r.-ICrUi^ TVPE OSCILLATORS 52J 



is i'<|ual to thai tliu- to the output coupling. It is. thert-forf. (Ii-sirahlf 

 to make the oiii()hnj; to the input of the tiilie as ertirienl as [)ossil>]e 

 in order to (x^rniit the eouplinR 1<j the output to be reduced. F*"or this 

 reason the nuitual inifx-dance of the osciHatinf; coil has been kejit as 

 high as is practicable. 



By increasing the feed-l)ack resistance the ratio of tlic \(iltage at 

 B to the voltage at .4 may be refluced, thereby decreasing the ordinales 

 of the [Mnver loss family of the fre(iuency control unit — Fig. o. This 

 affords a control by means of which the system may be adjusted so 

 that lioth the amplifier and the freciuency control unit are operated 

 in regions where their power outputs are nearly porportional to the 

 power inputs or. in other words, where the separation between the 

 members in the gain and loss families is practically negligible. 



There is another advantage in keeping the feed-back resistance 

 high. In making it the major element in the network shunted across 

 the resonant circuit, the elTect of any variations in the output im- 

 jjedance of the tube or in the load imp)edance is reduced. 



It is evident from an examination of the power ratio families which 

 define the ofieration of the two elements of the regenerative system 

 that before the system can come into equilibrium, at least one of these 

 elements must enter a region where the relation between the pf)wer 

 which it receives and the power which it delivers is non-linear. This 

 means that the wave delivered by this element does not have the same 

 form as the wave received by it. Distortion of this kind is manifest 

 in the presence of harmonics of the fundamental frequencies in the 

 current delivered by the oscillator. In most cases the amplifier is 

 the distorting element and we find in the output ail multiples of the 

 fundamental. It has, however, been found advantageous in some 

 instances to so adjust the system that the iron core of the inductance 

 element in the frequency control unit overloads before the amplifier. 

 In this case, the resulting distortion is such that only the (\dd nuiltiplcs 

 of the fundamental frequency are present. 



By the proper choice of circuit elements, it has been found possible 

 to design commercial oscillating circuits, covering the range of fre- 

 quencies between 100 and 100,()()() cycles per second, in which the 

 frequency is but little affected by changes in elements external to 

 the frequency control unit. In one such commercial oscillator it 

 has been found, for example, that the average de\iation in the fre- 

 quency observed with any one tulie from the mean frequency ob- 

 tained with a number of tul)es is approximately [).Q'2'', . In this 

 siime circuit, as the plate potential changes from 100 to !.")() \-olts. the 

 frequency change does not exceed 0.04' i at aii>' portion of the fre- 



