This is a simplest FM transmitter circuit i built for educational purposes. many "simple transmitters" (Most transmitters on internet claim to be simple but many of them don't work) on internet will not work as those circuits are designed poorly.
I have built 100s of transmitters in the past and most of them were failed except a few, This one is working because the design is straightforward and reliable. This circuit is for those who have built many FM transmitters without any sign of working.
What is an FM transmitter?warning, building and using fm transmitter can be against the law depending your nation, although short-range transmitters below 1km or 500mw may be legal depending on your nation
An Fm transmitter is a circuit/device to transmit radio signals to an fm radio receiver through air (wirelessly). The input (audio)to an fm transmitter can be fed using a microphone or the output of your music player to be transmitted, and the signal which you transmit can be received using an FM radio, the advantages of FM TRANSMITTERS ARE many:
- You may transmit audio to another room/floor of your house without using any wires, wirelessly i mean
- You may transmit your own voice if you used a microphone in the circuit
- You don't need to build a receiver to receive the transmitting audio as any standard fm radio can be used to receive your voice/audio and many
Building the circuit
This circuit could transmit audio to a distance of around 50 meters if you used 2n3904 transistor and boost the supply voltage to 6V, and good range can be covered if used S8050 transistor with 9V supply.
Components you need
- R1 - 47K resistor
- R2 - 100 ohms resistor
- C1 - 22n none polarised capacitor
- C2 - 1n none polarised capacitor
- C3 - 4.7pf none polarised capacitor
- c4 - 22n none polarised capacitor
- T1 - Transistor BC547(short-range),2N3904(medium range,recommended),S8050(long-range)
- VC1 - 22pf Variable trimmer capacitor (trimcap)
- L1 - Aircore inductor, 6turns on a 3mm dia former eg.Wind over a pen refill.
- Antenna - a short length wire
- 3V battery (Use only battery)
- Good quality pcb or veroboard. (breadboards may not work)
After building is done,power the circuit using a 3V battery and connect any audio source to "audio input" pin properly, set an fm radio minimum 3 meters away. Start tuning the radio and tuning the VC1 at the same time untill you receive the transmitting audio, if you can hear the audio then you are DONE!.Notes
Use correct value components
If the transmitting audio is too loud and unclear, then add a 100K or 1 Mega ohm resistor across the audio input pin, the value of this resistor depends on how much powerful you audio signal is and should be selected untill you get a very clear voice.
The circuit has been tested and diagram is drawn by myself. comments are welcome