Cecil Moore wrote:

Jim Kelley wrote:

One should also carefully consider the more interesting variation of
the problem: an open transmission line. In the steady state we have
100 watts forward, 100 watts reflected, 200 Joules in the line, and 0
watts being sourced by the generator. :-)


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.

73, ac6xg

On Thu, 25 May 2006 22:04:12 GMT, Cecil Moore
wrote:

But what about the people who say there's no energy in the
reflected wave? Reckon how they sweep all those joules,
whose energy must be conserved, under the rug? :-)

with a jouler's brush?

--
73 for now
Buck
N4PGW

Buck wrote:
Cecil Moore wrote:

But what about the people who say there's no energy in the
reflected wave? Reckon how they sweep all those joules,
whose energy must be conserved, under the rug? :-)

with a jouler's brush?

All kidding aside, whatever number of joules of energy are
required to support the forward power and reflected power
is provided by the source during the transient condition
following power up.

If the source power is 100 watts, the forward power is 200
watts, the reflected power is 100 watts, and the load power
is 100 watts, all the joules per second needed to support
that forward and reflected power was supplied by the source
before steady-state was reached. Anything else would violate
the conservation of energy principle.

This is easily proven using a one second long lossless
transmission line as a conceptual training aid for the
uninitiated.
--
73, Cecil http://www.qsl.net/w5dxp

On Fri, 26 May 2006 03:16:38 GMT, Cecil Moore
wrote:



If the source power is 100 watts, the forward power is 200
watts, the reflected power is 100 watts, and the load power
is 100 watts, all the joules per second needed to support
that forward and reflected power was supplied by the source
before steady-state was reached. Anything else would violate
the conservation of energy principle.

This is easily proven using a one second long lossless
transmission line as a conceptual training aid for the
uninitiated.

I gathered that from an earlier post, but I think the confusion comes
in the second second, doesn't it? 100 watts of power is generated
from the generator for two seconds. the first second, 100 watts
travels to the antenna and only 100 watts is in the transmission line.
Then for the second second, 100 forward watts is moving towards the
antenna and 50 reflected watts are returning to the transmitter for a
total of 150 watts in the transmission line? Of course, since the
transmitter isn't matched to the antenna, the reflected power is
reflected again for 25 watts being reflected back to the antenna
bringing the power from 100 forward watts to 125 watts (the reason
power meters go up in wattage when SWR rises) thus the antenna
reflects 62.5 watts which adds to the 125 for a total of 187.5 watts
in the transmission line. Sooner or later one will have a meltdown
that will make Chernoble look like a firecracker compared to a
fireworks display. lol


--
73 for now
Buck
N4PGW

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

"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

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

"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