CB antenna warning on lower channels
 

I, I just installed a Cobra 29 LX with a Firestic II. When the vehicle is off I don't get any antenna warning throughout all channels. When I start the vehicle I get an antenna warning from channel 19 and below. The CB is wired directly to the battery and grounded to the firewall. The antenna is mounted on the rear tire carrier and I ran a ground wire to the frame. I checked the SWR and it is around 1 on channel 40, 20 and 1. Confused. Why would I be getting a warning when the vehicle is running and only on the lower half? Thanks for the help.

Sounds like you did a good job on install. How and where did you route the coax cable?

Sometimes if the coax is run alongside of the Jeep's wiring harnesses they can trade off some unwanted RF. Typically it is the Jeep that complains when you start talking on the CB.

What did you use to measure SWR?

I did run the coax next to the wire harness. I'll have to change that. I used the SWR that is part of the CB. Thanks for the info. Hopefully I'll get to change it later today and see if it works.

Also, it's helpful to run the extra coax in a serpentine random pattern between the CB and the antenna. Rolling or looping the extra will kill off a lot of range. I don't really understand radio or antenna theory, but I've experienced this after being given this advice by others. I had the extra zip tied on my work truck and the range was awful. I changed the lay and greatly improved the range. Weird...

Ok. I rerouted the coax. The only area that it is near the jeep wires is where it is routed in the tailgate. Still getting the warning when the jeep is running. Hmmm

Also, the 18' coax is spot on when running from the spare tire to the front where the CB is mounted.

I don't know what an "antenna warning" is supposed to be, but I would think the radio manual should give you something specific about it.

With the engine on there will be more voltage, however slight, to the radio. The radio will produce slightly more output power. Thus, if there is a little bit of reflected power with the engine off, there will be a little bit more with the engine on. That little bit more is apparently enough reflected power to create the "warning".

Your antenna should have some type of adjustment to correct for the reflected power. Since channel 1 is lower in frequency than channel 40, then antenna should be just a little bit longer (either mechanically or electrically) to reduce the reflected power.

Good luck -

Ok. I'll lengthen a bit a see if that works. I wish the book had a troubleshooting area for the warning that it is telling me but it doesn't. Thanks for the info, I'm going to try it now...

When you measured SWR and tuned your antenna was the Jeep running, all doors closed, cap on the antenna and in an open area?

Yup all of the above. I lengthened to the point where I started losing on the upper end. Now it's good from 15-40. Maybe the ground wire isn't heavy enough? I used monster cable speaker wire(all I had at the moment). Maybe a regular ground strap?