multirtl | hackrf-sox & channelize | hopping
WARNING: cs8 FILE EXTENSION DOES MATTERS!
echo $arfcn
freq=`arfcncalc -a $arfcn -d`
echo $freq
echo $ppm
invppm=$(( 0 - ppm ))
echo $invppm
capture for 10 seconds (10 x times more sambles than bandwidth)
hackrf_transfer -r $arfcn.hrf.cs8 -f $freq -a 1 -l 40 -g 24 -s 2e6 -n 20000000 -C "$invppm"
inspectrum --rate 2e6 $arfcn.hrf.cs8
sox -t raw -b 8 -e signed-integer -c 2 -r 2000000 $arfcn.hrf.cs8 \
-t raw -b 32 -e floating-point -c 2 $arfcn.hrf.sox
# rate 1000000
# -v 2
inspectrum --rate 2e6 $arfcn.hrf.sox
grgsm_channelize -s 2e6 -f $freq -i $arfcn.hrf.sox $arfcn
inspectrum $arfcn.hrf/out_$arfcn.cfile
Let’s try to decode the captured signals
# does not work
grgsm_decode --mode=BCCH --timeslot=0 --cfile=$arfcn.hrf.sox -v --arfcn=$arfcn --samp-rate=2e6
# does not work either
grgsm_decode --mode=BCCH --timeslot=0 --cfile=$arfcn.hrf/out_$arfcn.cfile -v --arfcn=$arfcn
Let’s say we need to target those two ARFCNs
23 ---> 939.6 bcast 939600000 26 ---> 940.2 hop 940200000 673 ---> 1837400000 (broadcast) 725 ---> 1847800000 (traffic)
and check there is something going-on at those frequencies with GQRX
The minimum bandwidth we need would be
>>> ( 940200000 + 100e3 ) - ( 939600000 - 100e3 ) 800000.0 >>> ( 1847800000 + 100e3 ) - ( 1837400000 - 100e3 ) 10600000.0
but since the channel bandwidth becomes 1M as for channelize
>>> ( 940200000 + 500e3 ) - ( 939600000 - 500e3 ) 1600000.0 >>> ( 1847800000 + 500e3 ) - ( 1837400000 - 500e3 ) 11400000.0 wide=2000000 wide=12000000
and the center frequency would be
>>> ( 940200000 + 939600000 ) / 2 939900000 >>> ( 1837400000 + 1847800000 ) / 2 1842600000 center=
check that normal 2M wide capture works and inspect the result
invppm=-22 hackrf_transfer -r air.cs8 -f $freq -a 1 -l 32 -g 24 -s 2e6 -n 10000000 -C "$invppm" inspectrum --rate 2e6 air.cs8
we can now proceed and capture that wider band. Also inspect the result (you should notice both channels in there - each one being close to every end of the band)
hackrf_transfer -r $arfcn.hop.hrf.cs8 -f $center -a 1 -l 32 -g 24 -s $wide -n $(( wide * 10)) -C "$invppm" inspectrum --rate $wide $arfcn.hop.hrf.cs8
here we do not need to re-sample, as channelize will do the job later on
sox -t raw -b 8 -e signed-integer -c 2 -r 12000000 $arfcn.hop.hrf.cs8 \
-t raw -b 32 -e floating-point -c 2 $arfcn.hop.hrf.sox
ls -lhF $arfcn.hop.hrf.*
you are now ready to channelize then de-hop