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David Robbins wrote:
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"Dr. Slick" wrote:
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The tricky part is measuring this correctly, because you
would need an SWR meter that is calibrated for the same Z as
Zo.
It is not nearly that tricky. 'Revised' rho, as you state,
predicts 0 Volts across the capacitor. This will be easy to
measure with any AC voltmeter that can handle your test frequency.
Perhaps, but i'm interested in the forward and reflected
waves, which you can only get with directional couplers on a line of
the same Z as the Zo, i suspect. So even if you get 0 volts, there
are still fwd and rev waves.
But what if you do not get zero volts. Sort of messes up the
'revised' rho theory a bit, does it not?
the 'revised' rho predicts zero reflect 'power waves' as defined by
kurokawa... it says nothing about voltage or current waves.
So is kurokawa proposing two completely different rhos?
One for computing voltages and currents and the other for power?
even worse... the 'new' one is based on kurokawa's specific definition of a
'power wave'. this 'power wave' is obviously defined to avoid some of the
discussion we have been having when talking about forward and reflected
powers, but it is not 'power' as discussed in most other places. it is
instead a contrived wave formula specifically chosen to make power
calculations easier as kurokawa states just before defining the forward and
reflected 'power waves' as:
a=(V+ZI)/2sqrt(|ReZ|) and
b=(V+Z*I)/2sqrt(|ReZ|)
(subscripts 'i' left off all terms for readability)
these definitions of course make it harder to calculate the underlying volta
ges and currents, but make it easy to calculate power and power reflections
from a multi port network as you simply define the 'power wave reflection
coeficient' as s=b/a and the 'power reflection coefficient' as |s|^2. note,
at no point does kurokawa use rho. In one point just after defining s (eqn
11) and expanding it by substitution to s=(Zl-Zo*)/(Zl+Zo) (eqn 12) and
further into R,X terms (eqn 13) it is compared to the significance of the
'conventional voltage reflection coefficient', there is no mention that this
should replace the 'conventional' rho, nor that it should give the same
results.
i think the more important thing now is to point out to the arrl the error
of using that form of the reflection coefficient in place of the
'conventional' one in the latest antenna book so it doesn't become gospel in
the future.