160 BELL SYSTEM TECHNICAL JOURNAL 



The Radio-Wire Transmission Circuit 



Two types of circuits were used in the experiments in operating 

 between New York and the vessel, as shown schematically in Fig. 12. 

 The radio link is the same for both. Different frequencies are used 

 for transmitting in the two directions so that in the radio link we 

 have the equivalent of two circuits, one for transmitting east and 

 the other for transmitting west. This is the same as the four-wire 

 telephone circuit. In the thru circuit first shown the radio four-wire 

 circuit is brought into a two-wire circuit at the land radio station, 

 making a regular two-wire telephone circuit from the radio station to 

 the New York toll terminal. This circuit was used in the tests for 

 calls local in New York. In the arrangement of the second circuit of 

 Fig. 12, each of the one-way radio channels is extended back to the 

 New York toll office by its own wire line and there joined into a two- 

 wire circuit, making the wire-radio toll line from New York to the ship 

 a four-wire system. This arrangement forms a high grade circuit and is 

 the one used in the experiments for connecting with long distance lines. 



Taking the four-wire circuit, the path of the voice currents may 

 be traced thru from one end to the other as follows: The currents 

 which are initiated by the land subscriber, for example, upon arrival 

 at the New York toll office divide in the hybrid coil between the east- 

 bound and the west-bound circuits. The currents are prevented 

 from being propagated over the west-bound branch because of the 

 unilateral nature of the repeater. The currents of the east branch 

 are amplified in the repeater of this circuit in order to make up for 

 the attenuation suffered in the cable circuit, and upon arrival at Deal 

 Beach are amplified to power proportions, modulated upon the radio 

 carrier and radiated into space. Upon being received at the ship end 

 of the radio circuit they are sharply selected in respect to frequency, 

 are again amplified, and delivered to the listener. When the ship 

 subscriber talks, the voice currents are amplified, pass directly into 

 the radio transmitter, are transmitted over the radio link in the usual 

 way, received at the shore station, amplified and sent out over the 

 wire circuit to New York. Here they pass in the reverse direction 

 thru the hybrid coil and divided between the two-wire circuit on the 

 one hand and the balancing network on the other, thus getting back 

 into a regular two-wire telephone circuit. 



Interconnection Between Radio and Wire Circuits 



It will be well to recall at this point just what it is that makes 

 possible automatic repetition or thru transmission between the wire 

 and radio circuits. 



