On 4 mayo, 01:11, dave wrote:
On May 3, 2:01*pm, Wimpie wrote:

On 3 mayo, 02:09, Cecil Moore wrote:

On May 2, 5:23*pm, Wimpie wrote:

I am very sorry Cecil, but I still don't see the point where the
discussed method may go wrong.

Everyone seems to be charging ahead, willy-nilly, without seeing the
point which is that there are other effects present besides
reflections.

I think most of the discussion is ignoring lots of things... first of
all you must answer the question; Does it really matter? *If it does,
then i will assume that you are a designer and know how to apply the
tube characteristics to come up with a design that matches your
selected tube to the expected load... but does that process really
ever describe the 'output impedance'?? *Then you must also consider
the tuning parameters employed... sure, you can measure the output
impedance at a given operating point, but answer the question again;
Does it really matter? *Or do you need to measure it over a wide range
of operating conditions? *Every operator i have seen tune up one of my
amps has done it a little bit different... heck, i don't even do it
exactly the same twice in a row i bet. *So when i am running an amp
into a switchable set of 7 different antenna combinations on a given
band, can tune from one end of the band to the other without touching
the settings, and can make an infinite number of small adjustments to
the drive, tune, and load settings, and on some bands can tweak a
tuner after the amp to 'make it happier', do I really care what the
'output impedance' really is? *As long as the matching network
provides adequate adjustment so i can get out the desired power into
my various loads while keeping the tubes within their operating
limits, do i really care what the 'output impedance' really is at any
one set of conditions that i may never exactly duplicate again? *I
think not. *So this boils down to an academic discussion, and as in
many cases where no one has, or can, make an exact statement of the
problem the specific answer remains elusive. * So consider this, until
you have a complete statement of the problem you will never be able to
derive a value that any two of you will agree on, let alone actually
try to set up a measurement of.

Hello Dave and John,

When you look to my first posting to this thread, you may conclude
that I agree with you.

We had such a discussion about a year ago where I stated that most RF
amplifiers do not have 50 Ohms output impedance. That statement was
heavily disputed by some persons. I tried to support that statement
with simulations, but without any success.

Regarding the "academic discussion" I also agree. In my professional
career where I designed several RF PA's, only 2 times the output
impedance of the amplifier was of importance. In one of these cases I
couldn't meet the specs and had to insert attenuation (some waste of
power…).

The thing I don't like is that some people criticize methods used by
some of the group members without a solid foundation.

Regarding the two-port single-port issue. One can setup a reasoning
based on a two-port setup, but that significantly complicates the
matter without giving any additional insight. I tried to keep it
simple by referencing to a VSWR measurement (with an antenna analyzer)
of an antenna when a strong transmitter is nearby, but it seems I
wasn't clear enough for all people following this thread.

With kind regards,


Wim
PA3DJS
www.tetech.nl
Remove abc first before setting free the pigeon.