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Dipping a toe into SDR waters
10 December 2015 | by The big shack renovation meant I had to put all my stuff back into boxes. No problem spending some time without my rigs and tools, but I didn’t want to spend a couple of months without any form of radio. So I left out the RTL-SDR dongle and a mobile whip to see if I could get some more out of it than digital TV. I have had the dongle for a while now, but I was never impressed by it. Lots of white noise and very few signals to be seen on the waterfall. I even boxed it up nicely to avoid EMI.
The first step was to see if the dongle still worked by scanning the DVB-T bands. After installing the necessary RTL-SDR packages I fired up VLC to see if it would decode signals. There are packages like MythTV and MeTV that can let you watch DVB-T, but I don’t like cluttering up my system especially since VLC is such a versatile piece of software. For it to work you need to open an console though, but the internet is awash with good tutorials to help you get it done.
Step 1: install dvb-apps with sudo apt-get install dvb-apps
Step 2: use the scan application that comes with dvb-apps: scan /usr/share/dvb/dvb-t/tw-All > channels.conf
Step 3: open the channels.conf file with VLC
Step 4: choose your favourite channel and enjoy
Most of the time Linux provides an alternative and in this case it’s w_scan: w_scan -X -c TW
substitute your own country code in place of TW; a list can be retrieved by issuing the command w_scan -c ?
Before I knew it I was watching the WBSC Premier 12 baseball games and found out Taiwan’s public broadcaster is airing Person of Interest. Usually I find that watching tele is just a big waste of time, but I do also find that it is the only time I am not physically active and I do need to rest more. My wife likes PoI too, so now we have a date every Monday through Wednesday at 10.
The FM band was another check to see if the RTL-SDR dongle works as advertised. On Windows the prevalent SDR software is SDR#. On Linux this is GQRX, which is based on GNU Radio, a very powerful but complex piece of software. Before you can start GQRX you need to deactivate the dvb_usb_rtl28xxu driver as this conflicts with the rtl2832 driver. Issue the following command: sudo rmmod dvb_usb_rtl28xxu. If you never watch TV then blacklist the driver in order for it to be never loaded when you insert the dongle.
I could indeed receive FM broadcasts, but as many as I could with my Sangean ATS-909, so no big win there. GQRX also has a build in AFSK demodulator and I tried to decode some APRS signals on our local frequency of 144.640 MHz. I could hear signals and see them on the waterfall, but not decode them. After trying some other antennas and even taking everything outside in the open I grew a bit frustrated and searched for some other signals to decode. Tracking aircraft using ASD-B seemed fun (G4VXE wrote about it before here on AmateurRadio.com ) so I tried to set that up. And in doing so I got a big surprise.
[to be continued]
2 Responses to “Dipping a toe into SDR waters”
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Heh my first response was oh it can do tv too then it hit me dammit its a tv dongle to begin with. i use mine mostly for Tetra/GSM decoding as there is not much else in the way of digital around here (aside from tv thou)And once i get an LNA(and manage to build a helix) i will be trying to put my large dish to use and receive Inmarsat messages.
You can also receive and decode DAB and DAB+ radio stations, but there aren’t any here in Taiwan. Nowadays people have TVs in their cars instead of radios. Radio as we know it is slowly dying, I’m afraid and DAB is too little, too late.
I have not looked into GSM decoding yet, although I used it to calibrate the dongle. In part two I will tell about aircraft monitoring and that is something you can do as well in remote radio areas.