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High SWR



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1 hour ago, Stechkin said:

I have a Tram 1173 5/8 over 5/8 wave 5.5 dB gain antenna that reads 3 on 462.562 and 3 on 462.725.  The antenna is mounted to the hood of my car with a nmo lip mount, the radio is a B-Tech GMRS HT.  What do I need to do to get the reading closer to 1.5?

Since it looks like the antenna should be pretty well tuned to the GMRS band, I'd look at a couple of other things first.

The first thing I'd check is the SWR meter you're using. Is it intended for the frequencies you're checking? Have you used it with another antenna in the same frequency range to be sure it's providing an accurate reading? Are you using adapters to connect it? If so, they could be causing a bad connection.

The second thing I'd suggest checking is the mount. With a lip mount, you want to be sure there is metal to metal contact between the body of the vehicle and the body of the mount, so the screws on the bottom that hold the mount in place need to penetrate the paint on the vehicle for good contact. If you have access to another mount, such as a magnetic mount, try the antenna with that mount to see what your readings are.

If you have access to another similar antenna system that you know is within the desired SWR on the same frequency, you can try switching the antennas between the systems to see if the problem follows the antenna. If it doesn't, then you know to look further into the mount. If it does, then you need to look more closely at the antenna. If it was a "70cm" or "dual-band" ham antenna, then it would likely be a little longer than desired, and it could be trimmed for GMRS. An antenna designed for the 450-470 MHz range should be about right, though, and should not need trimming.

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