I'm not sure if the thing actually operates on the 5th overtone. I have some
mystery TO5 44.7 MHz crystals that it puts out 223.5 MHz. The actual freq at
the collector seems to be 74.5 MHz (but it is a complex waveform).
The circuit generates a short burst every second or two. It is VERY low net
power. It runs for weeks on a couple of LR44 cells but can be tracked a mile
away laying on the ground. This app needs to be fairly cheap as the
transmitters will not be recovered. Circuit cost is a few cents plus the
crystal. Commercial transmitters are $150-$250 dollars.
These types of circuits are usually hand built out of hand selected components.
They are tweaked until they work then potted up in epoxy. There are only a
very few people who make them (in hollow trees, dark dungeons, and troll
infested caves) and they keep their circuits and suppliers secret.
I once did some work for a company that made road construction flashers...
much the same. All hand selected parts to get the right flash rate, intensity,
and minimal power draw. Much more art than science behind these things.
International built me some crystals a while back, but none could be made to
work.
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