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post #1 of 6 Old 04-28-2012, 08:20 AM Thread Starter
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CB Tuning Question

Just installed the CB last night and attempted to tune it this morning. The SWR meter says 2.9 on CH 40 and about 1.9 on CH 1, I know this is not optimal at all. I have done some research and it appears to me that bad readings could be attribuited to two things. First, when I grounded the antenna mount to the frame I did not remove the paint before doing so. Also, I had a few feet of coax cable left over that I needed to hide. I ran it back-and-forth in the space above the mirror before I hooking it up to the CB to get rid of the extra cable (my CB is mounted above the mirror). It appears that the bending of the coax cable up there could be causing an issue. What are your thoughts? Also, until I get a lower SWR reading am I safe to be using my CB or am I risking damaging it?

Thanks for the help!

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post #2 of 6 Old 04-28-2012, 08:35 AM
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SWR <=2 is generally safe to use, albeit not optimal. I would avoid using the radio other than for listening with an SWR over 2.

You already have a couple of good troubleshooting first steps in mind. A bad ground or tightly coiled coax can both cause high SWR readings.
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post #3 of 6 Old 05-03-2012, 09:26 AM
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Reground your antenna mount, and add additional body grounding straps if you think they are needed, it can't hurt.
If you can run your coax by itself away from other wiring.
If you must coil extra coax, do so in about 6~8" coils, tightly wrapped, as close to the anteena end as possible, it can actually clean up some RFI if present.
Most CB's can handle an SWR of 1:3 without issue.
At 1:5 you may be doing damage.
Anything under 1:2 is very good for any mobile configuration.
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post #4 of 6 Old 05-03-2012, 12:50 PM
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Is your antenna tune-able? Lower readings at 1 than 40 I believe means you should shorten your antenna if you have a tune-able tip.

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post #5 of 6 Old 05-06-2012, 05:28 PM
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I always grind of the paint from the underside of where ever I mount my antenna, so far it's always pretty good.

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post #6 of 6 Old 05-06-2012, 09:09 PM
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The three biggest problems with SWR are tight bends, looping the cable and poor ground. Tight bends compress the dielectric foam core and cause variations in the distance between the center conductor and outer braid. Looping (or running back-and-forth in a confined space) allows cross-inductance. A poor ground is a poor ground.

Once you've had a tight bend in the coax, straightening it out might not correct the problem, as the foam has already been compressed. Heat and vibration will cause that foam to permanently be deformed. Coax is relatively inexpensive, I would replace it. Get a piece of coax with a PL259 pre-attached on only one end and then a solder-on PL259 for the other end. Avoid tight bends (less than 3" radius), pinching or sharp edges while routing the cable. Cut the cable to length (leave enough to put on the connector and a little wiggle room), strip off 2" of outer jacket, separate and fold-back the braid and then strip the foam about 1/8" higher than the braid. Make sure none of the braid can touch the center conductor. Then trim the braid, screw-on the connector and solder/trim the center conductor.

If the mount is actually connected to the chassis then make sure you remove the paint from the frame and back of the mount, attach the mount, then spraypaint the mount and frame to prevent rust. If it's on a tire carrier, bumper, tailgate, etc., run a braided ground strap from the frame to a screw on the mount, removing paint for good contact on both ends.

Hope this helps

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