[Amps] Looking to build a Solid-State HF amp.

[Duane Brantley]

Hello everyone,

I'd like to build a solid-state HF amp using FET's, but want to do it
right.  I want to match the input and output impedance as best as I can.
But, in doing research, the first thing I ran into is: How do you determine
this?  I can't seem to find any equations for the input and two for the
output: 1) standard Ohm's Law - R=E^2/P  and 2) In a NXP (Phillips) app note
on making a 300 watt push-pull HF amp using BLF177 MOSFET's, they use Rload
= (0.85*Vds)^2/2Po   <-- Why twice the Po?  Does anyone have any insight on
this?  Are there any formulas for the input impedance?

My first amp will be the 300 watt BLF177 amp, but I want to better
understand what is going on.

Thanks,
Duane - W4DMB