328 



BELL SYSTEM TECHNICAL JOURNAL 



was in or out of circuit. Furthermore, distortion of this type is largely 

 eliminated when compressor circuit No. 2 is used. In that case it will 

 be noted that, if the two terminals are connected by a substantially 

 distortionless transmission system, the identical control circuits of 

 the two devices receive identical operating voltages. As the gain 

 changes put in are reciprocal and occur now with equal time lag, the 

 deviations from ideal compression are virtually counterbalanced by the 

 inverse deviations from ideal expandor action. In Fig. 7 are shown 



A-1 

 A-2 

 A-3 



B-1 

 B-2 

 B-3 



C-1 

 C-2 

 C-3 



\. INPUT TO COMPRESSOR 2. OUTPUT OF COMPRESSOR 3. OUTPUT OF EXPANDOR 

 i 



■^^^^ m/IjVV\'V\' ^-nv^^ai ^^^\^f^ WM^A 



'NAAAyv/'WV v^ A'v-WVw '\r*AfW\/V^ 



■/\/^/^v/vVy^^M/"'v^¥A/\^^ 



vVwV-'-'W vA W^'A/WVV^^' 









0.02 0.03 



TIME IN SECONDS 



0.04 



0.05 



Fig. 7 — Operation of compandor on beginning of word "bark." A. Compressor 

 circuit No. 1. B. Compressor circuit No. 2 with low-pass filter in control circuit. 

 C. Compressor circuit No. 2 without filter. 



oscillograms taken of the first part of the word "bark." Each record 

 shows the intensity changes before the compressor, between the com- 

 pressor and expandor and on the output of the expandor. 



Application to Transatlantic Circuit 



A compandor system has been in service on the New York-London 

 long-wave radiotelephone circuit since about July 1, 1932. At first 

 compressor circuit No. 1 was used, and later a change was made to 

 compressor circuit No. 2. Figure 8 is a photograph of the experimental 

 installation at New York. It occupies about five feet of standard 

 relay rack space. The blank panel shown in the photograph indicates 

 the saving of apparatus resulting from the change to compressor 

 circuit No. 2. Figure 9 is a schematic diagram showing the method of 

 inserting the compressor and expandor in the radio telephone terminals 

 at each end of the circuit. Since the two ends are similar, only one 



