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Magnetrons & Radar

The prototype magnetron designed by J. Randall and H. Boot in February of 1940
In the 1920s, a General Electric employee, Albert Hull, was researching Vacuum Tubes when he created the magnetron. However, Hull could think of few uses for his invention, and the magnetron remained largely unused for another 10 years. In the late 1930s and early 1940s, 2 engineers named Harry Boot and John Randall decided to explore the magnetron further. Instead of using glass to create the outer casing of the magnetron, they used heat resistant copper to create a magnetron capable of incredible microwave output. Their creation allowed for an output of 400 watts in a space smaller than 4 inches (10cm). As Boot and Randall developed stronger magnetron tubes, they discovered the tubes were ideal for Radar. During World War II, United States submarines began utilizing these tubes, which allowed the Radar equipment to help them detect enemy ships more quickly. In the late 1940s, Dr. Percy Spenser, who worked for Raytheon Corporation, further tested the output of magnetron tubes in his lab. He noted that the candy bar in his pocket had completely melted while working with the tubes. He decided to place a few kernels of popcorn near the machinery to see what would happen, and noticed it made the kernels pop.

Radar Tutorial

In June of 1940, Eric Stanley Megaw, based on experiments with General Electric Company E821 Glass Magnetron, had designed a Cavity Magnetron in England which worked on 10cm and became available for aircraft interception. This Magnetron was air cooled and J Randall and H Boot turned it into a water cooled unit. The Magnetron became the heart of the H2S Radar which also used a PPI CRT (Plan Position Indicator - Cathode Ray Tube) installed in British bombers. The Cavity Magnetron had a substantial increase in performance over other magnetrons of its time and it played a substantial role in the history of Radar. Unlike the disclosure of the German Radar secrets, the British worked in the strictest of confidence and secrecy during WWII and developed the H2S Airborne Radar which used a Magnetron and a  PPI-scope. This unit worked well and could identify targets on the ground for night and all weather bombing.  In February 1943, a Stirling bomber with the H2S Radar was shot down near Rotterdam and the radar was found by the Germans. The Germans tested this radar. They built a improved unit by June of 1943 called the LMS 10 "Berlin."

FuG 202 Lichtenstein B/C
Early FuG 202 Lichtenstein B/C units were not deployed until 1942. They operated at a maximum RF output power of 1.5 kW, on the 75 cm wavelength (490 MHz, or low UHF band), requiring complex Matratze (mattress) antennas, consisting of a total of 32 dipole elements, mounted in 4 groups of 8, each at the forward end of 1 of 4 forward-projecting masts.

FuG 212 Lichtenstein C-1
During 1943 the Lichtenstein B/C was improved as the FuG 212 Lichtenstein C-1, with longer range and wider angle of view, still operating at UHF Frequencies between 420 and 480 MHz and using the complex Matratze aerial set.  By this point in the war, the British had become experts on jamming German Radars. A B/C-equipped Ju 88 R-1 night fighter, Werknummer 360 043, defected in April 1943 and landed in Dyce, presenting a working example of the German Radar for the 1st time, with the aircraft itself, still in existence as of the 21st century, becoming a museum exhibit in the UK.  The subsequent refinement of 'Window' (known as Düppel by the Luftwaffe, from the German Town it was 1st found near) rendered Lichtenstein B/C almost useless for several crucial weeks.

FuG 220 Lichtenstein SN-2
By late 1943, the Luftwaffe was starting to deploy the greatly improved FuG 220 Lichtenstein SN-2, operating on a longer-wavelength of 90 MHz (lower end of the US VHF FM broadcast band) frequency which was far less affected by electronic jamming, but this required the much larger Hirschgeweih (stag's antlers) antennas, with only 8 dipole elements, looking like a much-enlarged version of what occupied the forward end of each one of the earlier quadruple Matratze masts. This aerial setup also produced tremendous drag and slowed the operating aircraft by up to 50 km/h (30 mph).  The 1st SN-2 set had a problem with a huge minimum range of 500 Metres, initially requiring the retention of a supplementary B/C or C-1 set with its full set of 4 Matratze masts, but the alarming drag that full sets of both types of antennas caused, from both Radars being installed, later changed the requirement to only a "1/4" subset of the earlier Matratze array at the end of a single mast, centrally mounted on the nose of the aircraft when the BC or C-1 UHF Radar remained installed. Improvements in Spring 1944 led to newer SN-2 versions with lower minimum range, which allowed the older UHF radar system to be removed entirely. In July 1944, the newest version of the SN-2 radar fell into Allied hands when a fully equipped Ju 88 G-1, of 7 StaffelNJG 2, flew the wrong way on a landing beacon and landed in England by accident, with the crew not realising the mistake until it was too late to destroy the Radar or
IFF gear. This led to successful jamming of several frequency bands of the FuG 220 (I to III, 72, 81 and 90 MHz) but several other bands were still operational.  After the Allied jammings the FuG 220 antenna setup was optimized for the still operational bands, the 90-degree vertical dipole setup was changed to a 45-degree diagonal setup.


Interception

Werknummer 360043, PJ876 was reportedly flown by a defector(s) (or an Agent of the Secret Service) from Norway to RAF Dyce, Aberdeen, on the 9th May 1943.  Two (pilot and wireless op/gunner) of the 3 man crew fully co-operated much to the consternation of the 3rd man, the Flight Engineer, who was incarcerated as a POW.  The pilot could have arranged this defection with the British Secret Service which wanted to acquire information about German night-fighter Radar technology.  The aircraft had been in service with 10./NJG 3 in Norway and was registered as D5+EV.  Reporting a fake engine fire to his German Radio Station the Pilot landed at Dyce under Spitfire (165 Squadron) protection.  It has been suggested that he had pro-British sympathies and whilst serving with 2/NJG2 he had landed in the UK at Debden (14th /15th February 1941) and in Lincolnshire (20th May 41) on clandestine intelligence missions connected with British intelligence.  Believing that the plane was lost in the sea the Germans declared it lost.  One month later they learned by a Radio transmission from the BBC what really had happened.  On the 11th May 1943 Professor R V Jones (Assistant Directorate of Scientific Intelligence and an expert on German Radar Systems) arrived at Dyce to take charge of the evaluation of the aircraft and its equipment.  On the 14th May, under Beaufighter escort, PJ876 was flown from RAF Dyce to the Royal Aircraft Establishment (RAE) at Farnborough by Sqn Ldr R A Kalpas for consequent day and night time testing.  At this time RAF Bomber losses were exceptionally high due to night-fighter interceptions.  Detailed analysis of 360043 brand new FuG 202 Lichtenstein Radar revealed that the night-fighter was using the signals from Monica (a 1cm Radar device fitted to a Bomber to give early warning of an impending night-fighter attack) to “home in” on the Bomber itself.  The Germans had developed the technology to receive centimetre wavelength Radar signals but not the technology to generate them using a magnetron which had been invented at Birmingham University PJ876 was also used to evaluate the impact of “Window” or chaff (aluminium strips) on German Radar.  On the 6th May 1944 PJ876 was flown to the 1426 (Enemy Aircraft) Flight base at RAF Collyweston.  When 1426 was disbanded on the 21st January 1945 PJ876 being selected for preservation, along with other aircraft, and stored.  In 1976 PJ876 was restored to Luftwaffe livery and placed on display at RAF Hendon during August 1978


Junkers 88

RAF School Hill - Angus
School Hill provided low level raid cover for the central east coast of Scotland and the approaches to Aberdeen. Became a CHL station.  Schoolhill Radar Station provided low level raid cover for the central east coast of Scotland and the approaches to Aberdeen. The East Coast Chain Home station at School Hill, West of Aberdeen was opened in about 1940 and remained operational through the War. There is little recorded operational history about the station but in mid 1942 - 2 of the 350' steel towers were taken down to be supplied to a Gee Radio Station and they were replaced by 325ft guyed masts which would normally only be supplied to west coast Chain Home stations.  At the end of the war RAF Schoolhill was placed on care and maintenance but was later selected as 1 of 15 stations promoted to a 'readiness chain home'. The station was equipped with a Type 1 Radar and 2 channels, as part of the 1st Phase of the Rotor programme. (Code HSL). With introduction of Type 80 Radar in 1955, RAF Schoohill was redundant. 

RAF Doonies Hill
Doonies Hill provided long range early warning for raids approaching central Scotland and Aberdeen.

Hillhead nr Fraserburgh
The location was selected by the Air Ministry as a Radar site in 1939 and it was photographed by the Luftwaffe in 1940 whilst still under construction being named as Smiddyseat after the farmsteading to the South. The evidence on the photograph was interpreted by the Germans as a Radio Station.  The station would appear to have become operational as a final type Chain Home station during March 1942, though it had been working as an Intermediate Chain Home (ICH) from 1941.  The Radar Station at Hillhead closed operationally during March 1946 and dismantling, such as it was began at the end of that month.


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Last modified: 01/09/2013