A transponder is an electronic device that produces a response when it receives a radio-frequency interrogation. Aircraft have transponders to assist in identifying them on air traffic control radar; and collision avoidance systems have been developed to use transponder transmissions as a means of detecting aircraft at risk of colliding with each other. interrogation reply

Pulse code - a set of pulses, arranged in accordance with the encoding rules. pulse duration number of pulses the distance between pulses frequency and phase the presence or absence of pulses at certain positions pulse-time and position types

T k - code interval t k – interval of coding The maximum number of two-pulse codes N:

a) four digit binary position code with passive pause b) each of the four bits of the binary number is provided two temporary positions