Transponder in octal

Mike Lewis

Shadow Administrator
Staff member
I used to know the answer to this question, but I seem to have forgotten it.

Does anyone know why a transponder uses octal instead of decimal?
 

pscraig

Well-Known Member
I believe your answer lies in the nature of a digital signal. A 4096-code transponder would likely reply to ATC with a 4-byte packet, consisting of 32 bits. The easiest way to encode this with analog knobs would be four knobs, each with eight possible positions-zero through seven.
 
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