CB Radio with new antenna - SWR Alert?

Question

I have recently baught a new Galaxy DX 949 CB radio and used it with my old CB antenna and it worked fine. Today, I recieved the Wilson 500 antenna that I ordered. I went to tune the antenna, using the instructions provided with the antenna. They said to hook everything up, close the car doors, make sure the antenna is level and away from power lines and so I did. The tuneing part of the instructions said to check the SWR on channel 1 and on channel 40 and if it is higher on 40 than on 1 to take off 1/4 inch of whip. The SWR readings on 1 was about 3.1 and on channel 40 it was about 3.2. I removed about a quarter inch off the top of the antenna and it seems to be the same and the SWR alert light comes on. (When SWR is above 3.1) Why is my SWR so high on a brand new, top of the line antenna? Am I tuneing it wrong?

Answer 1

An SWR over 3:1 indicates a short.  Double check your coaxial connectors to make sure stray strands haven't contacted the center conductor.  Also double check that your antenna mount is proper, again not making contact between the chassis and the antenna connection itself.

Something that also seems to be missing from CB documentation is that the coaxial cable should be exact multiples of the center frequency (Ch 19) half-wavelength.  In between the multiples adds to SWR.  Also, coiling excess coax tends to act as a pisspoor antenna, which further creates nasty SWR.  Pinched coax is another problem.

If the antenna is a magnetic mount, it has to couple THROUGH the paint in order to make good electrical connection.  Ideally, a CB antenna should be ½ wavelength, but that's so long that it's impractical.  So it's half the length or ¼ wavelength and relies on the car's body to reflect the other ¼ wavelength needed for ideal transmission.  Move the antenna, if necessary to improve your SWR, to the flattest part of the surface.

New antennas are deliberately made long to give you room to accommodate YOUR system's other factors such as I mentioned.  Trimming the antenna down as necessary is a lot easier than trying to add to it.

But first get your system a lot closer to an SWR reading of 2 by checking the other factors.  And THEN trim the antenna for ideal length.