On Thu, 13 Oct 2005 09:53:08 -0700, Richard Clark
wrote:

Owen,

To respond to your last question:
Has anyone experimental evidence to the contrary?
is consistently NO. Your own time at the bench has already drained
the pool of ability in that regard. Your only expectation ever after
having bellied up to the bench is to watch your work being gummed to
death.


I fully expected someone to object, not only to object, but to do so
without any original experimental evidence and to devalue the
experiment that I did so that some readers who do not have even a
meager understanding of transmission line theory fall to being
convinced by whoever is most tenacious is defending their position.

However, for completeness' sake, and as no one here really understands
what accuracy is about anyway, there is one factor to be considered.
The numbers offered verge on the limit of the Bird's ability to
resolve a power anyway. There is a built in probability of ±5W of
error from the get-go, and any snake oil salesman can craft an
argument leveraging that error to prove anything. We have seen that
±5W error in the form of an argument that uses both + and - (not
simply one or the other) to please a theory.

Owen, the same experiment with a deliberate mismatch of 3:1 would be
just as effective at busting the myth AND providing data that
overwhelmed the inherent meter inaccuracy.

Indeed, and I considered a number of other experiments that did so,
but this one was based on components at hand, and should have been
easily understood by a person with the most basic understanding of
transmission line theory. It was important to surround the Bird with
line different to 50 ohms.

I expect the argument to twist an turn, to focus on everything but the
assertions that:
- there should be approximately a 50+j0 Z presented to the load side
terminals of the Bird Thruline (ie the ratio of V/I is 50+j0 where V
is the net or forward and reflected voltages, and I is the net of
forward and reflected currents);
- the Bird Thruline is a 120mm section of 50 ohm transmission line;
- in the region of the Bird Thruline sampler element, the ratio of V/I
is approximately 50+j0;
and that the observed Bird 43 readings were reasonably consistent with
those assertions.

The arguments that knowing that the Bird measurements are valid at the
point of measurement is of little value are unrelated to the issue and
a diversionary tactic, but wrong nevertheless. I won't add to the
diversion to identify them.

I will extract the essence of the analysis and write a separate web
page on it that may in the longer term assist others in their
development, go being "gummed to death" doesn't totally devalue the
information behind the case, and it might just be the cost of exposing
the proposition to review.

Thank you for your support.

Owen

PS: I am planning my next mythbusters (oh no! I hear...) Myth: SWR
meters measure SWR. Now this is not to bag SWR meters, I think that
they are very useful instruments, but they have limitations, and the
greatest problem is not the meters, but probably the knowledge base of
those (ab)using them.
--