How the Type 72DP encoded a usable bearing

The Type 72DP retained a once-per-minute rotating aerial but changed what the aircraft received. As the beam crossed each true bearing, the transmitter added a modulation characteristic of that direction, while stabilization compensated for alterations in the carrier's course. The passage corrects a slide error and gives the practical homing accuracy as about plus or minus seven and a half degrees, adequate for reaching the carrier's vicinity before the final landing approach. The transmitter covered roughly 200 to 250 megahertz and used crystal-controlled carrier and modulation frequencies. Its rotating pedestal, parabolic reflector, dipole, slip rings, and mast-level hut show how much shipboard engineering supported the apparently simple indication in the cockpit. Ease of use in the aircraft depended on moving technical complexity into the carrier.