Gqrx with RTL-SDR and UHD support

[Alexandru Csete]

Originally posted on: http://www.oz9aec.net/index.php/gnu-radio/gnu-radio-blog/472-gqrx-with-rtl-sdr-and-uhd-support

Support for RTL2832U-based DVB-T dongles and USRP devices from Ettus Research is now available in the Gqrx source code repository.

Support for RTL2832U-based DVB-T devices is available via the rtl-sdr and gr-osmosdr libraries. This also provides support for Ettus Research USRP's if the gr-uhd package has been installed prior to compiling gr-osmosdr. A complete build from scratch that would support all hardware devices would thus include the following steps:

1. Install UHD
2. Install GNU Radio with gr-uhd and gr-fcd
3. Install the Osmo SDR driver library (if you have an Osmo SDR)
4. Install the RTL-SDR driver library
5. Install gr-osmosdr
6. Compile Gqrx SDR

Be sure to test your devices using the test applications included in the respective driver packages:

• For RTL2832U devices use rtl_test
• For Funcube Dongle use fcd_nfm_rx (or the GNU Radio Companion flow graph)
• For UHD devices use uhd_usrp_probe or uhd_fft

The video below shows reception of FM broadcast using an RTL-SDR dongle and the Funcube Dongle: Watch video on YouTube.

Please note that this is still very much a work in progress and only recommended for people who know their way around linux, compilers and building software from source. Don't expect a finished and fine polished product with comprehensive documentation.

What works:

• Automatic detection of Funcube Dongle, RTL2832U, UHD and Osmo SDR devices connected to the computer.
• Basic AM, SSB, and FM functionality at any sample rate supported by the hardware.
• Spectrum analyser mode which disables all DSP processing (Mode → Demod Off).
• Tested with Funcube Dongle and various RTL-SDR dongles (including rtl_tcp).

Known problems:

• Pressing the OK button in the device configurator using the same device as before causes crash.
• Latency can be several seconds when using RTL2832U-based dongles. If it becomes too painful, try Mode → Demod Off then back to the mode you were using.
• Funcube Dongle will crash on systems with libusb-1.0.9 (you can use the 2.0 branch until fixed).
• Doesn't compile on Mac OS X (I know about this and I will fix it – sending me "fan mail" will make no positive difference).

Feedback is welcome preferably via the Gqrx SDR group. Please remember to always include details about your hardware and software setup, including versions and how you installed them.

Alex

[Jasper Ragworth]

Looking good. Using it with an FC0013 stick, Ubuntu 12.04 AMD64, latest gnuradio from git.

The display is a little jerky but nothing's pegging the CPU. If I set the RX bandwidth to 2MHz the jerkiness goes away. ISTR GRC behaving exactly the same with this stick. Demodded audio is fine, no jerkiness at all. I get quite a lot of:

AVG I/Q: 0.00748284/-0.000583404
No audio FFT data.
AVG I/Q: 0.00317803/0.00728676
No audio FFT data.
AVG I/Q: -0.00117176/0.000106474
No audio FFT data.
No audio FFT data.

on the terminal.

[Alexandru Csete]

Thanks for the feedback.

I found that some sample rates work better than others. You can try to
see which one looses more than others using the rtl_test application.

The "No audio FFT data" simply means that there were not enough
samples in the buffer when the audio FFT was trying to get some. This
is partly because it runs close to the limit of what can be done with
48 ksps. A lot of tuning is still TBD here, but the jerkyness can be
reduced by reducing the audio FFT size or FFT rate. The latter is the
easiest, you simply change line 49 in qtgui/dockaudio.h

Alex

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[Jasper Ragworth]

I'm fine with 2M bandwidth - the only "problem" with that is that it can be a little tricky to land exactly on a signal as everything is relatively narrower.

One thing I've noticed is that it's not possible to click on something more than +/-900kHz away from the centre. I guess this is a hard coded limit somewhere.

[Alexandru Csete]

On Sun, Jun 10, 2012 at 10:23 PM, Jasper Ragworth <trof...@hotmail.com> wrote:
> I'm fine with 2M bandwidth - the only "problem" with that is that it can be
> a little tricky to land exactly on a signal as everything is relatively
> narrower.

You are correct, however, this is why I have added the offset control
in the "Receiver Options" dock window. With that you have 1 Hz
resolution and it even works with the keyboard. You can also use the
mouse wheel within the FFT plot; the step size depends on the
demodulator chosen.

Later on I will enable zoom and pan along the frequency-axis as well
(the same that exists on the dB axis today).

> One thing I've noticed is that it's not possible to click on something more
> than +/-900kHz away from the centre. I guess this is a hard coded limit
> somewhere.

Yes, it is hardcoded nas a percentage of the bandwidth. It's one of
the parameters that need tuning.

Alex

[Benoittt]

Thanks a lot for the anwser.

 

I had the same problem

"No audio FFT data. "

 

Bye ;)

[Jasper Ragworth]

You can add Debian testing to the known working list. I had to 'ln -s /usr/include/gnuradio /usr/local/include' but I think that's because I had built gnuradio from git and installed it locally at some point.

[Alexandru Csete]

Thanks for the info.
Yes, it sounds like you have leftovers from different versions. Gqrx
uses pkg-config to figure out where GNU Radio is installed. So, if you
use GNU Radio from Debian repository and the files should be in /usr/
check that you have /usr/lib/pkgconfig/gnuradio-*.pc files. Then you
could delete the ones from /usr/local/lib/pkgconfig/ which is probably
what gives you trouble.

Alex

[dspstv]

yes, can confirm that gqrx finally compiles under debian.. that libusb "bug" seems to 'by-gone'

Linux dspstv 3.4.0-4.dmz.1-liquorix-amd64 #1 ZEN SMP PREEMPT Sat Jun 23 16:19:15 CDT 2012 x86_64 GNU/Linux

PRETTY_NAME="Debian GNU/Linux wheezy/sid"

NAME="Debian GNU/Linux"

[Alexandru Csete]

That's good news, thanks for the info!
I assume this means that also runs without crashing (as far as I
remember the problem was with crashes, not compilation).

Alex

[Jasper Ragworth]

I don't think so. I'm on up-to-date debian testing + gqrx from git and I'm still seeing crashes on frequency change. My current workaround for this is to start gqrx with strace -eopen. This seems to impair gqrx to the point where the race condition doesn't occur :-)

[Jasper Ragworth]

Just to be clear, I'm talking about FCD here, not anything else.

[Alexandru Csete]

Thanks for the info. It is indeed only the FCD block that has problems
with libusb-1.0.9

Alex

[Pawel Janowski]

microPC (Allwinner A10 : Cubieboard.org) as RTL-SDR server and GQRX as Client : http://sq7mru.blogspot.com/2012/12/cubieboard-w-suzbie-amatorskiej-cz2.html (in Polish)

with Regards

Paweł, SQ7MRU

[Alexandru Csete]

That very cool Pawel! Thanks for the info.

Alex

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[George -]

Sorry, might be off topic for group...

I got the standard blue SDR dongle working on Gqrx on a Raspberry Pi.

I can tune into a local radio station and does not sound to bad...

But not able to tune into any aircraft traffic comm's.

still using the standard extendable aerial that came with the dongle.

Suggestions.

G

[Simon Kennedy]

Hi George,

The most likely answer to your question is that you need a better antenna, higher up, preferably outside and in the clear and at the appropriate length for the frequency band you want to receive.

While airband signals are not too far from FM radio in wavelength terms they are a lot weaker unless you receive a transmission from a plane directly overhead.

However, before you change the antenna make sure you have optimised the gain settings while listening to the radio station. I think there are two gain sliders shown with the RTL device and there is a checkbox to set hardware AGC. Optimise the setting of these for best signal strength, highest signal to noise ratio and fewest intermodulation products (spurious signals that appear when the gain is set to high). Make sure you make a note of the best settings, then try listening for a local air comms. If you are near a large airport there should be several busy frequencies but if you are a little off the beaten track transmissions may be few and far between.

However, don't expect much from that little antenna. Search the internet for ways to make a cheap airband antenna that you can put in a better location. 

Hope this helps

Simon.

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[George]

Hi Simon

Ye... starting to think this little antenna is included to just drive you mad to go back to the original seller and then buy a proper unit.

I've found a pdf that actually list different frequencies and antenna lengths... Just confused, surely you don't buy a antenna for every frequency...

Was able to start getting intermittent air comms as planes travel close by, I'm about 5km from a local busy air port and 10km from OR Tambo (Johannesburg International)

Did discover I need to be scanning for AM signals, hehehe. 

I've placed my Piaware antenna on the roof, original unit cut down to length, thinking I will place the radio antenna next to it. Just need to figure out how to place it up there, run a co-ax cable down to study and have a good/strong enough signal still, atm the piaware is also hanging in the roof.

noob at this...

G

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[Simon Kennedy]

Hi George,

you don't need an antenna for every single frequency but for best performance you need one for each block of frequencies. For example a VHF (118 MHz to 136 MHz) airband antenna will not work well at UHF (> 300 MHz) frequencies and vice versa. Similarly an ADS-B antenna will not work well at lower frequencies as the ADS-B signal is transmitted at 1090 MHz. However, there is an antenna called a discone that is a bit of a compromise but is what I would suggest as a good all rounder to get you going for VHF/UHF monitoring.

You will probably get good local advice from a South African amateur radio shop and they will almost certainly be able to sell you a discone antenna.

Regards

Simon.

[George]

Hi Simon.

Thanks, much appreciated.

G

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