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  • MultiMedia SRL
    ... From: bela ofori To: Sent: Sunday, October 07, 2001 5:28 PM Subject: VHF AUDIO VIDEO TRANSMITTER ...
    Message 1 of 1 , Jan 26, 2003
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      ----- Original Message -----
      From: "bela ofori" <erau_3000@...>
      To: <nsfetcu@...>
      Sent: Sunday, October 07, 2001 5:28 PM

      > 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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