THE L3 SYSTEM — DESIGN 811 



acteristic is closely equivalent to 4.0 miles of 0.375" coaxial cable plus 

 the loss of the other passive elements in the repeater. This unit is de- 

 mountable without tools for maintenance and is sealed in a die cast 

 housing as protection against moisture and dust. The detailed electrical 

 and mechanical design are covered in a companion paper.^ 



The regulator may be one of two types. The first, called the auxiUary 

 regulator, adjusts the gain-frequency shape of the amplifier in accordance 

 with the magnitude of the 7,266-kc pilot transmitted along the line. The 

 second type, the thermometer regulator, adjusts the gain-frequency shape 

 of the amplifier under control of an element representing an average 

 value of cable temperature. This element is a thermistor buried in the 

 ground near the cable. Such a control is, obviously, not as accurate as 

 pilot controlled regulation, but it is adequate for use at one-half of the 

 auxiliary repeaters and its simplicity results in considerable saving in 

 first cost and power requirements. The regulators are demountable 

 units similar to the amplifiers. Their detailed electrical and mechanical 

 design are covered in a companion paper.^^ 



The pilot alarm unit is provided with auxiliary regulators to indicate 

 pilot deviations beyond a predetermined limit. Its operation will be 

 described a lattle later in connection with the discussion of alarm and 

 control arrangements for the entire system. 



3.22 Power Supply 



Primary ac power for the auxiliary repeater is supplied on a constant 

 current basis from the main repeater over the center conductors of the 

 two associated coaxials. Power generating and control equipment used 

 at the main repeater will be discussed in Section 3.6. At the auxiliary 

 repeater, power supply equipment is required to convert the primary 

 power to suitable voltages for heater, plate and bias use as shown on 

 Fig. 16. Half of the input to the power supply is taken from each center 

 conductor and the output of the power supply is used to power the entire 

 two-way repeater. 



The heater voltages are obtained by simple transformation which is 

 complicated only by the fact that accurate and low loss transformers 

 are required and the primaries of these transformers must withstand high 

 ac potentials without generating corona noise which might be trans- 

 mitted through the power separation filter to the input of the amplifier. 

 Two separate transformers are used to split the load between the two 

 center conductors even though the secondaries are connected together 

 to feed the repeater. This arrangement eliminates one crosstalk path 



