tasa wrote:
> You said that you limited audio bandwidth
> inside program processing but when you synthesized audio output
> spectrum is it also limited bandwidth or not? My headphone is a very
> good HI-FI product and I detect easy all unwanted products?
Tasa,
SDRadio first moves the input signal to baseband using a quadrature
software mixer and a NCO. After this down-conversion a complex FIR lowpass
filter is applied with cutoff frequency = 9600Hz
Then the baseband signal is demodulated, which means that for SSB signals
the wanted sideband is recovered, and for AM or FM signals the modulation
info is extracted.
At this point a bandpass filter is applied, whose low and high limits are
set by using the light blue window with borders settable with the mouse.
Then AGC is applied and the binary data are sent to the sound card DAC
to be given back to the analog realm.
So the output signal does not contain components higher in frequency than
the highpass frequency you have set with the mouse or 9600Hz, whichever is
less. This of course is true if the analog reconstruction filter after the
DAC on the sound card does its work in an acceptable way.
73 Alberto I2PHD
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