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Old 08-07-2010, 06:04 PM   #1
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High SWR

Alright, I've got a 102" steel whip mounted onto a horizontal light bar (also holding four 100 watt floodlights) which is mounted onto a chrome roll bar which is mounted in the bed of my truck. Knowing that the bed is made out of that plastic material, I grounded (with solid copper wire) the roll bar to the chassis, and then I ran a ground wire from the light bar and coax connector to the chassis, without the antenna or hot line of the coax being grounded. The radio I'm currently using is a Connex 4600 Turbo, which is also grounded well. I've made sure there's no paint or anything keeping me from getting a good ground too. I'm using just enough coax needed from the antenna to the radio, but I have tried one 18' line as well, just to check. My problem is my external meter is showing I've got a standing wave of at least 2. I'd love to have it down around 1.4 or lower. I was previously using a Superstar 121, which also was giving me a SWR of 2-3. I've tried just about everything I can think of. I've covered up the roll bar and lights from causing a high SWR, I've tried different antennas and different lines too. The base of the antenna is even with the top of my truck, and there's nothing else around to interfere with the signal. Is there some interference from the truck's computer system or something else I haven't thought of? Thanks.
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Old 08-07-2010, 06:14 PM   #2
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Swr

try shorting whip half inch at a time or u may need to make it longer depending on what frequencies u are on .
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Old 08-07-2010, 08:31 PM   #3
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try removing the ground that's connected to the coax. if the bar is grounded good and the mount is connected to it, that should be well enough for the ground. you could possibly be grounding out the signal.
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Old 08-08-2010, 06:02 AM   #4
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swr

High swr has nothing to do with grounds if your coax is in good shape then u must adjust antenna as needed you could also try antenna analyzer or tuner.
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Old 08-08-2010, 06:09 AM   #5
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Check the SWR on Ch 1 and on Ch 40 or whatever CB has these days, this will let you know whether you need to have a longer or shorter radiator (antenna). If SWR is better at lower channels then your radiator needs be longer and visa versa at the high end. Hopefully you can loosen the set screw and be able to pull the radiator out and push it in.
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Old 08-08-2010, 04:06 PM   #6
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I've tried taking off some grounds, adding them, and using different lines. My antenna doesn't have any set screws, so I can't adjust it up or down. As for my SWR, it's the same at 1 and 40, ranging from 1.8 to 2.1. I hooked my radio into my base antenna today and the SWR dropped flat-now if I could just get that on my antenna. I also tried some others antennas and coax lines, but the SWR stayed the exact same.
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Old 08-08-2010, 04:22 PM   #7
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I'd say you're mounting is just not going to work, is there anyway you can move it to the rear bumper?
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Old 08-08-2010, 05:04 PM   #8
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It's almost funny if you knew all the different things I've tried the last two days, without any luck. I'm going to have to move it and try that I guess.
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Old 08-08-2010, 06:15 PM   #9
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That is exactly what is needed...if you tried different antennas and another coax...the "Mounting area" is your problem......Move onto another area and good luck..
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Old 08-08-2010, 06:42 PM   #10
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RF is a funny thing, what works great one place it doesn't work at all the other and that's what makes it fun. When you feel like you want to learn more go for you ham license, it's easy to get and you'll learn more about radios and stuff. Here's a website you can take the tests on http://kb0mga.net/exams/index.php, the entry is the Technician Class.
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Old 08-09-2010, 03:55 PM   #11
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Ok, I finally got my hands on a Wilson 5000 from a friend of mine. I set it in the dead center of my roof (magnetic), and connected its line into my own. Results: High SWR gone! So I've come to the conclusion that somewhere, somehow, the way the truck is layed out, I'm just not getting the "right" ground to make everything click. I'll keep experimenting for a while until I find that "sweet spot", but for now, the 5000 will work for me. In fact, by keeping my whip in its same place, the SWR was lower. Thanks again for all the ideas!
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Old 08-09-2010, 08:40 PM   #12
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I just went to get a new Wilson 5000 (magnetic). The guy who runs the shop has installed mobile units for years. He said any antenna installed on a light bar like mine won't work because the RF will travel down the bar each way. It doesn't matter how many grounds you put on, the interference will just be too much. So, I've put the 5000 on my roof and run its coax back to my old line. I'll take the whip off in a few days, but in case anyone else has a problem like this, I'll put up a photo so you can see the layout.
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Old 08-10-2010, 04:31 PM   #13
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Ah, resolution at last! It looks like it all to do with the ground plane! Good job and in being persistent!
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