Follow up on Fixing your cheap nrf24l01+ pa/lna module.
The LC-Filter is a low pass filter and, like the name suggests, consist of a inductance (L) combined with a capacitance (C). In our case the 3.3µH choke and the 220µF capacitor.
A low pass filter will filter out high frequencies, like the 50 kHz ripple that a cheap switching voltage regulator generates, and will let pass low frequencies, like the 3.3V DC (0 Hz) you want.
Because the ripple generated by the switching voltage regulator has a relativ high frequencies of about 50 kHz you can use a small and cheap Axial lead inducter like the one shown left. (The ~50kHz are generated by cheap LM2596s clones, better devices have higher switching frequencies.)
- 3.3µH Axial lead inducter
- 220µF capacitor
Building a LC-Filter is easy you can place the LC-Filter on a tiny bit of prototype board, design it into your circuit or solder it directly into a piece of wire. Refer to the schematics below.
Low pass filter example in circuitjs.
Note: The typical noise sourcing from a cheap switching regulator will probably be higher then 25khz (more like 50khz and above) and lower in ripple then 1Volt (more like 0.1-0.2V) but the simulator is limited in its functionality and never the less it demonstrates quite well how the LC-Filter works.