Brainteaser
 

"Jim Kelley" wrote in message
...

Cecil Moore wrote:
Yes, but the 200 joules in the line was previously sourced
by the generator during the transient state. It's hard to
sweep 200 joules under the reflected power rug.

So is this your proof that Joules of energy are likewise reflected from
antireflective surfaces?

No, the two subjects are conceptually only distantly related so your
posting is a diverting of the above issue - changing the subject back
to an earlier thread:

Every impedance discontinuity causes reflections. An antireflective
surface is an impedance discontinuity, i.e. a change in the index of
refraction between two mediums. If properly designed, the anti-reflective
surface causes 100% destructive interference between the internal and
external reflections each of which contain joules of energy. It is easy to
prove
that the internal reflection contains joules of energy. If the external
reflection
didn't contain any energy, then destructive interference would not be
possible. Therefore, both reflections associated with an antireflective
surface must contain an equal magnitude of joules.

In his QEX article, Dr. Best gave us the physics equation that governs
100% destructive interference: Ptotal = P1 + P2 - SQRT(P1*P2).
Assuming that power cannot exist without energy, if the energy in P1
equals the energy in P2 and the associated waves are 180 degrees out
of phase, then of course 100% destructive interference occurs at the
antireflective surface. That's how antireflective surfaces and Z0-matches
work.
--
73, Cecil http://www.qsl.net/w5dxp

Brainteaser
 

Richard,

I'm pretty sure steady state isn't
achieved in that short a time when there
are significant reflections on a line
that long.

Consider this. Initially, forward power
from a 100 Joule per second source is,
naturally, just 100 Joules per second.
After one second, (the first second in
particular), there should be 100 Joules
on the line.

It follows that the initial reflection
would be 50 watts. When we assume that
everything is re-reflected from the
source, then at two seconds the forward
power at the front of the line would be
150 watts. At four seconds, 175 watts;
six seconds, 187.5; eight seconds,
193.75, and so on.

When the number finally reaches 200
Joules per second at the load, the
reflected power would have become 100
Joules per second back at the source one
second earlier. At that point we can
multiply the sum of forward and
reflected power by the length of the
line in seconds and gleefully announce
that 300 Joules are being/have been
stored in/on/at the xmission line.

73, ac6xg


Richard Harrison wrote:

I`ll speculate that after one second, 200 joules are contained in the
forward wave on that line. Then, after two seconds, another 100 joules
has been reflected back toward the line feedpoint where it opposes
growth of power input to the line. Total joules on the line is 300.

Forward power minus the reflected power equals 100 watts being supplied
by the generator to the load with 200 watts forward power and 100 watts
reflrcted power in the line.

Best regards, Richard Harrison, KB5WZI

Brainteaser
 

In article ,
Jim Kelley wrote:

Expanding on my earlier response - For the first two seconds,
the source doesn't know it is looking into an open transmission
line so a 100 watt source would faithfully output 200 joules
into a one second long open circuit transmission line. That
200 joules cannot be destroyed. Is it mere coincidence that
the forward and reflected waves are 100 joules/sec*(one second),
exactly equal to the 200 joules supplied by the source?

But you're missing, or trying to
circumvent, the most interesting aspect
of the problem. It's the one which
highlights the very core of our
disagreement. The energy stored in the
line, remains stored in the line as long
as steady state is maintained without a
single Joule of additional energy moving
into or out of the line. To me, this
illustrates clearly how the fields at
the impedance interfaces of a matching
transformer can be maintained without
requiring multiple rereflections of
energy. I'm hoping some day you'll see
it too.

Jim,

How would your model view the case in which the source transmitted
into the T-line for 1.5 seconds (delivering 150 joules into the line)
and was then disconnected, leaving both ends of the T-line
open-circuited.

In this case, you'd continue to have 150 joules of total energy stored
in the line (modulo the amount of energy which does manage to radiate
out sideways). However, there would be periods (of 500 milliseconds,
one per two seconds) when the voltage near the source end of the
T-line, and the amount of current flowing through the T-line in this
area, were both zero. For the intervening 1.5 seconds out of each 2
seconds, there would be strong current flow through this portion of
the line (having a standing-wave characteristic for all but a very
short transition time on either end).

This state of affairs can, I don't doubt, be modeled purely as a
matter of interaction and interference between fields. The model
would appear to me to have to become extremely complex, in order to
produce the correct results at all points over the two-second
long-term periodicy of this system.

It can also be modeled as the effect of interference between forward
and reflected waves... and this is a somewhat simpler model to use to
describe systems such as this which do not exhibit a purely
steady-state behavior.

As far as I can see, *neither* of these models (fields, or reflected
waves) is fundamentally superior to the other. They are both equally
capable of producing an accurate description of the output of the
system at any point in time, given a set of inputs to the system.
Hence, by the usual standards of the validity of a scientific theory,
both models are equally valid.

Under certain circumstances, one model may be more "practically
useful" than the other. My impression is that your model of fields
may be more useful in looking at relatively local behavior (e.g.
within a wavelength or two) within a system that's at, or close to a
steady state. Cecil's preferred model of reflected power may be more
practical to use (i.e. simpler computations to produce a valid result)
when dealing with systems far from steady state.

In between those two extremes, it looks to me as if which model one
prefers is simply that - a personal preference.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Brainteaser
 

"Jim Kelley" wrote in message
...
But you're missing, or trying to circumvent, the most interesting aspect
of the problem. It's the one which highlights the very core of our
disagreement. The energy stored in the line, remains stored in the line
as long as steady state is maintained without a single Joule of
additional energy moving into or out of the line. To me, this
illustrates clearly how the fields at the impedance interfaces of a
matching transformer can be maintained without requiring multiple
rereflections of energy. I'm hoping some day you'll see it too.

You are, of course, talking about NET energy, and I agree with you about net
energy. But it is easy to prove we are NOT dealing with net energy by
observing
ghosting on a TV signal. It is easy to prove that multiple re-reflections
are
indeed actually occurring in reality.

Your argument is that if 5000 cars cross the bridge into the city during the
day
and 4990 cars cross the bridge out of the city during that day, that only 10
net cars have crossed the bridge in a day. I agree with your net figure but
note that the bridge cannot be replaced with a 1 car ferry boat operating
tens times per day which is akin to your above argument.
--
73, Cecil http://www.qsl.net/w5dxp

Brainteaser
 

"Jim Kelley" wrote:

I'm pretty sure steady state isn't achieved in that short a time when
there are significant reflections on a line that long.

I'm glad you brought that up. Here is the EXCEL spread sheet for that same
signal generator equipped with an auto-tuner. You are right in that it takes
a longer time to achieve steady-state but everything becomes completely
clear after 30 seconds and the results are exactly the same (using a 100
watt
signal generator).

http://www.qsl.net/w5dxp/1secsgat.gif
--
73, Cecil, W5DXP

Brainteaser
 

Very nice, Cecil. It would be also
useful to know how you obtained these
numbers.

73, ac6xg

Cecil Moore wrote:
"Jim Kelley" wrote:

I'm pretty sure steady state isn't achieved in that short a time when
there are significant reflections on a line that long.


I'm glad you brought that up. Here is the EXCEL spread sheet for that same
signal generator equipped with an auto-tuner. You are right in that it takes
a longer time to achieve steady-state but everything becomes completely
clear after 30 seconds and the results are exactly the same (using a 100
watt
signal generator).

http://www.qsl.net/w5dxp/1secsgat.gif
--
73, Cecil, W5DXP

Brainteaser
 

"Jim Kelley" wrote:
Very nice, Cecil. It would be also
useful to know how you obtained these
numbers.

The same way you obtained your numbers, Jim, when you said:

It follows that the initial reflection
would be 50 watts. When we assume that
everything is re-reflected from the
source, then at two seconds the forward
power at the front of the line would be
150 watts. At four seconds, 175 watts;
six seconds, 187.5; eight seconds,
193.75, and so on.

Please note that your numbers and mine agree exactly.
Also please note that I posted those numbers days ago
on qrz.com under a brainteaser thread. I have the EXCEL
file if you or anyone else would like to have it. (In a
one second long transmission line, when the load reflects
50 watts, it has essentially reflected 50 joules because
nothing changes during the following second.)

In fact, I'll present a challenge for you and everyone
else. In any one second long lossless transmission line
with any forward power and any reflected power, I defy
you to come up with an example where the number of joules
stored in the line is not equal to the forward power plus
the reflected power. Those joules are the joules sourced
by the generator that have not made it to the load. The
conservation of energy principle will have it no other
way. The laws of physics win once again.
--
73, Cecil http://www.qsl.net/w5dxp

Brainteaser
 

Cecil Moore wrote:
"Jim Kelley" wrote:
Very nice, Cecil. It would be also
useful to know how you obtained these
numbers.
The same way you obtained your numbers, Jim, when you said:

It follows that the initial reflection
would be 50 watts. When we assume that
everything is re-reflected from the
source, then at two seconds the forward
power at the front of the line would be
150 watts. At four seconds, 175 watts;
six seconds, 187.5; eight seconds,
193.75, and so on.
Please note that your numbers and mine agree exactly.
Also please note that I posted those numbers days ago
on qrz.com under a brainteaser thread. I have the EXCEL
file if you or anyone else would like to have it. (In a
one second long transmission line, when the load reflects
50 watts, it has essentially reflected 50 joules because
nothing changes during the following second.)

I'm not saying I think there's anything
wrong with your numbers. They're
actually very......precise. You wrote
something about a SG-AT autotuner, and
that could have a tendency to lead
someone to believe that you were
claiming to have made measurements. I
now understand that you didn't use an
SG-AT autotuner or make any
measurements. Thank you for clarifying
that point so eloquently.

In fact, I'll present a challenge for you and everyone
else.

Do you mean "everyone" - in the same
sense that Gary Oldman intended in "The
Professional"? :-)

In any one second long lossless transmission line
with any forward power and any reflected power, I defy
you to come up with an example where the number of joules
stored in the line is not equal to the forward power plus
the reflected power. Those joules are the joules sourced
by the generator that have not made it to the load. The
conservation of energy principle will have it no other
way. The laws of physics win once again.
--

Kinda melodramatic. I'm not sure who
you're arguing with. I gotta tell ya
though, it reminds me a little of one of
those guys who stands out on the street
corner shaking his fist and shouting at
traffic. Ever try to converse with one
of those guys?

73, ac6xg

Brainteaser
 

"Jim Kelley" wrote:
I gotta tell ya
though, it reminds me a little of one of those guys who stands out on the street
corner shaking his fist and shouting at traffic.

Most of us have agreed to cut out the ad hominem attacks and non-
technical crappola. How about you joining us in that endeavor?

What is your technical objection to what I have posted?
--
73, Cecil http://www.qsl.net/w5dxp