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Old 09-02-2012, 02:10 PM   #1
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Need help with SWR

Hi
I am in the process of installing an CB into my 98 TJ. I have a Uniden pro 510XL. I am using the antenna and coax cable from the PO. The cable is radio shack rg58 and I believe the antenna is a 36" firestik 2. I am not sure how long the cable is but is probably 12-18ft long. I would have to pull it out to measure which is not easy task.

The antenna is directly mounted to the rear bumper.

The best SWR reading I can get through adjustment is 2.0 on ch 20 and about 2.4 on 1 and 40.

I am thinking that I cannot get it better because the antenna is too short and mounted too close to the back of the Jeep.

Is the best I can expect with this setup? Any suggestions?
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Old 09-02-2012, 04:54 PM   #2
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Double check your coax with an Ohm meter, center point to center point, center point to collar (this should be open), collar to chassis.

Probably as good as it gets without going up, or mounting to the front bumper.

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Old 09-02-2012, 05:48 PM   #3
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Quote:
Originally Posted by BlueRidgeYJ
Double check your coax with an Ohm meter, center point to center point, center point to collar (this should be open), collar to chassis.

Probably as good as it gets without going up, or mounting to the front bumper.
Hi thanks for the response. I checked continuity and all seems good.

I was thinking of raising the antenna with an aluminum rod threaded on both ends to receive the antenna and mount to the existing stud.

With the SWR that I have now, will I be able to communicate with others on a trail ride? I don't plan on using it for anything else?

Thanks
Scott
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Old 09-02-2012, 06:20 PM   #4
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If you tuned the antenna for whatever channel you use and got it to 2.0 or less, yes you could use it on the trails just fine. I wouldn't use it over 2.0. You will of course have a slightly lower range at 2 than say 1.3, but nothing too big. It's something like a 1/2db gain.

2.0-3.0 indicates a bad ground plane or bad coax conection typically, and your coax is good. Adding an extension on the antenna would lengthen your antenna, both in the obvious sense and in the mechanical sense. I can't really see how this would correct the issue, but adding length to some groundplane issue antennas can be a solution in some circumstances, if I remember right. That may only apply to NGP antennas though, I'm not sure.

The highly unpopular 108" would help. Ideally 60% of the antenna is above the roof line.

Maybe your mount isn't grounding due to being mounted on paint? (If you check continuity from radio side coax collar to common chassis it should show this, but won't really show how good of a ground it is)

Sorry, I'm not the smartest dude round here when it comes to antenna theory and application. Glad to help where I can.
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Old 09-02-2012, 06:34 PM   #5
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Quote:
Originally Posted by BlueRidgeYJ
If you tuned the antenna for whatever channel you use and got it to 2.0 or less, yes you could use it on the trails just fine. I wouldn't use it over 2.0. You will of course have a slightly lower range at 2 than say 1.3, but nothing too big. It's something like a 1/2db gain.

2.0-3.0 indicates a bad ground plane or bad coax conection typically, and your coax is good. Adding an extension on the antenna would lengthen your antenna, both in the obvious sense and in the mechanical sense. I can't really see how this would correct the issue, but adding length to some groundplane issue antennas can be a solution in some circumstances, if I remember right. That may only apply to NGP antennas though, I'm not sure.

The highly unpopular 108" would help. Ideally 60% of the antenna is above the roof line.

Maybe your mount isn't grounding due to being mounted on paint? (If you check continuity from radio side coax collar to common chassis it should show this, but won't really show how good of a ground it is)

Sorry, I'm not the smartest dude round here when it comes to antenna theory and application. Glad to help where I can.
I made sure the area where the stud went thought the bumper was sanded down to bare paint. I don't know know good the ground is through the bumper but I checked continuity at the front of the jeep if that matters.

I was thinking of raising so less of the antenna is blocked by the side of the jeep. Not sure if it would help but I have read that having it higher is better.

I could always mount it somewhere different. It was put there by the PO
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Old 09-02-2012, 06:41 PM   #6
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Sounds like a good ground.

Raising the antenna would be the easiest solution to improve the swr, that or mounting to the front bumper with a quick disco...

You just want to raise the whole antenna, mount and all. Just lengthening the shaft changes the frequency resonance of the antenna. Higher is alwas better, and it is the lack of groundplane AND the proximity to the tailgate that makes it so tough.
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Old 09-02-2012, 07:38 PM   #7
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Quote:
Originally Posted by BlueRidgeYJ
Sounds like a good ground.

Raising the antenna would be the easiest solution to improve the swr, that or mounting to the front bumper with a quick disco...

You just want to raise the whole antenna, mount and all. Just lengthening the shaft changes the frequency resonance of the antenna. Higher is alwas better, and it is the lack of groundplane AND the proximity to the tailgate that makes it so tough.
Good point on the height. I didn't think of that. I am going to try to run a ground wire to the chassis and see if it helps

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