TV transmitter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Телевидение
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The schematic diagram of the transmitter is shown in Fig.1.
The transmitter operates in the UHF (UHF) range and is built on one microcircuit and two microwave transistors. It provides ideal color picture quality at a distance of about 50 m. The maximum range depends on the sensitivity of the TV, the antennas used, and for a color image it is 300 m, and for black and white - more than 500.
(click to enlarge)
Coils L1, L4, L5 contain 1.5 turns each (a ring with leads down) of 0.5 mm PEV wire, and coil L3 2 + 2 turns of the same wire, and consists of two halves, between which the L4 coil is placed. The gap between the coils L3 and L4 is about 1 mm. The L2 coil is taken from the sound rejection circuit of any TV. The L2 C12 circuit is tuned to a sound subcarrier frequency of 6,5 MHz, so the C12 capacitor may be of a different capacity, which was part of the TV circuit.
The details of the transmitter are placed on a printed circuit board made of fiberglass laminated on one side. The circuit diagram is drawn in such a way that it is easy to draw the PCB layout from it. In this case, it should be borne in mind that the width of the conductors must be at least 1 mm. The ground conductor is made by solid filling of the free space of the board, at a distance of 1-2 mm from other conductors. It is important that the pins of the microcircuit 5 and 14 are connected to each other under the microcircuit and to the ground in the shortest possible way. You should strive to ensure that the remaining conductors are of a minimum length. It is obligatory to solder both conclusions of the emitter of microwave transistors.
The board is closed from above with a brass screen 20...25 mm high with holes opposite the adjustment elements (R7, C13, 14, 21, L2) and the antenna output. The screen is soldered along the contour from the bottom of the board. To install the antenna on the board, a brass sleeve with an M2 internal thread is soldered, where the antenna pin is wrapped. The antenna is a piece of bare copper wire from a lighting wire with a cross section of 2.5 mm2. The length of the antenna is selected experimentally and is approximately 30 cm.
The setting comes down to setting the modulation point with the resistor R7 (in this case, the operating frequency also changes) by the absence of green koturs and pink "draws" in the image, contours and matching with the antenna. Lastly, the L2 circuit is tuned to a frequency of 6.5 MHz (you can hear it by pure sound transmission). The output signal of the transmitter must have sufficient power to receive the TV “at the input” from a distance of about a meter.
Publication: N. Bolshakov, rf.atnn.ru
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