Transponder P-Codes, A/C/S all call

[EDFZ]

Hi pilots,


could someone explain the meaning/use of the different P-codes (P1-P4) in transponder technique and the difference between an A/C/S-all call and the regular all-call? I already googled the net and my books but didn't find any clear/easy explanation of the latter.


Thanks in advance!


Answer:

Ground interrogation signal is transmitted in form of P1 and P3 pulses when using modes A or C, P4 for Mode S.
The interval between P1 and P3 determines whether mode A or C is being used.
P2 control pulse after P1 is used to check for sidelobes and surpress them.

A/C/S- all call controls A/C transponders plus S.
all-call : checks only the response of all Mode S transponders.