THE RADAR RECEIVER 



777 



dition will not be afifected but the grid of V2 will be raised in potential by the 

 amplitude of the enabling pulse. The plate current flow in V2 under this 

 influence will reduce the plate potential of V2 and accordingly will tend to 

 decrease the positive bias of Vi . The accompanying plate current reduction 

 of V\ will increase its plate potential and this will result in increasing the 

 grid potential of Vi through the coupling resistance Rz . Again the cumula- 

 tive effect will be to abruptly cut off the plate current of Vi and operate V-i . 

 Thus an abrupt switching of this electronic circuit results when a single 

 enabling pulse is impressed upon it. The wave form across one of the plate 



(a) 



Fig. 47. — Basic Multivibrator Circuit Forms. 



resistances is of a rectangular form whose duration is determined by the time 

 interval which exists between the two applied excitation pulses. 



A basic modification of the fundamental trigger circuit which has been 

 found most useful in radar sweep circuit is given in Fig. 47b. Here the 

 original circuit form has been modified so as to permit a complete cycle of 

 operation upon excitation by a single actuating pulse. The duration of the 

 cycle is here internally controlled by the arrangement and value of the 

 circuit elements. This form of multivibrator is characterized by having one 

 stable equilibrium condition and is known as a "one shot" type. 



The chronological order of operation of this circuit type may be considered 

 as follows: Vi is normally conducting heavily because of the large positive 

 grid potential impressed u\^on it by the plate sujiply battery and the connec- 



