As many wish to make the cheap PA-70, PA-100 type Chinese SSPA using IRF530 based MOSFET. I always advise them to never operate a SSPA without final LPF. We do not want to ruin the spectrum (already it is filled with noise) not to interfere with other bands. Review of the kit type LPF sold in Aliexpress doesn’t sound good and needs a lot of tweaking. So I decided to design and make my own filter.
This PCB is designed to accommodate a 5th order/pole Chebyshev or Elliptic/Causer low pass filter covering 80m to 10m. For each capacitor C, 4x 1206 SMD pad is provided for parallel placement to achieve values. This will also increase the current carrying capacity. As dip silver mica capacitor is somewhat rare to find now a days and often comes with a premium price – I chose to use NP0/C0G MLCC. For 100W, 3-4 parallel 1000V MLCC should be fine. If you wish to make it dumb proof then chose higher voltage capacitor, price difference between 1000v and 3000v MLCC is not much.
Toroid cores upto T-106 should fit incase you want higher power. T-80 should be ok for PA-70 and such.
Inductor detail:
80m 23T on T80-6
40m 17T T50-6
20m 12T T50-6
15m 9T T50-6
10m 8T Air core, on 8mm drill bit
Please use multiple (2 to 4) parallel capacitor of Silver Mica or NP0/C0G MLCC to achieve each vale as close to the schematic. Beware of the PCB stray capacitance (In my PCB it was around 10pf), you must compensate it. Better is to check the final value with LC meter before soldering the inductor.
Measurement:
Will go here
Click here to download PCB gerber files.
