George Vranek wrote:

A low cost ACW based on GPS will be tested in Switzerland. See www.flarm.com

George

Numerous attempts were made in this domain. My brother proposed the
design of a such device as a project for students working on a
degree in electronics. Two members of my club designed and made
a cheap system which in not an anti-collision device but just a
position reporting system, but could easily converted into an anti-
collison system. But the problem with all these attempts is to
find an available radio frequency for the data transmission. The
above cited device, according to the WEB page, uses a frequency
in the "SRD-band". I don't know what it is, but the same page
says that its usage is free ON THE GROUND. I doubt that the same
will be true when used for air to air transmission, I am quite
sure that in France at least this is forbidden, as for any
frequency not explicitly allowed for air to air transmission.