Transponder modes
Hi guys,
I have a question regarding transponder modes :confused: Are the following statements correct? Mode A: Transmits squawk code and speed only. Mode C: Transmits squawk code, speed, and pressure altitude only. Mode S: Transmits squawk code, speed, pressure altitude, and callsign. Plus multiple information formats. Or all modes provides callsign? Thanks in advance! |
A bit of history: The first civil transponder was Mode A only and had only 64 codes (8 x 8). 4,096 Mode A codes came along in the mid or late 1960s. (8 x 8 x 8 x 8) Mode C was added separately; I believe after Mode A was expanded to 4,096 codes.
The Mode A transponder was an outgrowth of the military IFF developed during World War II. Mode S came along much later and is much more sophisticated. Mode A provides only position. ATC computers uses the change of position to determine ground speed. Tags added to the Mode A position tag, such a flight or registration number, etc, are generated by the ATC computer from flight plan data. Mode C provides pressure altitude only. |
Thank you guys.
I understand GS and callsign start shown on radar screen with mode S only. No GS/Callsign with modes A or C, That is correct? |
Originally Posted by aterpster
(Post 9851996)
A bit of history: The first civil transponder was Mode A only and had only 64 codes (8 x 8). 4,096 Mode A codes came along in the mid or late 1960s. (8 x 8 x 8 x 8) Mode C was added separately; I believe after Mode A was expanded to 4,096 codes.
The Mode A transponder was an outgrowth of the military IFF developed during World War II. Mode S came along much later and is much more sophisticated. Mode A provides only position. ATC computers uses the change of position to determine ground speed. Tags added to the Mode A position tag, such a flight or registration number, etc, are generated by the ATC computer from flight plan data. Mode C provides pressure altitude only. Don't know what Modes 1 and 2 were, but an 'ident' squawk is the same as IFF/SIF (Selective Identification Feature) |
Mode A and C transponders says "Hi, I'm 1234." The ATC system has been told 1234 is FastJet 100 and so the controller sees FastJet 100 with the data block. With a Mode S Transponder the flight enters FastJet 100 in FMS as part of the setup and the transponder says "Hi, I'm FastJet 100."
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I got it now! Thank you guys for help!
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This is a fun review.
Do we have a participant who can explain the interrogator/reply details of Mode A and the similarities to DME interrogators? |
Originally Posted by MarkerInbound
(Post 9852762)
Mode A and C transponders says "Hi, I'm 1234." The ATC system has been told 1234 is FastJet 100 and so the controller sees FastJet 100 with the data block. With a Mode S Transponder the flight enters FastJet 100 in FMS as part of the setup and the transponder says "Hi, I'm FastJet 100."
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Originally Posted by aterpster
(Post 9853372)
This is a fun review.
Do we have a participant who can explain the interrogator/reply details of Mode A and the similarities to DME interrogators? Don't ask me how TACAN works though!! |
Mode C info is transmitted from the aircraft based on 1013.2; it is then converted to altitude by the processor in the radar display which must have the correct local QNH input.
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