Below is the write up from the
builder. The units weren’t very expensive to begin with. I’ve also seen a diagram of how to build an equivalent in QST several years ago. IIRC it wasn’t much more than a couple of resistors.
This new unit works with Icom's having an
antenna tuner jack on the rear of the
radio. This device simply plugs into the tuner jack and your
radio will think there's an
Icom antenna tuner attached. This activates the 'tuner' button on the front panel of the 706, 7300, 746, 756, PRO, PRO II, etc.).
When the tune button is operated, the radio will transmit a 10 watt CW signal for approximately 8-10 seconds.
This
low power signal minimizes risk and damage to your finals while you check match, swr or tune the antenna with your own external tuner. This is most useful for tuning your amplifier and high
power tuner at much lower
power levels.