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From: "Marc H.Popek"
Subject: Re: Homebrew Microwave Interferometer
X-Newsreader: Microsoft Outlook Express 5.50.4133.2400
Date: Thu, 28 Nov 2002 17:27:50 GMT
NNTP-Posting-Date: Thu, 28 Nov 2002 17:27:50 GMT
Organization: AT&T Worldnet
Well if you wanted a slick chance you would:
A) modulate the carrier to chop the audio up to higher frequency
B) recover the phase, using a low sideband noise oscillator
c) demodulate the phase carrier to extract the 1/1000 p1/2 phase modulation
that you can expect to see with a 1 uM vibration.
"John Jardine" wrote in message
> markthomas77@Hotmail.com wrote in message
> > I am curious if a 10 mw cw x-band microwave radar could be used as a
> > non contact acoustic vibration sensor? For example: if the transmitted
> > beam from such a system were aimed at an acoustic target playing music
> > (stereo) a few feet away and the reflected beam is combined with a
> > sample of that beam that was sent straight into the mixer, could the
> > acoustic micro displacements in the i.f. be phase demodulated so that
> > the audio could be heard and understood?
> > How could this be done exactly? Could an audio amp be connected
> > straight onto the radars mixer pin and reproduce the audio, or would
> > it require that the phase information be detected in an audio version
> > of a pll and then amplified? What components would be needed exactly
> > to connect to the radars microwave mixer pin to acheive this?
> > I am curious if microwaves can be utilized like lasers can such as
> > used in the laser listener systems that are well known. There is
> > unending amounts of information on the laser systems, but none on the
> > microwave versions. Tia.
> A 10Ghz 'direct conversion' radar mixer like used on say, the burglar
> detectors is pushing out 3 centimetre radiation.
> A surface vibrating at an audio frequency would (I imagine) be moving to
> fro in the region of a few microns.
> I'd think that the resulting audio FM at the mixer output (including
> reflection and path losses) would be too low to usefully recover.
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