> >This is just a guess, but I think he wants to digitize the
> >50KHz signal and do some processing on it

I was assuming that this was some known tone from a HF
source (eg bat, ultrasonic transducer, dolphin, Barry Gibb),
in which case it's enough to know that the signal is there or
not. Perhaps there's some measurement like phase shift
that needs doing, and which could be done digitally, rather
than trying to determine the analogue quality of the wave.

Maybe the OP can fill us in a little

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