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Learn to build your own mini FM transmitter. This fun project will show you how to build a mini broadcasting device that can transmit an audio signal up to a quarter mile to any FM receiver. It's easy to build and a good learning experience.

This FM Broadcast Transmitter circuit will transmit a continuous audio tone on the FM broadcast band (88-108 MHz) which could used for remote control or security purposes. Circuit draws about 30 mA from a 6-9 volt battery and can be received to about 100 yards. A 555 timer is used to produce the tone (about 600 Hz) which frequency modulates a Hartley oscillator. A second JFET transistor buffer stage is used to isolate the oscillator from the antenna so that the antenna position and length has less effect on the frequency. Fine frequency adjustment can be made by adjusting the 200 ohm resistor in series with the battery. Oscillator frequency is set by a 5 turn tapped inductor and 13 pF capacitor.

If you want your tiny FM transmitter circuit to transmit music instead of spying or eavesdropping, you would probably find the following design interesting. The proposed FM transmitter will allow combining a stereo input simultaneously from the source so that the info contained inside both the channels get into the air for an optimal reception. The stability of the transmitter is improved by tapping the antenna from one top turn of the coil as shown in the above circuit.

This easy to build transmitter transmits high quality stereo sound from your MP3 player, computer, walkman or discman to any FM radio or car radio. The circuit is designed around the BA1404 single chip FM stereo transmitter from ROHM. The IC requires only a small number of external parts so it is well suited for hobbyist projects. The chip features excellent frequency stability, low power consumption & good channel separation. The transmitting RF frequency can be set by adjusting the coil (Lx). This 2 turn coils is paired with a 39 pF capacitor (Cx) to give a frequency range from 87 MHz - 106 MHz.

The FM telephone circuit is built on a PC board that is so small it can easily be fitted inside the housing of a telephone making it an instant pseudo-speak earphone. This FM transmitter circuit connects in series with telephone line, steals power from it, and transmits both sides of the conversation to an FM radio tuned between 90 and 95 MHz.

The goal of this project is for me personally to learn a little more about fm transmitters and fm bug making (may the HAM radio gods bless me in this pursuit). The ideal outcome of this project is a very small and full functional FM transmitter that we can stick into a plastic mint box. In order to be able to build this, we'll have to learn a lot about amplifiers, LC oscillators, mixers, antennas and FM. This project assumes you're already comfortable build your own PCB boards. If you're not please take a look at the homemade pcb's tutorial before you continue. It will help you out a lot.

Here is the circuit diagram of the simple FM transmitter using a transistor. Great performance or range is not guaranteed here, because this is an elementary design. General purpose radio frequency transistor BF 494 (Q1) is used here for obtaining FM modulation. A condenser mic is used here to pickup the sound.The condenser mic converts the sound to electrical variations and this variations are fed to the base of Q1 , which performs the amplification as well as modulation.The capacitor C2 and L1 determines the frequency of transmission.The circuit can be powered from a 9V transistor radio battery.

Here's simple FM transmitter circuit using medium power 2N2218 transistor. Micropohone is of electret type that connects to two input terminals and the antenna should be a copper wire from 15 to 40 cm. Below is schematic circuit of the fm transmitter.

This little 88-108MHz FM transmitter has a range of up to 1 mile in the open. The transmitter consists of three stages. The first stage is an audio pre-amplifier built around 2SC9014 transistor, second stage is an oscillator built using 2SC9018 transistor, and third stage is an RF amplifier built around 2SC9018 transistor. RF amplifier stage increases an output power, range and stability by separating the antenna from the oscillator.

Presented here is a low-power FM transmitter with varactor diode tuning using surface-mount devices (SMD) that will be received with a standard FM radio. Soldering surface mounted devices is not so hard and actually is quite easy. There are many designs for small FM transmitters but they have some problems. First, you need an audio amplifier to get enough modulation. Second, the antenna is attached directly to the collector. Third, the coil L must be wound by hand and adjusted by stretching. It all ads with a weak signal that tends to drift in frequency. In contrast the transmitter schematic we present here eliminates some of those problems, using varactor diode for tuning and modulation, givin great sensitivity without an audio amplifier.