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Roy Lewallen · December 12th 07, 09:55 PM posted to rec.radio.amateur.antenna

wrote:

I see your point. I assumed that the phase change specific to the
discontinuity was the same for all -j567 impedances. I do not have the
information to say it is true (or I lack the tools to prove it).

To end up with -j567 on a 200 ohm line, you must use 19.2 degrees of
length. 19.2 degrees of 200 ohm line brings you to -j2.84 on the smith
chart. Then, 200* -j2.84 = -j567. To get -j567 on a 100 ohm line, you
only need to go 10 degrees, corresponding to -j5.67 on the smith
chart. The 100* -j5.67 = -j567. Although we know that the 200 ohm line
is longer by 9.2 degrees, there is no indication that the length of
the 600 ohm line must or must not change. I cannot know that unless I
know the change in phase angle at the new -j567 discontinuity with the
200 ohm line. I do not have enough information on that without
additional measurements. I would need to measure it to to system
resonance (1/4WL = 90 degrees), as was the case using the 100 ohm
line. I was assuming that the phase change at the discontinuity would
not change but it is not immediately obvious that it will or will not.
But, assuming (rightly or wrongly) that the phase angle at the
discontinuity did not change and stayed at 37 degrees, you would have
had a new length of 600 ohm line of 90-37-19.2= 33 degrees which at
VF =1, l = 33/360*75 = 6.875m. I cannot make that assumption right
now. I would have to resort to measurement, same as was done with the
600-100 ohm combination.

In any case, this does not disprove the basic premise of the existence
of a phase change due to the impedance discontinuity. It does prove
that my minor point of elaboration may have had a false
assumption.Sorry for any confusion.

Sorry, I'm having trouble following that. But:

-- IF there's a phase change at the impedance discontinuity (which I
assume means the black box terminals), it's the same for all four (your
three and my one) black boxes. Whatever conclusions you might have drawn
about the relationship between the phase change and the contents of the
boxes, other than the impedance at the terminals, are wrong, and you
should investigate where you went astray in the process of reaching
those conclusions.
-- If you think you can distinguish the boxes by measurement (at the one
single frequency at which all their impedances are the same, in steady
state), show exactly how you'd do it and what the results would be. I
claim that you can't.
-- If the four boxes have different numbers of "electrical degrees" at
the same frequency, then "electrical degrees", as the term is used here,
is something you can't measure. That seems to be the case. And if you
can't measure "electrical degrees", how do you determine how many of
them are "missing"?

Of course, "electrical degrees" does have meaning. But like a number of
other terms, some newsgroup participants have made up alternate meanings
and given them properties which are nonsensical.

Roy Lewallen, W7EL