John Smith wrote:
Eric Greenwell wrote:

Do you have a reference to the regulation concerning power
requirement? I haven't been able to find it, and people just seem to
rely on the product descriptions when I ask about it.

Actually, I do, too. I see no reason not to believe the manufactorers.
According to Funkwerk, output requirements are higher for tansponders
which are operated in aircraft flying at altitudes above 15,000ft or
speeds above 175kt. Unfortuately (of fortunately), gliders often operate
higher than 15,000ft.

My problem is the manufacturers do not specifically say their 250W
transponders are required by the FAA, in gliders, above 15,000'. They
often refer to EASA or other regulations that just hint at it, or make
non-specific remarks that may apply only to certified airplanes. It
looks like Darryl has found what I want, however.

I write this with the European situation in mind where Mode S is already
mandatory. As air traffic is typically an international thing, I would
assume that the FAA and EASA have been reasonable enough to discuss this
and to agree to the same requirements.

And they probably have, for international operations, but for gliders in
just the USA? Or in a wave window? We should not assume anything about
in-country requirements, because regulations do vary. Note that Europe
is going to Mode S and 8.33 radio channel spacing; the USA is not.

BTW, problably not the cheapest but one of the more popular mode S
transponders in Europe is the TRT800H by Funkwerk.
http://www.funkwerk-avionics.com/cms...4&changelang=4

I know there are many choices in Europe for Mode S, but I am aware of
only two brands sold in the USA that have units suitable for gliders:
Becker and Garrecht. The least costly is still $600 more than a Mode C unit.

If the Mode S units had a significantly lower power requirement, they
might be worth the extra money. Comparing the datasheets of the Becker
models, both the standby and operating drains seem similar. Perhaps I am
misinterpreting the figures.

The Garrecht unit seems to promise a worthwhile reduction in drain, in
part because it does not require an external encoder. It costs almost
$1000 more than a Becker + encoder, however.

Perhaps some enterprising soaring supply company should buy a lot of
those unusable Mode C transponders from Europe and offer them for sale
to USA customers at attractive prices.

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

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

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