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The euphoria is difficult to understand, unless the results indicated a far greater range than the12 km actually recorded, at which range the target aircraft probably cleared the bottom of the Daventry beam. The aircraft would then have been at 18km from Daventry; at an angle of elevation of 5 or 6 degrees: the Daventry beam was at 10o elevation, according to Neale, but Baker(2) suggests that such beams were at 15o elevation. The signal-to-noise ratio as the aircraft flew through the peak of the beam was the key result, and must have suggested that the maximum range would be well beyond 12km. The minimum useful range for an air defence system could be set at, say, 120km, giving 24 minutes' warning of aircraft approaching at 300kmh-1. The radar equation, as such, did not appear until about 1941, but Wilkins' calculations must have shown an R-4 term where R is the range to the target, (the transmitter flux falls off as R-2, and the scattered power from the target also falls off as R-2 on its way back to the receiver). If the maximum range in the experiment had been only 12km, an insurmountable gap of 104 would have remained between what had been achieved (12km range) and the minimum useful range of 120km. It must be assumed that the experiment promised a range of, say, 50km: this would leave a gap of about 40 times, which it would have been reasonable to expect to fill after some development.

Even supposing the maximum range problem to have been solved by the results, there remained the formidable hurdle that what had been achieved was merely detection, without any hint of how the position or height of an uncooperative aircraft might be found. (In the experiment, the position of the aircraft at any time was known only from the pilot's dead-reckoning). It is not known whether there were already ideas on how the location and height problems might be solved. What is known is that enormous sums of money were immediately granted to cover the development of 'R.D.F.', or radio direction finding, under a 'Most Secret' classification. The title was meant to conceal the fact that it also, and for the first time, covered the location of uncooperative targets.

The Roots of CH Radar

As recounted in Baker's book(2), to which this section is greatly indebted, two developments in radio (or wireless, to use the contemporary name) in the early 1920s had profound and unforeseen effects many years later. The first of these was broadcasting, which led to the growth of radio shops to maintain and repair domestic sets, and to large numbers of amateurs who could build, operate and maintain their own receivers, and even transmitters. This created a civilian pool of skilled radio operators and mechanics, besides those already in the armed services. The Marconi Company was prominent in this development, and the first broadcast station in the UK was the Marconi station 2 MT, transmitting from a wooden hut at Writtle. As Baker(2) recounts, 2 MT was allowed, by a grudging and belated licence, to transmit for half an hour per week (on Tuesdays, 8- 8.30 p.m.) with a maximum power of 250W.

The second, more important, development was the use of short waves for long-range communication. It was believed at this time (c.1920) that the way to long range in a wireless link was to use high power and long waves. Indeed, Marconi's Wireless Telegraph Company (abbreviated to M.W.T. Co., a title which lasted until 1963 - here we shall use Marconi) had entered into contracts with the governments of Australia and South Africa to build long-wave high-power stations for communications with the UK: the UK government dithered, being unwilling for such a powerful tool to be in private hands. (As Colonial Secretary, Winston Churchill had a hand in these negotiations). As an indication of the technology at the time, the Australian station was to be of 1 MW power, and the aerial would be supported on 20 steel masts, each 240m high.

However, in 1923, Marconi himself began a series of experiments between short-wave transmitters at Poldhu in Cornwall and his yacht 'Elettra'. The term 'short wave' here is relative: the initial tests were on a wavelength of 97 m, and further experiments were on wavelengths of 92, 60, 47 and 32m. The conclusion of these tests was that over long distances, the shorter the wavelength, the greater the range. Accordingly, Marconi's proposed a short wave beam system to the governments involved. These proposals were accepted readily by Australia, South Africa and Canada, and somewhat grudgingly in July 1924 by the UK. The UK contract was so severe in its terms that Marconi made no profit from it: the Company was obviously run by risk-taking engineers rather than by lawyers or accountants. The work was technically, if not financially, successful and links were opened to Canada in 1926, and to Australia, South Africa and India in 1927. At the end of that year, traffic over the four routes averaged over 100,000 words per day, that is, about two and a half issues of the GEC Review.


 

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Constructed by Dick Barrett

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ęCopyright 2000 Dick Barrett

The right of Dick Barrett to be identified as author of this work has been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.