Hi everybody I’m trying to find a frequency correction burst of gsm.
This Burst is due to GMSK Modulation 67,7 kHz obove the carrier and
unmodulated.
I’ve got an older Nokia cell phone with some monitoring software where I
can
read out the arfcns the phone sees and thus the frequencies of the BCCH.
The phone sees a BCCH at 940MHz but if I use the usrp2/usrp1 and the
Constellation Sink in GRC I can’t see the phase shift of pi/2. But if I
use
the FFT sink I can see the BCCH, so it has to be there or am I mistaken?
The thing is if I use as file source the captured data from
https://svn.berlin.ccc.de/projects/airprobe/attachment/wiki/DeModulation/capture_941.8M_112.cfile
it works fine and I can see thephase shift of pi/2.
I know they’re doing some processing before but it should be possible
with
my configuration too.
Setting is as follows:
usrp2->multiply(1000000)->constellation sink
gnuradio 3.3
30 db LNA in front of the usrp2
USRP2:
gain:20 db
dec:192
freq:940M
Constellation Sink:
everything standard except
symbolrate: 270800 (gsm bitrate)
Hopefully somebody can help this is strange