The last/final stage of any FM transmitter is the FM antenna. This will give the circuit more dependability and more output. The FM transmitter circuit is enhanced by including this buffer or output stage so that the oscillator is not driving antenna. The signal handled by the oscillator stage is not exceptionally capable so we pass it to an amplifying stage called an output stage to increase the amplitude. This stage amplifies the output RF signal. The transistor and its components encompassing the tuned circuit essentially keep the tuned circuit working at its resonant frequency. Each transmitter circuit needs an oscillator part to create the RF waves. In this stage, the amplified audio input signal is adjusted for transmission. This stage is said to be AC coupled as it has a capacitor on both the input and output so the DC voltages of the different stages don’t impact the voltage on the stage. Just an exceptionally self-biasing emitter stage is used for the sound enhancer. In this stage, the signal is amplified moreover 70-100 times and is currently huge enough to be infused into the RF stage. The output waveform at the micro-phone is passed through a coupling capacitor to an emitter stage.

The capacitor disconnects the microphone from the base voltage of the transistor and permits just AC signs to pass through. It conveys these to the oscillator stage. The pre-amplifier is a self-biasing emitter fit for amplifying the signals got by the micro-phone. This capacitor is intended to divide the DC voltage on the receiver from the voltage concerning the transistor.

A 22n capacitor on the output of the micro-phone couples the sign to the first sound pre-amplifier stage. Alternately assuming that you need to utilize altered resistor as a part of the spot of the variable resistor and would prefer not to change the sound quality then a 5K resistor might be utilized. Commercial use of Radio frequencies (including FM) without permission is illegal in almost everywhere of the world.A variable resistor at a micro-phone is utilized to alter the audio quality of the amplifier and modify the variable resistor to get the best quality. Keep in mind that this type of simple FM transmitter circuit are allowed for personal use. You can add a microphone pre-amplifier in this circuit to transmit voice directly. For higher wattage outputs, the value is 0.01 or 103. This circuit is most suitable for miniature FM transmitter for use in computer, mobile etc to send music to home theater system without wires, and in homemade wireless walky-talkies.įor input from low power output devices, such as mobile, computer’s sound card, the value of the unlabeled capacitor is 0.1 or 104. The transistor gives a RF humming accordingly to the audio input, and the FM wave is spread by the external antenna(Ariel).īy using a standard T.V antenna, the range of this transmitter can go upto 1KM radius, using small(15-20cm) Ariel, it can work upto around 50M range. For even more low cost, use a new bicycle spoke for ariel, get it from cycle store at Rs 2/. The input from the audio output of computer/PMP/mobile is given to the biased base of the transistor. Try to use no wire in the main functional area(transistor and coil). 36 SWG wire 2.5turns only in 5mm diameter ferrite rod. A coil takes care of the output frequency. The circuit has a central RF oscillator NPN transistor BF494 (substitute: BF194).

This FM transmitter circuit runs at low voltage, on a CR2025 3V Lithium battery, current consumption is also low.Īnd the total size of this F.M transmitter(including battery, excluding antenna) is less than that of a matchbox. This circuit is really cool and cheap to build. This is the most simple FM transmitter circuit diagram you can ever find.

3 transistor fm transmitter