This whole topic has got me thinking....
Given that small signal RF generation is pretty much a non issue these
days, I have to ask why build amps intended to take a modulated RF
signal at significant power as the input at all?
Doing this makes a lot of really neat and highly efficient architectures
essentially impossible to implement cleanly and does not really save
much circuitry.
Would it not instead be better to have the radio output an I/Q pair at
baseband (Possibly as spdif or something) and simply tell the 'amp' what
the carrier frequency should be over CAN or RS485 or something?
This way the 'AMP' can play all sorts of EER/Class E/dynamic bias/
whatever type games and can implement ALC that actually works properly,
resulting is very much improved efficiency, and the overall chain
becomes simpler as the front end does not need (redundant) output
filters or in fact any significant heat generating parts.
Further, something like this could (because RF power is not being moved
from the exciter to the external PA) allow the link to be a simple
ethernet cable or such, making placement of the TX box close to the
feedpoint trivial.
There might be something to be said for building transmitters instead of
amplifiers.....
Regards, Dan.
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