At 03:45 AM 9/20/99 -0400, Mario wrote:
>Thanks for all the help and suggestions from everybody. Sorry my 'input'
>has been so long in coming, but I have been overwhelmed with things to
>do which were not remotely connected to electronics. Here, however, is
>my 'feedback' on some of the suggestions to correct my problem (I
>haven't had a chance to actually implemented any suggestions yet). I
>apologise for the mass reply, as it is aesthetically unpleasing and
>quite possibly distasteful, but the most efficient for this situation
>(that is, if anyone is still paying attention to this thread).

1. Remember the sampling rate must be at least 2x the max important
frequency in the signal. Better if 10x (the usual design rule).

2. The top frequency with any information content is 1/2 the sampling rate
of the ADC (Nyquist theorem).

3. Include an 'anti-aliasing' filter on the signal supplied to the ADC.
This should be a 2nd-order Bessel low-pass with 3 dB point at 1/2 sampling
frequency to maximize bandwidth (instrumentation case), or a Butterworth at
1/10 the sampling rate (audio case). In any event, the roll-off should
start at no higher than 1.5x the maximum signal frequency component needed.

4. The effect of white noise is based on the sqrt of the bandpass. So
reducing bandpass by 9x increases S/N by 3x.

5. Post-ADC digital filtering is much less useful.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral@lcfltd.com
Least Cost Formulations, Ltd.                   URL: http://lcfltd.com/
824 Timberlake Drive                            Tel: 757-467-0954
Virginia Beach, VA 23464-3239                   Fax: 757-467-2947

"Vere scire est per causae scire"
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