Mike Borgelt wrote:
"electronically enhanced see and avoid" is what we are really after
here, not a 100% guaranteed collision prevention system.

I spent some time looking at this a few years ago. Basically, establish
two virtual "bubbles" around the glider. The device would announce (by
voice) the call sign, bearing, and relative altitude of a similarly
equipped glider which, given the present speeds and courses of both
gliders, will enter the smaller bubble within some number of seconds. A
second announcement would be made if entry is predicted within a second
shorter time interval. After that, the glider would be ignored until it
exits the larger bubble. The sizes of the bubbles and times could be
established by the pilot, and might vary according to speed or
cruise/climb mode. My thinking was that the smaller bubble would be
around 500 meters radius, the larger 1000 to 2000 meters, the longer
time interval 20 seconds, shorter interval 10 seconds. Some additional
"smarts" would be required to deal with announcing simultaneous
potential conflicts with several other gliders.

Initial examination showed that a fast 8 bit processor could actually do
the necessary calculations to track as many as 32 gliders with a 2
second update rate, Use of fixed point arithmetic, and table lookups for
transcendental functions (or a much faster processor) would have been
required.

What made me give up on the project was an inability to find suitable,
low cost, unlicensed, radio transceivers that could be used legally in
the US for this sort of application. One needs to transmit with enough
power to allow reliable tracking out to 5 km or so, and enough bandwidth
to allow a position broadcast duty cycle of around 1/128 (to allow
periodic position reports at randomized intervals, with reasonably low
probability of collision). A proof of concept could be done using
(licensed) amateur frequencies. But, the difficulties associated with
trying to produce a salable product seemed insurmountable.

Marc