Transponder mystery

[Efermed]

Dear friends does any body knows the answer to this:

Excluding Mode S, how many transponder channels are there?

[Mark 1]

The transponder operates on 2 channels. It is interrogated on 1030 MHz and replies on 1090 MHz.

If you mean how many discrete mode 3/A codes are used in the replies, then the code consists of 12 bits, which allow 4096 discrete codes (0000 to 7777 in octal). These codes are all transmitted on the same channel, but only occupy that channel for a very brief interval allowing it to be shared with other aircraft in the vicinity.

[Fitter2]

Mode S, of course becomes more complicated, with addressing providing time-domain multiplexing.

But the basic answer is one, full duplex, channel.

[Dan Winterland]

Unless you are talking about the modes. As mentioned, 3A is the basic 4096 codes, 3C is the same with altitude reporting. Mode 1 is the original IFF (Identification Friend or Foe) which dates from the end of WW2 with just 64 codes. Mode 2 is the same as mode 3, but on a different frequency and mode 4 is digitally encrypted and regularly changes the squawk in a predetermined sequence. Modes 1,2 and 4 are used by the military only.



A bit of transponder trivia: IFF was known (and still is sometimes in the military) by it's wartime code name of ''Parrot'' which is why it replies to interrogation by ''Squawking''.

[On the beach]

....code name of ''Parrot'' which is why it replies to interrogation by ''Squawking''.

And why you sometime hear ATCOs say "Strangle the parrot".

[aterpster]

Non mode S: 4,096.

8 x 8 x 8 x 8 = 4096

or, code 0000 through 7777