How long can the control cable for the Icom AH4 be? I’m not sure but at least 170 feet (52 Meters).
Icom includes a 16ish (5 meter) unshielded cable (OPC-136) with the tuner. That doesn’t get you very far except for mobile and portable operation. Lucky for you they also sell a 32.8 foot (10 meter) shielded cable (OPC-420). Still 30 feet isn’t going to cut the mustard for my latest install sooooooo…
I bought a 500′ spool of Belden 5202FE to try and extend that a bit. I did some rough math to figure the voltage drop at roughly 200 feet and decided that 16 gauge or larger was probably best to avoid too much loss. I did some searching around and there are no cheap shielded options so I went for broke and looked through the Belden catalog and found 5202FE under security and sound. It has 4 conductors, is shielded, has a PE jacket, and is 16 awg. It even uses the same color scheme that Icom does.
Since Icom doesn’t give much of a spec you are just kind of guessing on how long you can actually run until it doesn’t work. On pure hope I hand buried 128 feet by hand and ran another 42ish feet through my house.
After getting the new 43 Foot DX Engineering antenna built and hooked up I was anxious to see if the tuner would work that far away. I got everything terminated and plugged it in to see. Sure enough antenna 1 showed (EXT), then a quick key up showed it tune on every band from 80-6! After that I gave 40M a try, which had always been a problem at the previous QTH, and worked Costa Rica and Italy right away. Tuner works!
No idea how far you can go, but it will probably work at least a couple hundred feet with 16awg shielded cable.