The AH-4 is an antenna coupler/tuner designed for long wire or whip type antennas.
This coupler, like the SGC brand, are typically used at the feedpoint of the antenna, as opposed to a standard antenna tuner located just downstream of the transceiver.

With an 8 foot "whip" freq coverage should be 6m-40m and with 23 feet of wire the range is 6m-80m.

This is the new AH-4 that arrived today.

In the box you have the AH-4, package of mounting bolts, package with 16' of coax and 16' of 4 wire control cable, and the instructions. The coax requires installation of the PL259 connectors.

Requires removal of 8 Phillips screws to get to the coax connector (shown center right) and control cable attach point (center left).
Notice the lip molded into the cases and the gasket used for weatherproofing. The "hot" side of the antenna attaches at the top insulated feed through.

AH-4 modified with coax and control cable pigtails for ease of experimentation. Coax is standard PL-259 with

double female bulkhead connector. Control cable uses a 4 pin male inline microphone connector.

AH-4 control extension cable is 50' of 18/5 solid copper sprinkler wire with UV resistant jacket (Home Depot $16.50)

Connectors are 4 pin female mic and 4 pin polarized Molex male (Radio shack #274-224 $2.50)

I used mic connectors due to the narrower width so that they could easily be fed through the wall from the shack

to an antenna.