asteriskHelp - RF Filters

Using the tool - Basics

  1. Click numbers then press the button for the data field you wish to update. For example, enter "2.0" then press the "F 3db" button to specify the desired 3 db frequency in Megahertz.
  2. Specify the load resistance RL in ohms. The source resistance will usually be the same as load resistance except for Chebyshev filters of even order (not recommended). If impedance transformation is required, use the Impedance Matching tool.
  3. Specify the "order" of the filter. The order indicates the number of poles in the transfer function affecting the steepness of the filter rolloff. it also indicates the number of parts needed to make the filter. Band pass filters requires twice as many parts (2 x order). Order must be 3 or greater.
  4. Select the desired filter characteristic: Low Pass, High Pass, Band Pass or Band Stop. Band Pass and Band Stop filters also require a lower 3 db frequency point to be specified. The filter configuration is shown in a figure at the bottom of the page.
  5. Select the desired filter type: Butterworth or Chebyshev. Chebyshev filters also require a Ripple tolerence to be specified.
  6. Filters can be implemented with the first component connected in a shunt or series configuration. The "First Shunt" checkbox selects which configuration you desire. The filter configuration is shown in the figure at the bottom of the page.
  7. A report at the bottom of the page summarizes the design. The components are listed in order of appearance from input port to output port and whether the component is connected in series or shunt. The component designation number such as "L3" inducates that the inductor is the third component encountered while traversing the schematic from input to output. See the filter configuration diagram. (iPod users can scroll the report textarea using 2 fingers)