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So, tried qt-dab yet?

Posted: Sat Apr 27, 2019 10:25 pm
by ab1jx
I just got a new rtl2832 dongle in the mail and it says DAB among other things on it so I thought I'd give DAB a try. My first search took me to https://wiki.opendigitalradio.org/DAB_reception and then I went to https://github.com/JvanKatwijk/qt-dab After checking the debs with Synaptic of course, it's not in there.

I had no luck building with qmake, eventually I got it built using cmake. Sort of the usual way, cd into where it is, mkdir build, cd build, but then

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cmake ../ -DRTLSDR=ON -DRTLTCP=ON  -DINSTALL_UDEV_RULES=ON -DDETACH_KERNEL_DRIVER=ON
which I had to figure out because the documentation assumes qmake is going to work. They also seem to use an airspy dongle, I have a Chinese rtl2832. That's all set: dump1090 works on it just fine. Being new, I haven't figured out what ppm correction I need to get it exactly on frequency, but this is a tcxo one, it may not need that, it's supposed to stay within 1 ppm.

But I can't find any signals, maybe there aren't any here.
qt-dab_ss.gif
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This is listening on VHF frequencies, there's something similar in use on HF/shortwave. https://en.wikipedia.org/wiki/Digital_Radio_Mondiale It sounds like a buzz saw if you run across it. I have gotten those to decode, several years ago. VHF (~170 - 200 MHz) is going to be very local, like 100 miles or so. Here in the US it's well, weird. https://en.wikipedia.org/wiki/Digital_radio Elsewhere it may well work, but searching this forum for qt-dab turned up nothing, plus it's not in the debs. The panel probably isn't supposed to say TextLabel on it, somebody goofed.

If you get it running (make and make install) it puts a ~/.qt-dab.ini file in your home directory, that holds the settings of the GUI widgets on the front panel.

Re: So, tried qt-dab yet?

Posted: Wed May 01, 2019 2:58 am
by ab1jx
OK , there is no DAB in the US but it should work elsewhere. There was never frequency allocation for it here because there's too much other stuff.
nodab.png
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If it works it should look more like the official screenshot:
Image
I'm trying to link https://github.com/JvanKatwijk/qt-dab/b ... qt-dab.png but access may need a github login or something. It's too big to post here.

Somebody posted on github that https://github.com/argilo/gr-nrsc5 can do HD radio (mostly for US I think) but it uses Gnuradio so it may take over your CPU. That's for transmitting as it turns out, https://github.com/theori-io/nrsc5/ is for receiving, and uses just librtlsdr.

Re: So, tried qt-dab yet?

Posted: Thu May 02, 2019 5:55 pm
by ab1jx
Yeah, OK, I got that working, just listened to something by Metalica. Hearing commercials though. It's (I guess) https://en.wikipedia.org/wiki/HD_Radio

This has no GUI, there's an API to add one. It works strictly like rtl_fm where you type a frequency and program number. There's no easy way to browse and see what's out there for signals.
rock102.gif
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Ran cmake like
cmake -DUSE_NEON=ON ..
CPU usage (plus Firefox) is about 20-25% on this Pi 3B

Old duffer in a rock world. But I grew up on rock, just haven't listened to it in 20 years or so. Classical for a few years then silence.

I just flipped from program 0 to 1 on that station and went from Stones to something else, interesting. But where can I get away from the commercials? This is a little like our ATSC digital TV though where station can have multiple programs going at once. Still in the same FM broadcast band, old style radios still hear just the first program.

This gets you a higher bit rate than analog, more like a CD. I'm seeing 48 - 50 kbps. So you could record a bunch (pipe it through Sox/rec if nothing better) and edit out the commericals, save as mp3 files or whatever. In Audacity commercials are probably quite visible. I'm not that into music anymore, more work than it's worth. Oh, some AC/DC, maybe. Set it to record for a few hours, dig out the music, add it to your mp3 library. Hmm, some Pink Floyd-ish thing, tempo is weird. Noticeable hiss, where's that coming from? I guess the medium doesn't dictate what the stations put on it. I'm using a good external USB sound setup, shouldn't be that. The hiss goes away in the commercials, so it's them, not me. Go to https://hdradio.com/stations/ and click on the GPS icon, you can enter your zip code. But it only shows me 6 stations, not including the one I already found.

HD radio looks like this
Image
on the air, the blocks at the outsides of the analog signal are the digital. Picture linked from https://www.rtl-sdr.com/decoding-and-li ... n-rtl-sdr/

Re: So, tried qt-dab yet?

Posted: Thu May 02, 2019 11:28 pm
by ab1jx
So you can record to a wav file for an hour or so then chop it up like this in Audacity. You can see where the song starts and ends. It's clunky but it works.
chopping.jpg
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This is a really old local rock station that's been around for 45 years or so, same frequency, they just added the digital stuff to it. Sounds better, I think.

Re: So, tried qt-dab yet?

Posted: Fri May 03, 2019 3:18 pm
by ab1jx
There is a GUI for it, and supposedly an API for making your own. See https://github.com/cmnybo/nrsc5-gui

What it shows depends on what the stations put on the air, it can do traffic and weather maps, album covers, but not here. I used fmfool http://www.fmfool.com/index.php?option= ... &Itemid=29 and wrote down the frequencies of the 10 strongest stations to try. Only 2 of 10 have digital stuff going on. One has too many CRC errors to do much, the other is the one I started with.

I think you could use rtl_power and take about 10 samples per FM channel width, then look for the blocks that are the digital data on the sides of the analog RF.
gui_running.gif
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You need to run it with Python3, 2.7 doesn't work

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 python3 nrsc5_gui.py
 
-----
The nrsc5 standard (PDF) https://www.nrscstandards.org/standards ... sc-5-d.pdf
-------
Different GUI, a fork by the looks https://github.com/ImDroided/nrsc5-gui That one has problems. You can't resize the form to fit the text on it, you can't stop it other than by doing ps ax and killing the process. And it doesn't seem to actually work, meaning receive anything. Skip it.

Re: So, tried qt-dab yet?

Posted: Sun May 05, 2019 3:34 am
by ab1jx
I listened a few minutes tonight and it was cutting out when I used the GUI, didn't happen with the bare command line program. The basic program is in C, the GUI is in Python. Too much of a performance penalty I guess. The GUI doesn't accomplish much in my case, the only HD station I've found isn't transmitting any graphics.