Creating an AM signal
We create an AM signal using
f(out) = f(carrier) * ( f(audio) + 1 )
with this script:
which modulates a 455Khz carrier with a 1000 Hz tone at 70%, followed
by a bandpass filter with low cutoff at 75Khz and high cutoff at 2mhz,
and 50Khz transition band width, and creates short data type output.
Run this briefly to create a file dummy.dat. Then convert to unsigned
and reset to about 2048 center.
$./sign2unsigned dummy.dat dummy_us.dat 0 500000 -30750
The amplitude of the signal is about 4000, so the above starts converting at the beginning of the source file, for 500,000 samples, and subtracts 30750 from each sample to center it about 2048. Then convert the raw data to numerical using
$./raw2num dummy_us.dat dummy_us.num 0 65536
then display with gnuplot and get
