The AN/SPA-4 was a self-contained range-azimuth indicator which was designed for operation with any naval search radar system having a pulse repetition frequency between 140 and 3,000 pps. This indicator was capable of receiving radar information from one of eight different radar systems as selected by a front panel control. This feature was not used in HMCS HAIDA but ships of succeeding classes did use it. That switch controlled a radar switchboard called the SB-440. Position 1 selected the SPS-10, 2 for SPS-12 and 3 for Sperry Mk2. On HAIDA there was an externally mounted selector switch that was used to select the radar input source. The AN/SPA-4 utilized a remote PPI type indicator using a 10 inch, flat CRT.
The AN/SPA-4 determined the azimuth by means of a mechanical cursor coupled to an electronic cursor; jointly they were accurate to within one degree. Azimuth information was also indicated by a mechanical counter when the cursor was moved. The SPA-4 had also the capability of transmitting electrically, the bearing and range information to other systems such as fire control or directly to a projector on the plot table. That would cut down on verbal communication.
Specifications for the AN/SPA-4 Indicator
Type: range-azimuth radar indicator
Vintage: September 1954
Range selection: 1.5 to 300 miles continuous using a centered PPI and limited by the pulse rate of radar set that it was connected to.
Weight: 378 pounds
Dimensions: 38" H x 19" W x 21" D
Power requirements: 120 VAC, 60 Hz at 10 amps
Contractor: RCA Victor Company, Montreal P.Q.
Contract number: FE 113375, A/T 2-P-1-1877