[Milsurplus] Smart People: Where'd the Harmonic Come From?

[Hubert Miller]

I don't know the output circuit of this transmitter. However I'm sure it is designed to work into a short reactive antenna.
Does it have a loading coil ? 
The loading coil must work against the capacitor in the 'antenna simulator',  Xc + R.  Loading coil must resonate with 
antenna or antenna simulator capacitance. Q of this sub-circuit is higher with a lower load resistance. Higher Q = better
harmonic attenuation. My thoughts, anyway.
Very interesting question, Dave.
-Hue