Transponder: Mode-C or Mode-S?

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

Eric Greenwell wrote:
What regulation makes it illegal for a glider to use the TT21 between
15,000 and 18,000'?

Of course it's not illegal to turn on a class 2 transponder above 15,000
feet. But with a class 2 transponder, you can't tell ATC above 15,000
feet that you're transponder equipped, because legally, you're not.
Where I fly, I pretty routinely enter protected airspace at that
altitude, and I would hardly get a clearance without a transponder. This
has been the main reason for me to buy a transponder, so buying class 2
transponder would have been pretty pointless.

I don't care whether "they" would notice or not that I carry only a
class 2 transponder. The price gap of a mere $200 is far too small to
even consider to cheat.

Of course all depends on where you fly and to whom you want to sell your
glider later. So all I've wanted to say is that when you consider to buy
a class 2 transponder, be aware of the limitation.

John Smith wrote:
Eric Greenwell wrote:
What regulation makes it illegal for a glider to use the TT21
between
15,000 and 18,000'?

Of course it's not illegal to turn on a class 2 transponder above
15,000 feet. But with a class 2 transponder, you can't tell ATC above
15,000 feet that you're transponder equipped,

Ah you want to show us a regulation or chain of regulations that says
that? Which country are you flying in? You keep using the word legal and
illegal etc. In the USA the FARs actually do not appear to place clear
requirements in this area on the PIC. Show us the regulations please...


And just for kicks 14CFR 91.215(c) "Transponder on operation" requires a
pilot say who climbs above 15,000' with a class 2 transponder to keep
operating that transponder.

because legally, you're not. Where I fly, I pretty routinely enter
protected airspace at that altitude, and I would hardly get a
clearance without a transponder. This has been the main reason for me
to buy a transponder, so buying class 2 transponder would have been
pretty pointless.

And buying class 2 would likely have made no difference to any if that.


I don't care whether "they" would notice or not that I carry only a
class 2 transponder. The price gap of a mere $200 is far too small to
even consider to cheat.

Of course all depends on where you fly and to whom you want to sell
your glider later. So all I've wanted to say is that when you consider
to buy a class 2 transponder, be aware of the limitation.


and that's all fair but the more important thing is getting pilots in
key high traffic areas to equip and use transponders (of any class or
type)). And for most pilots in the USA it is not about clearances, it
is about avoiding an encounter with an airliner or fast jet.

Darryl

If you intend to use any smart PCAS (e.g. PowerFLARM) you want a Mode-
S, since suppressing your own transponder signal is a lot easier and
more reliable if the source is a Mode-S.
Other PCAS are also somewhat more likely to make sense of your
transmissions.
So do yourself and the World a favor and buy a Mode-S.

Ironically your decision is between buying into technology of the
fifties vs. the seventies...

Enjoy
Urs

On Sunday, September 11, 2011 at 11:54:26 PM UTC-4, Morteza Ansari wrote:
I recently bought a new bird and need to put a transponder in it. The
choice was obvious (until I took a closer look). Trig TT21 seems like
a great choice: small footprint, built-in encoder, 1090ES ADS-B out,
and descent price. However a bit more looking revealed more questions
than answers. It seems it requires an ISO GPS and one could not use
typical GPS sources we have in gliders, it is not clear if the ADS-B
out work with PowerFLARM (at least from what I have heard), and the
biannual testing cost 2-3x as much as mode-C.

Any thoughts/suggestions from more knowledgable folks?


Cheers,
Morteza

==============

Not sure how you got your conclusions or that gobbledygook you just uttered..
I have been using the TT-21 for over 10 years and it is flawless. It and the TT-22 are identical except for the transmit power. I have no GPS hooked to it or anything else. It runs like a normal txpndr. I hooked it up in one afternoon, and as mentioned has been working perfectly.

You're responding to an eight year old thread. There is plenty of recent discussion that is more relevant.

PA

On Tuesday, April 16, 2019 at 8:01:31 PM UTC-7, wrote:
On Sunday, September 11, 2011 at 11:54:26 PM UTC-4, Morteza Ansari wrote:
I recently bought a new bird and need to put a transponder in it. The
choice was obvious (until I took a closer look). Trig TT21 seems like
a great choice: small footprint, built-in encoder, 1090ES ADS-B out,
and descent price. However a bit more looking revealed more questions
than answers. It seems it requires an ISO GPS and one could not use
typical GPS sources we have in gliders, it is not clear if the ADS-B
out work with PowerFLARM (at least from what I have heard), and the
biannual testing cost 2-3x as much as mode-C.

Any thoughts/suggestions from more knowledgable folks?


Cheers,
Morteza

==============

Not sure how you got your conclusions or that gobbledygook you just uttered.
I have been using the TT-21 for over 10 years and it is flawless. It and the TT-22 are identical except for the transmit power. I have no GPS hooked to it or anything else. It runs like a normal txpndr. I hooked it up in one afternoon, and as mentioned has been working perfectly.

Welcome to r.a.s. This is an *excellent* first post.