a/d scan rate

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I need to read a 40.1khz signal.  I know there is a rule of 2.  So that
means an A/D of 80khz.  But I need to do this real time.  Can anybody
make a suggestion.  A single analog chanel that can read at 80khz or
higher.

Also price is a consideration.  Any suggestions would be helpful.

Thank you.

Re: a/d scan rate

snipped-for-privacy@gmail.com wrote in news:1131664296.877968.224320

80.2k is a mathematically ideal number.  If your bandwidth really goes to
40.1k, you should be acquiring at about 95k or higher.

--
Scott

Re: a/d scan rate

The number two is the minium you should use. Better is an higher number. If
you have an Sinus of 40.1k exactly and sample with 80.2k exactly, and the
first sample is in the zero crossing, allt he samples will be 0 and you have
a DC signal after the conversion.
Of course this "never" happens. But any samplerate under the 80.2 will have
a this problem with some frequencies.

Alexander

Re: a/d scan rate

There is another reason why the sampling rate should be higher.  Any
frequencies above 40.1kHz with be aliased down.  You should try and filter
anything above nyquest or half sampling rate otherwise it will introduce
noise into the system.  IIRC telephone lines have a bandwidth of 3.3kHz and
have a sampling rate of 8kHz.  They use multipole filters to reduce
frequency components above inquest.

Re: a/d scan rate

I forgot to mention it.

Re: a/d scan rate

FWIW - Phones operate on 3.2KHz.  Sampled at 2.5 x 8 bits yields the
commonly known voice bit rate of 64 Kbps.  If you steal one bit in eight for
other purposes, you get another commonly known rate, 56 Kbps.  The 2.5 is
higher than the 2x Nyquist reuires to account for rolloff of non-ideal
filters.