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ptrkrysik / gr-gsm

Gnuradio blocks and tools for receiving GSM transmissions
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Problem with HackRF #473

Open Dimtios opened 5 years ago

Dimtios commented 5 years ago

Hello, I recently bought HackRF ONE and faced a problem, when using grgsm_livemon, everything goes well, but when you capture a channel, it becomes impossible to run it using grgsm_decode, wireshark does not see anything. With Rtl-Sdr v3, everything goes fine. Tell me what could be the problem with?

Capturing with: grgsm_capture -f 950.2M -g 40 -T 15 -s 1M out_hackrf_1S_15T.cfile

Console info output:

[INFO] [UHD] linux; GNU C++ version 8.2.0; Boost_106700; UHD_3.13.1.0-3
gr-osmosdr 0.1.4 (0.1.4) gnuradio 3.7.13.4
built-in source types: file osmosdr fcd rtl rtl_tcp uhd miri hackrf bladerf rfspace airspy airspyhf soapy redpitaya freesrp 
Using HackRF One with firmware git-509c8f4 
Decoding with:
grgsm_decode -f 950.2M -s 1M -c out_hackrf_1S_15T.cfile

Responding to command hackrf_info


hackrf_info version: git-509c8f4
libhackrf version: git-509c8f4 (0.5)
Found HackRF
Index: 0
Serial number: 0000000000000000909864c8385e1dcf
Board ID Number: 2 (HackRF One)
Firmware Version: git-509c8f4 (API:1.03)
Part ID Number: 0xa000cb3c 0x00554358
CPLD checksum: 0x05829db7

When using Rtl-Sdr v3 capturing with: grgsm_capture -f 950.2M -g 40 -T 15 -s 1M out_rtlsdr_1S_15T.cfile

[INFO] [UHD] linux; GNU C++ version 8.2.0; Boost_106700; UHD_3.13.1.0-3
Detached kernel driver
Found Rafael Micro R820T tuner
Reattached kernel driver
gr-osmosdr 0.1.4 (0.1.4) gnuradio 3.7.13.4
built-in source types: file osmosdr fcd rtl rtl_tcp uhd miri hackrf bladerf rfspace airspy airspyhf soapy redpitaya freesrp 
Using device #0 Realtek RTL2838UHIDIR SN: 00000001
Detached kernel driver
Found Rafael Micro R820T tuner
[R82XX] PLL not locked!
Exact sample rate is: 1000000.026491 Hz
[R82XX] PLL not locked!
Allocating 15 zero-copy buffers
Reattached kernel driver

Decoding with: grgsm_decode -f 950.2M -s 1M -c out_rtlsdr_1S_15T.cfile

HackRF cfile Rtl-Sdr cfile

velichkov commented 5 years ago

Hi @Dimtios,

I recently bought HackRF ONE and faced a problem, when using grgsm_livemon, everything goes well, but when you capture a channel, it becomes impossible to run it using grgsm_decode, wireshark does not see anything. With Rtl-Sdr v3, everything goes fine. Tell me what could be the problem with?

The HackRF has a big DC offset/spike that most probably causes this problem. Screenshot

See: https://github.com/mossmann/hackrf/wiki/FAQ#what-is-this-big-spike-in-the-center-of-my-received-spectrum https://github.com/mossmann/hackrf/wiki/FAQ#how-do-i-deal-with-the-dc-offset

grgsm_livemon works because it captures with an 400kHz offset but latest versions of grgsm_capture does not support capturing with an offset. This feature was removed in https://github.com/ptrkrysik/gr-gsm/commit/81ba56f59dcefb2d39d023c68d3a077b4a321520

See also. https://groups.google.com/d/msg/gr-gsm/Zt47sSi3NOM/USE9IGlWAAAJ https://groups.google.com/d/msg/gr-gsm/FhqNPtk3GME/28pMXO8SAgAJ https://dsp.stackexchange.com/questions/40734/what-does-correcting-iq-do?newreg=aea502529d314116984a46b8e8b34e3a

Capturing with: grgsm_capture -f 950.2M -g 40 -T 15 -s 1M out_hackrf_1S_15T.cfile

Console info output:

One possible solution to the DC offset problem is to capture with some offset, on a different center frequency then the one that you need and then use grgsm_channelize script to extract the needed ARFCN or create a simple gnuradio flowgraph an use the Rotator block to shift the center frequency similar to what grgsm_livemon.grc does, together with a file source block and a file sink blocks.

Another solution that you could try is to use an older grgsm_capture version (https://github.com/ptrkrysik/gr-gsm/commit/57431ed50cb3e2530e6f5337fea9a98c4e6b4b2d) or try reverting https://github.com/ptrkrysik/gr-gsm/commit/81ba56f59dcefb2d39d023c68d3a077b4a321520

P.S. We have a mailing list where you could post questions/problems like this one.