When out contesting with G3PYE/P, we often use Gavin, M1BXF's Icom IC-910 transceiver. A fine rig to be sure, but it doesn't have an internal voice keyer (or digital voice recorder) - a feature still lacking in the brand new IC-9100, for reasons best known to Icom.
Instead, we use SM3WMV's PC-based Voice Keyer software. This plays a pre-recorded sound file when you press one of the function keys, and puts the radio into transmit using the RTS line of a serial port.
So far, we've used this and a home-brew data interface to feed the audio into the data port of the rig, but there's a problem - this doesn't go through the rig's compressor, so average transmit power out is rather lower than using the mic.
To improve on this, we decided to build a small interface which accepts two audio sources (PC and microphone), two PTT lines, and routes the appropriate source to the radio when its PTT is activated. This avoids the mic being live when the voice keyer is transmitting, and prevents PC sounds being transmitted when using the microphone and foot switch.
The circuit is simple - a relay for audio switching, and a few transistors to drive the relay and pull the output PTT line low when the PC PTT is activated. A potentiometer on the front allows control of the PC audio level.
Here's the breadboard for an initial test:
And mounted in its box:
Under test with an IC-7000:
And the finished project!
This tuesday is the 23cm UK Activity Contest, where it will get its first on-air test. I hope to work some of you then!
comments powered by Disqus