330 



BELL SYSTEM TECHNICAL JOURNAL 



B and adjusting a potentiometer ahead of the transmitting repeater. 

 The waves then act on the vodas which consists of ampUfier-detector, 

 delay circuit and relays for switching the transmission paths in such a 

 manner as to prevent echoes, singing and other effects. When in the 

 transmitting condition, the vodas is arranged to have zero loss so that 

 the waves impressed on the compressor are practically the same as at 

 B. The waves put out from the compressor are then sent through the 

 privacy apparatus, the output of which is then sent over a wire line 

 to the radio transmitter. The radiated waves are picked up by the 

 distant radio receiver, amplified and transformed into voice-frequency 

 energy which passes over a wire line to the terminal at the distant end. 

 The path of received waves in either terminal may be traced in the 

 lower branch of the circuit shown on Fig. 9. After being made intel- 



TRANSMITTING 

 REPEATER 



UNITED 



STATES 



SUBSCRIBER 



1^- 



— a5cr| m^ — 



-^mJ \s£u — 



TOLL 

 SWITCHBOARD 



HYBRID 

 SET 



NETWORK 



EXPANDOR 



]£-: 



V 



COMPRESSOR 



RECEIVING 

 REPEATER 



LINE 



RADIO ^ 

 TRANSMITTER 



WIRE 

 LINE 



AUTOMATIC 

 VOLUME 

 CONTROL 



RADIO ^^ 

 RECEIVER 



Fig. 9 — Compandor applied to one end of a radio telephone circuit. 



ligible by passing through the receiving privacy device, the compressed 

 incoming waves are sent through the vodas into an automatic volume 

 control and then into the expandor. The expanded waves are sent 

 through a receiving repeater from whose output the amplified waves 

 pass into the hybrid set, part being dissipated in the network and the 

 other part going through the toll switchboard to the subscriber. Due 

 to imperfect balance between the subscriber's line and the network, a 

 portion of the received energy is transmitted across the hybrid set and 

 amplified by the transmitting repeater. This echo might operate the 

 transmitting vodas under certain conditions. For this reason a po- 

 tentiometer is inserted in the receiving branch of the circuit so as to 

 reduce the echo, and consequently the received volume, so that 

 false operation of the transmitting vodas is prevented. 



