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Yep! acoustic is one. another is infrared
Over this short distance RF travel time is in the 30 nano second range. This requires some pretty good timing measurements. Sound, on the other hand, has a speed of around 30 mili seconds for 10M (30 ft). Something I wanted to do for a long time is a model rocket altitude system. Rocket has a one transistor 10M Rx ( have the circuit around here from some 1960's Pop Electronics for a 1 tranny FM broadcast Rx) and a one or two transistor 2M Tx (FM) -- rocket antenna easier.. Ground station on 10M (lots of power available for the wooden rocket Rx) transmits a TONE (not a pulse). Rocket transponds (retransmits it on 2M). Measure the zero crossing time delay and subtract the overhead time. With proper (and simple) digital design, you can have a digital readout in feet, inches, whatever. With a tone, common ham radios are just fine. With audio, pulses are easy except how do you keep the target from hearing it's own echo and "oscillating by itself...? or use subcarriers - this is a little harder. Transmit an FM modulated tone (carrier, say 10KHz, tone 1KHz) and transponding it back on another carrier, say 15 KHz. Who was it that used to sell the sonar modules from the cameras for experimentation acoustic "Sverre Holm" wrote in message ... literally I am talking about a transmitter within a cuboid shaped enclosure around 10m maximum and being able to pinpoint that transmitter within that enclosure accurately, to around 1cm, perhaps 2cm. This is a typical application of an acoustic positioning system. With a speed of sound of about 340 m/s, this is feasible. I have made such a system with acoustic tags on 40 kHz using 8 receiver nodes in the room. That's more than required, but it gives enough redundancy to be robust against shadowing as things move around in the room. Accuracy is in the 1-2 cm range. -- Sverre Holm, LA3ZA --------------------------------- www.qsl.net/la3za |
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