FM transmitter sensor
Several circuits for constructing FM transmitter have been published by EFY. The power output of most of these circuits were very low because no power amplifier stages were incorporated. The transmitter circuit described here has an extra RF power amplifier stage, after the oscillator stage, to raise the power output to 200-250 milli watts. With a good matching 50 ohm ground plane antenna or multi element yagi antenna, this transmitter can provide reasonably good signal strength up to a distance of about 2 kilometers. The circuit built around transistor T1 (BF494) is a basic low power variable frequency VHF oscillator. A varicap diode circuit is included to change the frequency of the transmitter and to provide frequency modulation by audio signals. The output of the oscillator is about 50 milliwatts. Transistor T2 forms a VHF class A power amplifier. It boosts the oscillator signal’s power is generated at the collector of transistor T2.
FM TRANSMITTER
Componet list:-
Resistances
R1 – 3.3K
R2 – 33K
R3 – 4.7K
R4 – 33K
R5 – 1K
R6 – 100ohm
TRANSISTORS
T1 – 548
T2 – 548
CAPACITORS
C1 – 10uf/50V
C2 – 473K
C3 – 224K
C4 – 474K
C5 – 4.7
C6 – 0.02
C7 –
OTHERS
L1 – Coil
BAT9V – DC Battery 9Volt
ANT – Antenna
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Battery connector
