On Apr 4, 12:18*am, (Alan) wrote:
In article MKoerner writes:

The nation-wide glider transponder code is great news. I think it will
be very helpful for controllers in allowing them identify and
anticipate behaviors unique to sailplanes such as stopping suddenly to
thermal, then gaining altitude vertically; and following predictable
weekend flight paths such as along the top of mountain ridges.
We are also very lucky to get this particular code. Apparently the
time it takes to transmit low numbers is shorter than that for higher
numbers. The battery drain with the 1201 code should be lower than
with a code closer to 7777.

* Actually, the reply time is constant. *See
* * * *http://www.radartutorial.eu/13.ssr/sr07.en.html

* Having only 3 bits being 1 in the code may reduce the power if the bits
are sent non-inverted with positive modulation.

* The pulses are 0.45 microseconds long, so if all 12 of the bits, twice per
second, with an 80 percent efficient transmitter putting out 175 watts is
about 2.3 or 2.4 milliwatts of power input to the transmitter. *The
difference between code 7777 and code 1201 is 9 bits, or 1.77 milliwatts
power. *Since most are interrogated less often than twice per second, this
power savings will be less.

The transponder
exclusion for gliders is a fine example.

* Now that gliders have their own code, how long do you think this exclusion
will last?

* * * * Alan

A few random comments.

While a code like this may help reduce power consumption very slightly
doing that calculation requires a bit more work and it's likely to be
a very small overall benefit.

Power savings only apply to Mode A (squawk code) interrogations not
Mode C (altitude - where you can't control the pulse pattern returned)
interrogations. Different SSR systems can make Mode A and C
interrogations at different ratios/interlace patterns, it's not always
1:1.

Mode S transponders use a more advanced encoding than the traditional
Mode A/C pulse train and will have no power saving from this (when
interrogated as a Mode S transponder).

Many transponder interrogations come from TCAS and all those are Mode
C or Mode S only and there are no power savings for either of those
types of interrogations regardless or what the Mode A squawk code is.

Assumptions of a few interrogations per second will be way too low in
busy airspace. If you want to see the absolute worse case number
assume a interrogation rate of ~1 kHz, that's near the limit on most
transponders and can set a worst case upper bound on the power draw
numbers.

Modern transponders like the Mode S Trig TT-21 have very low power
consumption and power usage with modern transponders like these is
often a non-issue nowadays (but still run the numbers for your gliders
total power usage and battery capacity).

Darryl