On 14 jun, 02:13, Richard Clark wrote:
On Sun, 13 Jun 2010 14:08:59 -0700 (PDT), Wimpie
wrote:

This knowledge
resulted in my statement: "an RF PA isn't a 50 Ohms source", what was/
is heavily disputed by you.

Hi Wim,

Your conclusion:
"Under maximum power output matching given certain drive (not
necessarily being the maximum drive), the output impedance equals the
load resistor (the so-called "conjugated match condition")."

It was not the only conclusion, but it certainly disputes what you say
above.

Given the easy access to real amplifiers available to Hams at their
own bench, and further given that they do not present any more
complexity than your own simulation; then I have to wonder why we have
wandered into strange topologies.

My findings are from practice before I had the opportunity to do PA
simulations.

I am not interested in trying to follow 23 pages of dense presentation
where you could have simulated Walt's finals, validated or rejected
his data, and THEN formed your own conclusions. *If this is a problem
of simulation (you don't have that tube handy) what about topology? *

23 pages is not that much as graphs and circuit diagrams dominate. If
you can provide me a circuit diagram I will figure out whether I can
simulate it or not.


It looks more like a link coupled tank circuit from pre-WWII days. The
Tank Q looks to be non-existent. *When I rummage through the paper I
find 4.4! *This is certainly beyond the standard for PA design - and
we have swapped out of the tube into a mosfet (would you care to stick
to one objective?). *Elsewhere (wandering back in tubes) I find a
value of 10.3 (elsewhere it is 11) which inhabits the lowest margin of
good design. *Then an itinerant report of a cathode tank (????) whose
Q is 0.44. *Q appears to be of little concern.

Fully agree with the low cathode Q, therefore it doesn't affect the
simulations results significantly.


Again, typical Ham equipment shows Q as low as 10 - maybe, and that
would be for a dog; but those that I have seen typically fall around
15, sometimes 20. *As the Z transformation in plate/drain circuits
varies by the square of Q, this is not inconsequential and it once
again has me wondering why the strange topology?

Tell me what Q I should use (evt, give me component values) in the
simulation, and I will change it for you.


No, your paper lacks focus by trying to be all things (tubes, mosfets,
Class AB, Class C). *

This is to support my statement that under real world amateur
conditions many PAs do not obey ZL = Zout*. If I have some time I will
add a push-pull transfomer coupled amplifier also.

You examine the most inconsequential details as
if they were equally important as those details that bear on your
concern. *The paper lacks structure. *Headings are nothing more than
feature descriptions, not argument development. *There is a lot of
discussion of the idiosyncrasies of simulation - I am not interested
and that discussion creates the impression of hidden errors. *Really,
this stuff goes into an appendix not as the object of the narrative.
The graphs are pretty diversions, but they don't add much. *In the
software industry, this is spaghetti design.

I would prefer a conventional topology. *I suppose that has come
through clear. *Pick one significant point, re-edit this into 4 pages
and then you might have something interesting. *This advice comes from
one of our American writers, Mark Twain:
* * * * "If I had more time, I would have written you a shorter letter."

73's
Richard Clark, KB7QHC

simulation is general practice in the design flow, I know it has
limitations. Of course I could use ADS, but most people don't have
that at home, so I decided to use spice as this is used by many.

If you believe I am so wrong, why don't you present some simulations
to show that my original statement is completely wrong?

Best regards,


Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me.