54 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



twelve frequency-shift telegraph channels with 120-cycle carrier tele- 

 graph spacing. It is planned to use one of these for automatic regulation 

 of the other eleven. The U.S. half channel is at present unassigned. 



Two telephone order wires (speakers) and two teletype order wires 

 (printers) are provided for maintenance and administration purposes. 



The two speakers occupy a 4-kc telephone channel which is the lower 

 sideband of 20 kc on the Une. The 4-kc band is divided into halves by 

 Bell T\^pe-EB split-channel equipment, which yields two narrow-band 

 telephone channels. One of these is reserved for a "local" Clarenville- 

 Oban circuit, available at all times to the personnel at these terminals. 

 It constitutes a cleared channel which could be of great benefit in 

 emergencies which might arise. The other narrow-band telephone chan- 

 nel, the "omnibus speaker", is extended through to other control points 

 including the sj^stem metropolitan terminals. 



The two printer circuits are frequency -shift voice-frequency telegraph 

 channels, occupying line frequencies just below 16 kc. These are both 

 brought to dc at Clarenville and Oban, and extended by carrier tele- 

 graph to the metropolitan terminals. One is normally a "through" circuit 

 with teletypewriters at the metropolitan terminals only, and the other 

 is an "omnibus" circuit with teletypewriters connected at Oban, Claren- 

 ville and other control points, permitting message interchange be- 

 tween all connected points. 



92-kc group frequency pilots are transmitted over the Clarenville- 

 Oban link only, and blocked at its ends. The line frequencies correspond- 

 ing to the 92-kc group frequencies are 52, 100 and 148 kc. These pilots 

 are used for manual regulation and maintenance of the Clarenville-Oban 

 link. Information derived from them governs the manual setting of the 

 temperature equalizers. The sending power of the 92-kc pilots is regu- 

 lated to within ±0.1 db variation with time. 



84.080-kc group frequency pilots also appear on this link. These, how- 

 ever, are system pilots applied at the metropolitan terminals. They are 

 useful for evaluation of overall system performance and for quickly 

 locating transmission troubles. 



Alarms are provided in the manner usual for multi-channel telephone 

 systems. A special feature of the pilot alarm system is the "alarm relay 

 channel", a third voice-frequency carrier telegraph channel just below 

 the printer channels in line frequency. If all three eastbound 92-kc pilots 

 fail to reach Oban, a signal is transmitted over the westbound cable which 

 brings in a major alarm at Clarenville, and vice versa. This major alarm 

 would provide news of a cable failure immediately to the transmitting 

 cable terminal station. Failure of the pilot supply would, of course, give 



