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 