Radar and the Air War – Part 9 – by John Heys G3BDQ

A Personal View, by John Heys G3BDQ.

Part 9    REBECCA & EUREKA  

Soon after the War in Europe had ended, my Squadron converted to Dakota aircraft and in October 1945 we flew out to India, no longer a part of Bomber Command but instead a part of RAF Transport Command.
Two of us in the Radar Section were packed off to RAF Cranwell, ‘Home of the RAF’ and a place we regarded as ‘Bullshit City’ to learn something about some equipment that could used to drop paratroops or supplies very accurately and to within 750 feet of the ground target. This radar, American designed and built was in two units; an airborne interrogator ‘Rebecca’ and a ground positioned beacon ‘Eureka.’

Basic Statistics

g3bdq-radarp9-1The Eureka beacon used a receiver that was connected to a short vertical antenna and was tuned to a fixed frequency of 214 MHz. When it received an interrogating pulse from the airborne Rebecca transmitter it sent a return pulse on a frequency of 219MHz. The aircraft transmitter had an output power of 500 watts, which was radiated from a vertical ¼ wave antenna positioned on top of the aircraft’s nose. The response signals from the Eureka beacon had a peak power of only 8 watts.

The aircraft had a couple of very directional yagi beams located one to each side of the fuselage front. Each ant, (vertically polarised) was made up from two element radiators.  These antennas picked up signals to the front and to either the left or right of the aircraft. The Rebecca unit had a display CRT with a vertical timebase trace and its face was marked out in miles, which increased from zero at the base of the vertical trace and up to 50 miles at the top.

How it was used

g3bdq-radarp9-2The pilot and his co-pilot would head in the intended direction towards the ‘drop zone’ where the Eureka beacon was positioned and as soon as response signals were received from the beacon, often as far away as 30 to 50 miles, they could see at once if they were heading directly towards the beacon or instead were heading to its left or right. As the beacon was neared the return pulses descended the timebase trace and grew larger.  Eventually the pulses reached the Zero mark and the pilots knew they were very close to the beacon. The actual usable range of this equipment combination was dependent upon the topology of the ground below. In a mountainous region the range was reduced considerably. The Eureka beacon transmitter would only operate when it received a set-up pattern of pulses in a sequential code arrangement, and in wartime the Rebecca and Eureka sets could be fitted with explosive self-destruct devices should the pulse signals not be ‘Kosher.’

The Rebecca unit in the aircraft was quite small and its display CRT had a diameter of just 3¾ inches (95mm). The Eureka worked from batteries and the Rebecca connected to the aircraft battery supply, normally in American planes 28 v.

Some Memories

The Squadron with its full complement of airmen of all ranks and trades flew, via a succession of RAF Staging Posts (The furthest South SP used being Khartoum in the Sudan) to eventually, after two weeks, reach a grass airstrip near Bilaspur in the Central Provinces of India. This temporary destination had no hangars, no workshops and had tented living quarters which were beset by all kinds of ‘creepy crawlies.’ After a few weeks we flew back westwards to our permanent base at Mauripur Airfield just outside Karachi. This place has grown to become Pakistan’s Karachi International Airport. We were then still living in tents but had quite a reasonable workshop, a Radar Van etc. We performed the normal daily inspections our only responsibility being the Rebecca units, an exercise that was rather futile, for instead of performing parachute drops the Squadron was employed in ferrying former combatants in the Far East Jungle War and survivors of the Japanese POW camps from Dum-Dum near Calcutta to Mauripur.  From Mauripur, after a short rest the jungle veterans flew home in large four-engined transports.

Rebecca and Eureka actually used.

In the Spring of 1946 myself and one other (my mate who had also suffered Cranwell) flew with the squadron North to an airfield near Rawalpindi and close to the Himalayan foothills. Our Rebeccas were in use for a couple of weeks for the Dakotas were employed in a big Indian Army exercise, dropping supplies in the mountains. The Rebeccas performed faultlessly so we had no use for our toolboxes. I don’t ever remember having to replace or repair a Rebecca set. Well done the USA……

John Heys (G3BDQ) – Vital Spark March 2008.

Return to the index of Vital Spark articles.

 

g3bdq-radarp9-4

The Rebecca Left-hand antenna is just visible above the engine.

g3bdq-radarp9-5

Close up of John.

g3bdq-radarp9-3

The photo shows myself and others arriving back to base after our short spell in Northern India having just disembarked from the Dakota ‘Q’. Note the ‘Sten’ sub-machine gun in the foreground. We had to carry one around when on the ‘Pindi’ airfield for there was a growing fear of Civil unrest with the partition of India and Pakistan just a few months ahead.

 

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