M.J.B.Scanlan

The following article has been reproduced from the "GEC Review", vol 8, no.3, 1993 with the kind permission of the Editor:

by M. J. B. SCANLAN, B.Sc., ARCS.
(Formerly at GEC-Marconi Research Centre)

After graduating in Physics from Imperial College, London. M. J. B. Scanlan served four years in the RAF radar branch, working on decametric and centimetric radars in the UK and the Far East. He joined the Marconi Company in 1952. and ran the Applied Physics Group in what is now the GEC-Marconi Research Centre from 1963 to 1982 working on a great variety of systems, sub-systems and components. He began editing the Marconi Review in 1979, and became the first editor of the GEC Journal of Research in 1983 and of the GEC Review in 1985. He retired from full time employment in 1986.

This paper was written to celebrate 50 years in radar. It was begun in October 1992, fifty years after my first awed, ignorant and bewildered introduction to my first radar (an 'A' CH station at New-church in Kent) and finished in the spring of 1993, fifty years after my first real radar job as S.T.O. (station technical officer) at Ottercops Moss in Northumberland, an East Coast CH station. My position was immensely privileged, since after a degree in physics I was commissioned directly into the RAF VR: in even the lowest commissioned rank, I had relatively easy access to all classified documents, could mix easily with calibration and quarterly overhaul parties and learn on equal terms from the WAAF officer supervisors, who were highly skilled and experienced in CH operations.

There are good technical accounts of CH radar in the literature, but this paper attempts to give a broader picture, based on personal recollections as well as the technical accounts already noted. CH operation at Ottercops Moss in 1943 cannot have been as hectic or as important as operations at a South Coast station in 1940, yet the stations were virtually identical technically, and the modus operandi cannot have changed much either. Therefore it is hoped that this broad-brush account of CH radar will have some interest and value: in a relatively few years, there will be no one left to give a first-hand account.

This paper deals with only one aspect, albeit the most interesting technically and important operationally, of the complete CH (Chain Home) system. The East Coast stations described here were the first to be built and covered the south and east coasts from the Isle of Wight to the Orkneys, with the greatest concentration in S.E. England and the Thames estuary: with their massive free-standing steel towers and their gigantic, complex and horribly inefficient transmitters, they convey some-thing of the urgency underlying their building. For the rest of the country, the same coverage was achieved by the West Coast stations, with much simpler guyed towers and a smaller, simpler and more efficient transmitter. Small gaps in the coverage were finally filled in by a few 'A' (auxiliary) CH stations such as that at Newchurch: this design was similar to that of the mobile stations, one of which, allegedly left behind in France after the Dunkirk evacuation, supposedly led the enemy to believe that he had nothing to fear from British radar.

These OH stations, all working on a wavelength of about 10 metres (30 MHz), were supplemented by CHL (Chain Home Low flying) stations, which, working at 200 MHz and often sited on cliffs or towers, offset the one great weakness of the 1Gm stations, that is, the lack of low cover. There were also GCI (Ground Control Interception) stations, rather similar technically to CHL, but sited inland and designed for the direction of night fighters.

All these ground stations were controlled administratively by Wings which were more or less coterminous with the fighter groups to which the stations reported. Each radar station was autonomous on a day-to-day basis, but Wing H.Q. provided technical services (calibration, quarterly overhauls, etc.) and administrative back-up with such things as pay and personnel services. The whole country was covered by about eight Wings, which in turn reported to the H.Q. 60 Group at Leighton Buzzard. At Ottercops Moss, we reported administratively to H.Q., 73 Wing, which was then at Malton in Yorkshire, and later at Boston Spa. Operationally, we reported to the 13 Group Filter Room at Newcastle.

The so-called 'Daventry experiment', on 26th February, 1935, has attained the status of folk-lore in British radar history. In the experiment, carried out at Weedon, 6 km SE of Daventry, an RAF bomber at a height of 1800m flew down the radio beam of the BBC transmitter at Daventry: the transmitter frequency was 50MHz^†, and the wavelength therefore comparable with the size of the aircraft. At Weedon, two parallel horizontal wire aerials were erected perpendicular to the beam, and phased together so that the direct signal from the transmitter was almost cancelled out. The small residual signal was received, demodulated and applied to the Y-plates of a cathode ray tube (CRT). which was itself a rare instrument at the time. The passage of the aircraft modified the signals to the two aerials, causing the CRT spot to move.

^†this might be a typographical error, in "Pioneers of Radar" Dr. W.H. Penley describes the transmitter wavelength as 49m. He also states that the beam width was 30^o and inclined up at about 10^o