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MEDIUM-POWER FM TRANSMITTER


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The range of this FM transmitter
is around 100 metres at 9V
DC supply.
The circuit comprises three stages.
The first stage is a microphone preamplifier
built around BC548 transistor.
The next stage is a VHF oscillator wired
around another BC548. (BC series transistors
are generally used in low-frequency
stages. But these also work fine

Walkie-talkie arrangement
in RF stages as oscillator.) The third
stage is a class-A tuned amplifier that
boosts signals from the oscillator. Use
of the additional RF amplifier increases
the range of the transmitter.
Coil L1 comprises four turns of
20SWG enamelled copper wire wound
to 1.5cm length of a 4mm dia. air core.
Coil L2 comprises six turns of 20SWG
enamelled copper wire wound on a
4mm dia. air core.
Use a 75cm long wire as the antenna.
For the
maximum range,
use a sensitive receiver.
VC1 is a
frequency-adjusting
trimpot. VC2
should be adjusted
for the maximum
range. The transmitter
unit is powered
by a 9V PP3 battery. It can be
combined with a readily available FM
receiver kit to make a walkie-talkie set