COIL PULSERS FOR RADAR 607 



small. Hence the voltage drop across the coil is small. Little current 

 Hows in the output mesh, and practically all the input current flows through 

 the coil. Matters are much different during the next interval in which the 

 increase of current in L2 brings the core into the permeable region a-b. Here 

 the differential permeability is large so that part of the input current is 

 diverted to the output mesh, charging the output condenser until upper 

 saturation is reached at b. There the coil inductance falls to a low value, 

 switching most of the condenser voltage across the load resistance. A 

 current pulse accordingly develops in the output mesh lasting until the 

 condenser charge is exhausted. The form .of the current pulse shown in 

 Fig. 2d approaches that of a highly damped sinusoid, and the pulse duration 

 and magnitude are functions of the three elements of the discharge mesh. 

 During the next half-period of the input wave, the same situation develops 

 as in the first half-period, except that the corresponding currents and voltages 

 throughout are reversed in sign. 



According to this description the non-linear coil acts like a switch which 

 automatically shifts the inductance from relatively high to relatively low 

 values at specific coil currents. When the core is driven well into saturation, 

 as is the case here, the ratio of these two inductances can be made large, 

 usually in the neighborhood of several thousand. One feature of its action 

 important from the elBciency standpoint is that the pulse occurs for the 

 most part in the saturation region, where the contribution to eddy loss is 

 small. The principal core loss occurs in the permeable region while the 

 output condenser is charging, when variation of current through the coil 

 occurs at a relatively slow rate. 



In low-level radar applications the pulser output feeds a vacuum tube 

 amplifier biased so that pulses of just one polarity are passed, the other 

 oppositely poled pulse being cut off. 



Since the range sweep of the radar receiver is initiated prior to pulse emis- 

 sion, the pulse should occur at a time linked precisely to the input wave. 

 Otherwise the received pulse would be blurred introducing an uncertainty 

 in measuring target range. No blurring (jitter) is visible with normal coil 

 pulser operation. To get a measure of any variations which might be 

 associated with core magnetization, tests were performed on a communication 

 circuit in which jitter occurring at an audio rate would show up as noise. 

 Measurements with a sensitive noise meter indicate the corresponding varia- 

 tion of ])ulse emission time to be smaller than 10~^ second. 



Power Pulser 

 Operating Principles 



The power pulser has the same type of discharge circuit as the low-level 

 pulser just discussed. It differs in using a d-c. rather than an a-c. power 



