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From: gts@axiom.UUCP (Guy Schafer)
Newsgroups: net.analog
Subject: Looking for a method to invert a function.
Message-ID: <343@axiom.UUCP>
Date: Wed, 1-Oct-86 16:52:29 EDT
Article-I.D.: axiom.343
Posted: Wed Oct  1 16:52:29 1986
Date-Received: Sat, 4-Oct-86 01:37:19 EDT
Organization: Axiom Technology, Newton MA
Lines: 20
Keywords: h(t) = f(t) + h(t) - f(t)

I'm looking for an analog circuit that can perform two functions:

1. Reflect a function about the x-axis.  That is, turn f(t) into -f(t).
Where f(t) is the sum of many low frequency (less than 20kHz) sine
waves.

2. Add -f(t) to another signal, say g(t); where g(t) is a composite
of two functions: g(t) = f(t) + h(t).

This will reveal the imbedded signal h(t).

Any comments about the theoretical sensitivity of this procedure?  How
much energy must be in signal h(t) compared to f(t)?  Are FFT's required
to perform step one?  (If this is so, can a digital circuit be constructed?)

Mail to me, I'll summarize if the CIA lets me.

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