CARRIER SYSTEMS ON TELEPHONE LINES 



601 



with three vacuum tubes is the modulator-oscillator panel of one 

 channel. Below it is the demodulator-oscillator panel of the same 

 channel. Below the latter and in the center of the bay is the jack 

 mounting strip which makes it possible to disconnect, or switch for 

 testing purposes, the various units of the complete equipment. The 



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Figure 23 — Schematic showing principal equipment units in carrier repeater circuit 



demodulator-oscillator panel and modulator-oscillator panel, respec- 

 tively, are the next two panels of the second channel. The terminal 

 strips will be seen at the top of the bays. The metal shields sur- 

 rounding the vacuum tubes are useful for mechanical protection only. 

 The testing and power distribution equipment is located in the left- 

 hand bay. 



The pilot channel apparatus at the terminal station, which is 

 employed in regulating the performance of the system to compensate 

 for variations in the line equivalents, is assembled in a typical 

 installation as shown in Figure 22. This apparatus may be located 

 adjacent to the carrier terminal apparatus. The upper panel is the 

 indicator unit with the indicator meter shown in the upper center 

 of the panel. The panel immediately below this is the alarm panel 

 with its voltmeter relay. On both of these panels the associated 

 vacuum tubes are mounted in the rear. The lowest panel is the 

 oscillator panel with its vacuum tube and frequency control. 



Typical Repeater Station Installations. The equipment at each 

 carrier repeater station consists mainly of the units indicated in Figure 

 23. It is seen from this figure that the principal items are the line 

 filter equipment, the amplifiers, the equalizers, the directional filters, 

 and the jacks provided for testing and patching the equipment. Pilot 

 channel equipment, power supply equipment, and testing equipment 

 are also included. The amplifier equipment in each carrier repeater, 



