THE RADAR RECEIVER 811 



sion or electronic types are usually employed here, resulting in a nominal ± 

 3% voltage stabilization. The extreme variable electrical loads imposed 

 upon the aircraft power system by electrically operated gun turrets and 

 other combat equipment result in increased emphasis being placed on ade- 

 quate regulation capabilities of the radar receiver power supplies. In 

 addition, the ever-present requirement of minimum weight for aircraft 

 equipment results in motor generator designs employing a minimum of 

 magnetic material and usually results in a variation in output voltage wave 

 shape with load. This factor must also be considered in the detailed 

 design of the aircraft radar receiver power supplies. 



During the initial airborne radar development program, the power 

 frequencies in common use were 400 cps and 800 cps. The British use of 

 direct coupled aircraft engine driven alternators produced variable fre- 

 quency output voltages ranging from 12C0-2400 cps dependent on the en- 

 gine speed. In connection with the electronic warfare standardization pro- 

 gram for equipment to be used jointly by our allies, the aircraft radar system 

 was required to operate over the entire range of power frequencies extending 

 from 400 cps to 2400 cps. All of the airborne radar equipment developed 

 during the later half of World War II was designed to meet these variable 

 power frequency requirements. 



2.82 Low Voltage Power Supplies 



The electronic regulated power supply has been universally employed to 

 furnish the stable low voltages as required by the radar receiver. Here the 

 output voltages required extend from 50 volts to 600 volts with maximum 

 direct current required extending upward to 500 ma. 



The basic electrical circuit arrangement of such a power supply is shown 

 in Fig. 72. In this circuit, the regulating element consists of a variable 

 series impedance, furnished in the form of a vacuum tube and resistance 

 combination, whose magnitude may be controlled electrically from an error 

 signal associated with the output voltage of the power supply and a reference 

 voltage. The control circuit consists of a bridge network which includes a 

 constant voltage gas-discharge tube as one element. A d-c amplifier is 

 connected across the output terminals of this bridge circuit and serves to 

 amplify the error signal for use in the regulating element. If the output 

 voltage of the power supply varies from the desired value for any cause, the 

 error signal appears at the output terminals of the bridge circuit, due to the 

 effective unbalance of this circuit at all voltage levels except the reference 

 value. The error signal after sufficient amplification is impressed upon the 

 grid of the series regulating tube with a polarity such that a corrective 

 impedance variation results. The degree of regulation obtainable is a func- 

 tion of the loop gain provided and the absolute stability of the output voltage 



