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Cb radio help?

Posted on 3/9/13 at 1:14 pm
Posted by geaux481
richland parish
Member since Jan 2013
224 posts
Posted on 3/9/13 at 1:14 pm
Just bought two cobra cb radios with magnetic mount antennas. We mounted them on two of our new tractors but they won't work past 50 feet. I bought a swr meter and It giving
Me a high reading (4&5). I believe it is the ground. We have tried mounting them to everything and nothing will work. Please help. Thanks
Posted by KingRanch
The Ranch
Member since Mar 2012
61759 posts
Posted on 3/9/13 at 1:15 pm to
Paging downshift
Posted by cdaniel76
Ponchatoula
Member since Feb 2008
19783 posts
Posted on 3/9/13 at 1:18 pm to
Run power to the radios directly from the positive & negative terminals on the battery.

Antenna's should have a set screw on them to adjust for SWR. Should be a small set screw that will let you raise or lower the aerial.
Posted by geaux481
richland parish
Member since Jan 2013
224 posts
Posted on 3/9/13 at 1:20 pm to
I have tried moving it up and down but still a high reading on the swr
Posted by Kill Switch
Freeport, TX
Member since Sep 2010
2393 posts
Posted on 3/9/13 at 2:08 pm to
If you tried adjusting the stinger via the set screw and it's still too high you may have to trim the stinger (whip) a little at a time (1/4") to get the SWR reading down to acceptable levels. Also, if you bought a shite antenna you may just be SOL. Go get a Wilson Lil Will.

ETA: Also make sure the magnetic base is in the middle of the roof or whatever it is sitting on so as to make a complete groundplane for the antenna (or atleast the best it can).
This post was edited on 3/9/13 at 2:09 pm
Posted by DownshiftAndFloorIt
Here
Member since Jan 2011
72249 posts
Posted on 3/9/13 at 2:39 pm to
How long is the antenna?
Posted by geaux481
richland parish
Member since Jan 2013
224 posts
Posted on 3/9/13 at 3:26 pm to
3 feet antenna.
Posted by KingRanch
The Ranch
Member since Mar 2012
61759 posts
Posted on 3/9/13 at 3:27 pm to
Downshift will say you need at least an eight foot one
Posted by geaux481
richland parish
Member since Jan 2013
224 posts
Posted on 3/9/13 at 3:40 pm to
3 foot long one gets knocked off going under bridges and trees so a 8 ft won't work. I dont need much distance. A mile at max
Posted by DownshiftAndFloorIt
Here
Member since Jan 2011
72249 posts
Posted on 3/9/13 at 3:49 pm to
You're probably grounding it out or something. Do you have it on the roof away from any other metal stuff?

With that setup your SWRs should be around 2ish
Posted by geaux481
richland parish
Member since Jan 2013
224 posts
Posted on 3/9/13 at 3:53 pm to
I have tried it on the roof on a metal plate that is glued on a fiberglass cab. I figure that wasn't grounded. I put it on the mirror mount, the frame, everywhere. But everything is painted. No plain metal. Could that keep me from getting a ground?
Posted by DownshiftAndFloorIt
Here
Member since Jan 2011
72249 posts
Posted on 3/9/13 at 4:01 pm to
You should be able to just put it straight on the painted roof. That's how they're meant to be used.

Other than checking the simple things like connections I'm not sure what to tell ya. It could be anything. Putting the antenna cable certain ways can mess it up, metal stuff in the wrong places can screw it up, sun spots can screw it up, and there's a bunch of other stuff.

Just keep playing with it until your SWRs start getting down. You can actually screw up your radio with SWR's that high.

ETA: Wait I just saw that you have a fiberglass roof. Got some metal bolted to the frame somewhere that you can stick it to?
This post was edited on 3/9/13 at 4:02 pm
Posted by geaux481
richland parish
Member since Jan 2013
224 posts
Posted on 3/9/13 at 4:11 pm to
Yeah. I have tried everywhere on this tractor
Posted by DownshiftAndFloorIt
Here
Member since Jan 2011
72249 posts
Posted on 3/9/13 at 4:15 pm to
Not sure what else to check. Maybe try it on the roof of your truck to see if it's any better. Just stick the antenna to the roof and hook the radio straight to the battery and see what your SWR's are like that.

Don't be insulted, but does your radio have an SWR knob?

Posted by geaux481
richland parish
Member since Jan 2013
224 posts
Posted on 3/9/13 at 4:21 pm to
No swr on the cb. I just bought some cheep ones for my fertilizing crew. I have it plugged into cigarette lighters. Could that be my problem. I have no clue how to install these things. And I dont have time to shutdown to get someone to fix them. I appreciate the help
Posted by DownshiftAndFloorIt
Here
Member since Jan 2011
72249 posts
Posted on 3/9/13 at 4:24 pm to
Try it with the antenna on the roof of your truck.

I don't see why the cigarette lighter plug would be a problem.
Posted by Hammertime
Will trade dowsing rod for titties
Member since Jan 2012
43031 posts
Posted on 3/9/13 at 4:27 pm to
You can't adjust the SWRs down from 4 or 5 to lower than 2 by just moving that antenna.


Make sure you have solid power connected directly to the battery. Ground shouldn't be a problem unless where you stuck the antenna isn't grounded well.

I had to add an extra 8ft to my coax to get it down from 4 to 1.25



Don't talk on it too much with the SWR readings that high. The radio might have a light on it letting you know if they are above the threshold
This post was edited on 3/9/13 at 4:31 pm
Posted by cdaniel76
Ponchatoula
Member since Feb 2008
19783 posts
Posted on 3/9/13 at 4:28 pm to
cigarette lighters carry an aweful lot of "trash" through their power source. Sometimes in powered accessories plugged into the lighter you'll hear a "whine" that inscreases with engine RPMs. That can be interfering with the radio also.

Try doing like I mentioned and run power and ground straight to the battery.
Posted by hogdaddy
Krotz Springs
Member since Feb 2010
5154 posts
Posted on 3/9/13 at 4:32 pm to
Post the model number of the units you are installing.
Posted by Hammertime
Will trade dowsing rod for titties
Member since Jan 2012
43031 posts
Posted on 3/9/13 at 5:29 pm to
If I had to guess, it would be a 29 and a Lil will
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