776 BELL SYSTEM TECHNICAL JOURNAL 



2.52 The Timing Wave Form Generator 



The generation of the timing wave forms consists of the preparation of 

 specitic voltage wave forms for use in the following sweep generator in ac- 

 cordance with timing information available at the radar receiver input. 

 These timing data may consist of a pulse coincident or related to the out- 

 going radar microwave pulse serving as a reference for range display or, in 

 the case of direction sweeps, may consist of signals related to the instanta- 

 neous position of the antenna. 



The basic wave forms employed in this connection consist of rectangular 

 pulses where the duration of the pulse may be controlled to serve as a 

 measure of time, extremely short-duration pulses useful as time markers, and 

 various combinations of these. In general, these wave forms are character- 

 ized by their nonsinusoidal form. The generation of these nonsinusoidal 

 wave forms is accomplished by a number of specialized electronic circuits, 

 which though apparently quite complex can be resolved generally into a 

 combination of relatively simple basic circuit forms. 



The Multivibrator 



The "trigger" or multivibrator circuit was developed nearly thirty years 

 ago and provides the fundamental circuits for the sweep circuit designer. 

 Figure 47a illustrates a simple historical form of a trigger circuit which is 

 of the Eccles- Jordan type. The essential current-voltage relationship which 

 characterizes this circuit and all circuits employed for this purpose is a nega- 

 tive resistance characteristic which exists over a limited portion of the 

 operating range of the device. In the case of the electronic circuit shown in 

 Fig. 47a this negative-resistance characteristic is bounded by two stable 

 limiting conditions. Referring to the trigger circuit of Fig. 47a, the chrono- 

 logical order of operation can be described as follows: Assume Vi is con- 

 ducting a somewhat larger current than To so that the ])otential at the plate 

 of Vi is lower than the corresponding point at I'o due to the voltage drop 

 across the plate resistor Ri. This condition further implies that the grid 

 potential of l^ as determined by the connection from the plate of I'l through 

 the coupling resistor R^ is lower than that at the grid of I'l. Similarly the 

 grid potential of V\ is at a higher positive potential, due to its connection 

 with the ])late of ]'•_.. The action is cumulative and results in stablizing the 

 circuit under the condition where the plate current of 1% is entirely cut off 

 and the voltage drop across I'l is less than the grid bias voltage Ec. 



\{ now a voltage is imi)ressed across the input terminals of eitlier a positive 

 or negative form, the circuit will be driven away from this stable equilibrium 

 condition as follows. Assume now that a large ])ositive jnilse be applied 

 to the circuit shown. The tube I'l which is operating in a conducting con- 



