SrUn/ES IN R.IDIO I1R0.4DC.-1ST TR.INSMISSION 



201 



on at the transmitter. The receiving circuit was not changed during 

 the making of this record, so that the results obtained from the two 

 transmitters are directly comparable. 



The record of the signal from the normal transmitter shows an 

 abundance of second and third harmonics, at times equal in amplitude 

 (() that of the whole tone signal. The latter, of course, includes these 

 iiarmonics. It will be noted also that dark line shadows run through 

 the trace of the whole tone, indicating the presence of the wave form 

 distortion. The signal from the stable frequency transmitter as shown 

 by the record is practically free from wave form distortion. The 

 trace of the whole tone is also free from anv dark lines which would 



I iUW>>- 



-Jiii 



[■2 r 



Fig. 45 — Diagram of an oscillator circuit 



indicate wave form distortion. This record is substantial evidence 

 that a great deal of the wave form distortion may be eliminated when 

 the carrier is stabilized. However, the selective fading still remains. 



The selective fading we have already explained more or less satis- 

 factorily and we find that it does not materially affect the wave form 

 of audible frequencies transmitted by a modulated stabilized carrier 

 unless its changes are more rapid than any we have recorded. The 

 crippled state of originally perfect tone waves after they have been 

 transmitted by an unstabilized carrier, we have just observed. Now 

 let us consider the possible causes of this difference. The carrier stabil- 

 ization referred to here, may we repeat, is not stabilization against 

 slow variations in frequency from second to second or from hoin- to 

 hour but rather against rapid variations within the cycle of the modu- 

 lating frequency. 



The reason for such changes over the modulating c>'cle is that 

 the \-ariation of the impedance of a \acuinn tube across the 

 oscillating circuit necessarily causes a variation in the nature period 

 of the oscillation. As a simple case, the circuit in Fig. 45 is given. 



