Help: Bat detector

Rich Young young at
Sat Aug 27 08:00:49 EST 1994

In article <33ms7i$ikt at> harmoni at (Shafik Harmoni) writes:
>zeier at wrote:
>: I'm interested in buying a bat detector (makes bats "hearable"). Does anyone 
>: know a company which sells them (Here in Switzerland I didn't find one)? 
>: I would apreciate general hints about these devices too (Don't know much 
>: about it).
>: Thanks in advance. 
>I'm guessing here, but does it shift the inaudible bat sonic emissions
>down into human hearing range?  Maybe a parabolic dish with headphones?
>Or does it use radio wave reflections to track the target?  Possibly,
>it detects their infrared signature and plots it on a miniature cathode
>ray tube in an eye-piece?  Or maybe resonance in the bat wings it found 
>through laser refraction?

	In a truly blinding burst of intelligent repartee, our respondent
	seems to have accidentally hit upon an answer with some merit.  "Bat
	detectors" such as described by the original request do, in fact,
	shift ultrasonic bat sounds into human-audible ranges.  The ones I
	have seen are "tunable" to various ultrasonic frequencies, and I
	expect that they work like the RF to IF translation in a super-
	heterodyne radio circuit: by mixing a variable local oscillator
	with the incoming frequency to provide a relatively constant 
	difference signal in the human-audible range which can then be 
	amplified and sent to a speaker.

	I do not know brand names.

-Rich Young

(The view expressed herein may not reflect that of Eastman Kodak Company, Inc.)

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