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Homemade Low-Pass Filter

I made this filter for one of my friend. Unfortunately, we were below time pressure so I couldn't tune the S11 parameters properly. On the other hand, the cutoff frequency was correct and I am very happy that it worked well for his application. Take a look at the following images.

If you design a similar filter, make sure that the legs of the capacitors are as short as possible. It will help you to get better performance.




Smith Chart - Examples


1) Normalized impedance, short circuit



2) Normalized impedance, open circuit


3) Zin = ?, Z_l = (200+j100) Ω , Z_0 = 50 Ω, l = 2m,  λ_tl = 10 m

Oscilloscope - XY mode - images

Sometimes you have to try something, although it is not really useful. :) I used my sound card, Matlab for the signal generation and an oscilloscope in XY mode.










How to install GNU Radio

The installation of GNU Radio doesn't have to be straightforward. The following script works well for me. See the screenshot from GNU Radio website.

Screenshot GNU Radio