Though modern commercial FM radio stations utilize more sophisticated and advanced means of broadcasting than they did in the past, the most basic concepts can still be used to create a working transmitter. In an FM broadcast, the amplitude of the signal remains constant while its frequency varies, or modulates, and with the right tools and skills you can build a transmitter with an output signal adjustable to any point within the 88 to 108 MHz range of the FM band.

Instructions:

1.Obtain a printed circuit board complete with pre-drilled holes and a layer of conductive copper. You'll also require the necessary capacitors, resistors and transistors -- refer to the circuit diagram of the particular transmitter you plan to build to get the specific types and quantities needed of each (i.e. eight resistors varying from 1K to 100 ohm to 1 Meg), as well as the other required materials.

2.Wrap the 22-gauge solid wire around a 1/4-inch diameter bolt, using the threads of the bolt to create the coil of approximately 8 to 10 loops. Insert each end of the coil into holes at the upper right-hand side of the circuit board and remove the bolt. This coil will serve as L1 on the circuit diagram.

3.Insert a small, screw-adjustable trimmer capacitor into holes to the left of the L1 coil, near the coil's middle, and insert a ceramic capacitor below that. The former will serve as C4, which can be adjusted to create the best reception for the receiver, and the latter will be C5, which, along with L1 and C4, determines the oscillation frequency of the transmitter.

4.Insert the other transistors, capacitors and resistors on the circuit board, in the positions specified by the diagram. Use 2N3904 bipolar transistors for the Q1 and Q2 positions, and the specific capacity resistors (100k, 100 ohm, etc.) required for each of the R1 through R7 (or more, for larger transmitters) positions.

5.Insert the Electret microphone at the bottom left side of the array, below the C1 capacitor and to the left of the R3 and R5 resistors, and insert the positive and negative leads to the battery clip at the upper left side of the array. Insert a small wire (approximately 8 to 18 inches) on the right side below the coil to serve as the antenna.

6.Turn the circuit board over to expose the bottom side, taking care not to dislodge any of the added elements. Use a soldering iron (with a power not exceeding 25 watts) to solder the leads of the various elements together, creating a grid between them. Keep the iron's tip clean at all times, using a sponge to also keep it wet. Cut off any excess from the leads if they extend through the bottom.

7.Attach a battery (9 volt, for a small transmitter, more for a larger one) to the battery clip and test the transmitter by speaking into the microphone, listening for output on a nearby receiver. Adjust the C4 capacitor to improve reception if necessary.

Prev:Radio Waves: AM Vs. FM

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