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1954-55 Theatre Catalog, 12th Edition, Page 386 (348)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 386
Page 386

1954-55 Theatre Catalog, 12th Edition, Page 386

back to the higher frequencies at each switching point. Such switching is accomplished by means of remotely controlled switches under the control of an operating center.

Local Channels

The operating centers also provide for connections between intercity and local channels using the same push-button switching panel as for intercity facilities. These local channels may transmit a program to the network, such as one picked up at a theatre or a baseball field, or may transmit the program furnished from a distant point to a local theatre or television station. They may also be used for connecting studios with transmitters and other local pickup points. The facilities used for furnishing local channels may consist of either cable or microwave radio facilities.

Local or short haul microwave facilities used by the Bell System are generally single channel systems and can be either portable or permanently inv stalled, depending upon the type of service to be given. Figure 6 shows two types of microwave equipment on top of the Empire State building which are used to provide local channels in and around New York. Figure '7 shows some of the equipment installed in a temporary manner set up in Chicago for one

FIGURE 8 is an illustration of a video amplifier installation in a telephone central office designed to transmit frequencies up to four megacycles.


of the national political conventions held there in 1952.

Local channels using cable facilities generally consist of special shielded pairs with amplifiers spaced three to four miles apart. These amplifiers and the equalizer equipment associated with them are designed to transmit frequencies up to about four megacycles. Transmission over these facilities is at video frequencies. The balanced construction of the pairs helps prevent low frequency interference and noise which would be present if coaxial cable construction were used for the same frequency. An installation of video amplifiers in a telephone central office is shown on Figure 8.

Transmission Testing

Television circuits must perform very precisely with regard to both amplitudefrequency and delay-frequency characteristics in order to produce good television pictures. In order to maintain the channel facilities with such precision, routine tests are made at periodic intervals, using special testing equipment by which individual equipments, transmission channels and entire networks are measured and necessary adjustments made to provide satisfactory transmission. Many new and intricate pieces of testing equipment have been developed to meet these needs and to make avaiL

able to the tester a means of watching a wave pattern moving at a rate of millions of times a second to determine if the network is doing its job as it should.

As an example of this new test equipment, Figure 9 shows a visual gain and delay set which provides a measure of delay and amplitude responses on an oscilloscope.


Future theatre network developments will be shaped by the needs of theatre television. If more circuits similar to those in use by television broadcasters are required, these can be furnished. The development of improved camera and projector equipment, or of a theatre color television system are possibilities which might require network channels of greater band width to realize their full capabilities. The Bell System now has facilities in its ttL3" coaxial cable system and its TD-2 radio relay system which are capable of carrying a band width up to eight or 10 megacycles.

Future systems, one of which is already in the planning stage, will be capable of still greater band widths. With reasonable advance notice requiiee ments, the Bell System expects to be able to meet the needs of theatre television with regard to both quantities of circuts and quality of transmission.

FIGURE 9 is an example of new test equipment developed to maintain periect television transmission both to networks. and closed theatre TV.

1954-55 Theatre Catalog, 12th Edition, Page 386