Building a LC-Filter for your nrf24l01+ pa/lna module

Follow up on Fixing your cheap nrf24l01+ pa/lna module.

Theory

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.

Material

axial-lead-inductorBecause 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.)

 

  1. 3.3µH Axial lead inducter
  2. 220µF capacitor

Building

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.

lc-filter-schem

Simulation

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.

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3 Responses to Building a LC-Filter for your nrf24l01+ pa/lna module

  1. Pingback: Fixing your cheap nrf24l01+ pa/lna module | the ugly fix

    • Oitzu says:

      Well basicly both would work but your seems to be quite a little bit better in the simulation, yes.

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