Increasing the sensitivity of ZUSTST TVs. Scheme, description

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Increasing the sensitivity of ZUSTST TVs. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Телевидение

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For owners of ZUSCT TVs with a submodule of the SMRK-2 radio channel, living in an area of uncertain reception, I offer a simple way to increase the sensitivity of the UPCHI (and the TV as a whole) by 1,5-2 times by changing the values of several resistors.

An analysis of the differential amplifier circuit of the submodule of the SMRK-2 radio channel, assembled on transistors VT2 and VT3, using the technique taken from [1], shows that this cascade does not amplify the signal, but apparently only serves to obtain the paraphase voltage necessary for normal operation of the D2 chip type K174UR5 with a differential input. A fragment of the SMRK-2 scheme with changes is shown in the figure. The numbering of the elements corresponds to the manufacturer's scheme, and the resistor values are new. The gain of the cascade (calculated) with such ratings is 5, but the real one is somewhat lower due to parasitic mounting capacitances and the shunting effect of the D2 microcircuit.

Increasing the sensitivity of ZUSTST TVs, a circuit diagram

For radio amateurs who love to experiment and decide to repeat this scheme, I advise you to try to reduce the ratings of R9 and R13 (they should be the same). This will increase the gain, but may lead to self-excitation of the UPCH. Well, now from theory to practice. In the city of Lozovaya, my MB antenna of the 3-element "wave channel" type was directed to the Lozovskaya repeater "Bokom" received the signal UT-1 (channel 2) from the city of Izyum (distance about 90 km). Before the alteration, the image was black and white, the sound was noisy. After the alteration - the sound is clear, the image is colored with a slight "snow". In conclusion, I want to say that a further increase in the sensitivity of the TV is possible by replacing the channel selectors SK-M-24 and SK-D-24 with more modern all-wave SK V-41, SK V-518M, etc.

Literature:

Horowitz P., Hill W., The Art of Circuitry - M. Mir, 1984

Author: G.V. Volichenko; Publication: cxem.net

See other articles Section Телевидение.

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