Re: [Discuss-gnuradio] Unable to see GSM signals in USRP Spectrum Scanner (FFT)

[CEL]

Hi Amrit,

Well, usrp_spectrum_sense is a hopping observer, and GSM is a hopping
system: your probability of intercept is rather low.

Your probability of intercept is in fact, really zero, if your phone
doesn't do GSM (2G), but uses 3G (UMTS) or 4G (LTE): these use other
frequencies altogether. So, make sure your phone really does do GSM.

You also don't even have to look at the GSM900 uplink at all:
Telefonica (which Aldi resells) doesn't use that band at all.

The spectrum sense application is really badly suited for this kind of
task, as it hops: Instead, simply look at the whole band at once. A
simple GNU Radio Companion flow graph connecting the USRP source (samp
rate = total uplink bandwidth) to a Qt GUI Frequency Sink would make
more sense.

A word of secondary advice: If you're planning to experiment with 2G
networks of your own, or doing something about the basic properties of
microwave propagation and so on, observing spectrum of GSM is a
worthwhile thing to do. Just be warned that it will be increasingly
hard to find GSM signals "in the wild": T-Mobile will switch off GSM
end-of-2020, and thus, up to then, all phones that can do both LTE and
GSM will be instructed to use LTE whenever possible. Since there won't
be much Machine-to-Machine GSM-only  (which I assume are the primary
users that won't be able to switch) user equipment in cities, you'll
see that increasingly many phones don't use GSM anymore at all – even
if the network still exists; the calculation is very simple: The amount
of spectrum necessary to let a single user do a GSM phone call is worth
MB/s for a lot of LTE users. Thus, everybody not using GSM is desirable
for network operators.

Best regards,
Marcus

On Mon, 2018-06-18 at 11:25 +0200, Amrit Zoad wrote:
> Greetings everyone,
> 
> I hope everyone is having a good day.
> 
> I have installed GNURadio 3.7 and I wanted to see the GSM signals of my phone 
> (when I call someone) with the application "USRP Spectrum Scanner (FFT)". 
> But, I was unable to see any fluctiations in the spectrum from 890 MHz to 915 
> MHz & 1710 MHz to 1785 MHz. My location is in Germany and I own a sim card of 
> Aldi Talk (MEDIONmobile).
> 
> Then I tried with my phone's Bluetooth 5.0 and I could see the frequency 
> hopping from 2.4 GHz to 2.44 GHz along with the light Wi-Fi signals in the 
> spectrum.
> 
> I have the Etttus Research USRP B210 with Bandwidth of 56 MHz (of the 
> front-end filter) and thus I am setting the sampling rate to 40 MHz. The 
> antenna also works from 850 MHz to 6.5 GHz. so no problem with that as well.
> 
> What could be reason for me not able to see my phone's GSM signals in the 
> spectrum scanner?
> Your help would be very valuable.
> 
> Best regards,
> Amrit Zoad 
> +49 177 8474550
> 
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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