TRANSATLANTIC TELEPHONY 



181 



Since eastbound and westbound short wave channels are at entirely 

 different frequencies, there would be no interaction between the east 

 and west-going circuits when used in this way. For the long waves, 

 however, since the east and westbound circuits are at the same fre- 

 quencies, each transmitting station would send considerable energy 

 into the receiving station on the same side of the ocean, thus giving to 

 each subscriber a heavy side tone of his own speech. This effect, 

 however, could be considerably reduced by separating the transmitting 

 and receiving stations and arranging the directive antennae of each 

 receiving station so it would receive as little as possible of the cor- 

 responding transmitting station. Even with the long waves, there- 

 fore, a conversation could be held in this simple way. 



RADIO RECEIVER 



RADIO RECEIVER-" T T '—RADIO TRANSMITTER 



Fig. 13 — Transoceanic circuit schematic 



When the east and westbound radio circuits are brought together, 

 however, for a connection to a wire circuit at each end, we have intro- 

 duced some very serious difficulties. Consider first the simpler case of 

 the short waves where the eastbound and westbound transmission are 

 at different frequencies. 



The voice waves reaching London from an American talker will be 

 reflected in part either at the London office where the east and west- 

 bound channels are brought together or at some point before reaching 

 the European subscriber. Unless means are taken to prevent it, this 

 reflected energy can then pass to the English transmitting station and 

 be transmitted back to America. At the American end a similar 

 partial reflection can take place throwing part of the energy back 

 again to England. In this way, according to circuit conditions, it is 

 possible for the whole circuit either to build up and act as a widely 

 flung oscillator or if the damping at the moment makes this impossible, 

 the speaker and the listener can be much interfered with by electrical 

 echoes and distortion. 



In the case of long waves there is the added difficulty as already noted 

 that each transmitting station can throw a good deal of power into the 



