23 Dec 2011

Ultra-simple WSPR

G3XIZ has been having a lot of success on 40m WSPR recently using a 100mW DSB transmitter to generate a WSPR signal. All that is needed is an audio source (for the baseband WSPR signal), a balanced mixer and a PA. Of course, with this arrangement 3dB of power is lost in the "other" sideband which will appear outside of the WSPR sub-band. At some point - when I've got my lightbeam kit finished in January - I hope to try this arrangement on 28MHz WSPR. A very inexpensive 14.060MHz QRP frequency crystal will double to 28.120-28.130MHz so will be ideal to generate a 28MHz DSB WSPR signal at 28.1246MHz. Of course one could convert the TX into a phasing exciter and null out the other unwanted sideband. This should not be too difficult either as the phasing has only got to be good over just a 200Hz wide audio band, unlike speech which needs good phase balance over the full 300-2.4kHz band.

2 comments:

Julian Moss said...

I'm not sure that this really qualifies as ultra-simple if you need to use a computer to generate the signal. (Though you could probably record it and play it back using a cheap MP3 player.)

A WSPR signal is only 4 FSK tones so a PIC circuit modulating a VXO should be able to do it, though PIC programming is still beyond most people (myself included.)

If Jay W5OLF decided to make a 10m version of his standalone WSPR beacon I'd be interested. Another thought: the Elecraft XG3 can be programed with beacon text in CW or RTTY - I wonder if WSPR would be a viable option?

Me..... said...

You are right of course Julian. I am surprised no-one has produced (as far as I know) a simple stand-alone WSPR beacon kit in the same way QRSS beacon kits are available. Not sure about timing sync though.