Hobbies And Interests
Things You'll Need
Instructions
Purchase the components. Several hobbyist websites sell FM transmitter kits for beginners. These sets include all the necessary electrical components and a printed circuit board. You will likely have to buy the soldering iron and solder separately if you do not already have them. If you are not using a kit, the components you need will depend on the circuit design but will include at least a voltage supply, an antenna, a capacitor, a trimmer, a resistor and a microphone.
Design the circuit. If you are building your transmitter from scratch, then you need to design a circuit that can capture sound waves and translate them to an FM receiver you have either built or purchased. Eagle PCB is an excellent computer-aided design package for drawing clear, professional looking circuits that can easily be transferred to homemade PCBs.
Install the 2n3904 transistor first. First, insert the leads of the transistor through the designated holes in the PCB, then bend the leads to hold the transistor in place. Apply solder to the underside of the PCB where the transistor's leads come through. After the solder has cooled, snip off the excess wire leads with a wire cutter. The components of an FM bug transmitter sit on a extremely small piece of circuit board and thus can be very difficult to solder. In such cases, a helping hands device with a magnifying glass is useful. Some electronics stores sell helping hands units that come with two adjustable arms with alligator clips for holding PCBs in place and a magnifying glass that will allow you an even closer look at what you are soldering.
Install the 4.7 picofarad ceramic disk capacitor, which sits right against the flat side of the transistors. Solder in the same manner as the transistor.
Solder both the 360R and the 4.7 kiloohm resistors to the circuit board. Save space by standing the resistors up on one end, inserting one lead through the hole. Then bend the other lead down parallel to the resistor and insert it through its other designated hole in the PCB.
Solder the 1 nanofarad ceramic disc capacitor to the PCB. This component is located right against the rounded side of the transistor.
Soldier the 22 nanofarad axial ceramic capacitor at the other end of the board.
Solder the 5-30 picofarad air trimmer to the PCB.
Solder the 10 mm microphone. The microphone captures sound waves and translates them into an electric current that is amplified while moving through the rest of the circuit.
Solder the 6-turn coil to the PCB. You can construct a simple coil by taking a length of 0.6 mm copper wire. Wrap the wire six times around a 3 mm drill bit. Remove any enamel from the ends of the coil before soldering it to the board.
Solder the 35 cm antenna wire to the PCB. Most antenna wire comes with a plastic coating. Use a wire stripper to expose the portion to be soldered to the board.
Solder the 9-volt battery clip to the board. Double-check the clip for proper polarity. The red wire is positive and the black wire is negative.
Test the bug transmitter. Once all the pieces are soldered together, plug in the power supply (usually a 9-volt battery). Have a friend sit in one room with the bug and speak while you try to listen on an FM receiver in another room. The effective range of most simple FM transmitters is about 200 meters.