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Radar Development In England
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The British realized that an aircraft warning system must be developed and deployed in case of war. In January of 1935, M. E. Wimperis announced to Watson-Watt that radio waves may be used to spot aircraft. Click here to see what radar he was have been talking about. Watson-Watt wrote a memorandum to the Air Defense Subcommittee of the Committee of Imperial Defense to promote development of "Radio direction finding," RDF system. Based on this letter and the efforts of Henry Tizard, a concentrated radar development program began in England. See "Technical history of the beginnings of RADAR" by S.S. Swords.
In 1937, a prototype RDF station (called Chain Home or CH) was built at the Bawdsey Research Station and handed over to the Royal Air Force. The CM station operated at a frequency of 22 MHz (13.6 m wavelength) and aircraft at 3,000 m (10,000 ft) as far out as 150 km (80 miles) could be spotted in good weather. In rain, a range one half or more, depended on the target altitude. By September 1939 at the outbreak of war, 20 CH stations were operational. Because of the low operating frequency which is in the radio range, it has often been questioned if the CH was really a radar set or simply a RDF system.
Later, frequencies from 22 to 55 MHz were used to avoid interference between adjacent towers, noise or jamming. Although the CH had an elevation limit from 1.5 16 degrees and could not detect low flying aircraft, the system worked and was used in the Battle of Britain.
Development work in 1937 led to "beamed radar" for airborne sets and for Coastal Defense (CD) radar that operated on 1.5 m wavelength. The CD system was also called the Chain Home Low (CHL). The CHL used a rotating antenna, which rotated at 1-2.3 rpm and had a range of 160 km with an azimuth accuracy of 1.5 degrees. A PPI display was used. Height could not be determined. By 1941, 11 CHL were operational. The use of higher frequency made the radar less dependent on weather.
The Navy used a similar set to the CHL. Called the type 281; it was tested on the HMS Dido in October of 1940 and the HMS Prince of Wales in January of 1941. Over 59 sets were produced during the war. This set could operated on a wavelength of 50 cm and it could locate ships up to a distance of 20 km.

Above, the large stationary tower of a CH RDF system is seen with several CHL and CD antennas. The CH receiver towers were 240 feet (73 m) high and made out of wood. The transmitting towers were 360 feet (100 m) high and made out of steel. The receiver towers were hundreds of yards from the transmitting towers.
The prototype magnetron designed by J. Randall and H. Boot in February of 1940.
See Hollmann US patent 2,151,766 of 1935 for a description of how this unit worked. 


In June of 1940, Eric Stanley Megaw, based on experiments with Generel Electric Company E821 glass magnetron, had designed a cavity magnetron in England which worked on 10 cm 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 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.
Schematic of the classic magnetron transmitter by Hull. Habann Tube split into four segments.

Because Randall and Boot built a cavity magnetron, the claim that the British invented radar is made. This is simply not true. The book "History of Communications-Electrics in the United States Navy", 1963,  on pg. 447 claims, "British scientists took an American invention, the cavity magnetron, and improved it to where it was . . . ". "This device was invented by Dr. A.W. Hull, of the General Electric Co., in 1921."  However, Prof. Dr. H.E. Hollmann's book Physik und Technik der ultrakurzen Wellen, Erster Band, 1935," Chapter 4 deals with the history of the magnetron in its many variations. Hollmann states that Greinacher in Germany first discussed the theory of the magnetron and then Hull further developed it. See the schematic of the Hull Magnetron transmitter taken from Hollmann's book. Also in 1921, a German physicist by the name of Habann developed a split tube magnetron generator working on a wavelength of 3 cm. Habann is generally given the credit of being the inventor of the magnetron from which the cavity magnetron evolved. Furthermore, in 1935,  Prof. Dr. H.E. Hollmann filed a patent on the multicavity magnetron well ahead of Randall and Boot's work. Click here to see this and his other magnetrons.

All of the patents filed by Telefunken in Germany were also filed in the USA. These were most of H. E. Hollmann's patents, W. Runge, director of Telefunken, patents and tens of thousands of other relating radar patents. These patents were available to all General Electric Co., GEC, technical personal. You see, Telefunken owned the German company, AEG which was allied with GEC and traded all patents with GEC. In this way, most of the German radar secrets, were available to the Allies. The Allies, England and America primarily, used these patents to develop their radar systems.

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. 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."

During the war, the British worked closely with the US  to improve their radar systems and radar jamming methods.

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© Copyright 2007 Martin Hollmann