"Is FLARM an open standard (or at least an open spec)?"
I think not, from correspondence I have seen. They have licensed others to use the technology, however – “Ozflarm”, etc. See the LX website too.
LX avionics Ltd. Radio transceivers, Mode S transponders, variometers, flight recorders .
Chris N.
PS: FLARM posted the following (responding to criticism of their policy – original is at
Flarm hidden protocol, II - rec.aviation.soaring | Google Groups
but you may need to register to read it there)
“Flarm has always communicated openly and transparently, see our website for up to date information on technical and business developments, including IP:
Flarm - News In particular we have argued in detail why publishing the RF protocol is currently impossible:
http://www.flarm.com/product/Compati...ations_1_1.pdf
The explanations in that document are widely supported by independent experts. The changes (and underlying motivations) to the v4 version are described since many months here:
Flarm - Updates and yes, they do contain significant enhancements to the RF protocol which did not allow backwards compatibility, see
Flarm - Updates
[edited to add PS]