Dave,
Mathematically, it is impossible to implement the necessary filters at RF
[and have them track frequency-wise for ham-band use (assumed to be under
microprocessor/computer control)], to implement the high efficiency SSB
amplifier as you suggest.
There have been described "realistice" methods of developing high efficiency
SSB amplificaton using Class D, E, F, or S. These are all switch mode
designs, and evolve around four basic techniques: (1) envelope elimination
and restoration, (2) envelope feedback, (3) envelope tracking, and (4)
outphasing. Of the four, only (#4) lends itself to class C (as well as
D/E/F)and has been used commercially years ago in the 'RCA "Ampliphase" '
broadcast transmitters and in certain microwave systems. The cost of the
circuitry external to the "ham variety" SSB exciter would hardly justify any
of these methods, at least for amateur purposes.
Worthy of note: newer AM power amplifiers in use today in the AM broadcast
service have been designed for improved efficiency over class C by using
class D designs.
73, Dave, K1FK
Fort Kent, ME
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