AH-4 Tuner
The AH-4 tuner by Icom is a great, wide-range, remotely-operated tuner. Unfortunately the Icom manual is very sparse and only suggests a very basic way in which to use the tuner (wire hanging out of “output” terminal, other end stuck into “ground”). The described installation will work, but it’s possible to get high-end, top performance from this tuner by using it in a slightly different way.
Design of the AH-4 – how it works
The AH-4 Universal Interface (obsolete)