Transponder: Mode-C or Mode-S?

John Smith wrote:
Darryl Ramm wrote:
The TT-21 as a Transponder utterly blows away any other transponder
available in the USA for use in gliders.

Just be aware that the TT21 is a class 2 tansponder, i.e. not
certified for use above 15,000 feet, and therefore not suited for
gliders. Buy the TT22 instead which is class 1.


This has been discussed here a lot before. the power difference will
make no practical difference. By all means pay slightly more and install
the TT22 but the important thing is for folks that fly in busy airspace
near airliners etc. to have a transponder (and even an older Mode C
transponder works fine fir that). Most transponders installed in gliders
in the USA appear to be class 2.

Darryl

On Sep 12, 6:57*am, Darryl Ramm wrote:
John Smith wrote:
Darryl Ramm wrote:
The TT-21 as a Transponder utterly blows away any other transponder
available in the USA for use in gliders.

Just be aware that the TT21 is a class 2 tansponder, i.e. not
certified for use above 15,000 feet, and therefore not suited for
gliders. Buy the TT22 instead which is class 1.

This has been discussed here a lot before. the *power difference will
make no practical difference. By all means pay slightly more and install
the TT22 but the important thing is for folks that fly in busy airspace
near airliners etc. to have a transponder (and even an older Mode C
transponder works fine fir that). Most transponders installed in gliders
in the USA appear to be class 2.

Darryl

The TT22 draws about 20 percent more power when transmitting than the
TT21. It's not a lot, but with PowerFlarm going in to my panel as well
I will end up with a 1.5 amp total current requirement, so I figure
every milliamp is worth saving. It seems odd to me that Trig didn't
design with the Class A floor as the break point between design
specs. Then again...

9B

When the panel became a power hog, Rex Mayes installed a 2-panel
Strobl Solar system.
On blue days it produces almost half the required current, a decent
battery extender.
But not very efficient under clouds.
Jim

On Sep 13, 1:24*am, Andy wrote:

The TT22 draws about 20 percent more power when transmitting than the
TT21. It's not a lot, but with PowerFlarm going in to my panel as well
I will end up with a 1.5 amp total current requirement, so I figure
every milliamp is worth saving. It seems odd to me that Trig didn't
design with the Class A floor as the break point between design
specs. *Then again...

9B

Hi Gang
I had a Trig mode S transponder installed in my new Phoenix motor
glider. It appears to work fine as a mode C transponder. After
questioning NorCal while soaring they confirmed they could detect it
with their sqwark code, it would IDENT and so on - all the mode C
stuff. However most of the US including northern California/Nevada is
not yet set up for mode S so except for the future there is no reason
to have mode S in the US. Of course there are other reasons to have
mode S, probably the most important would be if you wanted to sell a
glider in Europe where mode S is becoming mandatory. For that market
having a mode S transponder will save the buyer about $2,500 - the
cost of replacing a mode C with a mode S transponder.
Dave

On 9/13/2011 9:27 AM, kd6veb wrote:
Hi Gang
I had a Trig mode S transponder installed in my new Phoenix motor
glider. It appears to work fine as a mode C transponder. After
questioning NorCal while soaring they confirmed they could detect it
with their sqwark code, it would IDENT and so on - all the mode C
stuff. However most of the US including northern California/Nevada is
not yet set up for mode S so except for the future there is no reason
to have mode S in the US. Of course there are other reasons to have
mode S, probably the most important would be if you wanted to sell a
glider in Europe where mode S is becoming mandatory. For that market
having a mode S transponder will save the buyer about $2,500 - the
cost of replacing a mode C with a mode S transponder.
Dave

A Trig Mode S unit is same cost as the comparable Becker when you add in
the cost of the encoder and harness the Becker requires, so there isn't
any financial reason to buy a Mode C transponder. The Trig has a much
lower current drain, making it the preferred choice anyway.

If you already have a Mode C, there probably isn't any reason to upgrade
now.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl

On 9/13/11 9:27 AM, kd6veb wrote:
Hi Gang
I had a Trig mode S transponder installed in my new Phoenix motor
glider. It appears to work fine as a mode C transponder. After
questioning NorCal while soaring they confirmed they could detect it
with their sqwark code, it would IDENT and so on - all the mode C
stuff. However most of the US including northern California/Nevada is
not yet set up for mode S so except for the future there is no reason
to have mode S in the US. Of course there are other reasons to have
mode S, probably the most important would be if you wanted to sell a
glider in Europe where mode S is becoming mandatory. For that market
having a mode S transponder will save the buyer about $2,500 - the
cost of replacing a mode C with a mode S transponder.
Dave

I think you may be confusing Mode-S and 1090ES data-out, or certainly
risk others confusing that.

The USA is well equipped with SSR Mode-S interrogators, all these
systems are also required to interrogate legacy Mode C transponders and
any Mode S transponder is also required to behave as a Mode-C
transponder if interrogated by a Mode-C only interrogator (Mode-S
interrogators have a way of locking out all Mode-S transponders from
seeing these legacy Mode-C interrogations).

In the USA when ATC sees your transponder return/squawk
code/altitude/ident from a Trig or other Mode-S transponder they are
likely seeing all that over Mode-S not Mode-A/C.

Mode-S transponders do have some benefits over Mode-C including a unique
ICAO ID (some folks may not think that is a benefit), better altitude
reporting (depends on the transponder), do not suffer from possible
congestion/correlation problems, optional Mode-S TIS traffic uplink (not
to be confused with TIS-B) at some USA sites (the Trig transponders do
support TIS), have ground/squat status switching, etc.. Those extra
things do *not* mean that a Mode-C transponder is not a great tool for
use near high traffic areas or that glider owners should upgrade from
Mode-C to Mode-S just to get these Mode-S improvements, but OTOH buying
a new Mode-C transponder nowadays makes no sense.

Mode-S is one thing (well actually many as its fairly complex overall
standard) and the ability to do 1090ES data-out is an option on top of
the data transmitter/extended squitter capability defined in the Mode-S
specs. Some older Mode-S transponders cannot do 1090ES data-out at all.
The ground infrastructure, products, regulations/interpretations to
support ADS-B/1090ES data-out is in it's early days as I tried to
explain earlier in this thread.

Darryl

Andy wrote:

The TT22 draws about 20 percent more power when transmitting than the
TT21. It's not a lot, but with PowerFlarm going in to my panel as well
I will end up with a 1.5 amp total current requirement, so I figure
every milliamp is worth saving. It seems odd to me that Trig didn't
design with the Class A floor as the break point between design
specs. Then again...

9B


The 15,000 feet "limit" comes from wording in the relevant FAA TSO and
ultimately the RTCA standards. That the level was not set to FL180 is
kind of unfortunate. And I expect Trig folks would say the same thing.
But then this all goes back to days of traveling wave tubes and much
different technology and reliability/power output/cooling issues/cost
factors.

Darryl