[Laser] modulated retroreflectors

[Tim Toast]

 A small speaker sounds like a good way to try modulating a homemade retro reflector, be it either optical or microwave. Even if the frequency response is only up to a few hundred hertz, it would still be useful for some modes. I bet it wouldn't be quite up to par for voice work, though good enough maybe with some EQ and a lower modulation percent. For better voice quality we'd have to go with smaller or lower mass mirrors or some higher tech (and more expensive) modulator type. Still for the price this makes an interesting project and demonstates one of the cutting edge devices in optics today. 


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...If one searches for modulated retroreflector on the web, you'll find plenty of info about ongoing projects of that type. A few years ago I visited  a project at UCSD here in San Diego doing just that.
 - Kerry N6IZW - 


...I proposed to build into some large front bumper mounted,  rally lamps, (rubber covered, of course) ,  a modulated retroreflector corner cube.  Two right angle metal "mirrors", the third side being  a thin  membrane, metallized plastic foil that was modulated with an audio carrier.  Peraps even a small speaker with a flat "cone" mounted at a slight off angle from 90 degrees. 
Build a small audio oscillator driving a tiny speaker to modulate the return wave, and Voila!  You can get the desired 45, or 65 mph, or whatever  to read on the radar gun.  Whether the corner cube signal in the rally lamp housings overwelmed the "Real" reflected signal from car, was never tested.

Best Regards,    73,   
Pat Barthelow  apolloeme at live.com


...If you think of the intensity of the beam, or as the reciprocal of the area over which the beam has expanded, you can get a rough first order of 
magnitude estimate of the range.  It is a matter of trading the aperture of 
the receiver against the expansion of the beam.

James
 n5gui