MAGNETIC GENERATION OF A GROUP OF HARMONICS 451 



Another comparison between calculated and observed values is 

 shown in Fig. 9 for a fundamental input of 120 kc. with two values of 

 resistance load. Fair agreement is observed over the greater part of 

 the frequency range which extended to 5 MC. The distribution curve 

 for the smaller resistance load undulates as the load resistance is re- 

 duced, since multiple oscillations and recharging are then promoted, in 

 consequence of which the output power tends to become concentrated 

 in definite bands of harmonics. In general, agreement within a few db 

 is found over a wide range of circuit parameters when working into a 

 resistance load, provided that recharging does not occur. 



30 



I 



J. 26 



a 14 



1.6 2.0 2.4 



npCaRz 



3.2 



3.6 



4.0 



Fig. 9 — Comparisons of calculated and measured harmonic distributions plotted as 

 functions of npCiRi, with R^ as parameterl 



When the resistance termination is replaced by a bank of filters as it 

 is in practice, the resistance termination is approximated over the 

 frequency band covered by the filters. Where the band is wide the 

 results obtained do not differ greatly from those with the pure resist- 

 ance load, but when only a few harmonics are taken off by filters and 

 the impedances to the other harmonics of large amplitude vary widely 

 over the frequency range, then the wave form of the current pulse is 

 substantially altered, with corresponding effect upon the frequency 

 distribution, and the calculations for a pure resistance termination do 

 not apply. 



A difficulty sometimes arises in getting a desired value of funda- 

 mental current into the coil. Under certain circuit conditions the 

 current amplitude is found to change rapidly as the input voltage is 

 smoothly varied. This phenomenon has been described by various 

 terms such as Kippeffekt, ferro-resonance, and current-hysteresis.^* If 

 the operating point is located close to one of these discontinuities, the 



