10km Range FM Radio Transmitter with Two Transistors

FM Radio Transmitter Circuit Diagram
FM Radio Transmitter Circuit diagram electrobuff.blogspot.com

A simple two-transistor FM radio transmitter circuit is a basic design that allows you to broadcast an audio signal over short distances. This type of circuit is often used for educational purposes or small-scale personal projects.

Let's break down the operation of the circuit:

Components Needed:

First Transistor (Q1): NPN transistor (e.g., 2N3904)
Second Transistor (Q2): NPN transistor (e.g., 2N3904)
Microphone
Resistors: Various resistors for biasing and limiting current
Capacitors: To filter and couple signals
Inductor (L1): To create a tank circuit for frequency modulation
Antenna.
Power Supply.

Circuit Operation:

Microphone Preamplification (First Transistor - Q1):

The microphone is connected to the base of the first transistor (Q1).
Q1 operates as a common-emitter amplifier. The audio signal from the microphone modulates the base current of Q1, causing variations in the collector current.
The variations in collector current result in an amplified audio signal at the collector of Q1.

Frequency Modulation (Second Transistor - Q2):

The audio signal from the collector of Q1 is coupled to the base of the second transistor (Q2).
Q2 is configured as a frequency modulator. The tank circuit, consisting of an inductor (L1) and a capacitor C4, determines the frequency of the transmitter.
The varying audio signal causes the frequency of the tank circuit to change, leading to frequency modulation.
The modulated signal is then present at the collector of Q2.

Radiating the Signal:

The modulated signal from the collector of Q2 is fed to an antenna.
The antenna radiates the modulated signal as electromagnetic waves, allowing it to be received by an FM radio tuned to the corresponding frequency.

Important Considerations:

Frequency Adjustment: The frequency of the transmitter is determined by the values of the tank circuit components (L1 and the capacitor C4). Adjusting these components allows you to set the desired operating frequency.

Power Supply: Ensure that the transistors receive the correct power supply voltage and that the circuit has proper current biasing for reliable operation.

Antenna Length: The length of the antenna is a critical factor in determining the transmission range. The antenna length should be approximately one-fourth of the wavelength of the operating frequency.

Legal Considerations: Be aware of local regulations regarding the use of radio transmitters. Unlicensed broadcasting may violate regulations, and interference with licensed services should be avoided.

This basic two-transistor FM transmitter is a simple and educational way to understand the principles of FM modulation and radio transmission. However, keep in mind that its range is limited, and using it without proper authorization may lead to legal issues. Always adhere to local regulations when experimenting with radio frequency circuits