Expansion of the frequency range of the UHF set-top box. Scheme, description

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Expansion of the frequency range of the UHF set-top box. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Телевидение

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Until recently, many types of prefix-selectors UHF were released, designed to receive television signals on any of the 21 UHF channels (from 21 to 41) and convert them into meter range signals (1st and 2nd channel) . The absence of the UHF block in TVs of previous generations forced many to purchase UHF set-top boxes.

In Vitebsk, a transmitter was recently turned on for channel 48. To expand the received range to the 59th channel, I propose the simplest refinement of the prefix-selector "Uman" and the like with a range of 21 ... 41 channels. The improvement consists in increasing the tuning voltage (UH) of the varicaps to 26 V (instead of 18 V). To do this, it is necessary to break the connection between the resistors R2 and R3 of the stabilization unit and apply output 3 of the resistor R2 to the point R1 (Fig. 1).

(click to enlarge)

Expansion of the frequency range of UHF set-top boxes

You can do this by switching through a toggle switch (Fig. 2) - then the range of 21 ... 41 channels is saved.

Expansion of the frequency range of UHF set-top boxes
Ris.2

After that - tune to the 48th channel (or another of this order) as usual. This refinement is similarly done on other types of UHF set-top boxes, designed to receive 21 ... 41 channels. Their schemes are practically unified.

Author: V. Rezkov, Vitebsk; Publication: N. Bolshakov, rf.atnn.ru

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