Henry Kolesnik wrote:
Not much but neither does much of this thread regarding my original query.

They have a lot to do with the subject of the thread. :-)

I hope someone that understands the question can answer in a way that my
feeble brain can comprehend. At least we're eliminating what's not the
answer.

Back a dozen years ago, or so, Mr. Bruene tried to 'ping' a final
amp with a slightly off-frequency signal to ascertain the output
impedance of the amp and he published his results in QST. His apparent
error was that he didn't do it at the frequency of operation of the
amp and he didn't know what the 'Q' of a final amp really is. There
has been a running argument ever since, probably best documented in
QEX magazine. There are basically two sides to the argument.

1. If load-pulling causes a falloff of power on each side of the
operating point, then the system is conjugately matched. That
conjugate match includes such things as non-dissipative resistances.

2. Conjugate matches do not exist in a typical amateur system.

Brilliant minds have been trying to prove one or the other and
both sides (IMO) have failed in that proof. There is no final,
definitive proof of either position. If there was such, there
would be no argument. That's why we cannot answer
your question. The picture is further clouded by a definition.
If reflected energy makes its way back into the final amp, it
was never generated in the first place, by definition.
--
73, Cecil http://www.qsl.net/w5dxp


"Reg Edwards" wrote:
Cec et al, what have circulators, S-parameters, etc. to do with HF ?



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Then why can high SWR on a TV Tx cauuse ghosts or smearing on the TV Rx?
Hank WD5JFR
"Cecil Moore" wrote in message
...
Henry Kolesnik wrote:
Not much but neither does much of this thread regarding my original
query.

They have a lot to do with the subject of the thread. :-)

I hope someone that understands the question can answer in a way that my
feeble brain can comprehend. At least we're eliminating what's not the
answer.

Back a dozen years ago, or so, Mr. Bruene tried to 'ping' a final
amp with a slightly off-frequency signal to ascertain the output
impedance of the amp and he published his results in QST. His apparent
error was that he didn't do it at the frequency of operation of the
amp and he didn't know what the 'Q' of a final amp really is. There
has been a running argument ever since, probably best documented in
QEX magazine. There are basically two sides to the argument.

1. If load-pulling causes a falloff of power on each side of the
operating point, then the system is conjugately matched. That
conjugate match includes such things as non-dissipative resistances.

2. Conjugate matches do not exist in a typical amateur system.

Brilliant minds have been trying to prove one or the other and
both sides (IMO) have failed in that proof. There is no final,
definitive proof of either position. If there was such, there
would be no argument. That's why we cannot answer
your question. The picture is further clouded by a definition.
If reflected energy makes its way back into the final amp, it
was never generated in the first place, by definition.
--
73, Cecil http://www.qsl.net/w5dxp


"Reg Edwards" wrote:
Cec et al, what have circulators, S-parameters, etc. to do with HF ?



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Henry Kolesnik wrote:
Then why can high SWR on a TV Tx cauuse ghosts or smearing on the TV Rx?

Hank, You're preaching to the choir, asking me that question.
I don't like that definition but if you poll the gurus on this
newsgroup, most will say that reflected power that is incident
upon the transmitter was never generated in the first place.
(Never mind the ghosting that they can see with their own eyes.)

Lots of steady-state ills can be swept under the rug by assuming
nothing but fixed frequency sine waves with zero modulation. A
guru's answer to you question is that "ghosting is not steady-
state". :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Quote below

Actually, it depends upon where that high SWR physically is located.

A dummy load with a 1.3:1 SWR connected directly at the tx output connector
will not produce a visible ghost in the demodulated TV picture.

A 1.3:1 antenna SWR at the far end of more than about 500 feet of otherwise
matched transmission line connected to that same transmitter WILL produce a
visible ghost.

-RF
__________

"Henry Kolesnik" wrote
Then why can high SWR on a TV Tx cauuse ghosts or smearing on the TV Rx?

Richard Fry wrote:
A dummy load with a 1.3:1 SWR connected directly at the tx output connector
will not produce a visible ghost in the demodulated TV picture.

Of course, a same-cycle reflection has virtually no effect on ghosting.

A 1.3:1 antenna SWR at the far end of more than about 500 feet of otherwise
matched transmission line connected to that same transmitter WILL produce a
visible ghost.

Of course, a different-cycle reflection is what causes ghosting.
--
73, Cecil http://www.qsl.net/w5dxp



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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).

The visible part of a TV image is scanned onto the display screen at a
horizontal rate of about 1 line per 50 microseconds.* An internal
reflection from a transmit antenna connected to the tx by 1,000 feet of
transmission line will create a ghost image ~1 microsecond after the main
image -- or ~1/2" to the right side of it in a 25" wide picture. As the
narrowest vertical line that can be viewed on a display using a 4MHz video
bandwidth is a bit less than 0.35 microseconds wide, a ghost image of it
displaced by 1 microsecond is clearly and separately visible on a 25" wide
display, and will not appear as a "smear" of the main image.

Ghosts also can be produced by external reflections of the radiated TV
signal from buildings, large signs, etc. Often these ghosts have much
greater displacement from the main image than those that can be transmitted
from reflections in the TV transmit antenna system. This is the result of
the greater transit time for those reflections w.r.t. the direct ray, that
are common for reflecting and scattering surfaces where located in the
propagation environment.

Reflections with "short" time displacements are more difficult to resolve
separately as ghosts, but still affect and limit the visual quality of the
TV image. Reflections 40dB or more suppressed from the main image have no
practical, visible affect on it -- regardless of their time displacement.

R. Fry, RCA Broadcast Field Engineer 1965-1980

*allows for the H&V sync pulse intervals and some overscan

_______________________

R. Fry wrote
A 1.3:1 antenna SWR at the far end of more than
about 500 feet of otherwise matched transmission
line connected to that same transmitter WILL produce
a visible ghost.

"Cecil Moore" responded
Of course, a different-cycle reflection is what causes ghosting.

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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"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

Cecil Moore quote below & 'steady state'

The transmitter is continuously generating incident power, which is
continuously subject to reflection(s) by any mismatch in the antenna system.
Given the right magnitude, phase and time displacement, each reflection will
produce a continuous ghost on the TV screen.

These ghosts can be seen (continuously) in/on the output waveform of a TV
demodulator connected at the output of the transmitter -- both in time
domain on an oscilloscope, and visually on a monitor. I've seen these
continuous reflections scores of times at TV tx sites all over the US as a
field engineer for RCA Broadcast Division.

"Conventional wisdom" on this NG may say otherwise, but hopefully some may
learn the reality from this exchange.

- RF
____________________

"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).