K7ITM wrote:

Low level modulation is a huge waste of RF power?? Hey, _AM_ is a huge
waste of RF power, and of spectrum to boot! Except with unusual
modulating waveforms, 2/3 of the power is in a useless carrier. Now,
compared with plate modulation of the PA, low level AM modulation
followed by a linear amp may be somewhat less efficient (though a waste
of DC power, not RF power), but remember, the modulator, presumably
being a linear audio amplifier, isn't all that efficient either. In
addition, there ARE ways to generate AM with low level modulation and
efficient RF amplification--they have been used in AM broadcast
transmitters.

For the cost of a good high-level modulator, how many kilowatt-hours
can you buy?

Cheers,
Tom

The only modulation method that I've ever found to be of any real efficiency
in generating AM is "outphasing" or "ampliphase". You can use the /most/
effective PA designs - optimised FET-based Class E stages can be over 90%
efficient! This approach completely obviates all the problems with
modulation transformers or big chokes. Haven't tried it with valves
("tubes" - US) - perhaps that should be a future project.

Bob

--
Everything gets easier with practice, except getting up in the morning!