REPEATER DESIGN — NEWFOUNDLAND-NOVA SCOTIA LINKS 251 





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Fig. 1 — Internal unit. 



repeater, and these units may operate at 3 kv do to the grounded brass 

 cylinder. Fig. 1 shows the construction. 



A schematic of the electrical circuit is given in Fig. 2. The direct cur- 

 rent for energizing the repeater is separated from the carrier transmission 

 signals by the A- and B-end power separating filters, and passes through 

 the amplifier tube heaters and a chain of resistors developing 90-volt 

 high- voltage supply for the amplifier. The carrier-frequency signals pass 

 through the same amplifier \-ia directional filters. Equalization is pro- 

 vided in the amplifier feedback circuit (about 20 db) and in the equal- 

 izers and the bridge networks which combine the directional filters. The 

 main purpose of the bridges, however, is to reduce the severe harmonic 

 requirement on the directional filters due to having high- and low-level 

 signals present at the repeater terminals. The whole carrier circuit is 

 designed on a nominal impedance of 55 ohms. Attached to the B-end of 

 the repeater is the loop-gain supervisory unit and also, via a high-volt- 

 age fuse, a moisture-detector unit used primarily during the high-pres- 

 sure test to confirm that the housing is free from leaks. The latter com- 

 prises a series-resonant circuit at about 1.3 mc, in which the inductance 

 is varied by the gas pressure on an aneroid capsule mounted in the space 

 between the electrical unit and the housing. The presence of moisture 

 in this cavity increases the gas pressure owing to the release of hydrogen 

 by the reaction of water vapor with metallic calcium held in a special 

 container. At a later stage the fuse is blown to disconnect this circuit. 



The circuit design of the repeater introduces multiple shunt paths 



