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BELL SYSTEM TECHNICAL JOURNAL 



signals for transmission west on the telephone line will produce no 

 voltage at the terminals of the transmitting amplifier. 



At the receiving station the incoming wave is impressed upon a 

 loop antenna and the receiving set. The resulting detected output is 

 then amplified as indicated and returns to the hybrid coil, passing 

 out on the telephone line without producing a voltage on the speech 

 amplifier of the transmitting set if the hybrid coil balance is perfect. 



On the ship, this physical separation of transmitting and receiving 

 set is, of course, not practical, and, as indicated before, transmission 

 and reception take place upon one antenna so arranged that the 

 receiving circuit offers a high impedance to currents of the outgoing 

 frequency and low impedance to the incoming signal. Actually, 



Fig. 3 



the outgoing signal is not entirely excluded from the ship's receiver 

 and there is present a side tone of about the magnitude of the incoming 

 signal. This is by no means an undesirable condition and is the one 

 which holds approximately in an ordinary telephone subscriber's 

 instrument. The presence of side tone assures the speaker that his 

 system is functioning properly. 



Fig. 3 is a view of the operating room showing the four trans- 

 mitting units at the back; the power switchboard for supplying the 

 plate circuits of the tube at the right; the telephone switchboard 



