Gsm and usrp2

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

I’ve got an older Nokia cell phone with some monitoring software where I
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
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
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
my configuration too.

Setting is as follows:

usrp2->multiply(1000000)->constellation sink

gnuradio 3.3

30 db LNA in front of the usrp2


gain:20 db

Constellation Sink:

everything standard except
symbolrate: 270800 (gsm bitrate)

Hopefully somebody can help this is strange