[Amps] SS amps and auto-tune. Is it even necessary?

[Steve Thompson]

I think Manfred has a point - where the harmonics aren't going 
into a load and are being 'reflected' by the harmonic filter, I 
think the phase between fundamental and harmonics matters. The 
right relationship can enhance Po and linearity, the wrong one can 
hurt badly. It's not as simple as looking at what the filter is 
presenting, there's also the effects of matching circuits going 
back to the drains.

With the hf bands being mostly narrow frequency segments, it 
should be possible to tweak the filters for optimum results. In 
broadband systems such as commercial or mil use, that's difficult 
and it's quite usual to have to find fixes for frequencies where 
an amp struggles when presented with harmonic filters.

A real convenience of diplexer harmonic filters for the 
experimenter is that you can develop a broadband circuit running 
into a dummy load and then get very similar results when you hook 
up the filters and antenna.

Steve

> Gentlemen,
>
> The real issue here in respect of this excellent discussion about diplexer
> termination of harmonic energy is the profound impact on IMD and linearity.
>
> These MOSFET and LDMOS RF power devices have non-linear voltage dependent
> parametric capacitances that engender intermodulation distortion generation
> and reflected harmonic energy control plays a key role; efficiency is just
> one parameter consideration in the overall design objective that must be
> judiciously balanced.
>
> Leigh
> VK5KLT