K3 to Tokyo Hy-Power HL 1.5KFX amplifier
From Zerobeat
After exchanging much e-mail with Elecraft discussion list members and Tokyo Hy-Power support staff I've come up with the interface circuit below for automatic band switching when using the K3 with the Tokyo Hy-Power HL 1.5KFX amplifier.
When interfacing a Yaesu transceiver with a Yaesu amplifier, the transceiver provides the 5V pull-up voltage for the band-data lines. The K3 emulates Yaesu's band-data switching matrix but the four band-data lines in the K3's KIO3 ACC 15 pin jack are open-drain outputs and do not provide this pull-up voltage so it is necessary to provide them externally.
All the parts necessary are available from Radio Shack. If you already have a 5V power supply you can omit the 5V regulator shown in the circuit below. I built the interface in a 2" x 3" project box and power it from the 12V accessory power RCA jack on the back of the K3.
THP Band data interface diagram
Elecraft 4/16/2008 - It is strongly advised to add at least a 10 uF cap on the input of the regulator to ground, and on the output of the regulator to ground, to prevent possible oscillation of the regulator.
