--- In [email protected], Nick Whyborn <[EMAIL PROTECTED]> wrote:
> Perhaps you have a dc offset in the test_audio.wav data which would
> result in the presence of the carrier after the modulate step?
>
> Nick, g4jnx.
>
Nick-
Great minds work alike :) Last night after my last posting and some
more thought I came to the same conclusion.
I modified my Matlab code to remove the DC offset with the detrend
function (which accomplishes x - mean(x)). The DC offset of the
modulating signal is now down in the noise.
The resulting modulated signals now look much better. Still a bit of
carrier but it is suppressed to a much more respectable level (about
30 dB down from voice peaks) I haven't checked to see how that
compares with the suppression when driven with a single or two tone
signal yet. Not the sort of thing I'd want to put on the air, but
entirely adequate for the purpose of testing different SDR
demodulation algorithms.
After a bit more testing and fine tuning I'll generate some more test
files with different modulation formats.
-Ray WB6TPU
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