Icom CAT Interface Mk III

A new interface was designed to achieve proper galvanic isolation between radio and computer for operating digi modes on HF radio. This new interface was made for the the Icom IC-718 (and IC7410), it should work for any similar Icom radio. I now use a SignaLink USB as the audio device for the computer. There are a number of ways in which this can be achieved and there are a number of designs published. This simple interface operates at the limit of 9600 baud and no faster, as the opto-couplers appear to run out of steam beyond this point. To enable the interface to run faster would require a higher Opto coupler LED drive current, and this may not be possible from new and old RS232 serial ports.


The two options shown gives the opportunity to run the interface either from the current limited eight volt supply from the microphone socket or the twelve volts derived from a separate power supply. The latter was the choice I have chosen in the shack.



Two versions are shown here, the first one shown draws current from the microphone socket of the IC-718. This supply is 8.0v and limited according to the manual to 8mA.


The second version adopted in the current arrangement at the home QTH uses the second circuit where the supply is derived from a separate 12v dc supply.