Transponders
 

G'day

I've been reading, i'm trying to find out why transponders only use the numbers 0-7.
Any info would be appreciated.

Cheers :)

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In three words I can sum up everything I've learned about life: It goes on.

I suspect for the reason that anything digital seems to be in powers of 2. 8 bits to a byte, etc.


Aha, edited to include a link I found. Scroll halfway down the page..

http://www.airpark.org.il/articles/a.../transpon.html


[This message has been edited by Lurk R (edited 22 May 2001).]

Yeap,

The decimal (octal actually) digits are converted to binary, and the digital string is sent back to the radar site.

0 - 000
1 - 001
2 - 010
3 - 011
4 - 100
5 - 101
6 - 110
7 - 111

i.e. code 7700 is 111111000000, 7500 is 111101000000.

A discussion on mode s transponders just finished, a few external references are in there if you would like further info.

:rolleyes:

See also: Mode S

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Tech Log forum moderator

w.r.t. Transponders, what does T.A.R.A. mean? http://www.pprune.org/ubb/NonCGI/confused.gif

TRansition Altitude...something...something...???

[This message has been edited by swashplate (edited 25 May 2001).]

TA/RA refers to Traffic Advisory & Resolution Advisory.

These are displayed if the aircraft has Traffic Collision Avoidance System (TCAS) fitted and another aircraft is predicted to come close.

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PPRuNe Radar
ATC Forum Moderator
[email protected]

To round this off with a condensed history lesson -

In the dark ages, not long after the first abacus was wired to the mains, the early computer chips used 8 bits, (0-7) to store digital info. This gives, as already stated, 4096 code options. Computers have moved on a bit to 32 bits, giving (aah! can't do it!) a lot more options. 64 bit processors (and 128) are around . Transponders have not yet moved. They will.

BOAC,
just to be picky and fit in with the rest of the crowd... :) Eight bits give you 2^8=256 combinations. Mode C uses 12 bits (3 bits gives 2^3=8 combinations, thus 0-7, times four digits = 12 bits) giving 2^12=4096 combinations. Mode S uses 64 bits IIRC, giving 2^64=18446744073709551616 possible combinations. When we reach that number of A/C flying with mode S we will have to think of something else! ;)

Cheers,
/ft, former computer geek who decided that Al, Ti and Jet-A was more fun than Si :)

How embarrassing! You weren't my maths teacher were you?
I think I took the 4096 out of another thread without stopping to check!
Thanks for the correction.
Mike