[time-nuts] Toy radiolocation and LORAN envelope

Andrea Baldoni erm1eaae7 at ermione.com
Tue May 27 09:12:32 UTC 2014


Years ago, I sometimes played the transmitter hunting game, probably known to
most of the members of this list.
A friend of mine recently suffered a theft so I thought about the opportunity
to embed little marker transmitters in some object usually left in the yard
(like bicycles for example), and have inside the house a system that
constantly monitors them for unwanted movement, while at the same time be
eventually able to recover them once "disappeared" using portable equipment.
I think that the very simple RF power way to monitor movement is inadequate,
but at the same time I would like to keep things very simple, little and really
cheap, so no things like gps receivers on it: maybe just a 8 pin
microcontroller and a crystal.
Also, the battery life should be the maximum possible, so the RF power will be
little and this also exclude to put a transponder inside the gadget, unless
its on-time could be limited to short and precise slots, because a
constantly-on RX will consume more power than a low duty cycle (say, 0.1pps)
pulsed TX.

Obviously, the goal is to reach the best positional accuracy possible within
the constraints.
The frequency is yet to choose, but I think it should stay in the ISM band
around 40MHz.

The angle could be found with a directional antenna or inerferometry, but about
the distance? There is the need of a very good accuracy of the transmitter
pulses. It's obtainable at least in the short term (the time needed to
recover the object, for instance) for low power and low price? The long term
inaccuracy could tracked and offset when the system is aware that the target
is not moving.

By the way, the LORAN envelope, was so shaped just to limit harmonics, push
up energy efficiency, or there were other reasons not to transmit a square one?

Best regards,
Andrea Baldoni

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