small FM transmitter

Small And Long Range Fm Transmitter circuit

Fm transmitter is always an interesting circuit idea. This circuit provides the FM frequency signal of about 80 to 115 MHz. You can receive the signal of this transmitter on a receiver at a distance of around about 200 meters. This is a small range portable FM transmitter circuit that requires very few components.,this makes FM transmitter circuit is very simple and portable. This can be operated at 9v DC supply voltage.

Working

This circuit requires two NPN BC 546 transistors and some other components. This is low power and so simple circuit of FM transmitter. BC 546 transistor is connected with the microphone, the signal from mic is fed to the base of transistor T1. And this signal to be amplified and then it is passed to the base of T2, which is connected with the collector of T1 through the capacitor, and the emitter of T2 is connected with the ground through the resistor. The Transistor T1 is connected as the preamplifier which is preamplified the signal which is given by the mic. And Transistor T2 portion operates as the power amplifier of signal and inductor and capacitor modulated the signal which is amplified by a transistor. Use a proper antenna to maintain the maximum capacity of range of transmitting the signal. a signal can be set by tunning of variable capacitor (trimmer) C7. A non-metal screw is suitable for tunning the trimmer because it does not affect the frequency by touch the terminals.

This small FM transmitter circuit is very easy to construct on a general-purpose PCB board. connect all components as shown in the circuit diagram and give a supply of 9v regulated DC.

Testing

Test on any FM receiver on fm tunning by the adjusting of frequency by the trimmer. 

Although it is low-power, it might be illegal to regular transmit. Always use a battery for power this ckt because ac-dc adaptor can make a noise like humm. 9v battery is better or 9 v voltage regulator used for 9v at 12 v main input before 9v.

Circuit diagram:
 
Long range small FM transmitter circuit diagram
 
components list
 
capacitor-
2.2uf-1
4.7nf-1
47nf-1
2.2nf-1
1nf- 2
15pf-1
10pf-1
trimmer(variable capacitor) 15-50pf – 1
 
Transistor
BC546 or 547 – 2
 
Resistor
10k-1
120 ohm -2
560k-1
2k7- 1
27k-1
 
Inductor 
 
100uh – 1
 
Mic-1                                                                                            
 

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