Chain Home - Use By The Germans

Use By The Germans

The Germans deployed a passive radar system, the Kleine Heidelberg Parasit or Heidelberg-Gerät, which allowed them to track British aeroplanes using the radio signals from the Chain Home radars. The "floodlight" nature of the Chain Home transmissions provided a pair of signals which could be used to locate aircraft. The primary signal was received directly by the German receiver from the Chain Home transmitter; the second, weaker, signal was that reflected from the aircraft. The time delay between these two signals established how much longer was the reflected path compared to the direct path, and from geometry this longer path described an ellipse on which the aircraft must lie. The focal points of this ellipse were the transmitting and receiving antennas, and the Germans knew the location of both. A direction-finding antenna searching for the echo could be used to establish where on the ellipse the aircraft was. This system gave the Germans a radar with a range of up to 400 km (250 mi; 220 nmi), and an accuracy in range of 1–2 km (0.62–1.2 mi; 0.54–1.1 nmi) and in bearing of about 1°. The Heidelberg Parasit was not affected by Window.