Software Defined Radio fiddling

I had some time these past few days to have a reasonable fiddle with a new SDR I acquired – the Watson W-SDRX1 mark 3. This is essentially one of the RTL style SDRs with a switchable HF front end and two aerial inputs, one for HF and below, and one for VHF and above. Coverage is 100kHz to 2GHz.

VHF-wise it works just the same as the RTL-SDR dongle from eBay. Gqrx plays well and with the wide screen on my Linux desktop it shows a good bandwidth.

But it took me a while to figure out how to get the HF side working. The paperwork suggests the cutoff between HF and VHF operation is 40MHz but gqrx out of the box only understands the coverage of the RTL-SDR, so 27MHz to 1700MHz or so. The trick is either to tune 40MHz up, or set an LNB Offset of -40MHz, the latter resulting in the correct frequency being displayed. One does need to remember to set the LNB Offset back to zero when changing to VHF, but hey.

So now I need to have a play in Gnu Radio and see if I can fiddle up a few decent receivers. However it does need a decent aerial. The wideband scanner whip I have sat by the PC does little other than pick up QRM. Unfortunately my ‘active’ aerial is in the workshop and the Linux desktop isn’t, well not yet anyway.

CPU load is not excessive with gqrx on my i5 based desktop, the 4 cores average 20% overall with the waterfall and FFT displays running.

It will be interesting to see how well gqrx and this SDR plays on a Raspberry Pi Mk3. More on that when I find a spare HDMI TV to plug the Pi into…


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