CB Radio: High SWR - JeepForum.com

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post #1 of 32 Old 05-02-2012, 04:36 PM Thread Starter
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CB Radio: High SWR

Installed a CB and no matter what I do, I can not get the SWR reading down below 2.8-3. I have tried the following.

Four different Antennas.
Four different radios hooked to different power sources and grounds.
Two different coax. (18', 15')
Replaced the Firering coax end on the 18' with a normal connection.
Re-grounded the antenna base with an extra strap, the mount is metal on metal.
Ran continuity test in every possible combination.

When I by-pass the entire antenna set-up and hook up a magnet mount antenna that I have I get 1.1-1.3 readings with that antenna in the same location as the other which is driver side hood near the windshield. I started out using the system in the link below.
http://www.stu-offroad.com/cb/cb1/cb-2.htm

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post #2 of 32 Old 05-02-2012, 06:06 PM
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You might get more answers in the CB forum:

http://www.jeepforum.com/forum/f20/

http://www.jeepforum.com/forum/f9/diy-alignment-kit-steps-w-pics-2264465/
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post #3 of 32 Old 05-02-2012, 06:19 PM
Jerry Bransford
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A high SWR is, 99 times out of 100, the result of a mis-assembled mount that is shorting the antenna to ground. If you have the most common mount like shown below, make sure it is assembled per the instructions and like in the below illustration.

The usual problem is either the insulated shoulder washer is missing, installed off-center, broken, or not where it should be. The insulated shoulder washer's job is to prevent the antenna from touching the mount which would short it to ground.

Only the bottom of the mount, the "SO-239 Coax Connector" is supposed to have an electrical connection to the mounting bracket. The only thing above the mounting bracket that can touch the mounting bracket is the Insulated Shoulder Washer.

And moving this to the 2-way radio forum.
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ant-mount-showing-no-touch.JPG  

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post #4 of 32 Old 05-02-2012, 06:53 PM
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Not mounting the antenna on a hinged tire carrier or the tailgate helps also...
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post #5 of 32 Old 05-02-2012, 07:23 PM
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Where are you parked when you test your swr's?
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post #6 of 32 Old 05-02-2012, 08:01 PM Thread Starter
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Quote:
Originally Posted by robncar View Post
You might get more answers in the CB forum:
DOH! Yeah, I'm a newb.

Quote:
Originally Posted by Jerry Bransford View Post
A high SWR is, 99 times out of 100, the result of a mis-assembled mount...

And moving this to the 2-way radio forum.
All good on the mount. Tried the Firestick FireRing and two different stud mounts for the standard PL259 connectors.
Thanks for moving this for me, I totally forgot about this sub-forum.

Quote:
Originally Posted by Knuckelhead View Post
Not mounting the antenna on a hinged tire carrier or the tailgate helps also...
Mounted on the front fender.

Quote:
Originally Posted by Necromancer_tat View Post
Where are you parked when you test your swr's?
At the end of my drive way, actually in the street which puts the Jeep about 30 yards away from the nearest building and there are no trees or power lines.

I have tuned lots of radios over the years and this one really has me baffled.
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post #7 of 32 Old 05-02-2012, 08:11 PM Thread Starter
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Here are a couple of pics of the mount that I am trying to use now.
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post #8 of 32 Old 05-02-2012, 08:21 PM
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What antennas are you trying? What SWR readings are you getting with them? Some of them really won't tune in very well no matter what you do.
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post #9 of 32 Old 05-02-2012, 08:24 PM
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Quote:
Originally Posted by -sean- View Post
Here are a couple of pics of the mount that I am trying to use now.
And you said you ran a ground strap to the bolts that hold the mount to the fender? Have you tried running a ground strap from the bolt underneath the fender mount, to the body tub? I would also run a ground strap to the frame as well.
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post #10 of 32 Old 05-02-2012, 09:22 PM
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Quote:
Originally Posted by -sean- View Post
Installed a CB and no matter what I do, I can not get the SWR reading down below 2.8-3. I have tried the following.

Four different Antennas.
Four different radios hooked to different power sources and grounds.
Two different coax. (18', 15')
Replaced the Firering coax end on the 18' with a normal connection.
Re-grounded the antenna base with an extra strap, the mount is metal on metal.
Ran continuity test in every possible combination.

When I by-pass the entire antenna set-up and hook up a magnet mount antenna that I have I get 1.1-1.3 readings with that antenna in the same location as the other which is driver side hood near the windshield. I started out using the system in the link below.
http://www.stu-offroad.com/cb/cb1/cb-2.htm
The fender mounts to the body. Both the fender and the place it mounts are probably painted. Even if you are bare metal to bare metal on the fender where the fender mounts there is allot of paint. Try grounding to the cowl.

-or-


It has to be the antenna and/or mount and/or coax and/or ground. But if you have tried a few different ones of these I would go back to the ground issue.

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post #11 of 32 Old 05-02-2012, 09:33 PM
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Are you using the same wire for the magnetic antenna and the mounted antenna? Is this perhaps a no ground plane antenna and wire?

"Never look down on anyone unless your helping them up"- Jesse Jackson
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post #12 of 32 Old 05-02-2012, 10:03 PM Thread Starter
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Thanks for all of the input guys!

The antennas that I have tried:

http://www.wearecb.com/store/wilson-...ck-p-3446.html (3.0-3.3 SWR)
http://www.wearecb.com/store/procomm...na-p-4098.html (SWR at the top of the range...4plus?)
http://www.wearecb.com/store/firesti...nna-p-200.html (2.8-3.2 SWR)
Also a 65" base load similar to the procomm above. (3.0-3.2 SWR)
And the Lil Wil Wilson magnet mount which is a stand alone unit with its own RG58 attached to it. And that one works great. (1.1-1.3 SWR)

My ground strap runs from the bottom of the mount inside and underneath the fender and is attached to one of the stainless bolts. It runs to the factory grounding bolt that is on the firewall which has multiple OEM grounding straps attached to it.
RG58 is new (Firestick) and all PL259 connectors are new. No coax is coiled anywhere.

I have to be missing something.
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post #13 of 32 Old 05-02-2012, 10:06 PM
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Quote:
Originally Posted by -sean- View Post
Thanks for all of the input guys!

The antennas that I have tried:

http://www.wearecb.com/store/wilson-...ck-p-3446.html (3.0-3.3 SWR)
http://www.wearecb.com/store/procomm...na-p-4098.html (SWR at the top of the range...4plus?)
http://www.wearecb.com/store/firesti...nna-p-200.html (2.8-3.2 SWR)
Also a 65" base load similar to the procomm above. (3.0-3.2 SWR)
And the Lil Wil Wilson magnet mount which is a stand alone unit with its own RG58 attached to it. And that one works great. (1.1-1.3 SWR)

My ground strap runs from the bottom of the mount inside and underneath the fender and is attached to one of the stainless bolts. It runs to the factory grounding bolt that is on the firewall which has multiple OEM grounding straps attached to it.
RG58 is new (Firestick) and all PL259 connectors are new. No coax is coiled anywhere.

I have to be missing something.
I'm not a big fan of any of the antennas you listed. I'd run a wilson 2000 or a K40 antenna and be done with it. I've never had any luck tuning those antennas that you posted.
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post #14 of 32 Old 05-02-2012, 10:42 PM
Jerry Bransford
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Firestik antennas, particularly the FS series with the tunable tip, tune up just fine. I've probably tuned 50+ Firestik antennas and once they were installed properly, I never had any problem getting any of them down to sub-1.5:1 and most closer to 1.2:1 SWRs. It's not the antenna itself causing this SWR problem.

If you can't get an antenna's SWR down to an acceptable number, when talking about a commerically manufactured antenna we typically use on our Jeeps, it's not very darned likely it's the antenna itself. Look at the mount to see if it was misassembled, see if the antenna's mount is able to get an adequate RF ground (not just a simple DC ground), look for a poorly soldered connector, etc. but don't spin your wheels and blame the antenna itself or the brand of antenna.

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post #15 of 32 Old 05-02-2012, 10:49 PM Thread Starter
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Quote:
Originally Posted by Necromancer_tat View Post
I'm not a big fan of any of the antennas you listed. I'd run a wilson 2000 or a K40 antenna and be done with it. I've never had any luck tuning those antennas that you posted.
That makes two of us!

Funny you mentioned K40, I almost bought this one when I first got started doing this project.
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