ICOM 718 and 120 Tuner

[Rick D]

Was at the boat the last couple of days and looked at the old 700 SSB I have. Thinking I should replace it with an ICOM 718. Far more user-friendly in the ham bands and I would likely never use the SSB unless an emergency or close. So is the AT 120 compatible or should I just sell the whole thing on e-bay and get an AH 4? Disclaimer: curiosity question... I have spent only a little time researching.

 

[Brian D]

I think it would be compatible. There are only 4 connections, Earth, 13vdc, Start, and Key. There might be a slight difference in the Start/Key voltage, but I am not sure what the voltages should be. I know that my IC707 will activate a MFJ autotuner with a 330Ω resistor between the Start and Key lines. Maybe that is all you need to key the AT120.

 

[Brian D]

Rick, a little more reading and I find this...
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From the AT-120 User Manual

If the "KEY" line voltage, which controls the radiotelephone output power. is more than 8 volts at the radiotelephone end; place switch S1 in the position nearest the shielding can of the adjacent LOGIC unit. S1 is located near the control cable terminals as shown in the figure.
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I believe this to be in regards to using a different radio than an Icom. I also believe that since you are moving from an Icom M700 to an Icom IC718, the "KEY" should be compatible. You can measure the key voltage on the IC718 to determine its voltage, but I think it will be less than 5 volts. I recall doing the same basic research for my IC707 when looking for a suitable tuner. The SGC does not require a KEY and START line but the radio does. The radio must key a 10 watt carrier long enough for the tuner to find a match.

Not presuming to lecture here.

 

[Rick D]

That is very helpful. Thanks, Brian!~

 

[windward54]

Any chance you could pick up an 802? The 802 will work with your tuner, and the radio is a lot more user-friendly.

 

[Brian D]

There are also lots of M710s on ebay for very reasonable prices. I almost got one but went with a smaller IC-707. It is somewhat easy to program with all available software on the Yahoo User Group, and a DOS based laptop.