"Cecil Moore" wrote in message
...
That's a steady-state shortcut which assumes pure sine waves that
don't exist in reality. Please don't confuse steady-state shortcuts
with reality. Noise and modulation cause the "steady-state complex
impedance" not to be steady-state at all. Many will say it's close
enough, but one cannot understand reflections by assuming an un-
varying steady-state.

In a TV system with ghosting due to reflections, the unvarying steady-
state condition doesn't exist. In fact, when you assume steady-state
conditions, you eliminate ghosting, at least in your own mind. In
reality, steady-state doesn't really exist because of random noise
and unpredictable modulation.

The more you talk about 'steady-state-, the more apparent it becomes that
you don't really understand what it means.

73, Jim AC6XG

Henry Kolesnik wrote:

Richard
This is in response to your answer of last night. Before going to bed I got
out the book REFLECTIONS II by Walt Maxwell W2DU. I'm typing verbatim from
page 2-2 and 23-1 for those who don't have the book.page 2-2 "Contrary to
what many believe, it is not true that when a transmitter delivers power
into a line with reflections, a returning wave sees an internal generator
resistance as a dissipative load. Nor is the reflected wave converted to
heat and, while at the same time damaging the final amplifier....the
reflected power is entirely conserved...." from page 23-1 "One of the most
serious misconceptions concerned reflected power reaching the tubes in the
RF amplifier of the transmitter. The prevalent, but erroneous thinking was
that the reflected power enters the amplifier, causing tube overheating and
destruction. However, I dispelled this misconception in the above mentioned
publications, using wave-mechanics treatment, discussed here in greater
detail, by showing that when the pi-network tank is tuned to resonance, a
virtual short circuit to rearward traveling waves is created at the input of
the network. Consequently, instead of the reflected power reaching the
tubes of the amplifier, it is totally re-reflected toward the load by the
virtual short circuit appearing only to waves at the network input".

Please note that when this was written, there were no solid-state transmitters
with fixed 50 ohm outputs. Walt was talking specifically about tube transmitters
with built-in adjustable pi-net antenna tuner circuits, like my old Globe Scout.
The closest present-day transmitters to match the above statements would be
something like my IC-756PRO with a built-in auto-tuner.

I'm guessing it's a virtual short because the pi-network is resonant but
what happens if it is a bit off.

If it is a bit off, reflected voltage and current flow into the finals
and superpose with the source voltage and current. Since the reflected
voltage and current are 180 degrees out of phase, the superposition
usually causes the load on the amp to become reactive. Even if the
voltages are in phase or the currents are in phase, the load on the
amp becomes something other than the designed-for load. The result
can be over-voltage or over-current or both. That's not good.

Also what happens in a transistor final with no pi?

Note: most transistor finals have a fixed pi-network designed to
operate into a fixed 50 ohm load. The results would be the same as
the detuned example above. Such commercial finals are protected
from over-voltage and over-current by decreasing the source power.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

On Tue, 25 May 2004 13:50:09 GMT, "Henry Kolesnik"
wrote:

Richard
This is in response to your answer of last night. Before going to bed I got
out the book REFLECTIONS II by Walt Maxwell W2DU. I'm typing verbatim from

Very familiar stuff which I have held Walt accountable for. We have
had considerable correspondence to this point and he is holding my
argument in suspension, pending his bench work confirmation of my
simple experiments that I have posted here to this effect.

I'm guessing it's a virtual short because the pi-network is resonant but
what happens if it is a bit off. Also what happens in a transistor final
with no pi?

What you describe is consistent with Walt's language, you deserve
points for following his logic. As for your question about the
transistor final with no pi network. That was handled quite
explicitly by me for the thread "Loop Antenna for Class-E amplifier"
in correspondence with Toni, ea3fya and Marc Battyani. If you will
note, this thread was entirely devoid of ego so puffed up in these
issues, and we had the rare opportunity of a third, independent
observer who also sat at the bench and followed the instructions and
comments I offered with actual construction and testing to POSITIVE
results. You may also note the absolute vacuum of other's comments
imploring that his data was chimerical, illusions of a meter. In fact
it was one of those rare threads with a question much like yours, with
the same simple observations offered by me, confirmed and ending in
very much less than 600 postings of supposition and superstition.

However, back to Walt's treatise and your reading of it. I again
simply ask: "Do you have a tuner in line each day you fire up your
rig? Why, if you have faith in your logic, do you need it?"

As I've pointed out, there's the recent thread, and any number of
simple tests and experiments that I have offered here. These etudés
are typically ignored in favor of vacuous theory-spinning - NONE of
which answer the simple question: "What is the Source Z if it is not
50 Ohms?"

73's
Richard Clark, KB7QHC

Before it came down my 20 meter antenna had a SWR approaching 20:1 and I was
running a Collins 30S-1 and no tuner!. I did that for several years and
would be still doing if the roofers hadn't destroyed ~130 ft. dipole. One
of these days after my back improves I'll put another one up.

--
73
Hank WD5JFR
"Richard Clark" wrote in message
...
On Tue, 25 May 2004 13:50:09 GMT, "Henry Kolesnik"
wrote:

Richard
This is in response to your answer of last night. Before going to bed I
got
out the book REFLECTIONS II by Walt Maxwell W2DU. I'm typing verbatim
from

Very familiar stuff which I have held Walt accountable for. We have
had considerable correspondence to this point and he is holding my
argument in suspension, pending his bench work confirmation of my
simple experiments that I have posted here to this effect.

I'm guessing it's a virtual short because the pi-network is resonant but
what happens if it is a bit off. Also what happens in a transistor final
with no pi?

What you describe is consistent with Walt's language, you deserve
points for following his logic. As for your question about the
transistor final with no pi network. That was handled quite
explicitly by me for the thread "Loop Antenna for Class-E amplifier"
in correspondence with Toni, ea3fya and Marc Battyani. If you will
note, this thread was entirely devoid of ego so puffed up in these
issues, and we had the rare opportunity of a third, independent
observer who also sat at the bench and followed the instructions and
comments I offered with actual construction and testing to POSITIVE
results. You may also note the absolute vacuum of other's comments
imploring that his data was chimerical, illusions of a meter. In fact
it was one of those rare threads with a question much like yours, with
the same simple observations offered by me, confirmed and ending in
very much less than 600 postings of supposition and superstition.

However, back to Walt's treatise and your reading of it. I again
simply ask: "Do you have a tuner in line each day you fire up your
rig? Why, if you have faith in your logic, do you need it?"

As I've pointed out, there's the recent thread, and any number of
simple tests and experiments that I have offered here. These etudés
are typically ignored in favor of vacuous theory-spinning - NONE of
which answer the simple question: "What is the Source Z if it is not
50 Ohms?"

73's
Richard Clark, KB7QHC

On Tue, 25 May 2004 07:27:03 -0500, "Richard Fry"
wrote:
However careful measurement of heat production and AC power consumption of
broadcast txs (for example) does NOT support the belief that the source Z of
a tx designed for 50 ohm loads IS 50 ohms.

Hi Richard,

This quote above bears directly to one of my observations. You define
by negatives, and that is a shoddy technical discussion worthy of the
creationist argument.

Tell us what it IS instead. A simple complex number is all that is
asked, derived from actual measurement. I've done this numerous
times, and not simply for milliwatt signal generators and have
returned these readings to the client with certificates of
traceability to Primary Standards Labs.

Barring any explicit answer that yields this complex number; then that
answer is simply conjecture and illusion that is commonplace in this
discussion. Draping it with programs and formula doesn't give
substance to the shape of that dream.

73's
Richard Clark, KB7QHC

Tam/WB2TT wrote:
You can get the same answer from knowing that the impedance looking
into a 1/4 wave section of shorted transmission line is infinite.

Ever measure the forward and reflected currents halfway into a
shorted 1/4WL stub? How can currents be flowing unimpeded into
and out of an infinite impedance? Hint: it's the net current
that is zero at the input of a 1/4WL stub. The forward current
and reflected current are equal in magnitude and opposite in
phase. Their individual magnitudes can be very large.
--
73, Cecil http://www.qsl.net/w5dxp





-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

On Tue, 25 May 2004 16:12:05 GMT, "Henry Kolesnik"
wrote:
Before it came down my 20 meter antenna had a SWR approaching 20:1 and I was
running a Collins 30S-1 and no tuner!. I did that for several years and
would be still doing if the roofers hadn't destroyed ~130 ft. dipole. One
of these days after my back improves I'll put another one up.

Hi Hank,

I used to teach this Collins equipment in the Navy. I presume yours
had a finals tuning circuit still in it? Hard to imagine it
otherwise.

Tubes are different from transistors only by approaching the Source Z
with an inverted ratio of transformation. Ever hear of plate
resistance? It is literal resistance. Ever see a plate glow when
under the stress of hi SWR? It is literal heat. The same heat is
generated irrespective of it being explained by wave mechanics or
lumped equivalent circuits. Choose the model you are comfortable
with, and then tackle the SWR if you care about efficiency.

If anything, tube sets prove the problem of reflected power through
your ability to directly observe the heat generated and experience the
cost of new finals tubes through their degraded life span. This stuff
is all rote teaching; and my students were given practical tests to
troubleshoot, tune, and repair against such scenarios.

I've had hands-on experience with this topic both academically and at
several benches - the sophistries that deny these points are amusing,
but remain amateur scribblings.

73's
Richard Clark, KB7QHC

The source Z of a typical tx having a single-ended Class C PA is just a few
ohms. The exact value depends on circuit design and tuning adjustments.
Heavy loading of the output tuning network of the PA reduces the return loss
looking back into the tx, and lighter loading improves it.

Please read my post using the new subject line "Tx Source Impedance & Load
Reflections" that I started for this a few minutes ago. The paper I refer
to and quote there (not mine) is accepted in the broadcast industry as a
benchmark on this subject.

- RF
____________

"Richard Clark"
Hi Richard,

This quote above bears directly to one of my observations. You define
by negatives, and that is a shoddy technical discussion worthy of the
creationist argument.

Tell us what it IS instead.

On Tue, 25 May 2004 11:42:42 -0500, "Richard Fry"
wrote:

The source Z of a typical tx having a single-ended Class C PA is just a few
ohms. The exact value depends on circuit design and tuning adjustments.
Heavy loading of the output tuning network of the PA reduces the return loss
looking back into the tx, and lighter loading improves it.

Please read my post using the new subject line "Tx Source Impedance & Load
Reflections" that I started for this a few minutes ago. The paper I refer
to and quote there (not mine) is accepted in the broadcast industry as a
benchmark on this subject.

- RF

OK you cannot give us a specific answer derived from actual
measurement.

73's
Richard Clark, KB7QHC

Henry Kolesnik wrote:
Before it came down my 20 meter antenna had a SWR approaching 20:1 and I was
running a Collins 30S-1 and no tuner!.

If the 30S-1 doesn't have a built-in tuner, what are those knobs
and meters for?
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----