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Unread 05-16-2013, 09:46 PM   #1
Rproject
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CB antenna warning?

Since this is a multi-generational question, I felt it best to ask here.

I have a Cobra 29LX with a 4' Firestick. Worked perfectly the first time I went out, then about half way through the day I started getting an occasional "CB antenna warning" error on my display. I believe it was still working fine as I could hear others just fine.

Fast forward to today, I'm getting ready to head out tomorrow so I decided to fire up the CB again and check my SWR readings. Every time I key the mic I get the antenna warning. The firestick is mounted with a spring to a conical base that's plastic with a grounded core. The mount location is my spare tire carrier (I know, not the best ground, but it's what I've got to work with). At any rate, my SWR readings are all under 1, on channel 1, 20 and 40. I did adjust the antenna slightly and the warning is now intermittent, but still there.

Thoughts? Could it be my ground? I like my mounting location and would really hate to have to change it. I could possibly run a 12awg or 16awg jumper wire from the tire carrier to the interior of the tub to really ground the carrier if that would help.

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Unread 05-16-2013, 10:12 PM   #2
KG7IL
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When you say that the SWR is under 1 ? I am not sure what you really mean.
1:1 ~ 1 is the best you can do. Normally you will find it above this, more like 1:2

Also, check on CH1 , CH 20 and CH 40 and post the results.
You should see some difference as you move up in frequency.

If you are getting 1, then I think that meter is bad or it is being operated incorrectly.
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Unread 05-17-2013, 06:32 AM   #3
Rproject
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On the 29LX, there is an SWR calibration. Which I performed according to the instructions. Once calibrated, when you key up the mic, you can see the SWR signal on the display. When inside the garage, the SWR reading is about 2.7-3, so I know the display is working. When I back out, the SWR reading barely moves. I maybe goes to 1.2 or 1.3, but not even close to 1.5.


Late last night I did put an 18awg (because it was the wire I had handy), jumper from the spare tire mount to the rollbar. The antenna warning went away for 90% of the transmissions. I'm thinking I'm going to have to make a nice grounding strap on the inside of the tailgate to the tub so the tailgate is solidly grounded to the tub.

Here is the 29LX display:
29lx_amber_lg.jpg  
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1996 White ZJ
1987 Maroon YJ (sideways build)
1996 Forest Green XJ

The "sideways" build thread: http://www.jeepforum.com/forum/f22/r...hread-2164793/
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Unread 05-17-2013, 08:36 PM   #4
SteveBad
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Correct.....you should have a separate wire which grounds the tailgate to the tub.
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Unread 05-17-2013, 10:52 PM   #5
Rproject
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I'm going to get a nice, 1/2", flat, braided, grounding strap and attach it to the inside of the tailgate then to the tub. That should make me well grounded.
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1996 White ZJ
1987 Maroon YJ (sideways build)
1996 Forest Green XJ

The "sideways" build thread: http://www.jeepforum.com/forum/f22/r...hread-2164793/
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Unread 05-21-2013, 06:37 PM   #6
Rproject
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Problem solved. Internal to the unit, a rheostat needed to be adjusted. Cobra walked me through it. Everything was fine in the install end, the unit was properly tuned from the factory.
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1996 White ZJ
1987 Maroon YJ (sideways build)
1996 Forest Green XJ

The "sideways" build thread: http://www.jeepforum.com/forum/f22/r...hread-2164793/
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