> Dwayne Reid <dwayner@planet.eon.net> wrote:
> Hi there, Mario.
> Have a look at something called a "lock-in amplifier". =A0A brief
> overview can be found on WikipediA
> <http://en.wikipedia.org/wiki/Lock-in_amplifier>

Lock in amplifiers can be excellent, but note (from the Wikipedia page)

          Recovering signals at low signal-to-noise ratios requires a stron=
g,
          clean reference signal the same frequency as the received signal.
          This is not the case in many experiments, so the instrument can
          recover signals buried in the noise only in a limited set of
circumstances.

It's uncertain from information supplied so far by Mario whether his
situation matches that requirement.
General (Wikipedia):

   A lock-in amplifier (also known as a phase-sensitive detector) is a
type of amplifier that can extract a signal with a known carrier wave
from an extremely noisy environment (the signal-to-noise ratio can be
-60 dB or even less[citation needed]). It is essentially a homodyne
with an extremely low pass filter (making it very narrow band).
Lock-in amplifiers use mixing, through a frequency mixer, to convert
the signal's phase and amplitude to a DC=97actually a time-varying
low-frequency=97voltage signal.

Information only - lock in amplifiers were used by the "Blow Fly
position detector" that I mentioned a few weeks ago*. There there is a
strong reference signal (the excitation field) that the received
signals can be compared against.


     Russell McMahon

____________________

* Using miniature sensor coils for simultaneous measurement of
orientation and position of small, fast-moving animals
          http://iwi.eldoc.ub.rug.nl/FILES/root/1998/JNeurscMethSchilstra/1=
998JNeurosciMethSchilstra.pdf

BLOWFLY FLIGHT AND OPTIC FLOW
            http://jeb.biologists.org/content/202/11/1491.full.pdf
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