PI Filter Designer is a simple 3 element 50 ohm input and output impedance pi filter designing application. This program allows the user to design simple lowpass filters by selecting from a variety of standard capacitor values either empirically or to suit what you have on hand. The filter 3 dB cutoff frequency and required L1 inductance are automatically calculated and displayed. In addition, the user may select an additional capacitor value to put in parallel with both caps C1 and C2. In this app XL = XC = 50 ohms impedance. No other impedances can be calculated with this program.
This small app is for designing simple 50 ohms input and output impedance pi filters for RF applications. Suggested uses include following VFO’s or lowpass filtering transmitter output. Two filters may be connected together in series for further lowpass attenuation. This app allows the user to build filters from the capacitors that you have on hand. Standard value caps are given plus a second capability which allows the user to parallel additional capacitor values to allow a variety of cutoff frequencies to be chosen.
Using this program:
Use the drop-down combo box to select the primary capacitor values for C1 and C2 and observe the cutoff frequency and required inductor for a 50 ohm inductive reactance at the cutoff frequency.
Use the second combo box on the right of the schematic to parallel other capacitor values with both C1 and C2 in the schematic. The capacitive reactance of the capacitors plus the inductive reactance of the displayed inductor always equals 50 ohms in this program.