256 BELL SYSTEM TECHNICAL JOURNAL 



speak through the circuit. Certain interlocking arrangements are 

 provided so that the voice of only one speaker can go through the 

 entire system at one moment. In this way, the two speakers are 

 prevented from talking simultaneously without either one hearing the 

 other. In addition to facilitating two-way operation of the radio 

 channels on the same frequency band the voice operated devices have 

 other valuable features. 



The difficulties of reducing the transmission to the narrowest 

 possible band having been overcome, it was necessary to find a free 

 band of this width. Negotiations by the British Post Office people 

 with European stations and by the American Telephone and Telegraph 

 Company with United States stations finally resulted in the moving of 

 a sufficient number of stations to open up a free band having its central 

 frequency at 60 kc. and this frequency is being employed in service. 



The above description covers substantially the system which is 

 being used at the present time for giving the commercial transatlantic 

 radio telephone service. This service is not as yet free from difficulties 

 due to unsatisfactory performance of the radio portions of the system. 

 Further development work is being pursued in an attempt to improve 

 these matters. On the English side the British Post Office, after 

 having made comparative measurements of signals and noise in various 

 parts of Scotland, has undertaken and now has under construction a 

 new receiving station at Cupar near Dundee, Scotland. This will 

 provide the greater freedom from radio noise which can be obtained by 

 increasing the latitude of the receiving station. At both the receiving 

 ends of the system, improvements are being made in the directive 

 characteristics of the receiving antennas. 



So far very little has been said about the operation of the system. 

 At the New York and London terminals where the transmitting and 

 receiving circuits join, there is a considerable amount of apparatus 

 which includes the automatic switching devices, the repeaters with 

 their gain controls, and a variety of measuring apparatus for deter- 

 mining and maintaining the characteristics of the entire system. 

 This apparatus is under the charge of men called technical operators. 

 Two of them, one in New York and the other in London, have the 

 duty of maintaining the best possible transmission conditions on the 

 system by making the most favorable adjustments. The local 

 transmitting and receiving stations are under their charge in so far 

 as apparatus adjustments which affect the circuit performance are 

 concerned. Communication between the stations and the terminal 

 is provided by means of order wires. 



As the circuit passes out of the realm of the technical operator going 



