TELEVISION TRANSMISSION OVER WIRE LINES 63 



with all long-distance systems for multiplex telephony, the carrier method 

 of transmission is essential and has been found to be relatively straight- 

 forward. For long-distance television transmission, the carrier method 

 is necessary with the present coaxial lines and coaxial repeaters, due to the 

 fact that satisfactory long-distance transmission cannot be obtained at the 

 very low frequencies involved in a video television signal. Hence for 



Fig. 1 — Photograph of coaxial cable 



television the entire signal must be raised bodily to a higher frequency. 

 The modulating means developed for this purpose will be described in 

 detail later. In this section we will confine discussion to the transmission 

 of a broad band of frequencies independently of how this band is used. 



Cable 



The transmission characteristics of ideal coaxial cables have long been known. 

 The properties of practical structures so far built including matters of cross-talk 



