"Richard Clark" wrote in message
...
On 23 May 2004 19:02:20 -0700, (alhearn) wrote:

Hank:

Aren't you confusing the reflections that a TV signal experiences when
it bounces off nearby buildings and structures (causing ghosts) with
transmission line refections -- two entirely different things.

Al

Hi Al,

No, he has it correct. There is no material difference between the
two except for the velocity constant (which has no bearing on the
matter).

73's
Richard Clark, KB7QHC

There is a third case, which will cause the same results. Namely, the effect
of passing the signal through a filter with a nonlinear phase
characteristic.

Tam/WB2TT

Dave wrote:
no, only that you ignored the body of the message and answered what you
wanted to discuss instead of what was asked.

Yes, I did. I didn't know anything about the original question so
I kindly offered to discuss something I know something about. If that
is against netnews guidelines, could you show me where it says so?

nope, that is a real world situation, but not the one under discussion.

A 1/4WL matching section is not a "real world situation"? Since when?
Everything I post is a real-world situation except for the obvious,
e.g. one-second long lossless transmission lines.

so which is it, in phase or 180 degrees out of phase???

It depends upon which signal we are talking about and whether the
impedance discontinuity steps-up or steps-down. Assuming the generated
forward wave (a1) has the voltage and current in phase at zero degrees:

For a step-up impedance discontinuity, the s11(a1) reflection term
will have the voltage at zero degrees (and the current at 180 degrees).

For a Z0-match, b1 will be zero so s12(a2) must be equal magnitude
and opposite phase to s11(a1). That puts the reflection from the
load with voltage at 180 degrees (and current at zero degrees).
All interference at port1 is totally destructive for a Z0-match.

The s21(a1) term has voltage at zero degrees (and current at zero
degrees). All interference at port2 is constructive so s22(a2) also
has the voltage at zero degrees (and current at zero degrees).

For a step-down impedance discontinuity associated with a Z0-match,
the phases of the reflected voltages and currents are shifted by 180
degrees and b1 still equals zero.

The above is exactly what happens at the match point at the input
of a tuner. ***Therefore, the great majority of ham radio antenna
systems have the voltages and currents either in-phase or 180 degrees
out of phase at the tuner match point.*** In fact, all a tuner does is
shift the magnitude and phase of the reflected waves from a mismatched
antenna to be equal in magnitude and 180 degrees out of phase with the
reflections from the match point. Therefore, all reflections are canceled
at the match point but not between the match point and the antenna.

This was all explained 64 years ago (when I was two years old) by J. C.
Slater in _Microwave_Transmission_. Why do I have to explain it all over
again?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:
the
rearward-traveling momentum energy in those two waves is conserved by
changing direction to become part of a forward-traveling wave.

Yeeesh. You had it on, dog, up until that. And don't try to tell me
(again) that I'm lying that you said it.

(Remember when you wrote this? "If reflected energy makes its way back
into the final amp, it was never generated in the first place, by
definition." Hint: apply the same idea to your "rearward-traveling
momentum" and you'll have it.)

73, Jim AC6XG

Henry Kolesnik wrote:
SWR ghosts are usually smear because the transmission line is short and the
displacement fo the image is small compared to object reflection shost which
have a greater image displacement becasue the reflected signal travels over
a greater distance.

If reflected waves don't make a round trip back toward the source
and get re-reflected, how can there be ghosts? :-)
--
73, Cecil http://www.qsl.net/w5dxp



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On Mon, 24 May 2004 12:49:39 -0500, Cecil Moore
wrote:
I didn't know anything about the original question
Stock answer.

This was all explained 64 years ago (when I was two years old) by J. C.
Slater in _Microwave_Transmission_. Why do I have to explain it all over
again?
Possibly because you so ill understood it then as now?

Richard Fry wrote:

TV Ghosting (quotes below)

To elaborate, the visibility of a ghost image in analog TV systems is
related to the magnitude, phase and time displacement of the RF reflection
that produced it as compared to the original, or non-reflected waveform.

The round-trip transit time from the TV tx output to the mismatch in its
antenna system will determine the time displacement of the ghost, at the
rate of 1 microsecond of displacement per ~490 feet of distance between the
tx and the reflection plane (vp = 0.997c).

Richard, you know you are going against the conventional wisdom on
this newsgroup. Ghosting cannot exist during steady-state so if
ghosting exists it simply means that you are still in the transient
state and the steady-state doesn't exist (yet).
--
73, Cecil http://www.qsl.net/w5dxp



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Richard Clark wrote:

wrote:
This was all explained 64 years ago (when I was two years old) by J. C.
Slater in _Microwave_Transmission_. Why do I have to explain it all over
again?

Possibly because you so ill understood it then as now?

Well Richard, here's your chance. Please enlighten us on J.C.
Slater's meaning of: "The method of eliminating reflections
is based on the interference between waves. ... The fundamental
principle behind the elimination of reflections is then to have
each reflected wave canceled by another wave of equal amplitude
and opposite phase."
--
73, Cecil http://www.qsl.net/w5dxp



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"Cecil Moore" wrote in message
...
Dave wrote:
no, only that you ignored the body of the message and answered what you
wanted to discuss instead of what was asked.

Yes, I did. I didn't know anything about the original question so
I kindly offered to discuss something I know something about. If that
is against netnews guidelines, could you show me where it says so?

of course it is against guidelines. you were starting a new thread without
changing the subject. in effect hijacking the thread for your own
discussion.


nope, that is a real world situation, but not the one under discussion.

A 1/4WL matching section is not a "real world situation"? Since when?
Everything I post is a real-world situation except for the obvious,
e.g. one-second long lossless transmission lines.

i said it was real world, but it is not what the original thread was about.

Cecil Moore wrote:

Jim Kelley wrote:

Cecil Moore wrote:
rearward-traveling momentum energy in those two waves is conserved by
changing direction to become part of a forward-traveling wave.

Yeeesh. You had it on, dog, up until that. And don't try to tell me
(again) that I'm lying that you said it.

(Remember when you wrote this? "If reflected energy makes its way back
into the final amp, it was never generated in the first place, by
definition." Hint: apply the same idea to your "rearward-traveling
momentum" and you'll have it.)

Egads Jim, exactly how much of reality do you think I am capable of
ignoring?

You're evidently capable of ignoring at least some, Cecil.

I *don't* agree with that definition above and your implication that
momentum and energy don't need to be conserved is simply metaphysics
in action.

We both know that momentum and energy must be conserved. We just
disagree agree on how nature chooses to do that. And, because of that
disagreement, I'm forced to endure your beligerant rhetoric.

73, Jim AC6XG

"Cecil Moore" wrote in message
...
Richard Fry wrote:

TV Ghosting (quotes below)

To elaborate, the visibility of a ghost image in analog TV systems is
related to the magnitude, phase and time displacement of the RF
reflection
that produced it as compared to the original, or non-reflected waveform.

The round-trip transit time from the TV tx output to the mismatch in its
antenna system will determine the time displacement of the ghost, at the
rate of 1 microsecond of displacement per ~490 feet of distance between
the
tx and the reflection plane (vp = 0.997c).

Richard, you know you are going against the conventional wisdom on
this newsgroup. Ghosting cannot exist during steady-state so if
ghosting exists it simply means that you are still in the transient
state and the steady-state doesn't exist (yet).
--
73, Cecil http://www.qsl.net/w5dxp
Looking for the smiley face. It is probably fair to say that in the *general
case* there is no steady reflection in video transmission, unless the round
trip delay is N horizontal lines. BTW, weirdest case I saw came when the dog
chewed through the cable. Now I was seeing the main signal coming from the
cable, plus a ghost that was picked up directly from the transmitter. The
ghost was to the left and above the main signal.

Tam/WB2TT