The 914A Air Traffic Control Transponder replies on mode 3/A , B and C interrogations, and also on the (never implemented) mode D interrogation with 25 us double pulses.  The response on mode B is the same as on mode 3/A. For all these modes, the response may contain all 13 pulses, including the never used middle “x” pulse.

    Receiver:     1030 MHz, 5 uV sensitivity, sidelobe suppression

    Transmitter 1090 MHz, 1kW peak, up to 1500 pulses per sec, each 0.5us wide

Power requirement is 28Vdc at 2A ( internal fuse 3A). No fan used.


Circuit diagrams

  The complete Wilcox 914A diagram is here

                   914A with on top row, left-to-right the (shielded) self test module, video amp, side-lobe suppression and interrogation mode detectors, and the response assemblers for mode 3/A, C and D.

Bottom row :  60 Mc IF amplifier, modulator , power supply and delay line to detect the interrogation- mode. Behind the IF amplifier are the transmitter cavity and the local oscillator.


Transmitter with 7855 triode in cavity and the 2kV buffer capacitor.

The whole module is pressurized.

Updated  20 July 2012



IFF transponders


AN/ APX-25








This ATC transponder is the civil counterpart of the APX44, and almost size,- and pin-compatible. The Concorde was one of the civil aircraft that used it.  The APX44, 814, 914 and 1014 transponders were made by  Wilcox in the late sixties and seventies.