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The Magnetron

Page history last edited by Alan Hartley-Smith 2 months, 3 weeks ago

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Quote based on Tim Wander's book “Marconi's New Street Works 1912-2012'

 

Alongside the CH radar system and antenna development, Marconi's worked on the 'heart' of the later radar system, a new air-cooled valve called the magnetron. The development and production of this device was a vital Marconi war effort. The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field. The 'resonant' cavity magnetron variant of the earlier magnetron tube was invented by John Randall and Harry Boot in 1940 at the University of Birmingham, England working under Admiralty direction. Their pioneering work resulting in the resonant cavity principle made the generation of very powerful radio signals of many kilowatts on then minutely short wave-lengths possible at a critical moment in WW2, initially ~10cm (S band - at a stroke, answering the Maidens prayer!) followed by 3cm (X band) and eventually 1.5cm (K band, spearheaded by the Americans), and later up to 15 – 30 cm (L band). Its invention and development made centimetric radar a practical proposition.

 

When put into production by Marconi's it became the heart of the secret battle fought out between the laboratories of Britain and Germany.

Magnetron production began in August 1940, but the challenges of the cutting edge technology meant that by the end of the year only 20 a week were being produced. It was such a great novelty that the first units were passed round the Great Baddow Laboratories like a new scientific toy. Marconi's also started supplying the General Electric Company with the magnetron 'blocks' which were made under conditions of great secrecy. Just as the magnetron is the heart of the radar transmitter, so is the 'block' the framework of the magnetron. and the whole basis of its operation. This component involves a number of machine-tool operations carried to fine limits, and in a material not specially well-suited for mechanical processing. The picture shows the 1189 C328 Cavity Magnetron, the second prototype ever to be produced.

 

Even so, towards the peak of the output, the Marconi Works were producing hundreds of 'blocks' a week for different types of magnetron. As time went on, new types were introduced, and the Company was firmly established as one of the three main suppliers. The great secrecy which was observed in connection with the magnetron was such that even scrap 'blocks' had to be accounted for, and a serial number stamped on every one of them, all duly recorded.

 

With other manufacture underway the Great Baddow Laboratory moved to Waterhouse Lane to begin volume production and 9,000 sq feet of floor space was dedicated to production in a former Marconi van garage. Soon several hundred cavity magnetrons were being manufactured each month and by 1945 a peak of 2,500 a month was reached.

 

Microwave Magnetrons; A Brief History of Research and Development

 

Chain Home and the Cavity Magnetron

 

Magnetrons for Radar - Colin Latham

 

Basics

 

Wikipedia

 

CAVMAG 2010 , the International Conference on the Origins and Evolution of the Cavity Magnetron

 

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Comments (1)

Ian Gillis said

at 6:32 pm on Feb 15, 2016

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