Schematics > RF circuit > 4 Transistor Transmitter
4 Transistor Transmitter
4 Transistor Transmitter circuit
Circuit Notes:
This circuit provides an FM modulated signal with an output power of around
500mW. The input
Mic preamp is built around a couple of 2N3904 transistors, audio gain limited
by the 5k preset.
The oscillator is a colpitts stage, frequency of oscillation governed by the
tank circuit made from
two 5pF capacitors and the inductor.
Frequency is around 100Mhz with values shown.
Audio modulation is fed into the tank circuit via the 5p capacitor, the 10k
resistor and 1N4002
controlling the amount of modulation. The oscillator output is fed into the
3.9uH inductor which
will have a high impedance at RF frequencies.
The output stage operates as a class D amplifier , no direct bias is applied
but the RF signal developed
across the 3.9uH inductor is sufficient to drive this stage. The emitter
resistor and 1k base resistor
prevent instability and thermal runaway in this stage.
Title: 4 Transistor Transmitter
Source: unknown
Published on: 2006-01-15
Reads: 1003
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