Automatic antenna tuners are great. Just tune your radio to the frequency you want, flick the TUNE switch, and you quickly get an optimum match between your rig and the antenna. Well, not always. I have an ICOM IC-7000 with an LDG AT-7000 antenna tuner. This is a great little tuner, but it sure tricked me this time.
I wanted to try my rig on the 6 meter band for the first time. So I set up the station and was listening around for signals during this weekend’s VHF contest. There are some CW beacons I had heard before, so I tuned to that part of the band, activate the tuner, and heard nothing. Then I hit the TUNE button again, bypassing the Tuner, and the beacon suddenly appeared! So I hear no signal with the Tuner doing the matching, but I hear the beacon when I bypas the Tuner.
After noticing that the SWR was indeed lower when the Tuner was inline, I realized what was happening, The Tuner has many memories. If it found a “good” match at a frequency, it uses that information to shorten the tuning cycle next time you go to that frequency. The Tuner had apparently found a match that provided a low SWR, but it also resulted in a lossy signal path. The instruction manual showed me that I could go into the Tuner case and push a switch that would force it to retune, even though it thought it had a good match already. So I pushed the button, the relays clacked, and presto, a good match and the beacon reappeared. Guess this button should be on the front panel! Then I worked my first 6 meter station ever.
Kg3v Ham Radio Blog 