Wireless video program transmitter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Телевидение
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I bring to the attention of readers a simple transmitter of video programs. It can be connected to any VCR or computer via the bass output. The transmitter operates in the meter range (channel 5 ... 9), the supply voltage is 4,5 ... 6 V. The transmitter circuit is shown in fig. one.
(click to enlarge)
On the transistor VT1, a mixer-oscillator with an FM audio frequency conversion of 5,5 MHz (6,5 MHz) is assembled. The local oscillator frequency depends on the capacitances C4, C5 and inductances L1, L2. On VT2, a carrier local oscillator is made, the frequency of which depends on the choice of the television channel. Ha R12 mixes the video signal, FM audio and the carrier of the desired channel. Further on VT3 the signal is amplified and transmitted to the antenna.
The required level of 3H is set by resistor R1. LI, L2 are wound on a coil from an imported radio receiver, in which the tuning element is a ferrite cup. L1 contains 23 turns of PEL-0,1 wire; L2 - 24 turns of the same wire.
L3, L5 are wound on a 4 mm mandrel and contain 5 turns of PEL-0,35 wire. L4 - mandrel 4 mm, contains 4 turns of PEL-0,35 wire, wound round to round. After tuning, it is desirable to fill this coil with paraffin. As an antenna, you can use a piece of copper wire 20 ... 50 cm long or a telescopic antenna from any radio receiver.
Figure 2 shows the printed circuit board of the transmitter. In Fig.3, the location of the elements.
With proper assembly, the design begins to work immediately. When you turn on the TV, you need to tune it to the desired channel (in my case, TV-6). The setting is made by elements C 13 and L4. Next, you need to configure the elements L1, L2 (C3) of the audio carrier for better reception of the audio signal by the TV.
Ris.4
If it seems to you that the transmitter power is insufficient, you can assemble the amplifier circuit shown in Fig. 4. Only in this case it will be necessary to change the drawing of the printed circuit board and install a tuning capacitor instead of C14, which will later be tuned to resonance to the maximum of the transmitted signal. Additional information on tuning this cascade is given in [1]. In conclusion, I want to note that this transmitter was tested on TVs of the 4th and 5th generations and showed good results. Its power is quite enough for an apartment. The range is 5 ... 8 m, it can be increased by using an additional PA cascade.
Literature
1. F. Zhupanov. How to build a simple TV repeater.//Radio amateur.-1994.-M 7.-p.4-5.
Author: V.Papko, Vitebsk region, Ushachi town; Publication: N. Bolshakov, rf.atnn.ru
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