G3PJT’s pages on Amateur Radio

Antenna switch for the Elecraft K2.

This switch automatically controls up to 8 antennas. It gets data from the KIO2 and can work with or without a logging programme. It also has a 4 bit output compatible with Yaesu band data. It can either drive 1 of 8 open collectors or 4 bit BCD.

The picture is the first version. I have now rewritten the software so that the decoder has 1 of 10 output (including 5MHz) as well as the 4 bit BCD output ( 5MHz set same at 7MHz ) to retain compatibility. Also internal or external polling can be selected. It now runs in a PIC16F876 to give you a bit more space.

The circuit is shown here with a simple two transistor interface between the PIC and the RS232 signals.

I can supply pre-programmed PICs - just drop me an e mail at

Limitations or this is the fine print

All this information is given in good faith and no liability will be accepted by G3PJT in respect of any damage however caused. Except as noted this page has copyright G3PJT(2006). Last update 19 Dec 2006.