Cecil Moore wrote:

Jim Kelley wrote:
As far as I know, V/I ratios don't "cause" anything.

They sometimes cause 'rho' which then becomes an end
result and not the cause of anything.

I disagree. Reflections are caused by real impedances not reflected
ones.
Have you changed your mind about this?

At a two-port
network with reflections, rho usually cannot be calculated
from the physical impedances involved.

It can certainly be done using the optical formulas for a pair of
boundaries.

For the two boundaries as a network, and we call rho at the first
boundary r12 and rho at the second boundary r23 then
rho(network) = (r12 + r23)/(1 + r12*r23) = 0. Note that if we use your
value for r12, the network generates a reflection. I note the utility
of negative rho in this example.

But, with a transmission line at odd multiples of lambda/4, rho for the
network would be at a maximum and the network equation would be
(r12 - r23)/(1 - r12*r23). In such a case you'd want to use a load
impedance that would provide a r23 of +.5. (x - 150)/(x + 150) = .5,
so x = 450.

The moral is be
careful about saying that rho causes anything. Rho may
be only the end result of everything.

No question that rho is the end result of a ratio of impedances. It's
been my view that, like the V/I ratios we were speaking about, rho is
not a cause but a result.

73, Jim AC6XG

Cecil Moore wrote:

Jim Kelley wrote:

There can exist no real point where the characteristic line impedance is
both 50 ohms and 150 ohms.

I agree, and using the same logic, there also can be no such thing as real
steady-state conditions. That doesn't keep us from using it as a real concept.

No, but it made it difficult for me to anticipate every possible
observation you might want to make about what goes on at such a point.

73, Jim

Richard Harrison wrote:
I am not persuaded that reflection is caused by anything other than a
physical discontinuity, but Terman includes "coupled circuits" in his
list, and I think this indicates a physical discontinuity may be
referred to a reflection point from elsewhere.

I see, yes. Interesting that he would distinguish and include "coupled
circuits". Why do you suppose he felt "coupled circuits" were somehow
different than other circuits?

73, Jim AC6XG

Jim Kelley wrote:
Cecil Moore wrote:

Jim Kelley wrote:
As far as I know, V/I ratios don't "cause" anything.

They sometimes cause 'rho' which then becomes an end
result and not the cause of anything.

I disagree. Reflections are caused by real impedances not reflected
ones. Have you changed your mind about this?

Where did I say rho causes reflections? I didn't! Your statement
does NOT disagree with my statement.

At a two-port
network with reflections, rho usually cannot be calculated
from the physical impedances involved.

It can certainly be done using the optical formulas for a pair of
boundaries.

Unfortunately, only the index of refraction of one of the boundaries
is known in my statement above. The index of refraction of the second
boundary is unknown, i.e. only the impedances at the two-port network
are known - the load is unknown.

No question that rho is the end result of a ratio of impedances. It's
been my view that, like the V/I ratios we were speaking about, rho is
not a cause but a result.

But earlier, I thought you said rho caused a result.
--
73, Cecil http://www.qsl.net/w5dxp



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Jim Kelley wrote:

Cecil Moore wrote:

Jim Kelley wrote:
There can exist no real point where the characteristic line impedance is
both 50 ohms and 150 ohms.

I agree, and using the same logic, there also can be no such thing as real
steady-state conditions. That doesn't keep us from using it as a real concept.

No, but it made it difficult for me to anticipate every possible
observation you might want to make about what goes on at such a point.

All that proves is that you are not omniscient. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Jim Kelley wrote:
I see, yes. Interesting that he would distinguish and include "coupled
circuits". Why do you suppose he felt "coupled circuits" were somehow
different than other circuits?

Additionally, exactly what does he mean by "coupled circuits"? Is a
perfect transformer a coupled circuit? I don't see why there would
be any reflections at a perfect transformer.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:
All that proves is that you are not omniscient. :-)

Do you know anybody who is? :-)

73 de ac6xg

Cecil Moore wrote:

Unfortunately, only the index of refraction of one of the boundaries
is known in my statement above. The index of refraction of the second
boundary is unknown, i.e. only the impedances at the two-port network
are known - the load is unknown.

Only if you've forgotten what you said it was. :-) If it's unknown,
how could you have known what it was a half wavelength away? We are
speaking about the problem you posed yesterday, right?

No question that rho is the end result of a ratio of impedances. It's
been my view that, like the V/I ratios we were speaking about, rho is
not a cause but a result.

But earlier, I thought you said rho caused a result.

I'll repost what I said. If you find something in error, please
advise. Thanks.

"To my way of thinking, rho is entirely dependent upon the impedances,
and the voltages (reflected voltages in particular) are dependent upon
rho. Not the other way around."

73, Jim AC6XG

Jim Kelley wrote:

Cecil Moore wrote:
All that proves is that you are not omniscient. :-)

Do you know anybody who is? :-)

I know people who think they are. :-)
--
73, Cecil, W5DXP

Jim Kelley wrote:
If it's unknown,
how could you have known what it was a half wavelength away? We are
speaking about the problem you posed yesterday, right?

No, we are speaking about a statement I made unrelated to the problem
I posted. For that statement, the length of the feedline is unknown
and the load is unknown. What is known is the forward power and reflected
power on each side of the impedance discontinuity.

No question that rho is the end result of a ratio of impedances. It's
been my view that, like the V/I ratios we were speaking about, rho is
not a cause but a result.

But earlier, I thought you said rho caused a result.

"To my way of thinking, rho is entirely dependent upon the impedances,
and the voltages (reflected voltages in particular) are dependent upon
rho.

You said "rho is not a cause but a result" but then implied that
voltages are caused by (dependent upon) rho. Seems to me, rho
cannot both cause a voltage and be caused by a (voltage divided
by a current) which is an impedance upon which rho is dependent.
--
73, Cecil, W5DXP