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VHF
AUDIO VIDEO TRANSMITTER
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The
circuit presented here is a simple audio/video transmitter
with a range of 3 to 5 metres. The A/V signal source for
the circuit may be a VCR, a satellite receiver or a video
game etc. The circuit uses inexpensive components which
are easily available in the market.A block diagram showing
the principle of its operation and complete circuit diagram
are shown in the figure. A mixer which also operates as
an oscillator at VHF (H) channel 5 TV frequency is amplitude
modulated by video signal and mixed with frequency mo
enna, contains video carrier frequency of 175.25 Mhz and
audio carrier frequency of 180.75 Mhz.
The circuit consists of transistor T1 with its resonant
tuned tank circuit formed by inductor L1 and trimmer capacitor
VC1, oscillating at VHF (H) channel 5 frequency. Transistor
T2 with its tuned circuit formed using SIF coil and inbuilt
capacitor forms oscillator. The audio signal applied at
the input to T2 results into frequency modulation of 5.5
Mhz oscillator signal. The output of 5.5 Mhz FM stage
is coupled to the mixer stage through capacitor C8 while
the video signal is coupled to the emitter of T1 via capacitor
C4 and variable resistor Inductor L1 can be wound on a
3mm core using 24SWG enamelled wire by just giving 4 turns.
Calibration/adjustment of the circuit is also not very
difficult. After providing 12V DC power supply to the
circuit and tuning your TV set for VHF (H) channel 5 reception,
tune trimmer VC1. |
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