Using a sharp tunable BPF after the LC LPF at the output of the generator I was able to measure the still present second order harmonics at -73dBc so third measurement ( at -24dB fundamental) is becoming limited by the 2rd harmonic still present but the first two measurements are only seeing internal generated second harmonic. 3rd harmonic remained invisible using the BPF so it must be much lower as was expected from the LPF.
Thanks for making me double check!
