Video transmitter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Телевидение
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The transmitter is designed for amplitude-frequency modulation of a video signal from video equipment (video cameras, tuners, tape recorders, personal computers, etc.) to a television receiver. The transmitter is connected directly to the video device, which eliminates the need for a video input on the television receiver.
Combining such a transmitter with a frameless video camera, it is not difficult to obtain an installation for wireless video surveillance, and for economical operation of batteries, it is recommended to combine this device with an infrared presence detector, commercially produced by many foreign companies and relatively inexpensive, for example, the REFLEX detector from the TEHESOM company, capable of capturing Extraneous intervention, resistant to false alarms, electromagnetic and radio frequency radiation.
By supplementing the video transmitter circuit with a high-frequency amplifier made on a single transistor of the KT325 type, it is possible to increase the output power of the transmitter, and, accordingly, the range of wireless communication with a television tuner.
The circuit diagram of the transmitter contains one transistor VT 1 type KT 603 G. The transmitter is tuned to the frequency of one of the channels free from television broadcasting (for example, channel 1 .... 5). The tuning is carried out using a tuning capacitor C 4, which is used to capture the unmodulated signal. Fine tuning of the transmitter is made by the resistor R1. The signal from the video device is fed to the transmitter input to the emitter circuit of the transistor through resistor R6 and capacitor C9.
The modulated video signal from the collector is fed to the oscillatory circuit L1 C4 in the antenna. The current at point A is selected within 30 .... 35 mA.
A properly assembled transmitter works immediately. In the absence of generation, it is necessary to check the voltage at the emitter of the transistor VT1, and the voltage on it should differ from the voltage on the base by 1 ... 2 V upwards.
The transmitter should be powered from a stabilized power supply. The antenna must have a rigid structure, such as a telescopic one.
Instead of the KT603 transistor, you can use KT608B or another one with suitable parameters.
It is desirable to place the transmitter in a screen in order to reduce interference.
Publication: N. Bolshakov, rf.atnn.ru
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