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From: MarkThomas77@Hotmail.com (markthomas77@Hotmail.com)
Subject: Re: Homebrew Microwave Interferometer
Date: 29 Nov 2002 02:38:13 -0800
NNTP-Posting-Date: 29 Nov 2002 10:38:13 GMT
Thank you for your information. How would one modulate the carrier?
With a flat tone...at what frequency? Could an up-converter be used on
the mixer pin instead to simplify things? No? How about utilizing a
microwave frequency that the human voice box is generally resonant at?
What is the resonant frequency of water? Maybe a microwave beam that
takes advantage of the fact that the human body is composed of a high
percentage of water.
When a person speaks the water in their body has to be modulated much
better than a window....if the beam was just slightly above or below
the human bodies water/voice box resonant frequencies, would speech
cause enough vibrations to impose on the nearby carrier strongly
enough for decent demodulation levels? A method like this, it would
seem, might cause a person to sound monotone...like a robot, or like a
person with an artificial voice box because of a health problem. What
frequency would reflect off of speech modulated air?
The carrier it would seem would have to be near this resonance instead
of on it because if it was on it it would wipe out the micro
displacements by creating its own. Am I correct about any of this?
Please forgive my ignorance.
Anyway, I think that bouncing microwaves of the proper frequencies off
of people directly instead of windows or walls would stand a better
chance of working. Just my humble opinions.
"Marc H.Popek" wrote in message news:...
> 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
> > news:firstname.lastname@example.org...
> > > 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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