I tried tuning my MXT-275 last week. I picked up a Surecom SW-33 GMRS SWR meter.
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The kit doesn't come with the larger ends to connect to the radio and coax, so I had to order those separately. Best I could get is 1.94:1 SWR.That was after trimming a tiny bit off the antenna. As a test, I hooked up the smaller antenna that came with the radio and got an almost perfect 1.01:1 with it, so something is not right with my 6db antenna, or the cable. I checked the cable routing to be sure I had no sharp kinks. I hope I didn't trim too much off the antenna. I ordered a Browning antenna in the mean time and a new coax cable to trouble shoot.