In recent times, increasingly multi-channel cable TV networks, but often they use the CM range 110-174 MHz, located in the "hole" between 5 and 6 channels of conventional "essential" MV range, does not allow admission to TV receivers 2, 3 and 4 generations.
Offer a few tried-and-tested ways of refinement of PTC and selectors of PTK-3,STC-10, STC-11. They are used in lamp black and white TVs still many viewers. Since some of the channels ranges I-II and III for broadcast on cable networks are not used, it is necessary removing the drum from the PTC, to remove the antenna and heterodyne sectors of unused channels, and in their place to set sectors with rebuilt coils. Of channels for receiving SC-1...SC-7 (110-166 MHz) corresponding contour of the coil are made either from standard channels 1-5 the part of the coiling coils or other coils of the TV, rewound again.
The number of turns indicated in table 1.
Table 1
Channels
Frequency band, MHz
Contour coil
antenna
UHF grid
heterodyne
grid
anode
SC-1...SC-4
110.142
2
6
5
5
6
SC-5...SC-7
142-166
1
5
4
4
5
Coil antenna circuit harassed PEL-0.51, heterodyne PEL-0,31. For receiving channel SC-8 (166-174 MHz) are used in the standard sector of the 6th channel. SC-M-15 is used in color TV ULPORT, Data for rewinding coils are shown in table 2.
Table 2.
Channels
Frequency band, MHz
Contour coil
antenna
communication UHF
t. UHF
basic
mixture.
heterodyne
SC-1...SC-3
110-134
10
3
5
6
5
SC-4...SC-5
134-150
8
2
5
5
5
SC-6...SC-7
150-160
6
2
5
5
4
The antenna sectors is wound PEL-0,41, heterodyne - PEL-0,59. For sector antenna you can use the coil from 1-5 channels, rewind extra coils. Switching the coils and the winding direction must correspond to Fig. 1 and 2.
For SC-8 also used a standard coil 6-channel MV. When winding coils heterodyne sector need to pay attention to the last round base coil and the first collector was probably closer to or even touch each other. The set of contours on the specified channel is setting cores and (if necessary) change turn-to-turn distance, SC-M-24. Completely cover the range of SC-1 allows elementary replacement varactors III range VD2, VD5, VD8 and VD12 type SW109В on Philips BB910 or BB911 that have a much greater' coverage ratio capacity (from 2 to 38 pF).
Author: Julian Shevchenko, Kyiv; Publication: N. Bolshakov, rf.atnn.ru