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Four-Stage FM Transmitter Guide

This circuit diagram describes a 4-stage FM transmitter that uses a VHF oscillator, preamplifier, driver, and power amplifier to transmit FM radio signals. The oscillator uses a condenser microphone to generate frequency-modulated signals. These signals are then amplified by subsequent stages and transmitted via an antenna. Key components include transistors to generate and amplify the radio frequency signals at each stage, as well as coils, capacitors, and a voltage regulator to power the circuit and tune it to the 88-108 MHz FM radio band. The transmitter is designed for educational purposes only and using it with an outdoor antenna would be illegal in most places.

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Nikhil R. Lalwani
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© Attribution Non-Commercial (BY-NC)
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428 views1 page

Four-Stage FM Transmitter Guide

This circuit diagram describes a 4-stage FM transmitter that uses a VHF oscillator, preamplifier, driver, and power amplifier to transmit FM radio signals. The oscillator uses a condenser microphone to generate frequency-modulated signals. These signals are then amplified by subsequent stages and transmitted via an antenna. Key components include transistors to generate and amplify the radio frequency signals at each stage, as well as coils, capacitors, and a voltage regulator to power the circuit and tune it to the 88-108 MHz FM radio band. The transmitter is designed for educational purposes only and using it with an outdoor antenna would be illegal in most places.

Uploaded by

Nikhil R. Lalwani
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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circuit

ideas
electroni cs for you March 2010 103 www. e f y Ma g . c o M
the pre-driver stage. You can also use
transistor 2N5109 in place of 2N2219.
The preamplifer is a tuned class-A RF
amplifer and the driver is a class-C
amplifer. Signals are fnally fed to the
class-C RF power amplifer, which de-
livers RF power to a 50-ohm horizontal
dipole or ground plane antenna.
Use a heat-sink with transistor
2N3866 for heat dissipation. Carefully
adjust trimmer VC1 connected across
L1 to generate frequency within 88-
108 MHz. Also adjust trimmers VC2
through VC7 to get maximum output
at maximum range.
Regulator IC 78C09 provides stable
9V supply to the oscillator, so variation
in the supply voltage will not affect the
PradeeP G.
Four-StaGe FM tranSMitter
S.C. DW
IVEDI
T
his FM transmitter circuit uses
four radio frequency stages:
a VHF oscillator built around
transistor BF494 (T1), a preamplifer
built around transistor BF200 (T2), a
driver built around transistor 2N2219
(T3) and a power amplifier built
around transistor 2N3866 (T4). A con-
denser microphone is connected at the
input of the oscillator.
Working of the circuit is simple.
When you speak near the microphone,
frequency-modulated signals are
obtained at the collector of oscillator
transistor T1. The FM signals are am-
plifed by the VHF preamplifer and
frequency generated. You can also use
a 12V battery to power the circuit.
Assemble the circuit on a general-
purpose PCB. Install the antenna prop-
erly for maximum range.
Coils L1 through L5 are made with
20 SWG copper-enamelled wire wound
over air-cores having 8mm diameter.
They have 4, 6, 6, 5 and 7 turns of wire,
respectively.
EFY note. This transmitter is meant
only for educational purposes. use of
this transmitter with outdoor antenna
is illegal in most parts of the world. The
author and EFY will not be responsible
for any misuse of this transmitter.

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