THE NEW YORK-LONDON TELEPHONE CIRCUIT 739 



the amplifiers so as to keep the electrical volumes reaching the 

 radio transmitter at a predetermined value. The technical operator 

 also adjusts the received volume over the range indicated at {c) to give 

 the best operation under different conditions of static, and for different 

 types of connections. 



An interesting fact to be observed here is that the voice power is 

 amplified about 100,000,000 times in the radio transmitter and any- 

 where from 30,000 to 300,000,000 times at the radio receiver and 

 associated amplifiers, depending on the loss in the radio path at any 

 particular time as indicated at {h). Including the amplification which 

 it is necessary to use on the wire "links," the total power amplification 

 in either direction is approximately 10'*''. Although more amplification 

 is used in this circuit at a single point, such as at the radio transmitter, 

 than at a single point in any other commercial telephone circuit, the 

 total power amplification is less than in one of the telephone cable 

 circuits from New York to St. Louis, where it is approximately 10^". 



Having in mind the foregoing facts, one can appreciate the diffi- 

 culties which had to be faced in the way of operating this circuit and 

 which have been successfully overcome. The more important may be 

 summarized as follows: 



(1) The transmission losses through the ether in the radio links vary 



from time to time in an irregular manner at intervals which 

 preclude the possibility of making predetermined or systematic 

 compensating adjustments of the amplification at the radio 

 receivers. 



(2) The radio links are frequently more noisy than wire circuits. 



This noise consists principally of stray electric waves (static) 

 and varies considerably from time to time. 



(3) The tendency for strong echo currents to exist in this circuit is 



considerably greater than in ordinary wire circuits. This is due 

 partly to the methods employed for overcoming the difficulties 

 brought about by (1) and (2), and partly to the fact that radio 

 transmission in the two directions is carried out in the same 

 frequency band. 



These difficulties have been overcome by the following means: 



(1) To overcome the variations in the transmission efficiency of the 



radio links, adjustments are made from time to time of the 

 amplification in the radio receivers. Radio operators are in 

 constant attendance at the receiving stations in order to make 

 these adjustments. 



(2) To assist in overcoming the effect of radio noise, adjustments are 



