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iff transponder codes

Asked by: 2992 views Student Pilot

Hello sir, i would like to know why does the IFF transponder codes end at 7777 for mode 3A, and 73 for mode 1?

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1 Answers



  1. John D Collins on Nov 03, 2015

    There are 4096 transponder code values for mode 3A. This is because there are 12 binary bits in the code value and this can be represented in octal as 0000 to 7777. With mode 1 there are 64 transponder code values because there are 6 binary bits in the code value and it can be represented as two octal digits with values ranging from 00 to 77. Mode 3A is used by ATC for surveillance.

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