Radar Recollections - A Bournemouth University / CHiDE / HLF project


The prototype CH system - Chain Home Low (CHL)

Virtually all of the south and east coasts were covered by a new set of stations. The new CHL system used the same 'filter rooms' arrangements as CH and they were fully integrated with each other in 1940, just in time to cope with the Battle of Britain. The range was always less than the CH system could manage but in contrast, the altitude information was now accurate down to 500 feet. Thus the two systems complemented each other. The shorter wavelengths meant that smaller aerials and lower masts had to be employed. Even mobile units could be constructed. Aerial improvements continued; a single transmitter / receiver unit was devised so that it was no longer necessary to use two separate devices.

Professor G. E. Bacon
Mr A. E. Bennett


CHL Installation
A 'Chain Home Low' Coastal Installation
A further refinement was that the aerials could now be rotated at a steady 3 rpm and the resulting plot could be displayed using another invention; the 'plan position indicator' (PPI). This device produced a rotating scan and then a scaled map could be overlaid to give a far better indication of aircraft location, at least in the horizontal plane. At this point, the practical implementation of an effective Ground Controlled Interception (GCI) network became a reality. From 1941, it was now technologically possible to adopt a 10 cm format that had specific applications for the Army and the Navy because it made lower- looking, surface-based radars possible. These systems were known as CHEL (Chain, Home, Extra Low).