Q I have a remote-controlled antenna tuner installed at the feed point of a vertical antenna in my back yard. Although the system works pretty well most of the time, the tuner will occasionally “open” (switch to a direct connection to the antenna) for no apparent reason. This seems to only happen on particular bands. Do you know of a cure?
A Since the problem occurs only when you operate on certain bands, I suspect that RF is getting into the tuner control lines. If RF finds its way into the lines, it could easily wreak havoc with the tuner’s microprocessor circuitry and cause it to exhibit strange behavior, such as switching to the direct-connect mode.
If you can obtain enough slack in the control lines where they enter the tuner, wrap them several times through an FT-43 or FT- 77 ferrite core. This may sufficiently suppress the RF at the tuner. Update: Thanks Doc! I used an FT-43 core and that did the trick. I just wrapped about 10 turns through the core and now the tuner behaves itself.
From QST March 2000
