Micro FM Radio Transmitter Circuit
FM radio transmitter is radio transmitter that can be used for purposes like transmitting your radio signals throughout the air or for spying (eg.listening to one’s speech secretly). etc, Building and using transmitters are illegal and can put you in prison for a long time!, it’s better not to use this device against any person or for any kind of illegal activities, also building and using long range radio transmitters without a license is illegal in most countries because these unstable frequencies may confuse with fire,ambulance,police,aircraft frequencies.
I know the fact that these kind of small power transmitters have short range, but if you live near a traffic,police,hospital etc, even these short range can disrupt those signals, even if they use different bands to transmit their transmitters. for safety concerns, we must not use long range transmitters
So use this circuit at your own risk! Moreover i don’t recommend you to build this transmitter and if you used this device for some good purposes, such as ‘transmitting music in your college or just to your backyard’ then i recommend you to use it but never use a long antenna to get more range as it may jam the “life” frequencies that i mentioned above
This circuit requires SMD components to make it as small as possible, so you need to get some SMD components such as smd resistors,smdcapacitors..etc you may get all these from junk(eg.damaged circuit boards, but you must test them before soldering to the pcb) circuit boards if it’s not easy to get from electronics components selling stores.
You may need micro soldering iron although i used an ordinary one to get it all soldered, but it was quite hard to solder the SMD components onto the PCB using an ordinary soldering iron.
The picture below shows some SMD resistors and how to calculate their values
SMD resistor table
Here is the circuit diagram of micro FM TRANSMITTER, just change every components in the circuit to SMD except the Transistor,coil, and two 15pf and 5pf ceramic capacitors.
A tuning cap (variable capacitor) is not needed in the circuit, because you can replace it with a ’15pf’ ceramic capacitor, but if you want change the frequency of your transmitter, then gently spread the ‘spacing‘ between the turns of coils.
Needed Parts List
T1 – S8050 NPN transistor
VC1 – use a ’15pf’ ceramic capacitor (not SMD)
L1 – coil, get a pen refill(must be 3mm diameter) and a short length(1mm thick) copper wire,wind exactly ‘6 turns’ over the refill and scrap its both ends with a blade. Done!
C3 – 5pf ceramic capacitor (printed exactly ‘5’ on it)
C4 – ceramic capacitor ‘104’ (printed just ‘104’)
C1 – use an SMD one (just an smd capacitor)
C2 – 22n Ceramic
R1 – 47k SMD resistor (printed ‘473’)
R2 – 100 ohm (printed ‘101’)
ANT – a short length wire
3V ~ 9V supply (use only battery)
Here is the completed circuit which i made, It has more than 1 km range with a long antenna and a 9V powersupply
Note: a mic may be added in the circuit to transmit your voice, but you have to modify the circuit for this purpose!