W5DXP's IC-706 Screwdriver Antenna Tuning Circuit



The circuitry could not be more simple. There is one 10k ohm pullup resistor and one ~12vdc relay. Any small ~12vdc relay will work but I used the Radio Shack 275-248a relay priced at about $3. The operation of the circuit is as follows: If the present SWR needs to be known, the tuner button on the IC-706 is depressed. For a moment, the transmitter is put into 10 watt CW transmit mode and the SWR can be read from the display. Otherwise, the IC-706 need not be touched. When the screwdriver antenna tuning switch is depressed in either direction, the 12vdc relay is enabled thus supplying GND to the TKEY terminal. Anytime the screwdriver motor has 12vdc applied, the IC-706 turns on automatically in 10 watt CW transmit mode. The SWR can be observed anytime the screwdriver motor is powered and the tuning switch can be released when minimum SWR is achieved. W5DXP searched the web for similar designs and decided to roll his own. For about $5 worth of parts, this is the most convenient design available. Save about $25 and roll your own. W5DXP mounted the relay on a small PC board that plugs into the IC-706. The four-pin Molex plug is also available at Radio Shack.