74 THE BELL SYSTEM TECHNICAL JOUKKAL, JANUARY 1957 



TO HEATER 

 CIRCUIT 



TO GRID 

 OR PLATE 



TO BETA 

 CIRCUIT 



Fig. 4 — Coupling network. 



signal to noise performance, highest gain, and most effective shaping 

 with a minimum of elements. A minimum of elements is important in 

 view of the space restrictions imposed by the flexible repeater structure. 

 The sensitivity of the gain to variation in impedance is minimized by 

 close manufacturing control of the cable and networks. 



The schematic of a coupling network is shown in Fig. 4 and the equiva- 

 lent circuit in Fig. 5. Capacitor Ci and inductor L4 are part of the power 

 separation circuit. The effect of L4 in the transmission band is negligible 

 and it has been omitted from the equivalent circuit. However Ci is in 

 the direct transmission path and has a small effect at the lower edge of 

 the band so that it becomes a design parameter. The combination R2 , 

 L2 controls the low-frequency gain shaping of the network. Inductor L3 



R, C, Rj^ L3 L3I, 



■a 



^im^^^^ 



C1-HIGH VOLTAGE BLOCKING CAPACITOR 



Cr 



GRID CATHODE CAPACITANCE 



C3 - HIGH SIDE CAPACITANCE 

 Zc -CABLE IMPEDANCE 

 R, -RESISTANCE OF C, 



R,l^ 

 R3t^ 



L31 



Lm - MUTUAL 



Gm - CONDUCTANCE OF MUTUAL 



G-HIGH SIDE CONDUCTANCE 

 L3 -LEAKAGE BUILD-OUT 

 T - IDEAL TRANSFORMER 



R: 



-RESISTANCE OF LEAKAGE 



--LEAKAGE (LOW SIDE) 



LOW FREQUENCY SHAPING 

 "ELEMENTS 



Fig. 5 — Eqviivalent circuit of coupling network. 



