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