On Apr 2, 4:52 pm, Cecil Moore wrote:
K7ITM wrote:
You haven't moved beyond that "first amplifier that is taught in EE
202"?

If one can understand the simple amplifier then one
can move on to a more complicated amplifier.

If your goal is to deliver as much clean RF power to the external load
as you can, why would you put an RF-dissipating resistor into your
amplifier?

My goal is not to deliver as much power as possible.
My goal is to understand the nature of the source
starting with the simplest one.
--
73, Cecil http://www.w5dxp.com

If your goal "is to understand the nature of the source starting with
the simplest one," why would you add resistors you don't need and make
it more complicated than the simplest one? What if "the simplest one"
turns out to lead you into believing generalities that are not true,
when considering a more general one will avoid that?

My goal, in the context of Owen's basenote, remains to deliver as much
clean RF power to the external load as I can. Unnecessary resistors
need not apply. Matching networks better pass muster with respect to
their performance not only at fundamental frequencies, but also at
others, especially at harmonics. Not all the networks I've posted
about in this thread do pass muster, but are enlightening with respect
to Owen's observations, I believe. Simplest doesn't remain
interesting for very long.

FWIW, I don't see anything in Owen's postings in this thread that
_precludes_ a source impedance that's equal to some particular load
impedance, or to its conjugate. Rather, I see a suggestion that the
source impedance does not necessarily have to be equal to any
particular value, and in the general case does not have to be equal to
the conjugate of the design load impedance. With that I agree. I've
seen a great many examples of it. I gave a few of them earlier. I've
also worked on the design of broadband RF amplifiers which are
designed specifically to be 50 ohm resistive sources, through the use
of feedback to set that impedance. You don't need brute-force
resistors to do it; most of the time, you don't need to do it anyway,
but in the case of instruments used for measurement, it can be
important. In the case of video amplifiers where ghost-causing
reflections are to be kept to a minimum, it can be important. In the
case of a ham narrow-band SSB, CW, FSK, FM or AM transmitter, I
question whether the source impedance is ever important, or is ever
accurately known. Perhaps someone can convince me otherwise, though a
well-thought-out, well-presented example.

Cheers,
Tom