Great Britains ‘Chain Home’ radar system was conceived in the middle 1930s and put in place using the technology of the day to protect the eastern coastline by being aware of any aircraft within its coverage. Although the system was left behind by the rapidly advancing standards set by radar in the early 1940s, the whole system was so well integrated and did the job intended, it remained in place and was simply updated by adding better, shorter wavelength radar stations called Chain Home Low and Chain Home Extra Low. Naturally, these used the more familiar PPI (planned position indicator) circular displays rather than the older ‘A’ screen, so later Chain Home display consoles featured two separate screens, one of each type.

Using a simple ‘A’ screen display, the original Chain Home radar ‘contacts’ were shown as downward pulses on a horizontal line. To the far left was the large transmitted pulse, then moving to the right came numerous reflections and moving ‘grass’ at the base of the line. The actual contacts appeared as one or more very obvious downward spikes. By linking together data from neighbouring Chain Home stations, as well as by switching in different aerial arrays, it was possible to identify the bearing (compass heading) on which contacts were heading, as well as the speed and height they were flying at.

Our simple demonstrator model shows a typical ‘A’ screen display with constantly moving ‘grass’ (radar clutter) and three examples of indication as shown below: