WIDE-BAND TRANSMISSION OVER COAXIAL LINES 669 



same time about 30 db feedback, it is obvious that the total forward 

 gain through the amplifying stages must be about 90 db. The circuit 

 of an experimental amplifier meeting the gain requirements for a 

 frequency band from 50 to 1000 kilocycles is shown schematically in 

 Fig. 10. 



Gain- Frequency Characteristic 



As pointed out above, the line attenuation is not uniform with fre- 

 quency. For a repeater section which has a loss of, say, 60 db at 

 1000 kilocycles, the loss at 50 kilocycles would be only about 15 db. 

 Such a sloping characteristic can be taken care of either by designing 

 the repeater to have an equivalent slope in its gain-frequency charac- 

 teristic or by designing it for constant gain and supplementing it with 

 an equalizer which gives the desired overall characteristic. Both 

 methods have been tried out, as well as intermediate ones. Figure 11 



100 200 300 400 500 600 700 800 900 1000 1100 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 11— Gain of 1000-kilocycle repeater compared with line characteristic. 



illustrates such a sloping characteristic obtained by adjusting the 

 coupling impedances in a three-tube repeater, designed in this case for 

 60 db gain at 1000 kilocycles. The accompanying photograph, Fig. 

 12, gives an idea of the apparatus required in such a repeater, apart 

 from the power supply equipment. 



Regulation j or Temperature Changes 

 It is necessary that the repeater provide compensation for varia- 

 tions in the line attenuation due to changes of temperature. In the 

 case of aerial construction such variations might amount to as much 

 as 8 per cent in a day or 16 per cent in a year. If the line is under- 



