This Long Range FM Transmitter Circuit (2km) works like small radio station in one box.
We can put music or talk in microphone it sends sound far away in air more far than normal bluetooth speaker.
It is good for many thing like small community radio, wireless speaker in big garden or playing music for all people near our home.
But in some place but maybe one may need license to use this.
So better check the rules in their area before using it.
Circuit Working:
Parts List:
| Category | Item | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | R1 10k | 1 |
| R2 1k | 1 | |
| R3 22k | 1 | |
| R4 2.2k | 1 | |
| R5 68Ω | 1 | |
| R6 68k | 1 | |
| R7 18Ω | 1 | |
| R8 2.2k | 1 | |
| R9 1k | 1 | |
| Capacitors | Ceramic C2 0.01µF | 1 |
| Ceramic C3 1nF | 1 | |
| Ceramic C4 8.2pF | 1 | |
| Ceramic C5 0.1µF | 1 | |
| Ceramic C6 0.1µF | 1 | |
| Ceramic C7 1nF | 1 | |
| Ceramic C8 1nF | 1 | |
| Ceramic C9 1nF | 1 | |
| Ceramic C10 0.01µF | 1 | |
| Electrolytic C1 2.2µF 25V | 1 | |
| Electrolytic C11 100µF 25V | 1 | |
| Trimmers | Trimmer VC1 22p | 1 |
| Trimmer VC2 22p | 1 | |
| Trimmer VC3 22p | 1 | |
| Trimmer VC4 22p | 1 | |
| Trimmer VC5 22p | 1 | |
| Trimmer VC6 40p | 1 | |
| Trimmer VC7 40p | 1 | |
| Semiconductors | IC 7809 | 1 |
| Transistor T1 BF494 | 1 | |
| Transistor T2 BF200 | 1 | |
| Transistor T3 2N2219 | 1 | |
| Transistor T4 2N3866 | 1 | |
| Electret MIC | 1 | |
| Coil L1 4 turns | 1 | |
| Coil L2 6 turns | 1 | |
| Coil L3 6 turns | 1 | |
| Coil L4 5 turns | 1 | |
| Coil L5 7 turns | 1 | |
| Load Antenna 50Ω | 1 |
This long range FM transmitter have four parts for sending radio signal.
First part is VHF oscillator with transistor BF494 T1.
After that signal goes to small amplifier using BF200 T2, then to driver using 2N2219 T3 and last big amplifier with 2N3866 T4.
Microphone which is small condenser type connect at the start of oscillator.
When we talk in mic it makes FM signal at T1 output.
Signal goes stronger by preamplifier and a driver if required we can also use 2N5109 instead of 2N2219.
Preamplifier work like tuned class A amplifier and driver works as class C type.
Then signal goes to power amplifier class C and send out from antenna 50 ohm dipole or ground plane type.
Transistor 2N3866 need heat sink to not get hot.
We can also use 2N4427 for better result on 12V where it gives 1 watt RF power.
There is small part called VC1 near coil L1 and adjust this to set at FM frequency between 88 to 108 MHz.
Also adjust VC2 to VC7 to get best signal and more range.
Oscillator get stable 9V power from 7809 regulator IC so frequency does not change if voltage goes up or down.
We can run whole circuit using 12V battery.
Make this circuit on general PCB.
Antenna must be fixed well for long range.
Coils L1 to L5 made by 20 SWG copper wire on 8mm air core.
They have 4, 6, 6, 5 and 7 turns.
How to Build:
To build a Long Range FM Transmitter Circuit (2km) we need to follow the below mentioned steps:
- Look at circuit diagram and put all parts on PCB board.
- First solder small parts like resistors, capacitors and other small things.
- Then fix transistors BF494, BF200, 2N2219 and 2N3866 in right place on PCB.
- Put condenser mic at input of oscillator transistor BF494.
- Connect coils L1 to L5 same as given and count number of turns, wire size, etc.
- Give power from 9V or 12V battery.
- Use 78C09 regulator IC to make stable 9V for oscillator.
- Slowly adjust VC1 with coil L1 to make frequency between 88 to 108 MHz.
- Also adjust VC2 to VC7 to get strong signal and long range.
- Fix heat sink to transistor 2N3866 or 2N4427 so it does not get hot.
- Install antenna properly and use 50 ohm dipole or ground plane type for more range.
Conclusion:
This Long Range FM Transmitter Circuit (2km) is made to send FM signal very far or even many kilometers.
It give strong power, clear sound, good antenna, stable frequency and follows radio rules.
To make this circuit we need to build carefully and adjust it well so it works good and does not break any law.