LONG DISTANCE CABLE CIRCUIT 



587 



Attenuation Equalizers 



As will be observed from Fig. 4, the transmission loss of the cable 

 circuit varies considerably with frequency. Since the amplifier has 

 a flat gain characteristic, an attenuation equalizer is called for to 

 correct the distortion introduced by the cable. A diagram of one of 

 these equalizers is shown in Fig. 15. In Fig. 16 is shown the loss 



Hh- 



-*MAr- 



■Hh- 



•^ — f— ^MAAr<^^ 



^ — crQir?rv-o-||- ' 



2 



o— 



4 



— o 



Fig. 15 — Schematic circuit of attenuation equalizer. 



introduced by a 50-mile section of cable at average temperature, the 

 loss introduced by one of these attenuation equalizers and the total 

 loss of line and equalizer with the offsetting gain introduced by the 

 amplifier. 



Automatic Device to Overcome Effects of Varying Temperature Trans- 

 mission Adjusting 



As the temperature of the cable changes its attenuation changes, 

 the amount of the change being different at different frequencies. 

 Referring back to Fig. 6, it is seen that on a cable circuit 1,000 miles 

 long a temperature change from 55° F. to 109° F. causes changes in 

 the transmission as follows: 



At 100 cycles 18 db change, power change of 63 

 At 1,000 cycles 28 db change, power change of 625 

 At 8,000 cycles 3 db change, power change of 2 



When it is appreciated that in an aerial cable a temperature change 

 of 54° F. may take place in only a day or two, the importance of 



compensating for this effect may be appreciated. 



38 



