Radar Type 978

This system was used in frigates and larger ships. It operated in X-band using a ‘double cheese’ antenna, the upper half transmitting and the lower half receiving. It was based on the commercial Decca 45, which had a power of 20 kW, a rotation of rate of 24 rpm and a beamwidth of 1.2º.

The Type 978 radar and its power supplies are self-contained, the necessary switch functions being made by relay control from the Control Unit. Selection of internal or external triggering is possible by means of a switch in the front panel. A thermistor bridge in the RF section enables continuous monitoring of power output under true load condition.

The receiver and its power supplies are also self-contained and operated from the Control Unit. Logarithmic amplification is used to improve the performance when there is rain or sea clutter.

The reference signal for the AFC circuit is provided by a magnetron sample pulse fed directly from the transmitter. An X-band noise source is built into the receiver for accurate measurement of the overall noise factor. The maximum range is 40 miles; minimum range is less than 50 yards with a 0.2 μs pulse. Range discrimination is less than 50 yards on 1 mile scale. Beyond this, within a half radius of centre, 2% of indicated range, and outside half radius, 1% of maximum range. Bearing accuracy 1º.

This radar system was installed on HMS 'Blake' in 1961.