Control

There are four control wires:

• • voltage - 13.8v into the tuner
• Ground
• Start - Input to the tuner, tells it to start tuning
• Key - Output from the tuner, tells the radio to send some low power CW

Start

The start pin is normally held high (+5v) by the tuner. When this is grounded (or below 2v) the tuner starts a tuning cycle.

Key

This seems to be an open collector output. I use a pull-up resistor (5k) to pull it up to 5v. While the tuner is tuning, it will pull this down to about 300-400mv.

Preset switch

The AT-130 has the 'preset' switched in the off position.

RF

While tuning, power is supposed to be reduced to less than 10w. I'm tempted to connect the 'key' signal to the ALC voltage generator, thus ensuring that the radio will never overload the un-tuned tuner.

Official documentation

The official manual is here: http://www.icom.co.jp/world/support/download/manual/pdf/AT-130_Eng_4.pdf