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radio power needed to raise the temperature of this 'man' by 2 degree Celsius in 10 minutes at a distance of 600 m. Assuming black-body absorption and 22 dB gain in the antenna system, the radiated power would have to be 30 MW Thus on these assumptions, absurdly favourable to a death-ray, the radio power in the beam would have to be thousands and thousands of kilowatts, wildly in excess of anything which could be generated at that time. Quite apart from this Watson-Watt pointed out the obvious: if the aircraft were made of metal then the crew and the engine would be shielded from the radiation.

Having thrown cold water on a death-ray Watson-Watt concluded his memorandum with the pregnant sentence:

'Meanwhile attention is being turned to the still difficult, but less unpromising, problem of radio detection and numerical considerations on the method of detection by reflected radio waves will be submitted when required.'

Anyone who knew Watson-Watt will recognise 'less unpromising' as an authentic quotation. By using unusual words, double negatives and convoluted syntax he could make almost any subject, however simple, difficult to understand. At one time I used to collect his sayings but, sadly, I never wrote them down and can now only remember a few I still remember one of the workshop staff at Bawdsey Research Station asking Watson-Watt to explain what they got for their subscription to the Institution of Professional Civil Servants; without a moment's hesitation he told the bewildered man that for five shillings a year the workshop staff got 'a nucleus of crystallisation for systematic representation'. Many years later, in Washington, I heard him tell the Chiefs of Staff that they would be wrong to imagine his position in the UK to be one of 'putative innocuous desuetude'. I am fairly sure that nobody knew what he meant.

click on image for an enlarged viewTo get back to the 'invention' of radar. Watson- Watt's 'numerical considerations on the method of detection by reflected radio waves' were sent to Tizard's committee and a first draft memorandum entitled 'Detection of aircraft by radio methods' (Fig. 3 - click on image for an enlarged view - Ed.) was forwarded on the 12th February 1935. It was followed by a final draft3 entitled 'Detection and location of aircraft by radio methods'.

In this memorandum - the birth certificate of radar - Watson-Watt put forward his proposals in impressive detail. He estimated the strength of the radio signal reflected from an aircraft and discussed the optimum wavelength. He outlined how the range of the target could be measured by the use of short pulses and the plan position by the use of three range measurements; furthermore he suggested that a cathode-ray direction-finder might be developed to measure the bearing and elevation.

Demonstration of radar

The Committee promptly asked for a demonstration and appointed A. P. Rowe as their sole observer. It was arranged that a Heyford bomber should fly at a height of 2000 m to and fro in the main beam of the BBC Empire short-wave transmitter at Daventry which radiated 10 kW at 498 m. A simple but sensitive arrangement was used to look for reflections from the aircraft. At a distance of 10 km from the transmitter two horizontal half-wave dipoles were mounted on poles; the dipoles faced the transmitter and were spaced 5 m apart in that direction. By means of a phase changer and two receivers the signals from the two dipoles were applied in phase opposition to a cathode-ray tube so that signals arriving directly from the transmitter produced no deflection; signals reflected from an aircraft, arriving at a different angle, were not cancelled and produced a vertical deflection on the tube. The demonstration took place on the 26th February 1935 and was viewed only by Watson-Watt, Wilkins and Rowe. They saw signals reflected from the aircraft for about 4 minutes on three occasions as the aircraft passed overhead. Watson-Watt must have been rather disappointed that Rowe didn't jump up and down with


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Updated 18/12/00

Constructed by Dick Barrett

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ęCopyright 2000 Dick Barrett

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