Steve Nosko wrote:

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...?

Block the RX input for a few ohnoseconds[1] longer

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.

Might be a useful alternative. Have to have sharp filters.

Who was it that used to sell the sonar modules from the cameras for
experimentation

Polaroid, IIRC.

[1] The shortest possible unit of time: the interval between hitting
the "do it" key and the realization that you shouldn't have.

--
I swear to god, if people treated their cars they way they treat their
computers, half the cars on the road would be covered in bumper stickers
advertising porno, and their trunks would be filled with rotting garbage.
-- Christian Wagner