9V FM Transmitter Circuit: Build Your 100m Range

Description

This FM transmitter boasts a reach of approximately 100 meters utilizing a 9V Direct Current supply. The circuit is constructed with three distinct phases. The initial stage incorporates a microphone preamplifier utilizing a BC548 transistor. Subsequent to this, a VHF oscillator is implemented around another BC548. (BC series transistors are frequently employed in low-frequency applications, however, they also perform adequately within Radio Frequency stages when functioning as oscillators.) The final phase is a Class-A tuned amplifier that enhances the signals generated by the oscillator. Incorporating this supplementary RF amplifier expands the transmitter's operational range.

Circuit diagram:

Coil L1 consists of four turns of 20SWG insulated copper wire wound to a length of 1.5cm around a 4mm diameter air core. Coil L2 comprises six turns of 20SWG insulated copper wire wound on a 4mm diameter air core. A 75cm length of wire is utilized as the antenna. To achieve optimal performance, a sensitive receiver should be employed. VC1 is a variable resistor type trimpot used for frequency adjustment. VC2 necessitates adjustment for maximizing the transmission range. The transmitter unit is powered by a 9V PP3 battery. This transmitter can be readily integrated with a commercially available FM receiver kit to create a functional walkie-talkie system.

More about components

Integrated circuits, or ICs, play a crucial role in this FM transmitter circuit. Specifically, the BC548 transistors are fundamental semiconductor devices. These transistors act as switches and amplifiers within the circuit. They are commonly used to amplify weak signals from the microphone and boost the signal amplitude for transmission. BC548 transistors are NPN bipolar junction transistors (BJTs) and are known for their low gain and relatively simple operation, making them suitable for many general-purpose amplification tasks. They control the flow of current based on an applied voltage, allowing for signal amplification and switching functions within the transmitter's design.