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1954-55 Theatre Catalog, 12th Edition, Page 385 (347)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 385
Page 385

1954-55 Theatre Catalog, 12th Edition, Page 385

terminal equipment. Figure 4 shows a typical L repeater hut.

As previously mentioned, the coaxial cable system is not satisfactory for transmission of low frequencies, so that it is necessary to utilize carrier techniques to shift the television signal to a frequency band which the system will handle. The carrier frequency used with the "L1" system is 311 kilocycles and with the uL3" system 4.139 megacycles. Both systems employ vestigial sideband transmission, transmitting the upper sideband entirely, but only a vestige of the lower side band. In the uL3" system the frequency band below three megacycles is used for transmission of 600 telephone circuits on the same coaxial as the television signal.

Coaxial cables usually have a coaxial line in each direction set aside as a standby for replacing any of the other lines in case of trouble, similar to the arrangement used with the radio relay system.

Television Operating Centers

The intercity television channels. whether they are of the coaxial or radio relay type, terminate in a central test point or operating center. Such centers are located at strategic points along thc main routes to provide supervision and control of the usc of the facilities, as well as to provide points where maintenance work and testing can be haiidlcd. The actual television network assignments made to the broadband facilities

FlGURE 7 shows some at the equipment installed in Chicago for a national political convantion.


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FIGURE 6 shows two types of microwave equipment on top of the Empire State building used to provide local channels in and around New York City. the greatest TV concentration urea.

vary considerably throughout the period programs are supplied, and switching panels are provided at the control centers to switch different programs to the intercity facilities as desired by the various network or Hclosed circuit" customers. Service to an individual station along a route also requires the use of a switching panel as a station may take service from any one of three or more networks on successive programs. Similarly, switching panels are used to set up a theatre television program where a number of theatres along the intercity trunk route are to be switched to the main trunk line. To enable rapid and accurate switching under such circumstances, all incoming circuits and

all outgoing circuits in a particular operating center are connected to a push button switching panel which enables any outgoing circuit to be fed from any incoming circuit by pressing the proper button. Figure 5 shows a switching panel capable of handling 20 incoming and 24 outgoing channels, A switching panel of this type makes it possible to make the most economical use of available line facilities, particularly throughout the busy periods of the day since assignments can be changed in a matter of seconds.

Most of the switching that is done at other than the terminals of the network along a microwave route is performed at intermediate radio frequencies, rather than at video frequencies, to avoid the accumulation of distortion which might occur if the signals are modulated to video frequencies and then modulated
1954-55 Theatre Catalog, 12th Edition, Page 385