Sunday, June 15, 2008

Building a software defined radio

softrockfront.jpgI'm building the new Softrock "Xtall+Lite" v8.3 from Tony Parks KB9YIG.

He definitely needs to come up with a snappier name!

All seems well on the receiver front although it doesn't seem very sensitive and I suspect my front end isn't resonant in the right place. Shown above is the 40/80m front end.

Construction went well and all seems to check out ok. This board has a few surface mount components that take me a bit of concentration. The little DIP switches set the oscillator frequency.

First I had a go with Linrad on a Linux box but I seem to have sound troubles, so over to the Mac. My frustration is trying to get some SDR software running on the Mac. I spent several hours trying to get UWSDR to build on Leopard, after fixing all the little type casting complaints it wouldn't link with libfftw (missing symbols) so I'm stuck for now.
softrockback.jpg

In other news, I finally heard some PSK31 stations on 80m, VK2BOJ and VK2DD were heard on about 3.660Mhz with excellent signals. We were on our way out the door but I transmitted a few Hz away and they noticed and said hello. I only had time to say I had to go but this is a good sign.

It puzzles me why people give reports such as "599" when using PSK31, surely "S9 and -23db IMD" would be a more useful measure.

Update: I've just been pointed to some SDR software for the Mac by Sebastian DO8SEM here. Looks very promising although still under development. Currently, I'm not hearing too much but it has great promise.

Here it is on 80m. The audio seems rather distorted to me but it certainly works and I'm happily listening to SSB conversations.

SDRTransceiver.png

Tuning shortwave with a "waterfall" display is certainly the best way to operate.

Update 2:I figured out why my softrock was so deaf, the tuned RF front end is supposed to provide anti-phase signals at the input but in my case I had the phase of one side reversed. Works much better now.

1 comment:

Sebastian Mrozek said...

Nice! Please note that there is a Software update available! The URL is:
http://homepage.mac.com/smrozek/ ...
... downloads/DSPRadio.html

73, Sebastian