On Mar 23, 7:18 pm, Cecil Moore wrote:
Keith Dysart wrote:
I notice that you frequently use this example, unfortunately
never completing the analysis.
Since you leave it unspecified, let me choose the
output impedance of the TVSG to be 450 Ohms. Now there is
'reverse power' in the ladder line but no ghosts. Where did
the 'reverse power' go such that it does not produce ghosts?

Into heating the 450 ohm circulator load resistor that you
would have to install to get the generator impedance to
exhibit 450 ohms to the reflected waves. Otherwise, the
generator will exhibit a mismatch to the 450 ohm line.
It is *impossible* for the generator to see 450 ohms
when looking into a Z0=450 ohm line with reflections. So
it is impossible for the reflected wave to encounter a
V/I ratio of 450 ohms in the active generator (unless a
450 ohm circulator resistor is installed).

You are trying too hard. Even your problem statement said
"no circulator". So I offer a simple example of such a
generator: a voltage source connected by a 450 Ohm resistor
to the output terminal. Voila: a generator with 450 Ohm
output impedance. Not too efficient perhaps, but the design
is used when quality source matching is desired or when
reflections need to be suppressed but it is impractical to
terminate the load in the characteristic impedance of the
line.

Now back to the problem... and the questions...

Actually, "reflected energy" rather than "reverse power".
Here is very close to an experiment we did at Texas A&M
during the 50's. We observed the ghosting and the professor
explained reflected energy waves to us.

TVSG-----1000 feet 450 ohm ladder-line---75 ohm TV RCVR

If the TV Signal Generator is not equipped with a circulator
to get rid of the reflected energy wave, ghosts will appear on
the TV RCVR. The ghosts are exactly where they should be if
reflected wave energy exists. How would you explain the
ghosting?

I notice that you frequently use this example, unfortunately
never completing the analysis.
Since you leave it unspecified, let me choose the
output impedance of the TVSG to be 450 Ohms. Now there is
'reverse power' in the ladder line but no ghosts. Where did
the 'reverse power' go such that it does not produce ghosts?

If it is re-reflected, then it is a delayed copy of the original,
i.e. a ghost. So where does it go? Seems to me there is only
two ways and the way that does not produce a ghost is into the
generator, so we need an accounting of this power within the
generator, iff it is real power.

Of course there is no issue once you let go of the notion of
'reverse power'. The reverse voltage and current pass into
the generator since the generator is matched to the line and
nothing is reflected.

And since multiplying reverse voltage by reverse current does
not, in general, produce a real power, there is no power to
account for.

Suggest you review transmission line theory. If reverse
voltage and reverse current exists, the transmission
line forces their ratio to be Z0, i.e. 450 ohms, i.e. in
phase. V*I*cos(0) = watts. Since reflections are causing
ghosting, it is prima facie evidence that "real power"
is being extracted from the reflected wave.

Oh I can do the math, and the units are definitely Watts
but that doesn't necessarily mean they offer any reality.
The toaster in my kitchen has 120 Volts on it and the lamp
is drawing 1 Amp (and the two are in phase), but that does not
mean that 120 toaster-lamp Watts has any meaning.

....Keith

Keith Dysart wrote:
You are trying too hard. Even your problem statement said
"no circulator". So I offer a simple example of such a
generator: a voltage source connected by a 450 Ohm resistor
to the output terminal. Voila: a generator with 450 Ohm
output impedance.

The generator is an *active dynamic source*. It does
not have a 450 ohm output impedance just because you
install a 450 ohm resistor. Just as soon as reflected
waves are allowed to reach the source, the source
impedance dynamically shifts away from the 450 ohm
value.
--
73, Cecil http://www.w5dxp.com

On Mar 23, 9:21 pm, Cecil Moore wrote:
Keith Dysart wrote:
You are trying too hard. Even your problem statement said
"no circulator". So I offer a simple example of such a
generator: a voltage source connected by a 450 Ohm resistor
to the output terminal. Voila: a generator with 450 Ohm
output impedance.

The generator is an *active dynamic source*. It does
not have a 450 ohm output impedance just because you
install a 450 ohm resistor. Just as soon as reflected
waves are allowed to reach the source, the source
impedance dynamically shifts away from the 450 ohm
value.

I notice that you've skipped the important question posed in
the example. I'll try again.

Use my generator: voltage source, 450 Ohm resistor to the output.
No circulator.
Drive your system: 450 Ohm line terminated with a 75 Ohm TV receiver.

TVSG-----1000 feet 450 ohm ladder-line---75 ohm TV RCVR

Ghosts or no?
If no? Where did the 'reverse power' go?

If ghosts? Well, think very carefully before choosing this option
because there aren't.

....Keith

Keith Dysart wrote:
If ghosts? Well, think very carefully before choosing this option
because there aren't.

There will be ghosting but because of the attenuation
in the 450 ohm series resistor, the ghosting will be
below the level detectable on a TV screen by the human
eye.
--
73, Cecil http://www.w5dxp.com

On Mar 23, 11:06 pm, Cecil Moore wrote:
Keith Dysart wrote:
If ghosts? Well, think very carefully before choosing this option
because there aren't.

There will be ghosting but because of the attenuation
in the 450 ohm series resistor, the ghosting will be
below the level detectable on a TV screen by the human
eye.

It would be much more convincing if you were to compute the
magnitude of the ghost rather than handwaving an answer.

Though when you do so, you will find that it is exactly zero,
so be prepared.

....Keith

"Keith Dysart" wrote in message
oups.com...
On Mar 23, 11:06 pm, Cecil Moore wrote:
Keith Dysart wrote:
If ghosts? Well, think very carefully before choosing this option
because there aren't.

There will be ghosting but because of the attenuation
in the 450 ohm series resistor, the ghosting will be
below the level detectable on a TV screen by the human
eye.

It would be much more convincing if you were to compute the
magnitude of the ghost rather than handwaving an answer.

Though when you do so, you will find that it is exactly zero,
so be prepared.

...Keith

its all ghosts and mirrors!

forget power, forget energy, they are products of other calculations. all
that is needed is impedance and voltage OR current. once you know voltage
OR current and the impedance you can calculate all the rest.

Dave wrote:
forget power, forget energy, they are products of other calculations. all
that is needed is impedance and voltage OR current. once you know voltage
OR current and the impedance you can calculate all the rest.

What would you do if you were dealing with EM light waves
instead of EM RF waves? Optical physicists don't have the
luxury of dealing with "impedance and voltage OR current".
They are forced to deal with the essence of EM waves which
is photonic energy. They have done it for over a century
and have learned a lot about the nature of EM waves. They
did not "forget power, forget energy".
--
73, Cecil http://www.w5dxp.com

Keith Dysart wrote:
It would be much more convincing if you were to compute the
magnitude of the ghost rather than handwaving an answer.

I made the rough computation of -25 dB before I responded.
It is below the ability of the human eye to detect TV
ghosting.
--
73, Cecil http://www.w5dxp.com

On Mar 24, 8:45 am, Cecil Moore wrote:
Keith Dysart wrote:
It would be much more convincing if you were to compute the
magnitude of the ghost rather than handwaving an answer.

I made the rough computation of -25 dB before I responded.
It is below the ability of the human eye to detect TV
ghosting.

Would you care to reveal the details of the calculations
so that we can locate the error(s) that lead to a non-zero
answer?

....Keith