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Date: Thu, 28 Nov 2002 16:29:29 +0100
From: Rene Tschaggelar
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Subject: Re: Homebrew Microwave Interferometer
John Jardine wrote:
> 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 alarm
> detectors is pushing out 3 centimetre radiation.
> A surface vibrating at an audio frequency would (I imagine) be moving to and
> 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.
There was this case where after a certain period of time some embassy
employees became suspicious of the window cleaners. They came a bit too
often. They in fact did have a salty solution that was said to be radar
reflective. I forgot the where and when of this story.
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
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