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Is there any way to use a DSP (with a program) to analyze upwards of 50
frequencies (at at least 50MHz), or do I need at least 50 notch filters?
 
If I can use a DSP, please tell me how.
 
Please send all responses in E-mail (my news system is on acid)
 
peterc@sugar.neosoft.com           "Listen, there's a hell of a good
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 In a previous article, peterc@sugar.hackercorp.com (Peter Creath) writes:
>
>Is there any way to use a DSP (with a program) to analyze upwards of 50
>frequencies (at at least 50MHz), or do I need at least 50 notch filters?
> 
>If I can use a DSP, please tell me how.

Sure, there is.  You just need to do a bit of analog pre-processing.  This
little trick assumes that you want to analyze high frequencies, but they are
all closely grouped together.  Say (for instance) that you want to analyze a
spread of 100 KHz, but these are centered on 50 MHz.  You need to use a mixer
to downconvert the frequencies (in analog fashion, since this is an analog
mixer we are talking about) so that they fall within the range of something
convienient to work with in digital form.  This is kind of a function of your
DSP chip, but mixing with 49.8 MHz will change the band of interest into
one centered about 200 KHz rather than 50 MHz.  If you pick a closer mixing
frequency, you can even convert such signals closer to DC.  Make sure you
filter out any unwanted high frequency components generated by the mixer, and
then do your sampling and DSP stuff.  Since the frequency range is lower, the
DSP chip can handle it directly.  When you get the answer, just add the mixing
frequency to any values to find out where things really are with respect to
your original signal.

This trick assumes you have a pretty good mixer and local oscillator that
can produce some very pure tones for the mixing process.  It can be done, but
you have to be careful.  

>Please send all responses in E-mail (my news system is on acid)
> 
>peterc@sugar.neosoft.com
>peterc@sugar.hackercorp.com

  -dave

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Dave McMahan                            mcmahan@netcom.com
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