175 or 250 watt transponder?

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.

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.

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

On Jan 9, 12:17 am, (Alan) wrote:
In article Darryl Ramm writes:
[snip]
The guide says you can use the real cable loss if it isn't 3 dB. That makes
life easier for most with gliders, as a short length of low loss cable will do
better than 3 dB.

175 watts is 1.43 dB above the 21 dBW requirement for use above 15,000 feet.
So you simply need to get the loss below 1.43 dB in the feedline. That appears
to be not very difficult. For example, Times Microwave LMR240 cable shows up
as a total loss of 1.07 dB when connected to a load with an SWR of 1.5:1. It
takes 16 feet of this cable to get the loss to 1.42 dB.

If that is cutting it too close, you can get a better matching antenna, or
use a lower loss cable. At 1.2:1 SWR, that same 16 feet of LMR240 has a total
loss of 1.36 dB. LMR400 cuts the loss to 0.74 dB even with a 1.5:1 SWR. (It
has 0.69 dB loss for 16 feet with a perfect match at the end.)

Unfortunately, many aircraft installations use smaller lighter and more
flexible coax -- such as RG58, which will give 1.9 - 2.9 dB loss (too much).
(There is a lot of variety in types of RG58.)

Alan
wa6azp

Lets drill into this more...

Alan raises a good point by talking about a practical installation.

Since the approval agency doing the TSO (or equivalent) approval won't
know the actual cable loss of a particular installation they are going
to have to assume 3dB. And changing cable losses in a practical
installation won't change the transponder TSO-C47c approval type. It's
called out in the approval doc and required to be marked on the
transponder, etc. So I don't see how a manufacturer can avoid meeting
the +3dB power requirements. Which means that Microair is quoting the
3dB corrected theoretical antenna input power on their TSO Type 1A
approved transponder or I'm misunderstanding something.

A Type 1B transponder with lower power output might be just as good
for our uses in practice as a Type 1A (above 15000' spec) especially
with a good antenna installation and as Alan points out may meet the
power requirements of a Type 1A transponder. Which might all make some
pilots less concerned about worrying about all this in practice,
especially if a Type 1B transponder draws less power battery power
than a type 1A. But would that be legal? And does the transponder
Type approval really matter to us? Well FAR 91.215(a) might come to
our rescue...

---QUOTE---
(a) All airspace: U.S.-registered civil aircraft. For operations not
conducted under part 121 or 135 of this chapter, ATC transponder
equipment installed must meet the performance and environmental
requirements of any class of TSO-C74b (Mode A) or any class of TSO-
C74c (Mode A with altitude reporting capability) as appropriate, or
the appropriate class of TSO-C112 (Mode S).
---END QUOTE---

Note - that's just a "must meet the performance of" not a "must be TSO
approved". So this leaves open the possibility (especially for
experimental gliders, and Eric's glider is experimental) that you can
legally use a transponder outside its TSO Type altitude limits. One
gate to this would obviously be that the tests required under FAR
91.413 (ie. Part 43 Appendix F which circle back to the TSO specs)
must show that it did meet the Type 1A (above 15,000') requiremnts.
Who knows for sure whether the FAA would ever argue that you would
have to do more than that with a modern Type 1B transponder to show
"must meet the [1A] performance". But I'd be pretty surprised to see
this being an issue in practice.

It would be great to hear if other people have different
interpretations of the TSO and FAR requirements.

(I've deliberately kept this to Mode-C, not Mode-S, transponders here
since that what I think Eric is looking at).

The important practical thing, especially in high traffic areas, is to
have a transponder installed and turned on. If a lower power
consumption transponder is important to extend battery life then I'd
personally rather see people install that than turn off the
transponder during flight. Of course there may be options to install
more battery capacity, etc.


Darryl

On Jan 9, 5:35*am, Darryl Ramm wrote:
On Jan 9, 12:17 am, (Alan) wrote:
In article Darryl Ramm writes:
[snip]

Since the approval agency doing the TSO (or equivalent) approval won't
know the actual cable loss of a particular installation they are going
to have to assume 3dB. And changing cable losses in a practical
installation won't change the transponder TSO-C47c approval type. It's
called out in the approval doc and required to be marked on the
transponder, etc. So I don't see how a manufacturer can avoid meeting
the +3dB power requirements. Which means that Microair is quoting the
3dB corrected theoretical antenna input power on their TSO Type 1A
approved transponder or I'm misunderstanding something.
[snip]
Darryl

And I'll answer my own self-doubt about how Microair can have a Type
1A 200W transponder. Microair state in their installation manual "The
T2000SFL allows for 1.5dB cable loss from the unit to the antenna.".
That gets incorporated as a part of the TSO and supplants the generic
3dB assumption in the TSO and so I'm sure they are talking about
actual output power from the transponder being 200W.

Darryl

On Jan 9, 1:12*am, John Smith wrote:

Actually, I do, too. I see no reason not to believe the manufactorers...

I have this bridge for sale...

Hi Gang
This is what I call a weird discussion. Why? Think about it all of
you. How many of you know the difference in DBs between the 2 power
levels? Is it a very large number or a very small number? If it is a
very small number is it significant? One last question how accurate a
piece of measuring equipment would you need to have to distinguish
between the 2 power levels? Be honest each of you. Without seeing any
other responses to my post, post your answers to my 4 questions.
A clue! If you answer the 4 questions correctly you won't waste your
time ever discussing this subject again period! My low power watt
Beckers on each of my flying 3 machines (Stemme, LSA and ultralight
SparrowHawk) are just fine, thank you, for going to any altitude I
choose to. No one but no one (meaning ATC) could ever tell whether I
had a low or high power transponder! And, of course, neither could you
without checking the power levels under lab conditions.
Dave

This is an interesting thread because I'm also considering the
purchase of a transponder.
Unfortunately, it's necessary to pay attention to what's legal in
addition to what does the job.
If for any reason you bump into someone at 16K (and wouldn't I love to
get there) you can bet that the NTSB and the other guy's lawyer will
know the difference.

On Jan 9, 11:25*am, Bob Thompson wrote:
If for any reason you bump into someone at 16K (and wouldn't I love to
get there) you can bet that the NTSB and the other guy's lawyer will
know the difference.

Bumping into someone at 16 k is not legal. You're screwed anyway.

Andy

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

On Jan 9, 10:25*am, Bob Thompson wrote:
This is an interesting thread because I'm also considering the
purchase of a transponder.
Unfortunately, it's necessary to pay attention to what's legal in
addition to what does the job.
If for any reason you bump into someone at 16K (and wouldn't I love to
get there) you can bet that the NTSB and the other guy's lawyer will
know the difference.

I think the NTSB and FAA gave shown sensible restraint here. For
example in how they handled questions of transponder non-usage with
the Minden Hawker/ASG-29 mid-air collision. I believe they get the
need to focus on getting gliders to have transponders installed and
used in high traffic areas and I suspect they realize that other
actions they take at times could hurt that overall effort. But that's
just my impression.

To Dave's point I agree this technically a very silly thing to worry
about (which I tried to say earlier), and I also like the 175W Becker
transponder and highly recommend it. [So Dave please stop reading
now :-)] On the other hand when we get into these things about what's
legal etc. Lets actually get into the TSOs, FARs etc. what *exactly*
are the requirements. Otherwise we end up in even less useful
discussion about what people think with no proof points to validate
from. Hopefully some requiremtns are now clearer to folks but you can
also see its actually *not* clear that we need a TSO'ed Type 1A
transponder above 15,000' (just one that meets the TSO requirements,
but again however that is supposed to be determined). My personal
opinion is I'd ask a repair shop to install the Becker 175W
transponder and if it passes the install test I'm happy.

Back to worry about FAA action. I'm going out on a limb here (and I am
definitely not an aviation or any other kind of lawyer) but for FAA to
raise issues that a Type 1B transponder that during calibration checks
met the Type 1A power output yet was not acceptable for use under FAR
91.413 above 15,000' would raise the issue that the calibration tests
themselves really are not sufficient for checking the entire US fleet
of Type 1A transponders for their compliance with requirements. I'd be
kind of surprised the FAA wanted to go there. And more importantly
again I suspect they get the focus needs to be in getting transponders
installed.

BTW I much prefer the Becker Transponder (which I've installed in my
DG-303 and ASH-26E) from a usability viewpoint to other models,
especially the Microair (which is in rental gliders I fly). Other
people may disagree.


Darryl

On Jan 9, 1:09*pm, kd6veb wrote:
* This is what I call a weird discussion. Why?

Because it is RAS: Rampant Aviation Speculation. (with many DB)

But you already knew that ;-)