TELEVISION TRANSMISSION OVER WIRE LINES 75 



velope is relatively large, resulting in objectionable distortion at sharp 

 changes in the picture signal if the greater ratio of carrier to sideband is not 

 employed.'^ 



Figure 10 shows a box diagram of the terminal arrangements. In ad- 

 dition to ordinary video amplifiers and modulators and filters mentioned 

 above, a ''pre-emphasizer" and a "restorer" are shown. These networks 

 l^artially equalize the energy in the various components of the signal, and 

 thus help to override the noise and spurious modulation products intro- 

 duced by the line and amplifiers. A phase equalizer is also shown which, 

 in conjunction with a similar equalizer at the receiving end, is designed to 

 correct for the phase distortion in both the transmitting and the receiving 

 terminals. Before transmission over the coaxial, pilot frequencies of 64 

 kc, 2064 kc and 3096 kc are added, as well as a program channel from 73- 

 84 kc. Figure 1 1 shows the frequency allocation of the television signal and 

 Its associated channels on the coaxial line. 



At the receiving end the pilot frequencies and the program channel must 

 be removed. The 64-kc pilot and the program channel are eliminated by 

 the 200-3111 kc filter which precedes the first demodulator. The 2064-kc 

 and 3096-kc pilots, however, are within the transmitted television band. 

 The frequency allocation was so chosen as to place them approximately 

 in the center of the "empty energy regions"" of the television spectrum 

 where they can be eliminated by sharp selective networks without appre- 

 ciably distorting adjacent television signal components. 



Three carrier television terminals are shown in the photograph. Fig. 12. 

 The one on the right is a transmitting terminal, the two on the left receiving 

 terminals. Each terminal occupies one six-foot relay rack bay and is 

 complete with power supply and means for adjustment. 



Short Haul Lines for Television 



For the pickup or transmission of television within cities or metropolitan 

 areas, it appears to be more economical, as would be expected, not to use 

 the carrier method described above but to transmit "video" frequency 

 signals over cable circuits. For this purpose existing telephone cables 

 may be used or special cables may be provided. In either case amplifiers 

 and special equalizers are required which will overcome the attenuation 

 and delay distortion of the cable circuits. Because of high-frequency 

 crosstalk usually only a small fraction of the circuits in any existing tele- 

 phone cable can be used simultaneously. 



Video Amplifiers and Equalizers 



Television pickup and broadcasting equipment is quite naturally designed on 

 an unbalanced (i.e. one side grounded) basis. Unbalanced amplifiers for the video 



