Chain Home Radar - A Personal Reminiscence
The two transmitter arrays comprised a main array (eight horizontal dipoles stacked vertically at l/2 intervals to give a mean height of 65.5m) and a gap-filling array of four dipoles at a mean height of 29m: each dipole was backed by a reflector. The power from either transmitter could be switched to either array, and between the main arrays and the gap-filler in either case. The complete transmitter array system is shown in fig. 4, based on Neale's fig. 3.
The receiving aerial systems were three in number, denoted 'A', 'B' & 'C' (fig. 5, based on Neale's fig. 8). The 'A' system, at a mean height of 66 m, consisted of two pairs of crossed dipoles, with two pairs of 'sense' dipoles: the 'B' system, at a mean height of 31 m, was similar, but the 'C' system, at a mean height of 13.7m, had only a pair of stacked dipoles with fixed reflectors.
In the horizontal plane, the transmitter beam was 100o wide, centred on the so-called 'line of shoot'. In the vertical plane the coverage was determined by the ground reflection pattern. As the lowliest CH operator soon learnt, an array of dipoles at a mean height of h feet gives a ground reflection pattern, with a first lobe at 47l/ho , l being the wavelength in metres, a gap at 95l/ho, a second lobe at 141 l/ho and so on. These formulae, and their proof, were a standard part of a CH operator's trade test, by which she (operators were usuallyWAAFs) might progress in pay and prospects.
