I decided to design quite simple (but still efficient) output (TX) PI-type low-pass filters for all five basic HF bands (i.e., 80, 40, 20, 15 and 10m bands). They had to meet the following assumptions:
to be as simple as possible (they are only 3rd order filters),
to keep the values of the used L/C components very close to those from E6 or E12 groups.
The above assumptions were stated in order to help to apply these filters in simple QRP or QRPP transceivers with the use of standard (ready-made) L/C low-power components.
Here below you can see the solutions with the following filters’ magnitude and phase characteristics, simulated with the application of LTSpice professional tool:
If power amplifier (PA) in your transmitter (TX) works quite linearly (in A or AB class) and/or with small QRP/QRPP power – it can be perfectly simple and cheap solution for you!
