Icom IC-M80 (model 370)

The transceiver can be opened by removiong the six screws at the back and the four bolts on the sides.

R91 contains the unfiltered baseband audio signal

The location of R91

R91 can be spotted close to the small white block marked '455-D'. In the VHF set I have modified, R91 was connected to the ATIS circuit board (the yellow wire on the pictures).

The positive lead of a 10 uF, 25 V electrolitic capacitor is connected to R91. A small piece of wire is soldered to the negative lead of the capacitor. This lead is connected to a 3.5 mm mono chassis terminal.

The chassis plug can be mounted on the metal plate above the VHF set's power connector. As this metal plate is connected to the ground of the VHF set, no separate ground connection is necessary to the 3.5 mm chassis plug.

A 10 uF electrolytic capacitor, connected to R91

The 3.5 mm chassis plug in the back of the VHF radiotelephone

The end result, with the protective cover mounted