Cannot get packet using grgsm_livemon

[jjbaek35]

Hi~ all.

I just installed successfully grgsm_livemon with RTL-SDR dongle. When I run the capture command, I can't capture any signals or packets. I don't know why I can't not capture any packets of GSM band. Please look over my attached figure. I put the initial frequency 861e6. There are two messages "PLL not locked!" which means dongle can't set the requested frequency. I suspect that point. but I don't know why.

[E3V3A]

@jjbaek35 Unfortunately you're not supplying enough info to help sort your problem. So most likely the problem is you, and not gr-gsm, as it seem to work in your screenshot. Things to consider:

• You need to do a GSM scan first to get an active channel. (ARFCN)
• You need to calibrate to get the correct PPM
• You need to get the sample rate right (~1800000-2M)
• You need to have a good antenna
• You need to set the gain right (~30 for good RTL SDRs)

[jjbaek35]

My dongle RTL-SDR has 1PPM TCXO oscillator, it means calibrating isn't needed. Anyway, I tried to calibrate with Kalibrate as belows: Could you let me know how can I get the signal?

ubuntu@ubuntu:~/kal/kalibrate-rtl$ kal -v -s GSM900 -g 50 Found 1 device(s): 0: Generic RTL2832U OEM

Using device 0: Generic RTL2832U OEM Detached kernel driver Found Rafael Micro R820T tuner Exact sample rate is: 270833.002142 Hz [R82XX] PLL not locked! Setting gain: 50.0 dB kal: Scanning for GSM-900 base stations. channel detect threshold: 39540.808594 GSM-900: chan: 6 (936.2MHz - 5.178kHz) power: 1593200.24 chan: 11 (937.2MHz - 30.630kHz) power: 222674.68 chan: 13 (937.6MHz + 31.674kHz) power: 112603.63 chan: 14 (937.8MHz + 22.514kHz) power: 1510918.61 chan: 16 (938.2MHz + 36.322kHz) power: 290972.69 chan: 18 (938.6MHz - 17.571kHz) power: 426886.58 chan: 21 (939.2MHz - 18.739kHz) power: 336030.01 chan: 22 (939.4MHz + 6.370kHz) power: 2732522.87 chan: 29 (940.8MHz - 4.048kHz) power: 47734.90 chan: 82 (951.4MHz + 32.317kHz) power: 50797.78 chan: 88 (952.6MHz + 16.579kHz) power: 1060392.23

ubuntu@ubuntu:~/kal/kalibrate-rtl$ kal -v -s GSM850 -g 50 Found 1 device(s): 0: Generic RTL2832U OEM

Using device 0: Generic RTL2832U OEM Found Rafael Micro R820T tuner Exact sample rate is: 270833.002142 Hz [R82XX] PLL not locked! Setting gain: 50.0 dB kal: Scanning for GSM-850 base stations. channel detect threshold: 341526.327240 GSM-850: chan: 231 (889.8MHz + 38.297kHz) power: 353247.72

ubuntu@ubuntu:~/kal/kalibrate-rtl$ kal -v -s GSM850 -g 50 Found 1 device(s): 0: Generic RTL2832U OEM

Using device 0: Generic RTL2832U OEM Found Rafael Micro R820T tuner Exact sample rate is: 270833.002142 Hz [R82XX] PLL not locked! Setting gain: 50.0 dB kal: Scanning for GSM-850 base stations. channel detect threshold: 341526.327240 GSM-850: chan: 231 (889.8MHz + 38.297kHz) power: 353247.72

[E3V3A]

1. You are not calibrating it right. The right command is: kal -g 25 -c 22. That should give you a PPM.
2. You're running in a VM, so there seem to be USB latency causing dropped packets which prevents proper PLL locking. Just ignore.

[jjbaek35]

Thank you so much, E3V3A! I run that command with options, so what is the ppm value? and so, I need to install grgram on host OS without VM to remove the usb latency? I checked the source code "PLL not locked", my version is different. Let me try to update all source code and compile again.

Thanks so much again!

root@deli:~# kal -g 25 -c 22 Found 1 device(s): 0: Generic RTL2832U OEM

Using device 0: Generic RTL2832U OEM Found Rafael Micro R820T tuner Exact sample rate is: 270833.002142 Hz [R82XX] PLL not locked! Setting gain: 25.0 dB kal: Calculating clock frequency offset. Using GSM-900 channel 22 (939.4MHz) average [min, max] (range, stddev)

• 7.274kHz [5874, 8671] (2797, 860.250488) overruns: 0 not found: 15 average absolute error: -7.743 ppm

[jjbaek35]

I just updated librtlsdr, but still can't not get the GSM packets. I don't know why the 1700000 Hz and 1625000 Hz are appeared. I suspect the usb latency, how can I solve it?

root@deli:~/2gsm/librtlsdr-development/build# grgsm_livemon -f 934000000 -p -7 linux; GNU C++ version 6.3.0 20170221; Boost_106200; UHD_003.009.005-0-unknown

gr-osmosdr 0.1.4 (0.1.4) gnuradio 3.7.10 built-in source types: file osmosdr fcd rtl rtl_tcp uhd miri hackrf bladerf rfspace airspy soapy redpitaya Found Rafael Micro R820T tuner Using device #0 Realtek RTL2838UHIDIR SN: 00000001 Found Rafael Micro R820T tuner [R82XX] PLL not locked for 1700000 Hz! Exact sample rate is: 2000000.052982 Hz [R82XX] PLL not locked for 1625000 Hz!

[E3V3A]

Looking at that picture, there is nothing on that frequency, so you didn't scan for any ARFCNs first. Once you find an active ARFCN then re-run with that frequency. You need to read the Wiki and look at you tube how to do this.

[jjbaek35]

Ok Thank you, eventually, I got the GSM packets. US use PCS band 1900 Mhz, so I scanned

kal -s PCS -g 40

I found the beacon signal from T-mobile. The key is the frequency.

[ChillVibesMushroom]

So if grgsm scans on a gain of 30

I use kal -s 1900 -g 30 to pull the same info and some with grgsm then I use gqrx to get a more focused freq

[Polymorphic86]

Ive tried all the above and I'm running dragonOS and all I get is no valid pll values for xxxxxxxxxx Hz! R81_set_freq: failed =-1 all the way down the terminal