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BELL SYSTEM TECHNICAL JOURNAL 



tlnit frcciucncy modulation occurs in the transmitter circuit. The 

 frequency change is \ery apparent on the oscillograms when the 

 lengths of one cycle at maximum and minimum amplitudes are com- 

 pared. The realit\- of the effect is demonstrated in the two records, 

 which by their difference show the reversal of the increased and de- 

 creased frequency points with reference to the modulation cycle when 



Fig. 40 — Oscillograms showing frequency modulation accompanying amplitude 



modulation 



the beating frequency is moved in frequency from one side of the 

 carrier to the other. 



The next step was to determine to what extent a stabilization of 

 the carrier frequency to stop frequency modulation would affect the 

 distortion of signals. True, master oscillator transmitters capable 

 of giving the desired stability are not a new thing in the art. Several 

 such transmitters were built by the Western Electric Company some 

 years ago and used successfully in ship-to-shore radio telephone 

 experiments ^ in which frequency stability was of considerable im- 

 portance. To modify the ordinary broadcasting transmitter to in- 



2 See Fig. 1 and accompanying discussion in: Radio Extension of the Telephone 

 System to Ships at Sea by H. W. Nichols and Lloyd Espenschied Proc. I. R. E., Vol. 

 II No. 3. 



