COIL PULSERS FOR RADAR 611 



direction opposite to that of the discharge pulse. This takes the form of 

 a suitably poled diode shunted around tlie magnetron input terminals. 

 After the main discharge pulse is completed, reactive elements are left with 

 some little energy which tends to redistribute throughout the network. 

 In course of redistribution, additional pulses of lower energy may occur 

 shortly after the main pulse is completed. This tendency is a harmful one 

 if the after-pulses are large, since echoes from short-range targets are ob- 

 scured. Suppression of after-pulses is assisted by shunting around the 

 diode-magnetron a linear inductance known as a clipping choke. This 

 added inductance slows down the rate at which energy is redistributed, 

 and permits the diode to fulfill its second function of dissipating the greater 

 part of the residual energ>^ The shunting inductor, too, is made to fill a 

 second function. Through provision of a bifilar winding, it passes heating 

 current to the filament of the magnetron, thereby eliminating the need for 

 high-voltage insulation otherwise required in the filament transformer. 



Magnetic Bias 



Several arrangements have been worked out for supplying various amounts 

 of bias, some of them using a separate source, others being self-biased.^ 

 In general the use of external bias leads to a lower demand on the driving 

 tetrode and is associated with pulse production at best efficiency. Circuits 

 dispensing with an external bias source are that much more convenient in 

 use, where the added tube demand and the lower efficiency corresponding 

 can be handled without undue increase of the tube complement. In general 

 the energy delivered to the magnetron is roughly 25 to 55 per cent of the 

 plate energy input, with the higher figure applying to the higher outputs 

 and external bias. 



Transformer Coupling 



In some cases it is convenient to equip the non-linear coil with primary 

 and secondary windings providing voltage transformation or isolation to 

 avoid adding a transformer for that purpose. The first case arises in the 

 higher-powered pulsers, where the load condenser has to be charged to a 

 voltage greater than the driving tetrode can withstand. For the Western 

 Electric 5D21 tubes customarily used, voltage breakdown occurs near 20 kv, 

 while condenser voltages in certain of the pulsers reach 30 and 40 kv. This 

 situation calls for a step-up ratio from primary to secondare' to fit the 

 required potentials. The need for isolation may be illustrated by reference 

 to Fig. 3a where the bias battery £o is shown maintained at the plate supply 

 potential above ground. To avoid the resulting insulation problems in a 



3 One widely used circuit using a small amount of self-bias was developed by 1.. G. 

 Kersta and E. E. Crump. 



