> "Tokyo High Power marketed a cathode driven 2 X 4X150/4CX250 amp that had
> IMD
> on par with grid driven.
I did a "double-take" the first time I had seen one since Tokyo Hy-Power is
more commonly known as a SS amp manufacturer. What's really got me excited
is the use of adaptive pre-distortion in the new ADAT ADT-200A transceiver.
The transceiver is now in production and has the ability to sample RF at the
output of an external amp and apply complimentary non-linear distortion to
offset inherent non-linearities in the PA chain between the rig and external
amp. Adaptive predistortion is being used in the digital broadcast
industry, although its root can probably be traced to the MIL sector.
Typical 3rd-order IMD coming from the ADT-200A's 50-watt SS PA is -55dB,
although specification is -45 dB. If the typical figure is correct, that's
~ 20 dB better than most commercial amateur SS HF amps. But the real power
of that type of algorithm is its extension to any external SS PA. So, it
would seem quite possible that one could utilize the ADT-200A, coupled with
say...a Tokyo Hy-Power SS kilowatt amp and achieve IMD numbers unheard of
with some of the best vacuum tube designs.
Hopefully, one or more of the adaptive pre-distortion techniques being used
are not subject to patent protection and associated licensing fees. It
would be a great time to incorporate this technology into all new SSB
exciters.
Paul, W9AC
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