On Sat, 12 Jun 2010 21:52:41 GMT, Owen Duffy wrote:

Richard,

The article does propose a practical tolerance. I quote the relevant
paragraph below.

"Of course, nothing is perfect so an acceptable tolerance for depending on
the assumed Zs=50+j0? for Mismatch Loss calculations might be that ‘forward
power’ doesn’t vary by more than 10% of the ‘reflected power’ at any point.
The worst case ‘reflected power’ for the experiment as described is 4%, so
a variation of ‘forward power’ by more than 0.4% (ie 0.4W in 100W) at any
point would indicate significant error in any Mismatch calculations based
on an assumed Zs=50+j0?."

Hi Owen,

Excuse me for incorrectly referencing your material as lacking in that
regard.

I explained in the articles how I am able to reliably detect such small
relative power variation. In one of the tests, the measured variation was
21%.

What is the residual VSWR of your directional wattmeter?

My intention in publishing the two articles wasn't to prove the propostion
one way or the other, but to show practical amateurs a test that they could
make with relatively simple equipment, one that is relevant to the
application of Zs if it was known, and an explanation of why it works so
that they can understand the test and make their own interpretations about
significance.

On Fri, 11 Jun 2010 20:31:42 GMT, Owen Duffy wrote:

However, that
proposition is easily proven wrong by valid experiments

But what lead us here was that you had proof, at least through some
third party (the experience of your having seen something that
diminished the "proposition"). I asked for that specifically. I have
not seen any reputable counter to Walt's data supporting the
"proposition."

The point remains that out of tolerance loads do not invalidate the
"proposition:"
On Fri, 11 Jun 2010 20:31:42 GMT, Owen Duffy wrote:

there is a proposition that a transmitter "designed/adjusted
for, and expecting a 50 + j 0 ohm load" can be well represented by a
Thevenin equivalent circuit and naturally has Zeq=50+j0.
In fact they announce themselves as violating the "proposition."

I hope this does not return us to the vacant adjectives, which as an
English major, I can full well argue to greater advantage. I don't
think that is productive, but choices remain to pursue them, or to
introduce new facts.

***********

Now, let's return to your paragraph, how do you know where the 50 Ohm
point was? You are relying on relative accuracy to make an absolute
measurement. This only works if you have a standard to make a
transfer from. Walt did this but it is arguable that his 1400 Ohm
resistor was, in fact, that value - however, he had the correct tools
to measure it.

Your two test results could be inverted (fail/pass for pass/fail), or
they could both be pass, or both fail.

I have calibrated many loads from DC to 12 GHz - and most of them
failed for many and sundry reasons and had to be "qualified." In the
vernacular of the standards laboratories that means a table of
correction values that are valid as long as certain characteristics
are met. I prepared many such lengthy reports as no one was going to
buy a new load each calibration cycle (typically 3 or 6 months).

I own one that met 1% accuracy out to 1GHz (@150W), but that was luck
of the draw and I wouldn't be so naive as to claim it retains that
accuracy - however, experience has revealed that with care it should.
Aging loads is like aging wine - there is no stasis. Here we get back
into subjectives, but I know the limits of care, and I know how to
practice it. If pressed to prove my inference of 1%, I also have the
skill to do so to that accuracy according to methods practiced by
Metrologists. It would be exceedingly tedious. Exceedingly tedious.
Or I could pay for it to be done.

73's
Richard Clark, KB7QHC