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BELL SYSTEM TECHNICAL JOURNAL 



In this particular radar system the transmitting magnetron is pulsed from a 

 free-running modulator and, therefore, the controlling timing reference pulse 

 for sweep purposes must be obtained from the modulator circuit. In many- 

 other military radar systems it has proven desirable to time both the trans- 

 mitter modulator and the receiver sweep circuits from a common controllable 

 repetition frequency source. As shown in Fig. 49, a positive synchronizing 

 pulse as obtained from the transmitting modulator is delivered to the radar 

 receiver for range timing reference and here applied to the "clipper" portion 

 of the timing circuit. It was considered here desirable to clip or limit the 

 timing pulse to gain freedom from timing instability, due to possible ampli- 

 tude variations and to eliminate any possible negative excursions of the 

 timing pulse which might cause faulty operation of the following multi- 

 vibrator circuit. The multivibrator shown is a modified form of the "one- 



STOP PULSE 



l+B — !+B 



Fig. 49. — Radar Sweep Timing Circuit. Simplified schematic diagram. 



shot" type described previously. The grid of W is normally maintained at 

 a positive potential through its connection to the positive plate supply source 

 and accordingly Vi is normally cut off. 



Upon application of the positive synchronization pulse to Fi and the 

 resultant lowering of the plate potential of Vi the grid of F3 is driven below 

 cut-off decreasing the voltage drop across the common cathode resistance 

 and causing ¥> to conduct. This condition will be maintained until the 

 coupling condenser has discharged sufficiently to permit V^ to again conduct. 

 In the circuit here described, however, this controlling time constant has 

 been selected to be somewhat larger than tlie total period of the sweep rate 

 and the termination of the sweep timing [julse is accomplished by an external 

 stoj) pulse applied as shown. This stop pulse is developed in the following 

 sweep amplifier circuits not liere shown and is controlled directly by the 

 deflection current. Details of this stop-pulse timing and generation is given 

 in a later section. 



The out|)Ut of this timing circuit shown here then is observed to consist 

 of a rectangular i)ulse whose leading edge is related to the time of the out- 



