(USA) NTSB issues recommendations to the FAA and the SSA regardingtransponder use in gliders

Greg Arnold wrote:
I see they want to require transponders in all gliders, with the
transponders always on.


Nice summary. And, in compensation we'd get the low, low transponder code of 0440

I've never heard that low codes would save power, maybe they just wouldn't ping it as
often as 1200

Sarah

On Mar 31, 6:50 pm, Sarah Anderson wrote:
Greg Arnold wrote:
I see they want to require transponders in all gliders, with the
transponders always on.

Nice summary. And, in compensation we'd get the low, low transponder code of 0440

I've never heard that low codes would save power, maybe they just wouldn't ping it as
often as 1200

Sarah

Ah, that is not possible. The simple answer is all transponders seeing
an interrogation signal will reply. The SSR can interrogate the
transponder to send it's code (Mode A) or altitude (Mode C). There is
no concept of the SSR being able to "address" a transponder.

Darryl

Darryl Ramm wrote:
On Mar 31, 6:50 pm, Sarah Anderson wrote:
Greg Arnold wrote:
I see they want to require transponders in all gliders, with the
transponders always on.
Nice summary. And, in compensation we'd get the low, low transponder code of 0440

I've never heard that low codes would save power, maybe they just wouldn't ping it as
often as 1200

Sarah

Ah, that is not possible. The simple answer is all transponders seeing
an interrogation signal will reply. The SSR can interrogate the
transponder to send it's code (Mode A) or altitude (Mode C). There is
no concept of the SSR being able to "address" a transponder.

I assume what the NTSB is referring to is the duty cycle of the reply
transmission, I'm too tired right now to figure out the actual encoding,
but if 0440 has a lower duty cycle than 1200, it will save some amount
of power. How much, I don't know...

Marc

On Mar 31, 8:43 pm, Marc Ramsey wrote:
Darryl Ramm wrote:
On Mar 31, 6:50 pm, Sarah Anderson wrote:
Greg Arnold wrote:
I see they want to require transponders in all gliders, with the
transponders always on.
Nice summary. And, in compensation we'd get the low, low transponder code of 0440

I've never heard that low codes would save power, maybe they just wouldn't ping it as
often as 1200

Sarah

Ah, that is not possible. The simple answer is all transponders seeing
an interrogation signal will reply. The SSR can interrogate the
transponder to send it's code (Mode A) or altitude (Mode C). There is
no concept of the SSR being able to "address" a transponder.

I assume what the NTSB is referring to is the duty cycle of the reply
transmission, I'm too tired right now to figure out the actual encoding,
but if 0440 has a lower duty cycle than 1200, it will save some amount
of power. How much, I don't know...

Marc

Oh doh, thank you Mr. Governor. OK there is a basis to the claim, but
definitely not because of differences "pinging". 0440 is just two
pulses (binary 4 twice). And 1200 (binary 1 and 2) also has two
pulses, and there are always two framing pulses, and maybe an ident
pulse. So 1200 and 0440 should be no different in terms of radiated
power. And usually every second interrogation/response is going to be
an altitude code. So I guess they could pick a worse code and have
several more pulses (would have to look at the map of available codes
to see how bad it could be, luckily 7xxx is taken :-)) I'd be curious
to see actual differences in power consumption measurements.

Darryl

Darryl Ramm wrote:
Oh doh, thank you Mr. Governor. OK there is a basis to the claim, but
definitely not because of differences "pinging". 0440 is just two
pulses (binary 4 twice). And 1200 (binary 1 and 2) also has two
pulses, and there are always two framing pulses, and maybe an ident
pulse. So 1200 and 0440 should be no different in terms of radiated
power. And usually every second interrogation/response is going to be
an altitude code. So I guess they could pick a worse code and have
several more pulses (would have to look at the map of available codes
to see how bad it could be, luckily 7xxx is taken :-)) I'd be curious
to see actual differences in power consumption measurements.

Uh, no Mr. Boffin, tis not quite that simple. It's been a while since I
looked at this stuff, but I believe the actual transponder code is
encoded using a modified Gray code (as is the altitude code), so the
actual duty cycle is not quite that obvious. Second, the fashion in
which the transponder code and the altitude code are transmitted differ
significantly, as the transponder code portion of the transmission dates
back to WW II IFF, and the Mode C stuff came much later. I doubt the
NTSB would have brought it up, unless there was something to it.
Personally, I'm not interested enough to try to figure it out...

Marc

Marc Ramsey wrote:
Uh, no Mr. Boffin, tis not quite that simple. It's been a while since I
looked at this stuff, but I believe the actual transponder code is
encoded using a modified Gray code (as is the altitude code), so the
actual duty cycle is not quite that obvious. Second, the fashion in
which the transponder code and the altitude code are transmitted differ
significantly, as the transponder code portion of the transmission dates
back to WW II IFF, and the Mode C stuff came much later. I doubt the
NTSB would have brought it up, unless there was something to it.
Personally, I'm not interested enough to try to figure it out...

I'll take it back, Mode A and Mode C are transmitted the same way, and
while altitude is Gray encoded, the squawk code is straight binary. So,
I have no idea what the NTSB was talking about.

Marc