A simple VOX interface for WSPR.
Having recently acquired an FT-817 I was interested in trying it in WSPR mode. It didn’t take much research to discover that the DATA connector on the rear panel has bi-directional audio, labelled as data. PTT is also available on the same connector. Unfortunately there is no VOX capability when using this port.
I already had a couple of USB soundcards ( $5 on eBay ) so I decided to utilise one of them as an audio interface to the USB port on the laptop. I removed the USB plug and replaced it with a socket. A standard USB to USB connects the interface to my laptop. The audio jacks were also removed and the mini DIN was wired directly to the exposed pads.
Since the soundcard can produce a few volts of audio during transmit, I decided to use a simple voltage doubler to convert some of the audio signal to DC for the transistor switched PTT control. The audio is delivered directly to the voltage doubler, but is potted down for the transmit drive to the radio. A series resistor also helps protect the mic input of the soundcard. You should set the mode to DIG.
To my surprise, the whole thing worked first time and spots from Australia and USA were reported during the first 500mW transmit cycle. WSPR really is an amazing mode. The most difficult part was getting it in the box, neatly !
The box is the smallest from Jaycar. Shown without the lid. The braid simply bonds all the ground points with a low impedance path.
Took a little time to get the layout ‘safe’, so that none of the parts touched.
No box. Maybe some heatshrink tubing.