'Circuit diagrams of beacons' concerning Rebacca/Eureka project Contains a set of circuit diagrams from ASV beacon to Rebecca beacon, 'General layout' sheets, a list of circuit diagrams issued and three photographs of equipment, with a covering letter by R Trim. Also includes technical manuals for the use of equipment (in original envelopes). R Trim was an engineer who started to work on Identification Friend or Foe (IFF) equipment in the mid-1950s. IFF had been developed as a means of positively distinguishing friendly from enemy aircraft. It relied on a piece of equipment aboard the aircraft, known as the 'transponder' (a receiver/transmitter). 1990