Marc Ramsey wrote:
Martin Gregorie wrote:
Its a nice thought, but one-size-fits-all would most likely attract
all the glider pilot bitching about power consumption, size and price
that's currently directed at transponders and ADS-B.

There's one simple reason for this: a universal solution would also
need to be applicable to faster aircraft and would have to radiate
proportionately more power. A system that would give the same
avoidance time against a 250 kt airliner as for a 100 kt glider would
need 2.5 times the range and hence must radiate 6.25 times as much
power. Suddenly your 100 mA FALARM equivalent is eating 625 mA.

In practice a universal device would burn a LOT more power than I just
calculated because:
- the worst case warning range for two 250 kt aircraft is 42% more than
I calculated above, so the transmission power is doubled.
- airlines would want a longer avoidance period than we need.
- the range requirement at least doubles again (and transmission power
quadruples) when you consider jet transports at full cruising speed
above 10,000 ft or fast jets at any altitude?

Which is why ADS-B exists (in the US, and Australia now, I believe) in
two forms. An ICAO-approved Mode S "squitter" is basically layered on
top of a Mode S transponder, and has similar power requirements. A
Universal Access Transceiver (UAT) is intended for use by lower slower
aircraft (like gliders), and has significantly lower power requirements.
A network of ground stations provides the interface between ATC, Mode S
squitter, and UAT equipped aircraft...

As a matter of interest, how is the ground station network paid for? Is
it added into the UAT purchase price, an annual subscription, or does
the general taxpayer pick up the tab?

I'm not grinding axes, just curious.

--
martin@ | Martin Gregorie
gregorie. | Essex, UK
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