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DPRG: Sonar Reflections

Subject: DPRG: Sonar Reflections
From: tyce at ix.netcom.com tyce at ix.netcom.com
Date: Sat Mar 13 01:48:53 CST 1999

	Multipath should not be a problem. In time of arrival ranging systems 
like sonar, radar and lidar (ir) simple detectors (simple or no modulation) 
will return the first (shortest) range.
	The contest walls should be near perfect sonar reflectors. Therefore 
the transducer will have to be pointed at the wall to within half it's 
beamwidth (about 15 or 20 degrees), unless there is a seam, bracket or 
corner to reflect off.
	The agc (automatic gain control) on the polaroid sonar board is pretty 
simple. It blanks, then ramps the gain up to max. If I recall correctly, 
there is no capture function (ramp resets each range). A more complex agc 
could cause problems in a cluttered environment. The simple agc should 
return the first range in the beamwidth with a large enough reflection to 
trigger the threshold.
	The sonar board I have leaves the timing and calculation of the range 
delay up to an external processor. If the cpu does not implement a more 
sophisticated method than just averaging the data, the range may seem 
unstable when in reality the ranges are clustered in several tight groups 
(and maybe a few fliers). The wide beamwidth of these transducers 
exacerbates the phenomena.
	The board I have (from the first engineering kit) will allow the 
processor to reset the detectors flip flop, allowing multiple measurements 
per range pulse. Under the kitchen table makes a perfect test range.

Tyce Elkins


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