AN/SPS-43

The AN/SPS-43 was a long-range air-search United States Navy radar system introduced in March 1961 that had a range of 500+ km. This radar could provide bearing and distance information, but no altitude information. The small-ship antenna (AN/SPS-29) looked like a bedspring. Larger ships used the 12.8 m wide AN/SPS-37 antenna - about twice as wide and half the height of the SPS-29 antenna - and designed with a much narrower beam. Targets were much more accurately displayed when using the -37 antenna. The -43 operated at VHF frequency - somewhat unusual for any radar - mostly in the bandwidth of television channel 13. The main difference to the SPS-37 was the greatly improved ECCM performance, as the AN/SPS-43 could jump between 20 different frequencies to frustrate jamming attempts. A sea-skimming missile could be detected at a range distance of 30 km, a large high-flying aircraft at 500 km.

The SPS-43 also included MTI (Moving Target Indication) which enabled the operator to eliminate all stationary targets from his screen, but this was notoriously unreliable in practice given that it was, along with the rest of the electronics, entirely a vacuum-tube design. Vacuum tubes, operating at temperatures requiring cooling - or least properly ventilated cabinets - suffer varying temperatures in operation, so maintaining the constant output pulse leading edge - phase-coherency - (required for proper delay-line timing) was well-nigh impossible. Some operators took it upon themselves to bore a small hole in the front panel of the MTI timing cabinet through which to insert a screwdriver, enabling adjustment of a critical potentiometer without having to open and close the cabinet. This prevented the resulting heat loss and subsequent heat buildup which threw off all adjustments. Even this enterprising idea was of little help. SPS-43 MTIs went largely unused in regular operation.