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. 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. Then,
the transmitter is a B-System of CCIR compatible.
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.
Last Updated : April 19, 2002 
