> To smooth out transitions in the face of noise, it would be helpful to
> know the range of frequencies monitored.  Why only three cycles?  What
> does the noise look like.  Somethimes random noise included with the
> signal will improve detection.
> Wioth more info I may be able to make suggestions.  What is your
> response time?  (Sample time to decision time.)

Hi Gus, thanks for the response.

(1) Range of frequencies: about 150 Hz -- 150000 Hz

(2) 3 transitions for one cycle:

        ...........         ..........
        |         |         |
        |         |         |
  ......|         |.........|
        1         2         3

   Right now, that's all I'm measuring, but the noise is interfering
   with the signal.  I'm open to any SW/HW suggestion.  The problem is
   that I'm seeing noise primarily at *low* freqencies, around the edges
   of each transition.  At high frequencies, the transitions are pretty
   stable.

(3) The noise looks like jagged high frequencies as the transition edges
   low freqency signals.

(4) Response time preferably no more than .025 msec.

Thanks again,
Craig