An FM transmitter can cover the maximum distance, we always try to get the maximum range with maximum power output. there are various different types of fm transmitters circuits available in on the different online websites. but not all circuits are a capacity to cover more than 100- 200 meter site range. Here showing a circuit that can cover a distance up to 5 km and with the power of 1 w. Here presenting a small powerful circuit of a Long-Range FM transmitter that operates with 12v dc.
In this ckt is a high-frequency oscillator and whose output frequency changes according to the voltage applied at a particular control point. FM transmitter circuit consists of a voltage-controlled oscillator and this is a high-frequency oscillator. This high-frequency oscillator is a variable oscillator controlled by the capacitor. This FM transmitter works on 3 RF stages.
A (VFO) Variable frequency Oscillator (30 mw) , A class C driver stage (150 mw) as buffer and then A class C final RF power amplifier (1 Watt ) that gives output frequency ..Q1 with its associated components form the VFO. The VFO output is fed to Q2. Q2 being a buffer does not load the VFO but amplifies the power only. This output is fed to the final RF power amplifier Q3, the output of which feeds the tuned circuit. Several capacitors C 4,8,9 are used on the supply rail for HF filtrations. If one feeds the VFO transistor Q1 directly with a microphone at its base it becomes a FM Transmitter circuit.
A simple straight single wire aerial standing antenna can use. Using his antenna a receiver can receive the signal around 100-200 meters. This type of antenna is used for testing. The frequency of the transmitter can be set within 88 to 108 MHz FM band by adjusting the VC1 (Trimmer 1) of the VFO or by changing the spacing between the Coil L1.
You can test the circuit by using the radio set or mobile phone as a receiver device but firstly the distance between the transmitter and receiver not take farther away, try to nearly as possible at the time of testing, and start to give any input voice at on mic. If no signal found at the receiver then the full tuning of the receiver tune and check. and by the changing of trimmer value by moving it you can change the frequency bandwidth as required.Adjust the trimmer VC1 very (about 1 degree) little clockwise or anticlockwise, the transmission frequency will change. Then put the cell phone to search again and find the frequency. If it is very near a powerful transmitter you will not get the range. Change the frequency again to go towards 106 MHz where no commercial transmission usually takes place.
For the adjustment of transmitting distance of transmitter trimmer 2(TR2) adjust by the help of screwdriver with the non-metal terminal. TV antenna which was used earlier, or uses an aluminum pipe antenna for making a yagi antenna for better distance cover.
Some components might have accumulated dirt on their legs by oxidation due to storage. Must clean them thoroughly to remove the dirt with a knife all around before soldering. The metal transistor as an example as seen in the packet. Better clean all the component legs even if they have no dirt on them.
If the trimmer pins are not going inside the holes try to slightly make the holes on the PCB bigger by some sharp-pointed pin.
For the making of coil, the copper wire is enameled for insulation and before soldering terminals must be cleaned by blade or knife for removing the enameled polish. other components like the resistor terminal should be cleaned if they dirty.