Indicator, Radar Interrogator, BC-929-A, AN/APN-2 Rebecca Mk IIA

Rebecca / Eureka is a simple system designed initially to assist in the delivery of supplies to the Army or Resistance in occupied Europe. The system expanded into blind homing and approach aid for aircraft. Much of the credit for the development of this system must go to Dr.R.Hanbury-Brown and J.W.S.Pringle of the TRE (Telecommunications Research Establishment)

Principles

The Airborne Rebecca equipment radiates about 300 times a second a 4-5 uSec duration interrogating puls on a spot frequency. On receipt of the interrogating pulses the Eureka beacon located on the ground triggers its associated transmitter causing responses to be radiated on a different frequency but at a pulse recurrence frequency of the interrogating transmitter. The returned signal received on both the right and left Rebecca receiver aerials are displayed on a cathode ray tube in which the time-base is synchronised with the original pulse from the Rebecca transmitter and applied to the Y-plates of the cathode ray tube. The received signals are switched into the receiver in synchronism with the switching of the video-frequency output signals to the right and left hand X-plates of the cathode ray tube. In this way, if the beacon is to the right the signal to the right of the time base will have a greater amplitude, in which case a right turn will be necessary to make the signals on either side of the time base equal in amplitude and the aircraft will then be flying directly towards the beacon.

The Eureka transponder was based on a super regenerative receiver with a separate Transmitter valve and powered by a battery operated vibrator. A coding unit which is part of the Eureka beacon periodically causes the width of the beacon response pulses to vary at Morse code intervals for identification. This function may also be manually controlled for transmission of simple messages.

Rebecca / Eureka is a simple system designed initially to assist in the delivery of supplies to the Army or Resistance in occupied Europe. The system expanded into blind homing and approach aid for aircraft. Much of the credit for the development of this system must go to Dr.R.Hanbury-Brown and J.W.S.Pringle of the TRE (Telecommunications Research Establishment)

Principles

The Airborne Rebecca equipment radiates about 300 times a second a 4-5 uSec duration interrogating puls on a spot frequency. On receipt of the interrogating pulses the Eureka beacon located on the ground triggers its associated transmitter causing responses to be radiated on a different frequency but at a pulse recurrence frequency of the interrogating transmitter. The returned signal received on both the right and left Rebecca receiver aerials are displayed on a cathode ray tube in which the time-base is synchronised with the original pulse from the Rebecca transmitter and applied to the Y-plates of the cathode ray tube. The received signals are switched into the receiver in synchronism with the switching of the video-frequency output signals to the right and left hand X-plates of the cathode ray tube. In this way, if the beacon is to the right the signal to the right of the time base will have a greater amplitude, in which case a right turn will be necessary to make the signals on either side of the time base equal in amplitude and the aircraft will then be flying directly towards the beacon.

The Eureka transponder was based on a super regenerative receiver with a separate Transmitter valve and powered by a battery operated vibrator. A coding unit which is part of the Eureka beacon periodically causes the width of the beacon response pulses to vary at Morse code intervals for identification. This function may also be manually controlled for transmission of simple messages.

• Used for locating radar pulse beacons - often used for drops to resistance forces. Black box with crt screen, miscellaneous controls; signal corps.

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