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From: Don Pearce
Subject: Re: Radar Microphone?
Date: Tue, 07 Jan 2003 12:10:17 +0000
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On 7 Jan 2003 03:40:35 -0800, MarkThomas77@Hotmail.com
>I have one of those cheap Ramsey personal speed radars and was playing
>around with it pointing it at a fan and watching the speed display
>numbers rapidly change back and forth, when it occurred to me to
>connect a pair of headphones to the radars earphone output to see what
>I would hear. I could hear the fans blades rotating! I then set the
>unit down on a table and started trying to "hear" different objects.
>I clanked some keys together, compressed and then rapidly released a
>pair of tweezers, etc. I was able to hear the actual audio from these
>objects, but the audio quality was absolutely terrible. There was too
>much bass in the audio and the audio was terribly distorted.
>My question is this: what could I connect to the radars earphone
>output that would reduce the exaggerated bass frequencies, and also
>clean up the audios tremendous distortion?
These Doppler RADAR devices give an output signal that is identical
whether the target is coming or going. This means that the output, in
audio terms, is full-wave rectified, and as you say very distorted.
There is no way round this that I can think of. The bass heaviness is
due to the integration effect of a frequency modulated signal going
through a phase detector. A 6dB per octave filter will take care of
this. You will never get good results, though, because the very
considerable phase noise of the oscillator is converted down into the
audio band by the detector.
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