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Old 05-19-2017, 6:42 AM
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jonwienke jonwienke is offline
Join Date: Jul 2014
Location: PA
Posts: 6,373

There's nothing wrong with using LMR400 for CB, as long as the cable is in good condition, all connectors are properly attached, etc. IMO you've got something else going on that just the cable. Changing cable type shouldn't be a large enough impedance difference to make that much of a change in SWR.

I suspect you don't have the ground plane kit for your IMAX-2000, and your coax shield is acting as your RF ground. If that is the case, changing feedline anywhere (on the tower or in the house) will have random effects on your SWR reading. If you don't have the ground plane kit, get it. It would be ridiculous to run heliax but not have the ground plane--the ground plane will do far more for antenna performance than the difference between LMR400 and heliax, and it will cut down on RF radiating from your coax shield. It's sort of the RF equivalent of adding a spoiler when the engine is misfiring on two cylinders.

Also, unless you're measuring SWR with the meter attached directly to the antenna, switching to a less lossy coax will raise SWR readings simply because less of the signal reflected back from the antenna is being attenuated. It's not that the antenna match got worse, it's that you're getting a more accurate measurement of how bad it really is.
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