Hi Stefan,

You wrote:
> ...
> How have you found that? By guessing? :-)
> ...

The only guess was the sample rate used, 48 kHz.

(@Daniele: 48/2 = 24 kHz)

Many months ago I made some tests with a cheap USB-sound-system running at
48 kHz of sample rate. It has almost no anti-aliasing filters in front.

Using a ferrite antenna & 60dB pre-amp (*.*) five higher Nyquist ranges
could be seen folded in back and forth - a very special type of "Harmonic
Mixing".

I had the silly idea of recording all available signals at one shot,
forgetting that all horrible local interferences will accumulate too inside
0-24 kHz...

http://www.df3lp.de/misc/multinyquist-2.png .

73 from Kiel,
Peter