Pulling my hair out! HIGH SWR on my TJ's bumper mounted CB antenna - Jeep Wrangler Forum
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Old 03-25-2011, 09:47 PM   #1
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Pulling my hair out! HIGH SWR on my TJ's bumper mounted CB antenna

I don't know what else to do here. I have a standard Firestick tunable tip Antenna and a brand new Midland. I'm getting SWR readings across the board of 4 to 4.5. I tried a different coax, ground all paint off for the mount, made sure everything is just as it should be and no matter what, I can't get the DAMB SWR to come down? Its mounted right to my stock TJ rear bumper.

Is it possible my Frame and body are not grounded with each other???

I am seriously about to go crazy!!

Any ideas would be GREAT!!!!!

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Old 04-08-2011, 11:44 AM   #2
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yep could be no ground to your bumper ,run separate ground to your mount, its really a bad idea to put a antenna so close to the body of the vehicle but everyone one doe's it ,some get the sw's down some can't . i used a roof mount with a 2 ft wilson silver load and a spring , no problems on the trail . try re-grounding i'm sure you'll work it out . i use my roll bar as the ground plane ,works great

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Old 05-13-2011, 03:19 PM   #3
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Few questions:

How are you measuring the SWR? Does your radio have a meter on it?

The first thing I'd do is disconnect the radio & antenna and set it up in your driveway at least 15 feet away from big metal objects. Hook it up just as if it were in the truck. Run wires to your battery or run it from a big 12v power supply if you have one.

If the SWR is still high, you can probably eliminate the truck's grounding from the list of possibilities. What impedence output does the radio have? 50 Ohms? 75 Ohms? This number will affect the type of co-ax you use for the antenna.

Let us know those specifics and we can help more. I could see a metal bumper de-tuning an antenna to 1.5 or 2 on the SWR, but in order to get a 4 to 4.5 there's got to be more going on.
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Old 05-13-2011, 03:56 PM   #4
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Got any pictures (close up) of the antenna set up?
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Old 05-14-2011, 01:30 AM   #5
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the fire stick is not so hot of an antenna ! wilson silver load is a MUCH better antenna . i don't know why eveyone here swears on the Firestick . its a low cost low grade antenna .... anyway.. make sure your grounded to the frame ,keep the antenna away from the body of your Jeep and you mite have to move your antenna to your spare tire mount . i use the Wilson 1000 and have talked to Australia from New Jersey with my STOCK Radio Shack TRC-453 and 465 . other contacts include - England , Belgium , Falkland islands , Baffin Bay north pole and Germany . a good antenna ground is very important . some antennas have a wire with a round STA-CON connector , don't use it for the ground tape it to the stick
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Old 05-14-2011, 01:36 AM   #6
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Quote:
Originally Posted by AC0QR View Post
Few questions:

How are you measuring the SWR? Does your radio have a meter on it?

The first thing I'd do is disconnect the radio & antenna and set it up in your driveway at least 15 feet away from big metal objects. Hook it up just as if it were in the truck. Run wires to your battery or run it from a big 12v power supply if you have one.

If the SWR is still high, you can probably eliminate the truck's grounding from the list of possibilities. What impedence output does the radio have? 50 Ohms? 75 Ohms? This number will affect the type of co-ax you use for the antenna.

Let us know those specifics and we can help more. I could see a metal bumper de-tuning an antenna to 1.5 or 2 on the SWR, but in order to get a 4 to 4.5 there's got to be more going on.
but you'll still need a ground plane and i don't think he's using antenna wire for a house antenna , 50 ohms and 75 ohms ? you lost me with that one . isn't MINI the most common coax ? 50-75 ohms you still got me stumped with that one ?
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Old 05-14-2011, 02:23 AM   #7
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Originally Posted by hookuspookus View Post
yep could be no ground to your bumper ,run separate ground to your mount, its really a bad idea to put a antenna so close to the body of the vehicle but everyone one doe's it ,some get the sw's down some can't . i used a roof mount with a 2 ft wilson silver load and a spring , no problems on the trail . try re-grounding i'm sure you'll work it out . i use my roll bar as the ground plane ,works great
I have my willy 1000 mounted with a roof mount and i'm also useing my rollbar for my ground plane also its a LITTLE noisey in the brush but i like it ! has anyone tryed the Van Ordt 5/8 wave quad wound ? thats a smoking stick also .
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Old 05-14-2011, 02:25 AM   #8
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isn't Cb coax 50 ohms ?
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Old 05-14-2011, 11:00 AM   #9
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Yep as far as I know CBs are 50 ohm and so you'd use 50 ohm coax (like RG-58). But I don't want to make any assumptions and possibly miss the source of the problem!

A whip antenna over a "perfect" ground plane will have an impedance of about 35 ohms, which is close enough to get the SWR down to 1.5 (as long as your radio & coax are 50 ohm). If you tilt the antenna horizontally or get it close to large metal surfaces other than directly below it, the impedance drops to as low as 10 ohms. This sure would result in a high SWR!

You're right that locating the antenna away from the vehicle wouldn't provide a good ground plane (only the earth, which is so-so), but it sure should be good enough to get the SWR below 4, so long as the feedline is right.

But the first thing to check is that the radio & feedline are matched! Once you know that, then you can start relocating the whip for better SWR : )

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