I am an extreme beginner with SDR. I am trying to use the 820T2 & SDR device to capture uplink gsm packets sent by my phone to the nearest Base Station. I have an Rx Monitor App installed on my phone to see my Uplink and Downlink channel frequency (904MHz and 949MHz respectively). I am using grgsm_livemon on a Ubuntu VM installed on VMWare to scan for packets. I am able to capture downlink data easily via gr_gsm. However, I see no signals on the frequency monitor of gr_gsm in the uplink frequency. I tried to move a few steps within the band to find any peaks, but unfortunately no result.
I also tried getting a call on my phone and then I see some instantaneous peaks throughout the whole Uplink spectrum for unknown reasons. (This is totally opposite of what I thought, I believed a GSM uses TDM and FDM for multiplexing multiple users. And a particular user would be assigned a static frequency and one or multiple time-slots for communication, and hence I should see instantaneous peaks at my uplink frequency only). Also, I am unable to capture any packets from these instantaneous peaks.
I would appreciate it if I get to know what am I missing to capture the uplink data or any tweaks to do it. In case you need any more information, Let me know. Thanks in advance!
d) grgsm DOWNLINK output