Mike Schumann wrote:
Mode S and ADS-B are completely different technologies.

Potentially some overlap, though. I found this on the AOPA website,
dated July 5, 2006:

Also, in the United States the FAA chose UAT — universal access
transceiver — as the ADS-B datalink for general aviation. Australia
chose to use as its ADS-B datalink the 1090-MHz Mode S extended
squitter system. Mode S extended squitter does not have nearly the
data capacity of UAT, nor is it as robust.

What adds some confusion to this is the airliners will be using mode S
for the ADS-B datalink. From AOPA again:

A second ADS-B datalink is the 1090 Mode S Extended Squitter. The
1090 ADS-B datalink will be used by the airlines (which already have
Mode S systems they can upgrade).

So, it looks like general aviation types like us will be using the UAT
instead of mode S. Given that, buying mode S won't even be useful for a
USA pilot that wants to add ADS-B when it becomes available.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org