THE FUTURE OF TRANSOCEANIC TELEPHONY 5 



tion, and a concentric copper return conductor of 1700 pounds, making the 

 cable much heavier than any that had previously been laid in great depths. 



A 20-mile section of this cable was made in 1930 under the supervision 

 of Bell Telephone Laboratories engineers by the Norddeutsche Seekabel- 

 werke in Nordenham, Germany. There it was loaded aboard the cable 

 ship Norderney and taken to a location in the Bay of Biscay where a depth 

 of 2,500 fathoms was conveniently available. This depth was greater than 

 would be encountered on the proposed cable route. The 20-mile section 

 was paid out on the sea floor and its open-end impedance measured over 

 the telephone range of frequencies. From these measurements, changes in 

 its electrical parameters could readily be deduced. The cable was then 

 pulled in and carried to Frenchport Harbor near BelmuUet, County Mayo, 

 Ireland, whence it was laid out to sea to permit measurement of terminal 

 noise. Measurements of impedance both from the ship and from the shore 

 showed the cable to be quite unimpaired both at 2^ miles depth and after 

 recovery and relaying in shallow water. Measurements of noise from shore, 

 however, showed that the location was unsuitable for this type of cable 

 because of the rocky bottom. Such a cable is somewhat microphonic on 

 account of the strain sensitivity of perminvar and the terminal sections 

 of the cable must lie quietly on a soft bottom if a low terminal noise level 

 is to be assured. 



Simultaneously with the experiments on the cable, experiments were 

 conducted with the terminal apparatus in the laboratory in New York. 

 An artificial line had been built closely simulating the proposed cable in 

 electrical performance, and over this speech was transmitted at the levels 

 intended for the cable. The method of operation was extreme as well as 

 novel. The high attenuation made it impossible to balance the simulated 

 cable for two-way talking, and voice switching had to be used. At both 

 ends the receiving apparatus was normally connected to the line. The 

 speaker's voice currents caused his end of the line to be switched to the 

 transmitting apparatus. Arrangements were devised to avoid loss of 

 speech during the switching interval, and to minimize interference due to 

 the persons at the two ends of the cable speaking almost simultaneously. 

 The time required for speech to travel over such a cable is not negligible. 

 In this case it was about a tenth of a second. This is long enough to be 

 noticed but not serious enough to count as a major disadvantage. 



All of the measurements in the laboratory, at sea, and from shore joined 

 in giving assurance of the technical soundness of the proposal to install a 

 cable of this type. Its performance would have been superior to that 

 afforded by radio. The cost, however, would have been much greater than 

 that for a radio circuit. The cable system from Nova Scotia via Newfound- 

 land and Ireland to Great Britain promised to cost about $15,000,000. 

 When the project was first considered, the radio connection had been 



