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