Modulator. Scheme, description

Modulator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Modulators

The modulator-transmitter is designed to pair a VCR or camcorder with a TV at a high frequency.

Most VCRs have a high frequency output, but some VCRs and TVs do not have an intermediate audio frequency of 6,5 MHz, so there is no sound from the TV when connected to a high frequency.

Also, most modulators operate in the UHF range, which requires the presence of an ACS unit in the TV. This modulator-transmitter generates a complete television signal at a frequency of 1 ... 3 MB channels. The intermediate frequency of the sound is set by the potentiometer R6. The modulator can be connected to the TV with a shielded cable or over the air (like game consoles like "Dandy")

(click to enlarge)

On the transistor VT3, the generator of the carrier frequency of the image is assembled, and on the transistors VT1, VT2, the generator of the carrier frequency of the sound. The transistor VT3 converts low-frequency video and audio signals into radio frequency signals. Coil L1 is frameless, wound on a mandrel with a diameter of 6 mm with PEL 0,8 wire and contains 8 turns. L2 - 2 turns with PEL 0,4 wire over L1. Potentiometer R6 sets the required intermediate frequency. The modulator-transmitter can also be used in conjunction with a personal computer.

Author: N.Martynyuk; Publication: N. Bolshakov, rf.atnn.ru

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