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Old 05-11-2016, 07:47 PM
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High SWR, Please check my toubleshooting

Finally getting around to installing my Antenna. Radio's had been in for months.

Anyway antenna (Wilson Flex 4)is mounted to my tire carrier. Even though the carrier has a good ground reading I ran an addition 14 gauge wire from the carrier to the frame, removing power coat/paint prior to hooking it up. I figure everything is golden, wrong.

SWR is over 3, higher on 40 than on 1. Removed the adjust pin on the antenna, improved a little but still over 3. Rechecked ground, good all the way back to the battery. Center conductor can't touch ground as I made a plastic bushing to keep it off metal and tested, no short. Tried a different coax, same reading. Tried a different radio, same reading. Thought maybe a bad SWR meter but I think it is ok as I have blown a fuse or 2 in the process.

So unless I have some really bad luck with 2 bad radios, 2 bad coax's it has to be the ground plane or the antenna itself. I'm going to pick up a couple of grounding straps this even and make sure I have a great ground.

What do you all think?

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Old 05-11-2016, 09:49 PM   #2
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How about a couple well lit close up pics of the top and bottom of the antenna mount, where it attaches to its mounting bracket.

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Old 05-11-2016, 10:51 PM
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Will this work Jerry



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Old 05-11-2016, 10:56 PM   #4
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Click image for larger version

Name:	image-2078676008.jpg
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ID:	3029617 Mount should look like this. FWIW: I ran an 8 gauge wire to ground my antenna on my truck, didn't need it on my Jeep. Did you clean the powder coating off your mount?
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Old 05-12-2016, 12:41 AM   #5
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Quote:
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Will this work Jerry



That mounting job looks as good as it gets. Too bad there wasn't something obvious a second set of eyes could spot.
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Old 05-12-2016, 12:51 AM
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Well I will try and improve the ground. About all I can think of at this time.
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Old 05-12-2016, 12:59 AM   #7
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Any pinches in the cords? Are you wired straight to battery? Are all your doors and windows shut when checking SWR?

Just throwing out ideas...
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Old 05-12-2016, 01:24 AM
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Actually the radio that I plan to use is wired into my Spod. ANd when I checked it using the other radio it was hook straight to the battery. Same readings regardless of radio. As I said I also tried another coax and still no joy.
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Old 05-12-2016, 10:51 AM   #9
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Quote:
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Actually the radio that I plan to use is wired into my Spod. ANd when I checked it using the other radio it was hook straight to the battery. Same readings regardless of radio. As I said I also tried another coax and still no joy.
I had the same problem when I installed my radio. Turned out to be a ground problem.
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Old 05-12-2016, 12:16 PM   #10
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Keep in mind that there's a huge difference in the RF ground an antenna mount requires and a simple DC ground that something like a light bulb requires. A DC ground can be provided by a simple wire, an RF ground requires more surface area so a simple wire is not going to be enough.

Grounds with sufficient surface area to provide a proper RF ground require sufficient bare-metal-to-bare-metal contact for mounting brackets to what they're bolted to. And what they're bolted to has to have a similar good large surface area to the tub or chassis. It's difficult for tail gates to have sufficient RF ground ability so it's often necessary to provide that ground via a braided ground strap that connects between the tail gate and tub or chassis.

Having a good RF ground for the antenna mount is critical to having a good low SWR. Grounding the mount via a common gauge wire won't usually do it. RF only travels along the surface of a conductor so if that conductor doesn't have sufficient surface area, the RF sees a lot of resistance. That why when a normal large surface area metal-to-metal ground can't be provided, a braided ground strap can be used since it offers a lot of surface area for the RF signal to travel along.
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Old 05-12-2016, 07:55 PM   #11
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You might try disconnecting the coax from both the radio and the antenna and checking for a short between the center conductor and the shield.
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Old 05-12-2016, 08:22 PM   #12
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You might try disconnecting the coax from both the radio and the antenna and checking for a short between the center conductor and the shield.
Good suggestion but he already tried a different coax and got the same readings with it.
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Old 05-13-2016, 02:25 AM
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After reviewing all you guys have said plus talking to my radio guy and the better part of the day to correct it is complete.

First the ground, all of you are correct it is not good enough. And according to my radio guy grounding to the frame is not optimal. The body has more surface area so it makes a better ground plane than the frame. His words not mine but it makes sense, here is what I did.

I removed the mounting plate for my carrier to gain access to the inside of the tail gate. I then remove the paint and connect one end of the ground strap to the gate.



I then reattached the cover plate threading the ground strap through a slot in the plate. I removed a power coating from behind one of the bump stops and attached the other end of the ground strap under the stop.



I did put shrink tubing around the strap to keep it from scratching the paint up. Also if you do something like this don't forget to paint over any exposed sheet metal after you have attached the strap.

As we all know the tail gate is not a good ground so I didn't stop there. I added a second ground strap running from the tail gate to the body. I did this through the existing wire run covering the strap with shrink tubing again to prevent it from chaffing the existing wiring.



After everything was buttoned up the SWR had come down to under 3 across the board, 40 still higher than 1.

The antenna I am using is a Wilson Flex 4. According to my radio guy this are very long electrically. The top has a brass fitting about 2 inches long with a slide pin that will make it another 2 inches long. I removed the pin and it got a little better. After that I started grinding down the brass fitting, getting better every time I did. I basically too the brass fitting down to the shrink tube, removed over an inch. The end result is an SWR of 1.1 or less across all channels.

Now just to find some on the radio. Thanks for every ones help.

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