4 stage FM Transmitter

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4 stage FM Transmitter Powered By Docstoc

Four-StaGe FM tranSMitter                                                                                          s.c. dwiv

   PradeeP G.                            the pre-driver stage. You can also use
                                          transistor 2N5109 in place of 2N2219.

        his FM transmitter circuit uses   The preamplifier is a tuned class-A RF       frequency generated. You can also use
        four radio frequency stages:      amplifier and the driver is a class-C        a 12V battery to power the circuit.
        a VHF oscillator built around     amplifier. Signals are finally fed to the        Assemble the circuit on a general-
transistor BF494 (T1), a preamplifier     class-C RF power amplifier, which de-        purpose PCB. Install the antenna prop-

built around transistor BF200 (T2), a     livers RF power to a 50-ohm horizontal       erly for maximum range.
driver built around transistor 2N2219     dipole or ground plane antenna.                   Coils L1 through L5 are made with
(T3) and a power amplifier built              Use a heat-sink with transistor          20 SWG copper-enamelled wire wound
around transistor 2N3866 (T4). A con-     2N3866 for heat dissipation. Carefully       over air-cores having 8mm diameter.
denser microphone is connected at the     adjust trimmer VC1 connected across          They have 4, 6, 6, 5 and 7 turns of wire,
input of the oscillator.                  L1 to generate frequency within 88-          respectively.
    Working of the circuit is simple.     108 MHz. Also adjust trimmers VC2                 EFY note. This transmitter is meant
When you speak near the microphone,       through VC7 to get maximum output            only for educational purposes. use of
frequency-modulated signals are           at maximum range.                            this transmitter with outdoor antenna
obtained at the collector of oscillator       Regulator IC 78C09 provides stable       is illegal in most parts of the world. The
transistor T1. The FM signals are am-     9V supply to the oscillator, so variation    author and EFY will not be responsible
plified by the VHF preamplifier and       in the supply voltage will not affect the    for any misuse of this transmitter. 

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