"Jeff" wrote in
.com:

Owen and Cecil are right: the source (transmitter) has no effect
whatever on the VSWR on the line.

That isn't just an assertion - it is part of the bedrock transmission
line theory. Owen referred to "reputable textbooks", one of which
would surely be 'Theory and Problems of Transmission Lines' by R A
Chipman [1]. This book gains a lot of its reputation from its very
complete mathematical development of the theory, showing all the
detailed working.

I am sorry but you are not correct, I have not read Chipman so I
cannot comment on his analysis or your interpretation of his results,
but my understanding , practical experiments and CAD analysis would
lead me to disagree.

If we take the situation where the source is matched (50ohms) to the
5.35 wavelength transmission line (lossless to simplify things) with a
100ohm load, I agree that the vswr is 4:1, unchanging with frequency.

Plotted on a Smith Chart when swept against frequency this gives a
circle centred on 1 (50ohms) with a radius of 4. i.e. on a constant
VSWR circle.

Now if we change the source impedance to 100ohms and repeat the same
sweep and re-plot, keeping the chart normalized to 50 ohms, the circle
moves on the resistance axis, still with a radius of 4 and now passing
though 2 (100 ohms) resistive. The centre moves to about 0.6 (30ohms).
It then becomes obvious that the locus of the circle is NOT a constant
VSWR against frequency.

You will come to the same conclusion if you normalize the chart to 100
ohms, the new source impedance and re-plot.

The coax is acting as an impedance transformer, causing a shift along
the resistance axis.

Looking at it another way, the vswr changes sinusoidally with
frequency, in our example, between 2:1 and 8:1. (The same as the Smith
chart plot with a circle of radius 4 centred at about 0.6).


If you are asserting that VSWR on a real or even theoretical line varies
sinudoidally with displacement, it is time to go back to basics. You need
some time with a reputable text book.

Owen

Richard Clark wrote:

On Thu, 01 Mar 2007 09:58:02 -0800, Jim Kelley
wrote:


, is how is it that you were able to
ascertain that this heat energy was caused by energy that was
reflected from the load rather than having come directly from the
power supply within the source?


In the theological sense, this predicates that power never becomes
dissociated from "the source." That is ambiguous, isn't it?

Is that to include the batteries behind the collector supply? The
power supply charging the batteries? The power grid feeding the power
supply? The generator driving the grid? The Coal firing the steam
spinning the generator? The sun through photosynthesis growing plants
to provide the coal? The previous supernova that seeded the cosmos by
which coalescence formed the sun? ...and into an infinite regression
to that previous supernova?

The energy dissipated is computed from the Galactic Load Line.

Sarcasm clearly noted, and surprisingly uncalled for. I'll try asking
one more time. It is a simple metrology question: How were you able
to directly ascertain that the heat being dissipated in the source was
produced by energy being reflected from the load?

Thanks,

Jim, AC6XG

Jim Kelley wrote:
Cecil Moore wrote:
I think it depends on how long the energy has been flowing. But in the
steady state it's rather like posing this question: With a forward speed
of 200 knots, and with a headwind speed 100 knots, would you agree that
the apparent airspeed of the aircraft is 300 knots?

Of course, I was talking about steady-state conditions.
And I can prove that there is exactly the amount of
energy stored in the transmission line necessary to support
the forward joules/sec and reflected joules/sec readings.

Why violate the laws of physics to try to come up with some
other more esoteric explanation than forward and reflected
EM traveling wave energy moving at the speed of light?

It's kind of a boring problem though. Personally, I think it's more
interesting and enlightening to consider what goes on prior to steady
state.

That's exactly what I have done. During the initial transient
build-up period, *exactly* enough energy is supplied by the
source to the transmission line to support the steady-state
forward and reflected joules/sec - no more and no less. If
the source is disconnected during steady-state, the energy
stored in a lossless transmission line is dissipated in the
load during that final transient decay period.
--
73, Cecil, http://www.qsl.net/w5dxp

Owen Duffy wrote:
"Jeff" wrote in
e.com:

Owen and Cecil are right: the source (transmitter) has no effect
whatever on the VSWR on the line.

That isn't just an assertion - it is part of the bedrock transmission
line theory. Owen referred to "reputable textbooks", one of which
would surely be 'Theory and Problems of Transmission Lines' by R A
Chipman [1]. This book gains a lot of its reputation from its very
complete mathematical development of the theory, showing all the
detailed working.

I am sorry but you are not correct, I have not read Chipman so I
cannot comment on his analysis or your interpretation of his results,
but my understanding , practical experiments and CAD analysis would
lead me to disagree.


[...]

Looking at it another way, the vswr changes sinusoidally with
frequency, in our example, between 2:1 and 8:1. (The same as the Smith
chart plot with a circle of radius 4 centred at about 0.6).


If you are asserting that VSWR on a real or even theoretical line varies
sinudoidally with displacement, it is time to go back to basics. You need
some time with a reputable text book.

Agreed, but make that a textbook that specifically deals with the
subject in enough detail. Chipman was highly recommended by contributors
to earlier rounds of this debate. It isn't an easy read, but it's
certainly thorough.

I ordered the book from the other side of the world because I wanted to
be very sure of my answers next time around. We don't know where you
are, Jeff, but it would probably be easier and cheaper for you to do the
same.



--

73 from Ian GM3SEK

"Cecil Moore" wrote in message
. ..
Jeff wrote:
w5dxp wrote:
The Z0 of the transmission line has not changed to 100
ohms so normalizing the chart to 100 ohms is not valid.

It is just as valid as using 50 ohms, and the result is the same, a
changing vswr.

No, the center of the Smith Chart is the Z0 of the transmission
line (when used on a transmission line). One cannot willy nilly
change the reference Z0. The confusion from doing such is obvious.

You are mis-representing what I said; which was that you can plot the
problem using with the chart normalized to EITHER 50 or 100 ohms (the
impedance of the generator or that of the line) and the net result will be
the same answer.

The chart does not necessarily be normalized to the impedance of a
transmission line that you are trying add, otherwise you would never be able
to include a series line of an impedance other than that of the chart in a
matching network.

Jeff

" If you are asserting that VSWR on a real or even theoretical line varies
sinudoidally with displacement, it is time to go back to basics. You need
some time with a reputable text book.

Owen

No, I am saying that a fixed length line, mismatched at the far end, and of
a different impedance to that of the generator, will not present a constant
vswr to the generator with varying frequency. That variation being
sinusoidal between a max and min value.

Jeff

On Thu, 01 Mar 2007 11:27:36 -0800, Jim Kelley
wrote:

Sarcasm clearly noted, and surprisingly uncalled for.

Hi Jim,

I responded in kind is all, you revealed a trap and I jumped into it
with both feet. If that broke it, return it to the vendor for a
refund.

Is power/energy separable from its source? If this question is
obnoxious, why did you raise the prospect?

When it is generally accepted that our sources do not exhibit 50 Ohms
source resistance/impedance, what resistance/impedance do they
exhibit? If you don't have an answer, what was the purpose of this
uninforming assertion?

If these two questions have the trappings of sacrasm, I did not
originate their discussion. And putting your mock-shock aside, they
are part of the chain of denial you are adding links to, aren't they?

73's
Richard Clark, KB7QHC

On Thu, 01 Mar 2007 19:21:43 GMT, Owen Duffy wrote:

If you are asserting that VSWR on a real or even theoretical line varies
sinudoidally with displacement, it is time to go back to basics. You need
some time with a reputable text book.

Hi Owen,

Under the right circumstances (and they have been presumed in some
discussion here), then the power terms (as expressed by a power meter
inserted into the line) will vary sinusoidally with displacement, even
if the SWR does not.

73's
Richard Clark, KB7QHC

Jeff wrote:
The chart does not necessarily be normalized to the impedance of a
transmission line that you are trying add, otherwise you would never be able
to include a series line of an impedance other than that of the chart in a
matching network.

The point is that it is best to use one Smith Chart
for each Z0. Trying to plot multiple Z0's on the
same chart leads to the present confusion. The
fact that a piece of transmission line with an
SWR1 transforms impedances is NOT proof that
the SWR is changing. It is *only* proof the
the impedance is changing and that happens
with constant SWR.
--
73, Cecil, http://www.qsl.net/w5dxp

Jeff wrote:
No, I am saying that a fixed length line, mismatched at the far end, and of
a different impedance to that of the generator, will not present a constant
vswr to the generator with varying frequency. That variation being
sinusoidal between a max and min value.

Changing the length of the ladder-line changes the
50 ohm SWR seen by the source. That is a well known
fact. But that doesn't mean the SWR on the ladder-
line is changing. It simply means that the impedance
is being transformed by the constant SWR circle.
--
73, Cecil, http://www.qsl.net/w5dxp