Cb help

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rtguy1

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I installed a cobra 75. It's grounded to the battery. Ran my cable back under the carpet and through the vent on the gate. The insulating washers are installed facing the mount. I'm getting swr readings above 3. Any tips here of what may be wrong? I ran a separate ground to see if that was the issue and no luck. I have a 4' firefly antenna with a quick disconnect and spring.

View attachment 29235View attachment 29234
 
Try a better ground for the antenna and also check to see what the cable is running next to in the carpet.

Edit: how did you run the separate ground because I don't see it in the picture?
 
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Lol..I have it running next to some wires in one spot. Is that the issue?
I attached it to the bracket and then down to the frame. I removed it after there was no change in the readings
 
I had a similar problem with a teraflex antenna mount on the stock tire carrier. It was a bad ground on the antenna mount (I had added an extra ground wire from tub to tailgate per a Project JK write up on a CB install but still had a high swr reading). The problem was the ground of the bracket. I had to scrape of paint round mount bracket and use star washers to bite thru the paint - this did the trick. You can check the ground using an ohm meter between the frame and mount, see this Right Channel CB resource sight for how to check for ground: http://www.rightchannelradios.com/testing-for-a-ground-cb-installation.
 
I never have had a problem running next to wires, but I have read of other people having weird issues that they couldn't pin down and then, when they re-routed away from power wires, everything was fine.
 
I'm thinking when I drilled out my bracket I didn't make it 1/2". So it may be possible that the bolt is touching the bracket. The nylon washers that have the raised portions and face the bracket on both sides are supposed to sit down in the mounting hole, correct? This prevents contact between the bolt and the bracket where it passes through? I hope that makes since...lol. I've been up over 24 hours....lol. If you look at the pic the raised nylon portions of the washers are resting on top of the bracket, not seated inside the hole
 
rtguy1 said:
I'm thinking when I drilled out my bracket I didn't make it 1/2". So it may be possible that the bolt is touching the bracket. The nylon washers that have the raised portions and face the bracket on both sides are supposed to sit down in the mounting hole, correct? This prevents contact between the bolt and the bracket where it passes through? I hope that makes since...lol. I've been up over 24 hours....lol. If you look at the pic the raised nylon portions of the washers are resting on top of the bracket, not seated inside the hole
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the nylon washer raised portions should be facing each other in the hole - are they touching each other?

That looks like the TF spare tire mount...is it powder coated? if you run a ground from the mount to the frame, make sure it's not on a painted surface

is your radio properly grounded?
 
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ok one problem i see is that you have the plastic washers on top and bottom of the mount for the antenna, you should only have a plastic washer on top and a star washer on the bottom to ground the cable to the mount. also check bolt holes for paint, might be an interruption in grounding. i have my coax cable running next to my main wiring harness on the passenger side and with no carpet throughout the jeep it just sits on the metal tub and i haven't had any issues over the last year running it this way. if it continues to act up just bring some extra wiring incase we need to make a ground strap and we will get u all fixed up on saturday morning, unless you are free before i head up to Gorman at 2:30pm tomorrow?
 
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ant-mount.jpg

stud-washer-1.jpeg
 
You're going to need to drill the hole to 1/2" to keep the bolt from touching the mount and to get the nylon washers to fit properly. At 1/2" the nylon washers shoulders will fit snug in the hole. Also the Teraflex hinge should be grounded ok, as with mine I have no ground strap I get a SWR of 1.45. But if you want to run a ground strap you need to use a flat braided cable not just a piece of 12 volt wire. Also you could try removing the spring and try to see if that makes a difference.
pic of mine:
HDc6kEs.jpg
 
CombatVetJK said:
ant-mount.jpg

stud-washer-1.jpeg
Click to expand...

Combatvet is right on the money here, all I would add is make sure you mount and ground to the body not spare carrier and ditch the alloy bracket, look for a quality suitable mount or use half a mirror mount in the same way as Combatvet and clean away the paint to get a good ground. The body of the Jeep also forms part of the antenna so good connections are essential to put a signal out get it wrong and you'll burn out your transmit chips.
i can't tell which make of spare carrier you have but some have PTFE bearings which can insulate the carrier from grounding, a high SWR reading can be either poor grounding, too small a ground plane or both! be sure to use the longest physical length antenna you can and place it as high as you can on the vehicle and as far away from metal mass as possible, yep a struggle on a Jeep I know but these are guide lines so you will have to compromise.

Top loaded antennas will put more of the signal out from behind objects like spare wheels etc so I would use these in preference to center or base loaded types. I don't know if your aware but a full sign wave at 27mghz is about 34 feet end to end, antennas are divisions of this length the shortest useable length is 1/4 wave or about 8'6" so the wire of the antenna has to be coiled up to fit the physical length that you require hence longer and higher is better both in terms of the coil (load) and position. Of course a longer division of the sign wave works better than shorter so a 5/8 wave antenna will put out slightly better than a 1/4 wave antenna, if you have a Firestik then you are probably using 5/8wave and that would be my weapon of choice.

catch you on the skip some time. :)
 
The raised portion of the nylon washer is sitting on top of the mount because I didn't drill the hole to 1/2". The bolt may be touching the mount because of it.
 
rtguy1 said:
The raised portion of the nylon washer is sitting on top of the mount because I didn't drill the hole to 1/2". The bolt may be touching the mount because of it.
Click to expand...

You really need to start there. Fix that and you'll fix your SWR.
 
I'm gonna give it a go today. Thanks everyone for the help. This is my first cb that isn't a portable hand held unit:cool:
 
update! good to go!

I want to thank everyone for the quick responses in helping me with my cb issues. The problem is now resolved. The issue was the bracket that i drilled out. I failed to drill it to 1/2" which didn't allow the nylon washers to seat in the hole to shield the bolt from the bracket. I tossed the aluminum piece and made a new steel bracket. it is much stronger and doesn't flex at all. I drilled the new holes to 1/2" and the washers seat perfectly. My first test without any tuning put the swr at 1 for channel 1 and maybe 1.3 for channel 40. Gonna tune it a little later to get it dialed in as best i can, even though it will work fine how it is. Might as well take advantage of the tunable tip on my firefly. Thanks again for all the help guys. Happy wheeling!!!! :thankyou: :rock:
 
breaker! breaker! 10-4..happy trails :beer:

try to tune it in open space, I noticed a difference from tuning in the driveway to tuning it with no obstacles around
 
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