Rebecca/Eureka transponding radar

The Rebecca/Eureka transponding radar was a transponder system used as a radio homing beacon by means of a "Eureka" ground emitter responding to queries from an airborne Rebecca interrogator.

Operation

The airborne "Rebecca" interrogator transmitted 300 3-4 μSec pulses per second on a frequency between 170 and 234 MHz. Upon receiving this signal the mobile, ground based "Eureka" rebroadcast the pulses on a different frequency. This rebroadcast signal was received by two directional 'Yagi' array aerials on the aircraft carrying the "Rebecca" unit. The difference in signal amplitude between the two aerials gave the bearing of the "Eureka" beacon, while the delay between transmission and reception of the return pulses gave range. The system was effective only to within two miles, when the blip viewed aboard the aircraft merged with the signal transmitted by the interrogator, distorting the range, at which time the crew had to switch to visual means of locating the drop zone. Reliance on Eureka without visual confirmation invariably resulted in premature drops, as occurred during the American airborne landings in Normandy.

There were a large numbers of the versions of the system, early models were limited to a single frequency - later ones could switch between 5 frequencies.

The "Rebecca" code name was derived from the phrase "recognition of beacons".

References

* T. J. Morgan - "Radar" - part of the "The Mechanical Age Library" - Muller - c1950 - No ISBN.

External links

* http://www.qsl.net/pe1ngz/airforce/airforce-raf/raf-eureka-rebecca.html
* http://www.summerof44.org.uk/Menu/Equipment/Eureka.htm
* http://histru.bournemouth.ac.uk/Oral_History/Talking_About_Technology/radar_research/rebecca_eureka.html
* http://www.duxfordradiosociety.org/equiphist/reb-eureka/reb-eureka-hist.html