175 or 250 watt transponder?

Needing a replacment, my transponder shop told me that above 15k' the
FAR's require a 250 watt transponder (125w below 15k').

True?

I'm pretty sure that sailplane owners are mostly installing 175 watt
units and flying them to 18k' (and higher in wave windows). Right?

If this 15k' rule is real, I'm supposing that, since gliders aren't
required to have a transponder except in certain airspace (this
airspace is all below 15k' -- except Class A...) that we're generally
free to install anything we want (except 18k' in Class A?).

Bottom line -- 175 watts or 250 watts?

Eric Rupp
ER
(My Terra TR250D transponder is inop and I'm having trouble getting
parts - anybody have a dead one that we might be able to salvage from?)

On Jan 8, 1:01*pm, Itsaplane wrote:
Needing a replacment, my transponder shop told me that above 15k' the
FAR's require a 250 watt transponder (125w below 15k').

True?

Eric,

Have you tried Freeflight?

http://www.freeflightsystems.com/index.htm

Mike





I'm pretty sure that sailplane owners are mostly installing 175 watt
units and flying them to 18k' (and higher in wave windows). *Right?

If this 15k' rule is real, I'm supposing that, since gliders aren't
required to have a transponder except in certain airspace (this
airspace is all below 15k' -- except Class A...) that we're generally
free to install anything we want (except 18k' in Class A?).

Bottom line -- 175 watts or 250 watts?

Eric Rupp
ER
(My Terra TR250D transponder is inop and I'm having trouble getting
parts - anybody have a dead one that we might be able to salvage from?)

Bottom line: If you want to fly above 15k in airspace where a
transponder is mandatory, then 250W is required or you will not fly
there. Otherwise install whatever you want. As there is little
difference in price as well as in power consumtion, I don't see why you
would want to go for the weaker unit, though.

A side note: If you want to stick with a mode C transponder, then there
are a lot of used ones available in Europe pretty cheaply, as Europe is
mandating mode S now and everybody must switch. If on the other hand you
want to buy a new unit, then go for mode S. It doesn't cost much more,
it draws less current and it will have a much better resell value.

On Jan 8, 12:01*pm, Itsaplane wrote:
Needing a replacment, my transponder shop told me that above 15k' the
FAR's require a 250 watt transponder (125w below 15k').

True?

I'm pretty sure that sailplane owners are mostly installing 175 watt
units and flying them to 18k' (and higher in wave windows). *Right?

If this 15k' rule is real, I'm supposing that, since gliders aren't
required to have a transponder except in certain airspace (this
airspace is all below 15k' -- except Class A...) that we're generally
free to install anything we want (except 18k' in Class A?).

Bottom line -- 175 watts or 250 watts?

Eric Rupp
ER
(My Terra TR250D transponder is inop and I'm having trouble getting
parts - anybody have a dead one that we might be able to salvage from?)

Eric,

I don't believe that is true. I think that is from the specifications
from the Becker transponders. The Microair T2000 is 200w and specs
say 62,000 feet.


http://www.craggyaero.com/microair.htm

Richard
www.craggyaero.com

On Jan 8, 12:17*pm, Mike wrote:
On Jan 8, 1:01*pm, Itsaplane wrote: Needing a replacment, my transponder shop told me that above 15k' the
FAR's require a 250 watt transponder (125w below 15k').

True?

Eric,

Have you tried Freeflight?

http://www.freeflightsystems.com/index.htm

Mike



I'm pretty sure that sailplane owners are mostly installing 175 watt
units and flying them to 18k' (and higher in wave windows). *Right?

If this 15k' rule is real, I'm supposing that, since gliders aren't
required to have a transponder except in certain airspace (this
airspace is all below 15k' -- except Class A...) that we're generally
free to install anything we want (except 18k' in Class A?).

Bottom line -- 175 watts or 250 watts?

Eric Rupp
ER
(My Terra TR250D transponder is inop and I'm having trouble getting
parts - anybody have a dead one that we might be able to salvage from?)- Hide quoted text -

- Show quoted text -

Freeflight does no service the Terra transponder, but Gulf Coast
Avionics in Lakeland , Florida does . They can be reached at
863-709-9714.

Ramy

On Jan 8, 12:01*pm, Itsaplane wrote:
Needing a replacment, my transponder shop told me that above 15k' the
FAR's require a 250 watt transponder (125w below 15k').

True?

I'm pretty sure that sailplane owners are mostly installing 175 watt
units and flying them to 18k' (and higher in wave windows). *Right?

If this 15k' rule is real, I'm supposing that, since gliders aren't
required to have a transponder except in certain airspace (this
airspace is all below 15k' -- except Class A...) that we're generally
free to install anything we want (except 18k' in Class A?).

Bottom line -- 175 watts or 250 watts?

Eric Rupp
ER
(My Terra TR250D transponder is inop and I'm having trouble getting
parts - anybody have a dead one that we might be able to salvage from?)

In practice a 175W Becker appears to work fine above 15,000'. That's
what I'd use.

I'd worry more about getting something reliable, easily serviceable
and has an readout of pressure alt/flight level (ie. replace the
Terra) than whether 250W is important.


Darryl

On Jan 8, 12:21*pm, Richard wrote:
On Jan 8, 12:01*pm, Itsaplane wrote:



Needing a replacment, my transponder shop told me that above 15k' the
FAR's require a 250 watt transponder (125w below 15k').

True?

I'm pretty sure that sailplane owners are mostly installing 175 watt
units and flying them to 18k' (and higher in wave windows). *Right?

If this 15k' rule is real, I'm supposing that, since gliders aren't
required to have a transponder except in certain airspace (this
airspace is all below 15k' -- except Class A...) that we're generally
free to install anything we want (except 18k' in Class A?).

Bottom line -- 175 watts or 250 watts?

Eric Rupp
ER
(My Terra TR250D transponder is inop and I'm having trouble getting
parts - anybody have a dead one that we might be able to salvage from?)

Eric,

I don't believe that is true. *I think that is from the specifications
from the Becker transponders. * The Microair T2000 *is 200w and specs
say 62,000 feet.

http://www.craggyaero.com/microair.htm

Richardwww.craggyaero.com

Yes it's true, but it's also not...

The above/below 15,000' comes from TSO-C74c see
http://www.airweb.faa.gov/Regulatory...9?OpenDocument

See other specifications there to explain the differences, but for
power output the TSO requirments are

---QUOTE---

2.11 Transmitter Power Output.

a. For equipment intended for installation in aircraft which operate
at altitudes above 15,000 feet, the peak pulse power available at the
antenna end of the transmission line of the transponder must be at
least 21 db and not more than 27db above 1 watt at any reply rate up
to 1,200 per second for a 15-pulse coded reply.

b. For equipment intended for installation in aircraft which operate
at altitudes not exceeding 15,000 feet, the peak pulse power available
at the antenna end of the transmission line of the transponder must be
at least 18.5db and not more than 27db above 1 watt at any reply rate
up to 1,200 per second for a 15-pulse coded reply.

c. The standards of this section assume a transmission line loss of
3db and an antenna performance equivalent to that of a simple quarter
wave antenna. In the event that these assumed conditions do not apply,
the equipment must be adjusted as necessary to provide a transmitter
power output equivalent to that specified.
---END QUOTE---

But how to interpret this? The way I read these TSO requirements are -

below 15k feet 18.5dbW to 27dBW = 70.8W to 501W power at coax output
at the antenna
above 15k feet 21dbW to 27dBW = 126W to 501W power at coax output at
the antenna

below 15k feet 18.5dbW+3dB to 27dBW+3dB = 141W to 1kW power at
transponder output
above 15k feet 21dbW+3dB to 27dBW+3dB = 251W to 1kW power at
transponder output

Where I have assumed the 3dB cable loss in part(c).

I'm not aware of any requirement for what power output manufactures
are required to quote. Are they talking about the power output at the
transponder or the TSO-C74c specified power at the antenna input with
assumed 3dB cable loss? I suspect manufactures normally want to quote
the biggest power output they can however in the case of Microair I
assume they are talking about 200W at the antenna coupling since they
would not meet the ~250W requirement. Maybe one of their dealers can
clarify this. (and yes technically as well there is ambiguity about
peak vs. other power measurements, but again I'd assume manufactures
are going to quote peak to maximize the number and since that is also
what the TSO talks about).

Anybody got a different interpretation of the TSO?


Darryl

the transponder manufacturer (Becker) "recommends" 250 Watt above 15,000'
but to the best of my knowledge there is no FAA requirement for transponder
power
tim

Please visit the Wings & Wheels website at www.wingsandwheels.com


"Richard" wrote in message
...
On Jan 8, 12:01 pm, Itsaplane wrote:
Needing a replacment, my transponder shop told me that above 15k' the
FAR's require a 250 watt transponder (125w below 15k').

True?

I'm pretty sure that sailplane owners are mostly installing 175 watt
units and flying them to 18k' (and higher in wave windows). Right?

If this 15k' rule is real, I'm supposing that, since gliders aren't
required to have a transponder except in certain airspace (this
airspace is all below 15k' -- except Class A...) that we're generally
free to install anything we want (except 18k' in Class A?).

Bottom line -- 175 watts or 250 watts?

Eric Rupp
ER
(My Terra TR250D transponder is inop and I'm having trouble getting
parts - anybody have a dead one that we might be able to salvage from?)

Eric,

I don't believe that is true. I think that is from the specifications
from the Becker transponders. The Microair T2000 is 200w and specs
say 62,000 feet.


http://www.craggyaero.com/microair.htm

Richard
www.craggyaero.com

John Smith wrote:
Bottom line: If you want to fly above 15k in airspace where a
transponder is mandatory, then 250W is required or you will not fly
there.

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.

hough.

A side note: If you want to stick with a mode C transponder, then there
are a lot of used ones available in Europe pretty cheaply, as Europe is
mandating mode S now and everybody must switch. If on the other hand you
want to buy a new unit, then go for mode S. It doesn't cost much more,
it draws less current and it will have a much better resell value.

Can you tell me which Mode S transponder you are talking about? The ones
that I see for sale in the USA are much more expensive ($600 comparing
the 175W and 150W models of Becker; $1100 comparing the 250W models of
Becker).

--
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

In article Darryl Ramm writes:
On Jan 8, 12:21=A0pm, Richard wrote:
On Jan 8, 12:01=A0pm, Itsaplane wrote:
Needing a replacment, my transponder shop told me that above 15k' the
FAR's require a 250 watt transponder (125w below 15k').

I'm pretty sure that sailplane owners are mostly installing 175 watt
units and flying them to 18k' (and higher in wave windows). =A0Right?

Bottom line -- 175 watts or 250 watts?

Eric Rupp
ER



Yes it's true, but it's also not...

The above/below 15,000' comes from TSO-C74c see
http://www.airweb.faa.gov/Regulatory...TSO.nsf/0/ACB=
BA541FF4C071D86256DC10067F209?OpenDocument

See other specifications there to explain the differences, but for
power output the TSO requirments are

---QUOTE---

2.11 Transmitter Power Output.

a. For equipment intended for installation in aircraft which operate
at altitudes above 15,000 feet, the peak pulse power available at the
antenna end of the transmission line of the transponder must be at
least 21 db and not more than 27db above 1 watt at any reply rate up
to 1,200 per second for a 15-pulse coded reply.

b. For equipment intended for installation in aircraft which operate
at altitudes not exceeding 15,000 feet, the peak pulse power available
at the antenna end of the transmission line of the transponder must be
at least 18.5db and not more than 27db above 1 watt at any reply rate
up to 1,200 per second for a 15-pulse coded reply.

c. The standards of this section assume a transmission line loss of
3db and an antenna performance equivalent to that of a simple quarter
wave antenna. In the event that these assumed conditions do not apply,
the equipment must be adjusted as necessary to provide a transmitter
power output equivalent to that specified.
---END QUOTE---

But how to interpret this? The way I read these TSO requirements are -

below 15k feet 18.5dbW to 27dBW =3D 70.8W to 501W power at coax output
at the antenna
above 15k feet 21dbW to 27dBW =3D 126W to 501W power at coax output at
the antenna

below 15k feet 18.5dbW+3dB to 27dBW+3dB =3D 141W to 1kW power at
transponder output
above 15k feet 21dbW+3dB to 27dBW+3dB =3D 251W to 1kW power at
transponder output

Where I have assumed the 3dB cable loss in part(c).


I am sure I quoted way too much.


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