THE TYPE PI CARRIER SYSTEM 369 



S 



Fig. 14 — Example of PI carrier line network. 



wiring boards. They are potted with an asphalt compound in a cyhndri- 

 cal ahiminum can. The voice frequency transformers are wound on lam- 

 inated core structures of permalloy. The units are potted in an epoxy 

 resin in rectangular aluminum cans. The terminal plate carrying the 

 wire terminals for mounting is a cast unit of a styrene polyester. Both 

 types of transformer are shown in Fig. 13. 



4.5 Ldne Networks and Filters 



Also deserving mention is a new series of line networks and 

 filters (which do not form part of either the terminal or repeater equip- 

 ment) with specific functions described in Section 7. All of the networks 

 have been designed with the same tj^pe mounting arrangement sho'RTi 

 in Fig. 14 with two sizes used depending on the number of components 

 housed. The networks are cast in a styrene poh^ester. High voltage pro- 

 tection is self-contained and sturdy terminals are provided for bridle 

 wire connection. By means of side slots in the casting the network is 

 mounted on a wedge-shaped holder which is fastened to the crossarm or 

 pole. A flexible rubber cover is snapped over the face of the network to 

 protect against weather effects. 



5. EQUIPMENT ARRANGEMENTS 



The emphasis placed on economy in this development project made 

 it necessary to consider a number of different approaches before deciding 

 on the physical arrangement pro^'ided for both central office and pole 

 mounted equipment. At both locations the terminals for each channel 



