How to Build a High Powered FM Amplifier

By Simon Foden

Frequency modulation is a means by which information is transmitted over a carrier wave. That information can be digital or analog. Radio broadcast is a common frequency modulation application, although the signal is sometimes weak. There are three common reasons why your FM signal is weak: too much distance from the broadcast antenna, other frequencies interfering with your reception or your receiver is weak. FM amplifiers function like a signal booster, they strengthen the FM signal before sending it on to your receiver. You can build your own high powered FM amplifier to strengthen a weak signal.

Things You'll Need

  • Circuit wiring schematic
  • 9-volt battery snap
  • 9-volt battery
  • 30-by-35 mm circuit board
  • Solder
  • Soldering iron
  • Circuit enclosure
  • Standard electric drill
  • 3/4-inch standard drill bit

Step 1

Source your parts. You can purchase the circuit parts together from specialist audio project retailers. For example, the Quasar Electronics website lists a high-gain, 12-volt amplifier circuit. House the circuit in a protective enclosure, although these typically are not included with the circuit.

Step 2

Study the schematic that illustrates the layout of the circuit and how it is connected to the external devices.

Step 3

Turn on the soldering iron so that it is heated up when needed.

Step 4

Unplug the antenna from the radio and touch the tip of the soldering iron against the solder. Solder the tip of the antenna input to point No. 4 on the circuit board. Solder the jack of the antenna to point No. 3 on the circuit board. When forming a solder joint, gently press the soldering over the parts you want to connect. For example, connecting a wire to a board requires that you hold the iron over the wire and the board. The solder melts and forms a joint that fuses the wire to the board. Be careful not to drip any solder when moving the iron away from the joint. Solder blobs can interfere with the function of a circuit.

Step 5

Solder the radio output to the circuit board. Fix the connector that was previously attached to the antenna to the amplifier circuit. Solder the tip of the connector to point No. 5 on the circuit board and the jack of the circuit board to point No. 6.

Step 6

Power the circuit board. Solder the battery snap red wire to the positive eyelet on the circuit board and the black wire to the negative eyelet. Connect a 9-volt battery to the battery snap.

Step 7

Fit the amplifier circuit inside a chassis. If necessary, use a standard drill and 3/4-inch standard drill bit to create a hole in the side of the chassis to accommodate the antenna and radio connectors.

Step 8

Turn on the antenna and radio and tune to your desired frequency. The amplifier circuit will strengthen the signal it receives from the antenna before passing it to the radio for broadcast.

Tips & Warnings

  • Always solder in a well-ventilated environment.
  • Turn the volume of the radio down before powering it up with the new amplifier. The signal may be significantly stronger and louder than it was previously.