Cannot ground CB antenna

[Clown]

I am trying to install a CB in my 2004 pilot. I bought a Cobra 75 CB radio, which has all the controls and displays in the handpiece, and only a small box about the size of a cigarette box to mount under the dash or seat. I picked under the seat, and wired up the radio. So far, so good.

All CBs have the same power, so the most important thing is a good antenna. I've tried on-the-glass antennas before, but since they lack a groundplane, they don't perform well, you can hear, but transmission range is very very short. I don't like magnet mount antennas, they look tacky. When I've used them in the past, I've had magnet mount antennas fly off at highway speeds as well as get stolen. I wanted to do this job right with a good antenna.

I got a bracket for the antenna that I screwed into the rear hatch jamb and a good antenna. I got decent reception. Next step: trim the antenna in order to tune the SWR so as to maximize transmission performance...

I hooked up an SWR meter, and got a reading off the scale. Such a high SWR reading indicates that the antenna is not properly grounded and transmitting can damage the radio. I scraped off a little paint so that the antenna mount would be grounded but it didn't help.

I went to a truckers' CB shop for help. The mechanic first tried swapping out his own antenna, that didn't help. He verified that paint wasn't preventing ground. He swapped out his own connectors and antenna cable and used his own CB plugged into one of the accessory outlets. Nothing helped. So now, the only part that is the same is the mounting bracket. That means that the problem MUST be a poor ground; although I would think that metal screwed into the rear quarter panel of the vehicle would be a decent ground. He attached a wire to the antenna bracket and and tried grounding it all over--the screws holding the taillights, the child car seat brackets, even the trailer hitch before giving up.

So now I'm stumped. I can't understand why I can't get a good ground. Any ideas???

[N_Jay]

1) You sure the SWR meter and jumper cables are good?

2) How is the radio grounded?

What model radio is it?

[Clown]

1. I used my SWR meter and jumper cable, the trucker CB shop guy used his equipment. In fact, eventually everything but the antenna mounting bracket was his--we were using his radio with a cigar plug, his antenna cable, his antenna, and his antenna coupler. That leaves the antenna mounting bracket as the single variable.

2. My CB is a Cobra 75 WX ST, here is a link to a picture of one:
http://www.walcottcb.com/images/prod...XST/75WXST.jpg
There are a couple of old threads on this board of others who have installed this model radio in their pilots.

3. I grounded the radio with wire secured to one of the metal supports behind under the dashboard. The radio will turn on, receive, and transmit; but with SWR of 5 or greater. I also tried moving the radio ground wire to another location, no improvement. I think I can exclude improper grounding of the radio itself, since the CB shop guy used his own CB powered with a cigar plug (positive and negative wires from the radio go into the plug, which is connected to the factory-wired accessory outlet), but still had high SWR.

This problem vexes me...

[N_Jay]

Try grounding teh radio box.

the power leads might be a little long, hoverer I have general never had a problem with CB because the frequencies are so low.

Did you change out the antenna cable also?

[rocky]

I have that CB radio in my offroader with no problems on signal strength or ground.

Try this. Get a wire with crocodile slip at either end. Clip one on on to the mount and the other on to a different section of metal eg where the trailer wiring connector is located by the tailgate.

Now what happens to the SWR reading?

[whizmo]

I'm voting that you have some issue where your ground of the chassis of the radio is good enough for 12V DC, but not good enough for RF. I'd find a different ground for the radio.

- Mark

[macphanatic]

Originally Posted by rocky

I have that CB radio in my offroader with no problems on signal strength or ground.

Try this. Get a wire with crocodile slip at either end. Clip one on on to the mount and the other on to a different section of metal eg where the trailer wiring connector is located by the tailgate.

Now what happens to the SWR reading?

Exactly what I was thinking.

[Clown]

I'm still confused.
I tried moving the radio box's ground. The idea of a ground good enough for electrical continuity, but not good enough for RF sounded promising, although the fact that the radio technician's CB had the same problem when using an accessory plug for power and ground argued against it. Nevertheless, I tried and had no improvement.

I tried using jumper cables from the antenna bracket to other locations on the car to find a better grounding site including the towing hitch and various screws and bolts, no dice.

I tried connecting a magnet mount antenna instead of the permanent mount that is giving me so much trouble, and still had a very high (>5) SWR!!!! This is the most telling test. It means that the antenna and its mount are not the problem. The radio ground is not the problem. Since the technician used his own radio, I know that the radio is not the problem. The only variable left is the car! For some reason, my Pilot will not provide an adequate ground for radio transmission!

For the other folks who have installed two-way radios, did you ever measure the SWR, or simply assume that since you could hear and transmit then everything was OK? Am I the only one with this weird problem???

Any ideas? Anyone? Anyone?