Category Archives: Radio

Radio stuff

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…

 

Gnu radio

Not really valve related (ok, not in the least valve related!) but after a lot of messing about I finally got Gnu radio to work last night on Ubuntu 16.04. I say finally because it was the end of a lot of messing about off and on, and in no way the fault of Gnu radio.

First, some background. I’ve been using Ubuntu since version 7 I think. I settled on it because it was easy to install on the old and dodgy hardware I had at the time – other distro’s would not even install. My current PC had 12.02 LTS – I use the LTS versions as they have, well, Long Term Support. I had an older Gnu radio package set up and working but it later broke and I’d no idea why. Anyway, I had no time to fix thing back then.

I got back to it later but never fixed it, so I installed the then latest Ubuntu 14.04 LTS. No matter what I did I could not get the software to work. As it was nearly time for the 16.04 release I left it.

I installed 16.04 LTS a couple of days ago but again Gnu radio failed. The software would install via apt-get but gave errors when running. The script (below) failed to complete. Again, no time to fiddle.

Last night I wiped the PC and installed a clean Ubuntu 16.04 LTS and this fixed things. The excellent script (below) ran and set everything up. I had to fiddle with the USB settings and blacklist a kernel module but this is all documented. Finally, I got a basic FM radio working to prove the installation is ok.

So, although upgrading Ubuntu is generally OK for mundane stuff, it is clearly a tad off for actually getting the system up to grade. A clean install is a far better option, and indeed is recommended. Having more than one physical disk makes this a lot easier as one can copy anything needed to the other disk, or have home volumes on that other disk, and trash the o/s disk for each clean upgrade.

This script (http://gnuradio.org/redmine/projects/gnuradio/wiki/InstallingGRFromSource#Using-the-build-gnuradio-script) is really useful and does all thew work for you.

The morale – don’t be lazy! Now for the interesting stuff…

 

Amateur radio

I’ve had an interest in amateur radio since I was young. I’ve had all sorts of radios, built radios, wired all manner of aerial but never got round to taking the exam. Then the exam changed from the old class-B / class-A business to the new foundation/intermediate/advanced. Still I never took the exam.

Then I got interested and decided I would. So I wanted to find out where I could take the foundation exam. I contacted a large society and got nowhere. I tried the local clubs and never got an answer. So I gave up.

I just decided to look again. Apparently the nearest clubs where I might take the exam are at least 10 miles away and meet on evenings when I am busy. One club has a calendar, the latest event in which is some time back in 2013.

So I won’t bother…