FLEXIBLE REPEATER DESIGN 71 



(c) Aging. As electron tubes lose mutual conductance with age, re- 

 peater feedback decreases, repeater gain changes, and misalignment is 

 affected. Decrease in feedback increases the gain at the higher frequen- 

 cies so that the signal input must be reduced to prevent overloading, 

 resulting in a signal-to-noise penalty. Gain increase is inversely propor- 

 tional to the amount of feedback; in these repeaters, 33 to 34 db of feed- 

 back was the objective to keep this source of misalignment in bounds. 



Because repeaters are inaccessible for maintenance, facilities are pro- 

 vided to enable the individual repeater performance to be checked from 

 the shore end. This feature also permits a defective repeater to be identi- 

 fied in the event of transmission failure. 



REPEATER UNIT 



The repeater, for the sake of discussion, may be divided into two parts, 

 (1) the repeater unit, which contains the electron tubes and other cir- 

 cuit components and (2) the water-proof container and seals Avhich house 

 the repeater unit. 



Circuit 



The circuit of the repeater unit is sho^vn in Fig. 1. It is a three-stage 

 feedback amplifier of conventional design with the cathodes at ac ground. 

 The amplifier is connected to the cable through input and output cou- 

 pling networks. Each coupling network consists of a transformer plus 

 gain-shaping elements and a power separation inductor. 



The coupling networks directly affect the insertion gain as do the two 

 feedback networks. The design of these networks controls the insertion 

 gain of the amplifier. The required gain (inverse of cable loss) is shown 

 in Fig. 2. The 39 db shaping required between 20 and 164 kc is divided 

 approximately equally among the input and output coupling networks 

 and the feedback networks. 



The interstage networks are of conventional design. The gain of the 

 first interstage is approximately flat across the band. The second inter- 

 stage has a sloping characteristic, the gain increasing with frequency. 

 The gain shaping of these networks offsets the loss of the feedback net- 

 works so that the feedback is approximately flat across the band. 



Plate and heater power is supplied to the repeater over the cable.'* 

 The plate voltage (approximately 52 volts) is obtained from the drop 

 across the heater string. The dc circuits are isolated from the container 

 by the high voltage blocking capacitors Ci , C2 and C3 . 



