 Serrate used the Mk . IV equipment for reception and display , replacing only the receiver unit . This could be switched in or out of the circuit from the cockpit , which turned off the transmitter as well . In a typical interception , the radar operator would use Serrate to track the German fighter , using the directional cues from the displays to direct the pilot on an intercept course . Range was not supplied , but the operator could make a rough estimate by observing the signal strength and the way the signals changed as the fighter maneuvered . After following Serrate to an estimated range of 6 @,@ 000 feet ( 1 @.@ 8 km ) , the fighter 's own radar would be turned on for the final approach . 
