THE RADAR RECEIVER 797 



maximum range measurement of 40,000 yards with an accuracy of ± 40 

 yards at this range under normal field operating conditions. 



The use of the liquid range unit is practically restricted to ground and 

 naval vessel application because of its weight and the problems of handhng 

 these critical liquids. Another variable range unit development was ini- 

 tiated to meet the same accuracy requirements as above, but to be more suit- 

 able for aircraft and other extreme ambient applications. The phase- 

 shifting type of variable range unit whose operation is illustrated in Fig. 64 

 was the result of this effort. 



The input start-stop single-cycle multivibrator circuit produces a rectang- 

 ular pulse output wave form whose leading edge is coincident with the time 

 of the outgoing radar pulse and whose duration encompasses the maximum 

 range time to be measured, in this example 270 microseconds. 



The timing wave generator and associated phase shifting circuit is shown 

 schematically in Fig. 65. The resonant frequency of the oscillatory circuit 

 is 81.955 kc which period represents an equivalent radar range interval of 

 2000 yards. An initial d-c current of approximately 10 ma is present in the 

 Li Ci circuit in the absence of input start signals. Upon application of the 

 negatively poled rectangular start-stop pulse V\ and V2 are abruptly driven 

 to cutofif and the energy associated with the magnetic field of Li produces 

 local current flow and oscillation at a frequency determined by Li C\ . 

 The initial circuit conditions here are the same as the zero voltage condition 

 for each cycle of a sustained oscillation and the behavior of the oscillatory 

 system is the same as for the case of sustained oscillation. The absolute 

 average potential of the oscillation is maintained constant regardless of 

 the magnitude of the duty cycle. Positive feedback of the timing 

 wave is included in the F3 cathode connection in such a manner that uni- 

 form amplitude of the timing period throughout the active period results. 

 The purpose of the remaining circuits shown in Fig. 65 consisting of W , 

 Vi and F5 is to produce four output timing wave voltages whose relative 

 phases differ by 90°. These voltages are to be later combined in such a 

 manner that continuous phase shift of the output timing wave results. 

 Two quadrature voltages are here produced by the use of LR and CR net- 

 works so proportioned that C0L2 = — ^ = R2 at 81.955 kc. The desired 



C0C2 



four timing wave outputs are produced by the use of the phase inverter 

 stages V4 and F5 . 



The method here employed to combine four quadrature voltages to enable 

 continuous relative phase shift of the resultant output is illustrated in Fig. 

 66. This phase shifter capacitor consists of four quadrant shaped stator 

 sectors which are equal in area and shape and which are mounted parallel 

 to a ring stator as shown. A carefully shaped eccentric dielectric vane rotor 



