|
|
VHF AUDIO VIDEO TRANSMITTER
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.
