How to make an FM emitter circuit
As we can see in the block diagram of the circuit, it starts with a two-terminal electret microphone, followed by a BF preamplifier built from an operational amplifier (LM741). the voltage gain is about 50dB, which we can modify if necessary by varying the value of resistor R5. the radio frequency part is made up of a typical colpitts type oscillator. The signal amplified by OP1 is applied to the varicap diode DV1, which is connected in parallel with the tuned circuit L1/C2 on which the transmitter emission frequency depends.
The transistor TR1, which together with the components associated with it make up the colpitts oscillator, is kept in oscillation by the capacitor C5 connected between its emitter and its collector.
The emitted RF power depends to a great extent on the 330 ohm emitter resistor R9, being possible to modify its value to obtain a few more milliwatts.
Apart from simplicity, due to the possibility of building the emitter as we can see, with a prototype board. The inductive components of the circuit are not complicated to build.
The coil L1 is made up of four turns of 0.8mm copper wire wound in the air. The internal diameter must be 8mm and a length of 1cm. It is made by winding 4 turns of 0.8mm copper wire around an 8mm diameter drill bit.
How to make an FM emitter circuit
As we can see in the block diagram of the circuit, it starts with a two-terminal electret microphone, followed by a BF preamplifier built from an operational amplifier (LM741). the voltage gain is about 50dB, which we can modify if necessary by varying the value of resistor R5. the radio frequency part is made up of a typical colpitts type oscillator. The signal amplified by OP1 is applied to the varicap diode DV1, which is connected in parallel with the tuned circuit L1/C2 on which the transmitter emission frequency depends.
The transistor TR1, which together with the components associated with it make up the colpitts oscillator, is kept in oscillation by the capacitor C5 connected between its emitter and its collector.
The emitted RF power depends to a great extent on the 330 ohm emitter resistor R9, being possible to modify its value to obtain a few more milliwatts.
Apart from simplicity, due to the possibility of building the emitter as we can see, with a prototype board. The inductive components of the circuit are not complicated to build.
The coil L1 is made up of four turns of 0.8mm copper wire wound in the air. The internal diameter must be 8mm and a length of 1cm. It is made by winding 4 turns of 0.8mm copper wire around an 8mm diameter drill bit.
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