The Chain Home radar system
RECEIVER ANTENNAE
Wooden
towers, rather than steel, were used to avoid influencing the balance and symmetry
of the receiver dipole stacks by the proximity of any metallic parts. The towers,
240 feet high with servicing plat-forms placed at regular intervals and accessed
by a central ladder arrangement, are shown in figure 7
There were three discrete antenna stacks spaced one above the other, identified as the 'A' system at a mean height of 215 feet, the 'B' system at 95 feet and the 'C' system at 45 feet, see figure 8.
The 'A' and 'B' systems were identical, each consisting of two sets of centre-fed horizontal crossed-dipoles, vertically stacked by a half-wavelength, figure 8. The dipoles were aligned to look N-S, and E-W. The N-S dipoles were designated 'X' and the E-W dipoles designated 'Y'. On the N-side of the X dipoles and the W-side of the Y dipoles, at a spacing of quarter wavelength were placed centre-switched reflectors. With the centre of the reflectors open, the polar diagram of the dipole stack was simply a 'figure of eight', the reflectors having no effect. When closed, the reflectors were effective and the polar diagram was changed to a cardioid pattern increasing the signal strength in the E or S direction by some 3 db whilst reducing the W and N signals. These switches were relay operated and controlled by the operator at the console for 'sensing', as previously described.
The 'C' system at 45 feet was simply a stack of two single dipoles with non-switched reflectors. They were used only for heightfinding when the system was operating in the gapfiller mode and played no part in direction finding.
(This article is taken from "The GEC Journal of Research", Vol. 3 No.2 1985 pages 73-83 and has been reproduced with the kind permission of the Editor. The copyright of the material remains with the owner.)
