Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
Subject: Re: Undersampling and its complement?
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Date: Sat, 2 Nov 2002 08:03:55 -0000
NNTP-Posting-Date: Sat, 02 Nov 2002 08:03:58 GMT
"James Meyer" wrote in message
> I have to extract information from an 8 MHz signal. Nyquist says that
> 16 MHz should be my minimum sampling frequency.
No it doesn't.
This is a *very* popular *misconception*. The Nyquist Sampling theorem
says that you have to sample at twice the *bandwidth" of the signal. If
a frequency is centred at 100Mhz, and it only has sidebands to say
10Khz, you only need to sample at a rate of 20Khz. In fact it can be
less, if this sideband is composed of a line spectrum, e.g. TV., since
in this case, the sidband width is *not* the actual BW.
>However... if the bandwidth of
> the signal I'm interested in is something like 10 KHz centered around
> then I really only need to sample at 2 times 10 KHz, let the signal be
> or aliased down to 0 to 10 KHz and I wil not have lost any
So you understand this, but still quote an incorrect version of a
theorem that applies to it.
> My question is.... is there anything similar regarding generating an 8
> MHz signal? Do I really need a 16 MHz or better DAC in order to
generate 8 MHz
> signals if the signal will not have a very wide bandwidth?
Multiply the signal down to a lower frequency.
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