How to Build a 100W FM Radio Transmitter

  • 2-4 hours
  • Intermediate
  • 50-100
What You'll Need
FM Radio Transmitter Kit (Usually composed of the the following: Circuit Board, Battery Clip, R1 to R7 resistors, C1 to C5 capacitors, Q1 and Q2 transistors, L1, Microphone Electret or Omnidirectional Sub-mini Electret)
Non-conductive tool
Soldering Tool
Soldering Paste
Enclosure Box
Emery Paper
Mini Drill

A 100W FM radio transmitter can be used to transmit music from other audio devices to a car stereo or any other radio device. A FM radio transmitter usually sends radio signals at a range of 10-meters to 20-miles, depending on the type of antenna used. Here is how to build a 100W FM radio transmitter.

Step 1 - Purchase an FM Radio Transmitter Kit

Check the Internet or a nearby electronics shop for an FM radio transmitter kit designed for 100W. Capacitors, transistors and resistors come in variable wattage. Compare the wattage written on these components to the list of components on the assembly manual. If they don't match, return the kit and ask for a replacement.

Step 2 – Read the Assembly Manual Properly

The assembly manual should come with an illustration or a diagram of the circuit board, with a legend of where each component will go. If there is an R1 legend, then this means that a resistor with an R1 label should be soldered to that position.

Step 3 – Inspect the Circuit Board

The circuit board is where the pieces of the radio will be soldered. Notice that it has very thin layers of copper wires that run like a maze or puzzle all over the circuit board. Familiarize yourself with the connections on the circuit board to know where to solder or connect the transistors, capacitors, resistors, diodes, power supply and every other miscellaneous part.

Step 4 – Set the Trimmer Capacitor

Start by screwing the trimmer capacitor, the C4, onto the board. Search for a blank space with the clearest reception and then set the receiver. If adjustment has to be made (to get the clearest reception), adjust the C4 capacitor with a ceramic, non-conductive tool. It is time to set the rest of the pieces in place.

Step 5 – Connect the Pieces

Clean the leads of each component with emery paper before inserting it to the right slot on the circuit board. Refer to the manual for the wiring diagram to check if the component is placed at the right location. Bend the leads of the component correctly and place it on the circuit board. Apply a small amount of paste on the leads and heat the soldering tool. Place a small amount of solder on the tip of the soldering gun and apply it to the leads. Allow it to cool down.

Sometimes, some of the pieces leads have a larger diameter and may not fit into the holes on the circuit board. If this happens, use a mini drill to make the hole a bit larger to accommodate the leads. Be careful not to make the holes too large, as it may cause difficulty when soldering.

After every part is soldered onto the circuit board, connect the other parts, such as the power supply and other component listed on the manual.

Step 6 – Fit the Transmitter into the Enclosure Box

After finishing all the connections, fit the transmitter into the enclosure box to ensure that the finished product is protected from external elements. Test the transmitter to see if it works.