DIY Long Range Miniature FM Transmitter Circuit and Video Demonstration

DIY Long Range Miniature FM Transmitter (Homemade Radio Station)

FM Transmitter Circuit Diagram

Long Range Miniature FM Transmitter Circuit   electrobuff.blogspot.com

FM Transmitter in Action Video Demonstration

FM Transmitter Components and Working:

Electret Microphone (Audio Capture):

The process starts with an electret microphone, which converts sound waves (audio signals) into electrical signals. These signals are very weak and need amplification for transmission.

Pre-Amplifier:

The electrical signal from the microphone goes to a pre-amplifier stage. This stage amplifies the weak audio signal to a level suitable for modulation.

NPN Transistor Biasing:

The pre-amplified audio signal is then fed into the base of an NPN transistor. The transistor is biased in such a way that it acts as an amplifier for the audio signal.
Biasing Explanation: A simple biasing network (e.g., resistors) ensures that the transistor operates in its active region. This means the transistor amplifies variations in the base current caused by the audio signal, resulting in amplified variations in the collector current.

LC Oscillator (Radio Frequency Carrier Signal):

The transistor's collector is connected to an LC (inductor-capacitor) oscillator circuit. This LC circuit generates a stable radio frequency carrier signal at the desired frequency for FM transmission.

Oscillator Explanation: The LC circuit consists of an inductor and capacitor connected in a feedback loop. The feedback causes the circuit to oscillate at its resonant frequency, determined by the values of the inductor and capacitor.

Frequency Modulation (FM):

The audio signal from the pre-amplifier modulates the frequency of the carrier signal generated by the LC oscillator. As the amplitude of the audio signal varies, it causes slight variations in the frequency of the carrier wave.
Modulation Explanation: This modulation process (FM) embeds the audio signal onto the carrier wave. Stronger audio signals cause greater frequency deviations in the carrier wave.

Antenna:

The modulated signal, now containing the audio information on the carrier wave, is then sent to an antenna.
Antenna Explanation: The antenna radiates the modulated signal into space as radio waves. These waves can be picked up by FM radio receivers tuned to the same frequency.

Working Principle:

Audio Capture: The electret microphone captures sound waves and converts them into electrical signals.

Signal Amplification: The pre-amplifier amplifies the weak electrical signals from the microphone.

Transistor Amplification: The NPN transistor further amplifies the audio signal.

Oscillator Radio Frequency Generation: The LC oscillator generates a stable radio frequency carrier signal.

Frequency Modulation: The audio signal modulates the frequency of the carrier wave.

Transmission: The antenna broadcasts the modulated signal as radio waves, which can be received by FM radios tuned to the transmitter's frequency.

Summary:

A DIY FM transmitter uses an electret microphone to capture audio, a pre-amplifier to boost the signal, an NPN transistor biased to amplify the audio signal further, an LC oscillator to generate a stable carrier wave, and modulation to embed the audio onto the carrier wave. The transmitted signal is then radiated via an antenna as radio waves, allowing it to be received and played back by FM radio receivers within range.