need to provide coax cut different lengths other than 18' and that would confuse the poor customer. Yep, lucky that CB RF travels at the speed of light in coax unlike other RF signals.

Though when I use my HF gear that unfortunately on some bands does get close to the CB frequency I have to unplug my coax feed and replace it with specially cut lengths appropriate for the frequency/band I'm using. It's a real pain to have to carry a selection of different coax lengths.



cheers,
george.

 

[Cruiserdrew]

Yep, CB is special and needs special cable and lengths.

It is much more sensitive to cable length than our HAM stuff. Lucky for us that the HAM frequencies are not in the CB range otherwise we would need to bring along a lot of different cables (each cut to 1/2 wavelength). The CB frequency also strangely circumvents some laws of physics and its radio waves travel at the speed of light through the coax. This is fortunate otherwise the cable length would need to be changed depending on the type of coax in use rather than be able to just use 18' all the time. It would also mean that CB coax suppliers would need to provide coax cut different lengths other than 18' and that would confuse the poor customer. Yep, lucky that CB RF travels at the speed of light in coax unlike other RF signals.

Though when I use my HF gear that unfortunately on some bands does get close to the CB frequency I have to unplug my coax feed and replace it with specially cut lengths appropriate for the frequency/band I'm using. It's a real pain to have to carry a selection of different coax lengths.



cheers,
george.

10-4 Good Buddy

LOL

 

[ntsqd]

FWIW I bought a Firestick 2M antenna and vehicle specific mount for our CTD. Never got the SWR under 3:1. Tried all of the usual tricks to no avail. Gave up, built a post mount and put a 1/2 wave base loaded Larsen on top and got 1.7:1 after trimming the whip to the package's recommended length for the freq that I use the most.

Makes me pretty suspicious of any tech there.