THE RADAR RECEIVER 



793 



produced an entirely satisfactory range marker signal for radar search 

 systems. 



Variable Range Marker Circuits 



Variable range marker circuits are employed where more precise range 

 information is required for missile control applications of radar. Here the 

 observer may position the electronic range mark to obtain coincidence with 

 the selected target, and from an associated calibration of this positioning 

 control, determine the range coordinate. For search or reconnaissance 

 purposes it is often desirable to determine range with somewhat more ac- 

 curacy than is afforded by the display of fixed markers, and for this purpose, 



Fig. 60. — Variable range marker circuit of moderate precision — simplified schematic. 



several designs of moderate precision variable range marker circuits have 

 been developed and employed during the past war period. 



Figure 60 illustrates the circuit operation of a variable range mark gen- 

 erator of moderate precision. This circuit operation depends on a pulse 

 obtained from the transmitting modulator to serve as the zero time or 

 range reference. This is applied to a single-cycle multivibrator which pro- 

 duces a rectangular pulse whose leading edge is coincident with the time of 

 the synchronizing pulse and whose duration is somewhat greater than the 

 maximum range measurement required. A saw-toothed voltage wave form 

 is generated in the following RC wave generator by means similar to the 

 sweep wave form generation described in a previous section of this paper. 

 The coincidence circuit which follows consists of a vacuum tube biased be- 

 low cut-off whose exact cut-off bias is determined by the range mark poten- 

 tiometer setting. This coincidence circuit is thus inoperative until the 

 saw-toothed input signal has reached the value of the cut-off voltage, at 

 which time this circuit functions and produces a sharp decrease in its plate 

 potential. The effective time delay which is here produced with respect 



