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.

Versions

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

British

Eureka Mk VII was a rack mounted, non-mobile transponder used at RAF bases for aircraft to home onto.

A Mark X version of both Rebecca and Eureka that worked in the 1000 MHz range. This was developed for use during in-flight refueling, enabling the receiving aircraft to locate the tanker while maintaining radio silence. The Tanker aircraft carried the Eureka and the receiving aircraft carried the Rebecca. This equipment was trialled by 214 Squadron in the early 1960s.

American

• AN/PPN-1
• AN/PPN-1A
• AN/PPN-2

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

See also

• AN/UPN-1
• Signal Corps Radio
• List of military electronics of the United States

References

• T. J. Morgan - Radar - part of The Mechanical Age Library - Muller - c1950 - No ISBN.
• Graphic Survey of Radio and Radar Equipment Used by the Army Airforce. section 3 Radio Navigation Equipment Dated May 1945

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
• http://www.militaryradio.com/spyradio/early_mil.html picture of ground component