Scrambling and Cable-Ready TV Receivers

Standard TV receivers tune VHF channels 2 through 13 and UHF channels 14 through 83. Cable TV operators originally supplied their programming on the 12 VHF channels, so that no additional equipment needed to be supplied. When they eventually added more channels, they used the large frequency gap between channels 6 and 7 to provide nine more channels, designated A through I. Since TV receivers could not tune these channels, the cable operators supplied special tuners or block converters to be used between the cable and the TV receiver. Some cable operators put special pay programs on these " midband" channels, since these channels were secured by the need to use the special equipment. As cable-TV grew, more channels were needed, and these were added in the frequency space just above channel 13. These "super-band" channels were labeled J through W (35 channel systems) and beyond (for larger systems). New cable-system-provided equipment was needed to permit reception on TV receivers tuning only the standard broadcast TV channels. 35-channel converters became a standard product, manufactured by several companies. The cable operators supplied them to cable customers, specified to have the output on VHF channel 2, 3, or 4, whichever is not in use for broadcast TV in the area. The customer tuned his TV set to the specified converter-output channel, and never needed to change it again. UHF channels 14 to 83 were never seriously considered for cable use because of the high attenuation suffered in cables at UHF frequencies.