COIL PULSERS FOR RADAR 609 



source, and in charging the load condenser by a free, rather than by a forced 

 oscillation. Energy for the free oscillation is taken from the d-c. source in 

 a preliminary operation, in which energy is stored in a linear inductor. 

 This preliminary operation consists in closing a d-c. path from the plate 

 power supi)ly through the linear inductor by means of a high vacuum tube, 

 permitting current to build up with time. After a predetermined time has 

 elapsed, the tube circuit is opened, the d-c. |>ath is thereby interrupted, and 

 energy stored in the inductor transfers to the load condenser. In this way 

 the voltage to which the load condenser is charged can be made many times 

 greater than the voltage of the plate power supply. The simplified circuit 

 of Fig. 3(a) will serve to bring out salient operating features. Conduction 

 of the tetrode at the left is controlled by a rectangular wave of grid voltage 

 (Fig. 3b) developed by a multivibrator (not shown) which swings the grid 

 from a potential below cutoff to one just above cathode potential. The 

 plate power source Eb feeds two inductors in parallel, Li being linear, and L2 

 non-linear. A small biasing voltage £0 drives polarizing current /o through 

 the two inductors in series. 



The preliminary operation which serves to transfer energy from the main 

 power source to the inductors is initiated when the tetrode grid is driven 

 positive. Current from the main source builds up through the paralleled 

 inductors and the tetrode as indicated on Fig. 3c, inter\'al /. The region in' 

 which the non-linear coil works may be seen from the hysteresis loop of 

 Fig. 3d. Its operating point is displaced to the left of the origin near d by the 

 bias current. When the tetrode conducts, current in the non-linear coil 

 rises rapidly at first in the lower saturation region until a is reached. The 

 rise thereafter is comparatively small and slow in traversing the permeable 

 region a-b, while at the same time current builds up in the linear coil at a much 

 greater and practically uniform rate. When the core of Lo reaches saturation 

 near b its inductance again drops, preventing further rise of current in Li . 

 At this time the tetrode is driven below cutofT and remains out of the picture 

 until the start of the next cycle. 



The second interval, in which energy is transferred from the linear inductor 

 to the load condenser, starts with the cutolT of tetrode current. This trans- 

 fer is effected in an oscillation with frequency determined mainly by the 

 paralleled inductors and the load condenser. In this interval II of Fig. 3c, 

 current through the non-linear coil falls suddenly at first from b io c and then 

 more slowly from c to d. The rate of change in region c-d is much greater 

 than that in a-b as indicated by the fainter trace in Fig. 3d, so that eddy 

 currents in the core are increased and the slope of the descending branch of 

 the loop reduced correspondingly. Thus some of the energy previously 

 stored in the linear inductor is used up in completing the magnetization 

 cycle and this part, consequently, is not available for transfer to the load 



