EXTENSION OF THE TELEPHONE SYSTEM TO SHIPS 



149 



tain constant frequency, operates into a two-stage amplifier, the last 

 stage being fifty watt tubes, and from there into a bank of six radio 

 frequency power tubes, each with a rating of 250 watts plate dis- 

 sipation. Speech to modulate this radio frequency output enters 

 from a telephone line and is applied to a speech amplifier the output 

 of which operates into a bank of 250 watt modulator tubes in parallel. 

 Thus both the radio frequency and the speech frequency currents 

 are brought up to the high power level before modulation takes place. 

 The six radio frequency and six speech frequency tubas have their 



TWO-WAY RADIO-WIRE SYSTEM 



I" D£AL BEACH Transmitting - 1 



Fig. 2 



plate circuits connected together and operate as a constant current 

 modulation system. Thus current of the frequency Fi, generated by 

 the master oscillator and amplified and modulated, is radiated from 

 the antenna. The notation Fi^Si indicates the radiation of the 

 carrier and two side bands from this antenna. The incoming speech 

 Si, as it comes from the telephone line, passes through the hybrid 

 coil and to the balancing network shown. This balancing network 

 has an impedance characteristic similar to that of the incoming line, 

 and the combination of hybrid coil and network is similar to that 

 used in telephone repeater practice to secure two-way operation. 

 The object of this arrangement is, of course, to prevent signals, 

 coming in from the receiving station, operating upon the transmitter 

 of the outgoing channel. If the balancing network is an exact picture 

 of the incoming line and if the hybrid coil is properly made, incoming 



