FPGA Central

In article ceBOa.14788$[email protected], Jesper Buch at
[email protected] wrote on 07/08/2003 11:16:

> ---- Original Message -----
> From: "praveen" <[email protected]>
> Newsgroups: comp.dsp
> Sent: Tuesday, July 08, 2003 4:37 PM
> Subject: choosing a sampling rate lesser than nyquist rate(sub nyquist rate)
>
>
>> Hello,
>> I have a signal consisting of 4 harmonics (200k,400k,600k,and 800k Hz)
>
> You will never be able to produce an 800 Khz frequency with less than the
> double samplerate !

"double" is not sufficient. it has to be *more* than double.

>
>> and dc component.The signal is very pure and SNR better than 60 dB. I
>> have to sample it in sub Nyquisit rate(lesser than 1600k). What
>> sampling rate should i choose so that there no alaising. I cannot
>> chose higher sampling rate because of my hardware constraints.
>>
>
> Nyquist.
> Since a sine wave has 2 boundaries ( high and low) it takes 2 mesurements to
> mesure a wave.
> To be able to mesure at an 800 khz sine you have to mesure 2 * 800 khz =
> 1600 k times pr second.

double is not sufficient. those two samples ("measurements") could be from
an infinite number of sine waves. it is a mistake to assume that the two
samples came from the top and the bottom of the sine wave.

r b-j