TELEVISION TRANSMISSION OVER WIRE LINES 



77 



fiers are required at intervals of a mile or even less. Local telephone cables are 

 usually laid out with many branches. At high frequencies these branches intro- 

 duce irregularities similar to those produced by obstacles along a radio path 

 which cause delay distortion. Plant changes are frequently required to obtain a 

 clean circuit free from such bridged taps. When amplifiers and proper equalizers 

 are added, however, substantially flat transmission is obtained as shown in the 

 figure. 



O40 



60 



20 



-20 



2 + 



1/5 

 U1 

 O 



2^ 



z 

 o 



h- 



a. 



LlJ 



</) 



z 



-2 



0501 06 I 5 10 50 100 5001000 5000 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 14 — Transmission characteristics of cables 



Phase distortion characteristics of a typical cable circuit are also shown in Fig. 

 14. After the amphfiers and equalizers are added, the phase distortion is made 

 substantially neghgible. 



Coaxial Cables 



Coaxial cables may be used for video transmission for short distances but 

 power or other low-frequency interference may introduce serious problems. 



