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How to Make an RF Frequency Filter

A radio frequency, or RF, filter is an electronic circuit that selects a narrow band of radio frequencies from a broader range of signals. A radio or television uses an RF filter to tune in one particular channel. The simplest of these circuits has a resistor, a capacitor and an inductor, connected in series. The capacitance value of the capacitor and the inductance of the inductor determine the circuit's resonant frequency, which is the frequency it selects. The circuit is called an "RLC" filter, where the R represents resistance, L represents inductance and C represents capacitance.

Things You'll Need

Solderless breadboard
1-microhenry inductor
1-microfarad, 50-volt capacitor
4 pieces of 22-gauge wire cut to about 10 inches
1K-ohm resistor
Labeling tape and pen

Instructions

- 1
  Insert the leads of the 1-microhenry inductor into the solderless breadboard. The holes in the breadboard are arranged so those in the same column are interconnected but adjacent columns are not. So place each lead into a separate column on the board.
- 2
  Set one lead of the 1-microfarad capacitor into the breadboard so it connects to one of the inductor's leads. Insert a 10-inch wire so it connects to the inductor's other lead. Insert the free capacitor lead into an unoccupied column. Set the end of a second wire into this column.
- 3
  Insert one lead of the 1K-ohm resistor into the breadboard column shared by the second wire and capacitor lead. Set the the resistor's other lead into a free column. Place one end of the third and fourth wire so it shares this column.
- 4
  Wrap a label tape around the first and third wires. Write "Input" on this label. Wrap a second label around the second and fourth wires. Write "Output" on the label.
- 5
  Connect the wires labeled "Input" to a signal source such as a radio-frequency signal generator or an antenna. Connect the "Output" wires to an RF amplifier or other radio-frequency circuit. With the 1-microhenry inductor and 1-microfarad capacitor, the filter's frequency is 1 MHz.

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