Ian, thanks for that. There was also a difference between the two equipments. The GS aerial would hunt until the aerial was aligned along track, Twp beams forward, left and right and two astern. Around 8.9 GHz, IIRC. The DD 62 M was different. Fixed aerial, two beams radiating with side of heading and one abeam or maybe slightly abaft the beam. Each on a discrete J-band freq around 13.2 GHz. The DD 62 M was in use from 1970.