Highfields Amateur Radio Club
Low Pass Filter Calculator.
The Butterworth filter has a frequency response which is as flat as mathematically possible in the passband with no ripple.
The Chebyshev filter has a steeper roll-off and more passband ripple (Type 1) or stopband ripple (Type 2) than a Butterworth filter.
The higher the order of the filter (thus the more complex / expensive) the tighter the filter is to the passband.
To use this calculator
- Select the order of the filter.
(9 is default and the maximum this calculator is designed for).
Chebyshev types must be an odd number, this will be rectified automatically if an even number is selected.
- Enter the Cut-off Frequency in MHz.
- Enter the Characteristic Impedance (Zo) in Ohms.
- If you're looking to use a Chebyshev filter then enter the maximum ripple you will allow
(If left blank, "0" or invalid number defaults to 0.2 dB).
- Click on the Butterworth or Chebyshev button in the yellow box and the figures will be added to the diagrams in picoFarads and nanoHenries.
Calculations will return exact figures, constructors will have to ascertain which available component values are suitable.