Re: How can I capture the GSM signal?

[Cinaed Simson]

On 06/22/2017 03:35 PM, gsmfor wrote:
>
> Hi all~
>
>
> I just installed grgsm_livemon with RTL_SDR dongle.
>
>
> I'm trying to capture signals and packets by wireshark but there is no
> data from captured signal.
>
> Please look at below, and give me a hint how can I capture the GSM signal?

First, read the text in the terminal window at the top.

What does it say?

[R82XXX] No valid PLL values for 1800225000 Hz
R82xx_set_freq: failed=-1

Do you know how large 1800225000 Hz is? It's 1.80022500 GHz - the rtl
dongle receive signals at that frequency.

Use Google to find the maximum frequency for your rtl dongle - it's
probably around 1.1-1.2 GHz if you're lucky.

But there's no way the rtl dongle will receive signals at 1.8 GHz.

Here's you answer: as long ad you try to capture a signal at 1.80022500
GHz with a rtl dongle you will NEVER capture the signal.

-- Cinaed

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[Cinaed Simson]

On 06/22/2017 05:49 PM, gsmfor wrote:
>
> Thank you so much, Cinaed
>
> Yes, I got it,
>
> So, I'm trying to capture by adjusting frequency range from 850 to 990 MHz.
>
> But, it also doesn't show any packet. like 2b 2b 2b ...

As I already mentioned, your rtl dongle is tuned to 1.8 GHz - it is NOT
tuned to 850-990 MHz.

Type

grgsm_livemon --help

By default the frequency is set to 939.4 MHz on the rtl dongle.

So if add 900 MHz in our GUI, then frequency for the dongle will be set
to be over 1.8 GHz.

At least that's my take based on the error PLL error message from the
rtl dongle and the frequency displayed in your GUI.

I haven't used grgsm_livemon yet - I haven't had time. I hope to get
started on GSM in July.

Also, you should use grgsm_scanner so you have idea where to look. Type

grgsm_scanne --help

>
> As I know, BTS should sending common signal to find the phone through C0.
>
> In that case, it's downlink.
>
> If so, the dongle can listen downlink or uplink, or both?

One or the other but not both - the downlink may be easier. I really
don't know - it's what I was told.

And I believe the uplink and download link are separated by 45 MHz. In
any case the uplink and downlink are separated by more than the
bandwidth of the rtl dongle.

In short, I hardly know anything GSM - so check everything I say.

-- Cinaed


>
> Best,
>
>
> 2017년 6월 22일 목요일 오후 5시 23분 22초 UTC-7, deanic 님의 말:

> <https://groups.google.com/d/msgid/gr-gsm/966d3b18-5e80-405c-984c-758a9cb64394%40googlegroups.com?utm_medium=email&utm_source=footer

> <https://groups.google.com/d/msgid/gr-gsm/966d3b18-5e80-405c-984c-758a9cb64394%40googlegroups.com?utm_medium=email&utm_source=footer>>.
>
> > For more options, visit https://groups.google.com/d/optout

> <https://groups.google.com/d/optout>.

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[Cinaed Simson]

The PLL error indicates the the rtl dongle can't set the requested
frequency.

And yet you mindlessly keeping setting it to the same frequency.

I suggest you spend some time learning about your rtl dongle - in
particular the minimum and maximum frequencies operational frequencies.

Also, RTFM - type

grgsm_livemon --help

Presumably you haven't read the help which is why you can't understand
why it works "without any specified frequency."

It's because the frequency is specified by default.

-- Cinaed


On 06/23/2017 06:23 PM, gsmfor wrote:
> Cordially, I apologize the same question, even though you explained well.
> But I'd like to solve my problem at any cost.
> My dongle(R820T2 RTL-SDR) frequency range is 24 – 1766 MHz.
>
> The fail error message (over tuning to 1.8 GHz) you mentioned is not
> occurred initially.
> It occurs when I adjust the frequency value in GUI to the 1.7~1.8Ghz,
> That means, grgsm_livemon checks the my adjusting frequency value correctly.
>
> Attached please see the #1 image,
> This is the first view when I run grgsm_livemon.
> It has PLL not locked errors. PLL is Phase Lock Loop which relates to a
> radio crystal oscillator locking a frequency.
> So, I think initially the grgsm_livemon can't tune into the proper
> specified freq.
>
> and look #2 image,
>
> In this figure, I tuned the Frequency over 1.78Ghz as you see.
> In the left below, console shows "No Valid PLL values .. " occurred due
> to the change.
> That means the value in the GUI doesn't mean the incremental value.
> It is the adjusted value which I tuned.
>
> Anyway, I got the reason of "PLL not locked!" error.
> I should set the initial frequency to the dongle which can accept.
> But, I don't know why "PLL not locked error" occurs when it runs first
> without any specified frequency.
>
> Moreover, when I type grgsm_scanner, There is no any response. Just
> exit normally.
>
> I feel my installed SW is not working properly.
> But I have 3 installed grgsm SW. All of them issue the same problem.
>
> Thank you for reading.
>
> 2017년 6월 22일 목요일 오후 8시 9분 54초 UTC-7, deanic 님의 말:

> <https://groups.google.com/d/msgid/gr-gsm/79c398f6-c31e-436d-965b-57f55f5d4c03%40googlegroups.com?utm_medium=email&utm_source=footer
> <https://groups.google.com/d/msgid/gr-gsm/79c398f6-c31e-436d-965b-57f55f5d4c03%40googlegroups.com?utm_medium=email&utm_source=footer>>.
>

> > For more options, visit https://groups.google.com/d/optout
> <https://groups.google.com/d/optout>.
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[Piotr Krysik]

Hi,

Are you sure there is GSM beacon signal at 861MHz? I see nothing there.

For capturing signal to file you should use grgsm_capture.py.

Best Regards,
Piotr Krysik

W dniu 28.06.2017 o 05:24, gsmfor pisze:
> My dongle is R820T RTL2832U a.k.a RTL-SDR, and frequency range is
> approx. 24 MHz – 1766 MHz.
> (product information :http://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/)
>
> You said I'm keeping setting it to the same frequency.
> but I tried many times to change the initial frequency and gain like bellow.
>
> $ grgsm_livemon -f 861e6 -g 40
>
> But it has the same result.(see attached)
>
> You said, It's because the frequency is specified by default.
>
> So if I run "$ grgsm_livemon -f 861e6 -g 40 ",
>
> the frequency is default frequency(934e6) + 861e6 = 179e6 ?
>
>
> Thank you always.
>
>