On 7 jun, 19:46, Richard Clark wrote:
On Mon, 7 Jun 2010 09:19:59 -0700 (PDT), K7ITM wrote:
As Wim has pointed out, requiring an amplifier to be loaded and driven
in a very particular way unnecessarily dismisses some very important
classes of amplifier. *

This is the standard rebuff with "the rest of the world works
differently" distractions to Walt having stated a premise, described
initial conditions, taken measurements, and having shown the data
supports his hypothesis. *The hypothesis is dismissed through shifting
initial conditions to suit an avoidance of committing an honest answer
to Walt's specific and very explicit observation.

Walt, if this community were pressed for an "up or down" vote:

* "Does Walt's data support the evidence of a Conjugate Match?"

then you would be out in the weeds with your only supporting vote from
me (and maybe from others who would do this by email). *

I doubt this will set off a stampede to the ballot box, but what few
votes are stuffed in, I bet they will have the "up or down" stapled to
a dissertation of "however...."

To this last, if I sinned in that regard, I used only Walt's data, his
equipment references, and his citation sources. *As no one else seems
to tread that narrow path, much less commit beyond grandiose
statements, I don't feet too bad.

73's
Richard Clark, KB7QHC

Hello Richard,

I think, most people that are willing to read will support Walt's
statements on output impedance of an amplifier under matched output
power (given a certain drive condition). However there are many
practical circumstances where Walt's conditions are not met.

As soon as you change the drive (for example during an AM or SSB
transmission), your matching is no longer guaranteed, especially when
using circuits with current behavior (tetrode/pentode, common grid,
etc). See my EL34 posting. Note that under practical circumstances,
this is no problem.

As soon as you change the load (without changing the matching), you
may run into current or voltage saturation, of course depending on
phase of VSWR. As you know many people use non-tune solid-state
amplifiers, so they don't have the possibility to tune/match for
maximum output given certain drive. That means, live with it, or use
an external tuner where you don't tune for maximum power, but for
minimum VSWR presented to the PA.

Amplifiers for constant envelope modulation use saturation to increase
efficiency (and accept the loss in gain). These are deliberately used
under mismatch, therefore the gain is less with respect to a non-
saturating approach. You can also see this from the Pout versus Pin
curve for FM transistors. I know that severak CB owners retuned (or
even modified) the output stage to get 1 dB more power, but they did
forget that the final transistor had dissipate 2dB more. Result: some
japanese transistors became very popular (2SC1306, 1307, 1969, etc).

High efficiency circuits are the extreme case and are entering the
amateur world. Active devices behave like switches, output impedance
can have every value as long as it is close to the edge of the passive
Smith Chart. Amplitude modulation with these topologies can only be
done via supply voltage modulation. Tuning for maximum power with an
external tuner will surely destroy the amplifier if no protection is
present.

For me it was a surprise how this thread developed.

Best regards,


Wim
PA3DJS
www.tetech.nl