gts@axiom.UUCP (Guy Schafer) (10/01/86)
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.
>< ...{ decvax!linus || seismo!harvard }!axiom!gts
"Understand or leave."levy@ttrdc.UUCP (Daniel R. Levy) (10/06/86)
In article <343@axiom.UUCP>, gts@axiom.UUCP (Guy Schafer) writes: >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. I don't see what the great trick is here; you are just inverting the signal polarity! Now if what you MEAN is to turn f(t) into f(-t) (invert in time) that's a different story: If f(t) does not exist before t=0, that's easy; tie your signal input to ground :-). If it does exist before t=0, it is "impossible" to reconstruct anything more about the arbitrary function than is known in its past history. If it is presumed the function is periodic then construction of an approximation to the time-mirror image could be done by a simple (DIGITAL) sample-and-store-then-reconstruct circuit after observation of one cycle. >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. > >< ...{ decvax!linus || seismo!harvard }!axiom!gts > "Understand or leave." -- ------------------------------- Disclaimer: The views contained herein are | dan levy | yvel nad | my own and are not at all those of my em- | an engihacker @ | ployer or the administrator of any computer | at&t computer systems division | upon which I may hack. | skokie, illinois | -------------------------------- Path: ..!{akgua,homxb,ihnp4,ltuxa,mvuxa, go for it! allegra,ulysses,vax135}!ttrdc!levy