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How to Measure the Ripple of a Band-Pass Filter

The two types of electricity are alternating current and direct current. AC signals have a current that oscillates from positive to negative at a particular frequency. Electric currents can often be composed of mixed frequency AC signals. A band-pass filter is a device that can block electrical signals within a certain frequency range, and allows signals of other frequencies to pass. The signals that are allowed to pass can sometimes have a small ripple that oscillates with frequency. You can measure this with an oscilloscope.

Things You'll Need

Function generator
Oscilloscope
2 coaxial cables

Instructions

- 1
  Plug the coaxial cable between the output of the function generator and the input of the band-pass frequency. Plug a second coaxial cable between the output of the band-pass filter and the oscilloscope input.
- 2
  On the function generator, set an output frequency that the band-pass filter will not block. Set an amplitude of 1 volt on the function generator.
- 3
  Change the volts/division and time/division settings on the oscilloscope until you see a clear signal on the screen.
- 4
  Count the number of vertical divisions between signal peaks on the oscilloscope screen. Multiply this number by the volts/division to get the amplitude of the signal. Increase the frequency on the function generator in 0.1 hertz intervals, and measure the signal amplitude. Write down the amplitude for each frequency value. The amplitude should be rippling slightly. Subtract the maximum amplitude from the minimum amplitude to get the band-pass ripple.

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