STl'DirS IN R.I mo BRO.ITXWST TR.IXSM fSSION 



199 



signal was used to modulate the carrier. Special precautions were taken 

 to obtain a pure 250-cycle modulatinc: tone. The wave shape of the 

 signal detected from the carrier at the transmitter was frequently 

 checked ))>■ observations with an oscillograph. The signals detected 

 from the antenna current at the transmitter, both for the normal 



Audio 1 Oscillour 



frequency ^ for Slow Pa 

 AnphherJ — 1 Record" 



/dio — 1^ 

 quency S ) 

 plifier 1 



aph 

 'ape' 



1 r Audio — 1 



>-^ Frequency t=) 

 t Ampliher p — I 



Fig. 43 — Diagram of system used to ol)tain "Harmonic" anaKsis distortion records 



transmitter with frequency modulation and for the stabilized carrier 

 transmitter, were practically simple sine waves. The output circuit 

 of the radio receiver was connected to a group of filters designed to 

 transmit narrow bands of frequencies straddling the harmonics of 

 250-cycles. 



While below we have referred to the frequencies passing these 

 filters as "harmonics" it should be borne in mind that they are not 

 necessarily Inte harmonics since they deviate very slightly from the 

 true harmonic relation. The purpose of the test was to procure a record 

 which would show at a glance the presence or absence of wave form 

 distortion. 



The input circuits of the filters were connected in parallel and the 

 output circuits separately connected to the audio amplifiers arranged 

 to operate the oscillograph elements. The input of one amplifier was 

 arranged so that it could be switched either to the output of the filter 

 passing 250-cycles or the output of the radio receiver. In this way a 

 record could be obtained of either the whole tone from the receixer or 

 only the 250-cycle component. 



In Fig. 44, Strip 1 is a harmonic analysis record of the audio tone 

 detected from the carrier and both side bands, transmitted with a 

 stable carrier frequency. Strip 2 is a section of a record made a few- 

 minutes later when an unstabilized carrier was being used. On this 

 record the lower trace is the 250-cycle comi^onent, the center trace the 



