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On Mar 10, 5:18�am, wrote:
Hi chaps, I suspect a neighbour of a friend of mine is using an ultrasonic bird- scarer to frighten off his pets. The man concerned won´t admit to it, but there are times when his dog and two cats just seem to get suddenly very distressed and hypermanic for no apparent reason. I`d like to at least eliminate this possibility before considering any others. So the question is, what´s the simplest way to detect ultrasound? My web research leads me to believe the area of interest is between 20 and 30khz. Most common bird scarers warble between these two limits which are of course above the range of human hearing. I´ve acquired an ultrasonic transducer that transmits on 41khz. If I couple this up to a wien-bridge oscillator trimmed to the same frequency, I figure I ought to be able to hear a warble if indeed this guy is using a birdscarer, because the difference between 41khz and 20khz-30khz will be audible to me. Is this feasible to "air mix" the two frequencies in this simple way and hear a result, or is something more complicated required? Thanks! The obvious "detection" would be oscilloscope observation of the amplified microphone signal. That's been mentioned. Some commercial ultrasound detectors simply heterodyne the ultrasonic range down to audible frequencies...good if your hearing goes on up to the high end of human response. Expensive as portable devices but easily genned up on the average home workbench. There are a couple of claims of outdoor advertising via sound through using high-power ultrasound generators in pairs, one modulated in amplitude the other unmodulated. The air acts as the non-linear "mixer" and the claim is that such beams of ultrasound can be focussed on particular locations. One such company is located in San Diego, California, if memory serves. 73, Len AF6AY |
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