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BELL SYSTEM TECHNICAL JOURNAL 



shown and an output pulse is produced whose position on a time scale is 

 determined by the additive phase shift of the timing wave and the setting of 

 the pulse selector potentiometer. By mechanically gearing the potentiom- 

 eter and phase-shifting condenser, the final rotation of the control shaft will 

 result in an output pulse whose delay will increase uniformly and correspond 

 to 2000 yards per revolution of the control. F'urther amplification is fur- 

 nished in the output amplifier shown. 



Figure 67 illustrates the final equipment features of a phase-shifting type 

 of variable range unit as developed for naval vessel radar system application. 

 It will be observed that this unit is mechanically interchangeable with the 

 liquid range unit shown in Fig. 63. 



RELATIVE PHASE 

 OF INPUT VOLTAGE 



ECCENTRIC 

 ROTOR 



RING 

 STATOR 



EQUIVALENT 

 CIRCUIT 



Fig. 66. — Schematic outline of operation of phase shifter condenser. 



In this model, the parallel resonant timing wave oscillatory circuit is 

 maintained at a constant temperature by employing an electrically heated 

 oven. Measurements made on this design indicate that the range shift 

 error to be expected for a "warm-up" period of 6 minutes was .003% or 15 

 yards at 45,000 yards range. After 6 minutes time, thermal equilibrium is 

 reached and the total range error will be less than 20 yards at 45,000 yards 

 range. The unit here illustrated has been universally employed in the 

 majority of naval vessel fire-control radar systems of the past war and these 

 basic circuit principles have served for range measurement in other apj^li- 

 cations including precision radar bombing. 



2.7 Automatic Frequency Control and Atitomalir Gain Control 

 2.1 \ Automatic Frequency Control 



The automatic frequency control (AFC) of the local beating oscillator to 



