Easy method to higher harmonics supression #firmware #harmonics #txpurity


fyysik@...
 

Additional  suppression for 3-rd and higher harmonics in TX for lower bands (up to 14 MHz) can be done with minimal changes in code  of void setTXFilters(unsigned long freq) function.
Just don't switch off higher freq LPD when switching lower freq LPF:

else if (freq > 7000000L){
  digitalWrite(TX_LPF_A, 1); //was 0 in original code
  digitalWrite(TX_LPF_B, 1);
  digitalWrite(TX_LPF_C, 0);
  }
  else {
  digitalWrite(TX_LPF_A, 1); //was 0 in original code
  digitalWrite(TX_LPF_B, 1); //was 0 in original code
  digitalWrite(TX_LPF_C, 1);
  }

each additional filter adds less than 0.5-0.8 db losses in lower pass band.