Expansion of the TV frequency range for receiving transmissions via cable networks. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Expansion of the TV frequency range for receiving transmissions via cable networks. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Телевидение

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Recently, multi-channel cable TV networks have become more widespread, however, the CM band 110-174 MHz, which is often used by them, located in the "hole" between 5 and 6 channels of the usual "terrestrial" MW band, does not allow reception on TV receivers 2, 3 and 4 generations.

I offer several methods tested in practice to refine the PTK and selectors PTK-3, PTK-10, PTK-11. They are used in tube black-and-white TVs, which many viewers still have. Since some channels of bands I-II and III are not used for broadcasting over cable networks, it is necessary, after removing the drum from the PTK, to remove the antenna and heterodyne sectors of unused channels and install sectors with converted coils in their place. To receive channels SK-1 ... SK-7 (110-166 MHz), the corresponding loop coils are made either from standard 1-5 channels by winding part of the turns, or from coils of other channels rewound.

The number of turns is indicated in table 1.

Table 1
Channels Frequency band, MHz contour coils
antenna UHF grid heterodyne grid anode
SK-1...SK-4 110.142 2 6 5 5 6
SK-5...SK-7 142-166 1 5 4 4 5

Coils of the antenna circuit wind PEL-0.51, heterodyne PEL-0,31. To receive the SK-8 channel (166-174 MHz), standard sectors of the 6th channel are used. SK-M-15 is used in color TV ULPCT. Data for rewinding coils are given in Table 2.

Table 2
Channels Frequency band, MHz contour coils
antenna UHF communications collect. UHF basic
mix. heterodyne
SK-1...SK-3 110-134 10 3 5 6 5
SK-4...SK-5 134-150 8 2 5 5 5
SK-6...SK-7 150-160 6 2 5 5 4

Antenna sectors are wound PEL-0,41, heterodyne - PEL-0,59. For the antenna sector, you can use coils from 1-5 channels, unwinding extra turns. The switching of the coils and the direction of winding must correspond to fig. 1 and 2.

Expansion of the TV frequency range for receiving transmissions via cable networks

For SK-8, standard coils of the 6th MV channel are also used. When winding the coils of the heterodyne sector, it is necessary to pay attention to the fact that the last turn of the base coil and the first collector coil are as close as possible or even touch each other. The contours are tuned to a specific channel by tuning cores and (if necessary) by changing the turn-to-turn distance, SK-M-24. The SK-1 range can be completely covered by an elementary replacement of the III range varicaps VD2, VD5, VD8 and VD12 of the KV109V type with Philips BB910 or BB911, which have a much larger capacitance overlap coefficient (from 2 to 38 pF).

Author: Yulian Shevchenko, Kiev; Publication: N. Bolshakov, rf.atnn.ru

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