My W6JL amp didn’t seem to quite meet the spurious emissions limits in Australia with the 2nd harmonic a few dB short of 50dB down, though this was at the limits of my test equipment. This was a bit of a mystery as a 5 element LPF should have easiy taken care of the remaining 2nd harmonic.
Using the scalar analyzer neatly reveals why:
The filters are being rebuilt as 7 element pluggable units and with hopefully better construction this will be the end of that.
Measuring the new 20m LPF i became suspicious of the results and it turns out the buffer amp in the analyzer is not ideal and is being affected by the load.
Remeasured filter but with a 6dB attenuator after the amp:
I’ve now convinced myself that what i’m seeing of the 2nd harmonic is actually artifacts of the test setup. In any case, I’m moving to higher order LPF anyway.