REPEATER DESIGN — NEWFOUNDLAND-NOVA SCOTIA LINKS 253 



across the amplifier, and care has to be taken to ensure that there is 

 adequate attenuation in each path. In general, the design is such that 

 the combination will give a loop loss of at least 40 db in the working band 

 (to reduce rolls in the gain characteristic) and 20 db at all frequencies 

 (as a guard against instability), even when one repeater terminal is 

 open- or short-circuited to simulate a faulty cable. 



Unit Details 



Power Filter. 



The power filters are, in effect, a series pair of high- and low-pass 

 filters (see Fig. 2). The shunt capacitors may have to withstand 3 kv, 

 and clearances on the input cable and some wiring have to be adequate 

 for this voltage. The inductors have to carry the line current of 316 ma 

 dc, and the intermodulation must be extremely low (see section on in- 

 ductors below). 



Directional Filter. 



The directional filters are a conventional Zobel high-pass and low-pass 

 filter pair with a susceptance-annulling network. Silvered-mica capacitors 

 and carbonyl-iron dust-cored inductors are used. The bridges combining 

 the 'go' and 'return' filters reduce the distortion due to the ferromagnetic 

 material to an acceptable level. 



Bridge and Equalizer. 



A simple non-resonant bridge is used at the B-end of the repeater, but 

 the A-end bridge is a resonant type and provides a substantial degree of 

 equalization (see Fig. 2). 



The equalizers are of conventional form. Trimming capacitors (se- 

 lected on test) were provided for critical capacitances in order to utilize 

 standard tolerances on all capacitors. A pad of 0.2 db and 0.4 db is pro- 

 vided on each equalizer unit so that the repeater low-frequency or high- 

 frequency path can be independently trimmed to give the best match to 

 the target response for the repeater. 



The components in the above circuit were small air-cored inductors, 

 silvered-mica capacitors, and wire-wound resistors, except for a few high- 

 resistance ones, which were of the carbon-rod type. Included in this unit 

 are coaxial chokes whose purpose is to separate parts of the circuit to 

 avoid the effect of multiple grounding. They are merely inductors wound 

 with coaxial wire on 2-mil permalloy C tape ring cores. 



