Last week I posted a brainteaser over on qrz.com. Nobody figured
it out. I wonder how many on r.r.a.a can figure it out.

Given: A one second long lossless transmission line with a
steady-state forward power of 200 watts and a reflected power
of 100 watts. How many joules are contained in that feedline?
--
73, Cecil, W5DXP

I had Beaker set up an experiment to test this, and after he put out
the fire he started in his hair when the first load he tried melted a
hole in the lab bench, he finally got it set up right. He determined
that the mass of the line increased by about 3.338 femtograms when
powered as compared with it unpowered. We're now looking into what to
do with the line, as it's cluttering up the lab, and we're open to
suggestions.

Regards,
Bunsen

Cecil Moore wrote:
Last week I posted a brainteaser over on qrz.com. Nobody figured
it out. I wonder how many on r.r.a.a can figure it out.

Given: A one second long lossless transmission line with a
steady-state forward power of 200 watts and a reflected power
of 100 watts. How many joules are contained in that feedline?
--
73, Cecil, W5DXP

Dr. Honeydew wrote:

I had Beaker set up an experiment to test this, and after he put out
the fire he started in his hair when the first load he tried melted a
hole in the lab bench, he finally got it set up right. He determined
that the mass of the line increased by about 3.338 femtograms when
powered as compared with it unpowered. We're now looking into what to
do with the line, as it's cluttering up the lab, and we're open to
suggestions.

Regards,
Bunsen


That is the best response we will get.

Even if there are correct ones!

tom
K0TAR

Cecil, W5DXP wrote:
"How many joules are contained in that feedline?"

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

Richard Harrison wrote:
Cecil, W5DXP wrote:
"How many joules are contained in that feedline?"

Total joules on the line is 300.

That can be shown to be true by noting that during the
transient buildup to steady-state, 300 joules sourced
by the generator have not yet reached the load. That
remains true until the generator is powered down, i.e.
all during steady-state.

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.

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? :-)
--
73, Cecil http://www.qsl.net/w5dxp

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. :-)

ac6xg

Cecil Moore wrote:
Richard Harrison wrote:

Cecil, W5DXP wrote:
"How many joules are contained in that feedline?"

Total joules on the line is 300.


That can be shown to be true by noting that during the
transient buildup to steady-state, 300 joules sourced
by the generator have not yet reached the load. That
remains true until the generator is powered down, i.e.
all during steady-state.

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.


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? :-)

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. :-)

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.
--
73, Cecil http://www.qsl.net/w5dxp

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. :-)


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?

ac6xg

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?
--
73, Cecil http://www.qsl.net/w5dxp

is that line 1 second long, or 1/2 second long?? a 1 second long line would
take 2 seconds worth of energy from the generator before the reflection
returned to let it know the line is terminated. this is of course very
important if you are measuring lines with tdr's where you can really see
those returned waves, of course the time it takes them to get back to the
tdr is double the one-way travel time... mess it up and you are looking for
faults twice as far down the line as you calculate.


"Cecil Moore" wrote in message
. com...
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?
--
73, Cecil http://www.qsl.net/w5dxp