THE L3 SYSTEM — EQUALIZATION AND REGULATION 



851 



preach taken depends upon the regulation characteristic desired and the 

 experience of the designer. Since both loss and phase are involved, 

 familiarity with loss-phase relations is important. After a design has 

 been blocked out, repeated modifications of the network parameters 

 usually indicate the adequacy of the configuration chosen. Usually 

 several sections in tandem are required in the shaping network in order 

 to obtain precision of match, and some of these most likely will be all 

 pass sections in order to control the phase ^f/ independently of the real 

 part a. It may be noted that at cross over points in the regulation char- 

 acteristic, i.e., zero regulation, either the phase \f/ has to be 45 degrees, 

 or odd multiples thereof, or the loss <r has to be infinite. Usually the 



253.8 



nm^-^ 



30 < Rt < 1009 

 FLAT LOSS =8DB 

 I A^^yv^ , OHMS,//H,//;^F 



Fig. 6 — Circuit of the regulating network for repeater temperature. 



phase is made the controlling term in both zero and peak regulation 

 points. 



The designs presently used on the L3 system for the repeater tempera- 

 ture and tube aging equalizer are shown in schematic form on Figs. 6 

 and 7. The 0.27 microfarad capacitors and 10-millihenry inductors are 

 employed in order to supply the dc heating current to the thermistor. 

 The shunt resistors placed across the 75-ohm line, in one case 124 ohms 

 and in the other case 133.4 ohms are used in order to make the left side 

 driving point impedance equal 75 ohms at normal setting of the thermis- 

 tor. These networks are used in cascade with the manually adjusted, 

 constant resistance networks and it seemed desirable that the impedance 

 characteristic of the dynamic equalizers be relatively good at one pair 

 of terminals. 



