STUDIES IN R.iniO BROADCAST TRANSMISSION 



197 



elude this feature involves major mechanical changes and in order to 

 provide a suitable arrangement for these tests the Bell Telephone 

 Laboratories engineers merely added to the existing transmitter at 

 station 2XB a temporary separate oscillator and high-freciuency 

 amplifier which could be connected to drive the oscillator tubes of 

 the set as amplifiers. That this was free from frequency modulation 

 is seen by comparing (C) of Fig. 40 with (A) and (B). 



The transmission tests carried out with this arrangement yielded 

 highly satisfactory results as indicated by a comparison of Fig. 41 



Time 



Fig. 41 — Sluw lecoid of signal detected from tone modulated transmission with stabil- 

 ized carrier showing reduction in distortion. Made at Stamford, Conn., Oct. 10, 1924, 



3 a.m. 



with Fig. 37. Fig. 41 like Fig. 37 is the detected result of a signal 

 which started from the transmitter as a pure tone modulated signal, 

 but it shows that much of the wave form distortion has disappeared, 

 there remaining only a residuum which characteristically appears 

 at the lower amplitudes of the signal. The probable cause of this 

 residual effect will be discussed later. Tests of speech and music 

 were concurrent with these findings. Using the normal transmitter, 

 night-time transmission as received at the test stations was seriously 

 distorted. When the stabilizing arrangement was employed this 

 distortion was apparently eliminated except at the minima of fading. 



Having arrived then at this practical result we wished to make 

 further confirming tests, and tests to determine the whys and where- 

 fores of the result. We have already detailed the more basic of 

 these tests in previous sections of this paper and are now ready to 

 consider the practical distortion records more carefully and to build 

 up a theory to explain them. 



The records shown in Fig. 42 are similar to the records in Fig. 37. 

 They are shown here to illustrate the difference in the characteristics 



