Get signal level using rtl_power_fftw - very long  - LamaBleu
Resulting plot : https://imgur.com/45sn6wG

2 files : level-fftw.sh levels.gnu

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level-fftw.sh :  (start 98Mhz, stop 108 MHz, step 25kHz)
================

#!/bin/bash
rm levels.csv; touch levels.csv
stepper_start_int=98000000
stepper_stop_int=108000000
stepper_hop_dec=0.2
stepper_step_int=25000
i=$((stepper_start_int))
end=$(($stepper_stop_int))

while [ $i -le $end ]; do
	FFTW_MES=$(rtl_power_fftw -f $i  -g 450 -b 32  | grep -A17 'frequency' | tail -1 ) >&-
	#sleep 0.1
	LEVEL=$(echo $FFTW_MES | awk '{print $2}')
	echo "Freq:  " $i "     Level : "  $LEVEL
	echo $FFTW_MES >> levels.csv
    i=$(($i+$stepper_step_int))
LEVEL=""
FFTW_MES=""
done
echo "Stepper end.    "
echo "Drawing plot ..."
gnuplot -persist -e "fmax=$i;f0=$stepper_start_int" ./levels.gnu

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levels.gnu :
============

set term qt 0
set title "From   " . sprintf("%8.3f", f0/1000000) . " MHz to " . sprintf("%8.3f", fmax/1000000) . " MHz"
set xlabel "freq. [MHz]"
set xrange [f0/1000000:fmax/1000000]
set yrange [-60:-20]
set ylabel "Signal level [dB] (relative)"
set origin 20,20
set format x "%1.0f"
set size 0.95,0.95
set key at graph 0.95, 0.9
set origin 0.0,0.0
plot "levels.csv" using ($1)/1000000:($2) with lines lc rgb '#ff4500' title " "
replot
pause 10