Richard Harrison wrote:
Terman says on page 96 of his 1955 opus:
"The reflected wave is identical with the incident wave except that it
is traveling toward the generator."

Gene needs to tell us how the TV modulation that
causes ghosting makes its predictable round trips
to the source and back without the aid of the
reverse traveling wave.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote in news:7iYLh.73$Kd3.72
@newssvr27.news.prodigy.net:

Gene needs to tell us how the TV modulation that
causes ghosting makes its predictable round trips
to the source and back without the aid of the
reverse traveling wave.

Talk about echoes!

Cecil, at the time of writing, you have made 4 of the 7 responses to
Walt's posts, and there is nothing in what you have said that you haven't
said recently.

The language from various posters like:

"Some of the posters apparently are unable..."

"Some would say..."

"people obviously don't understand..."

"How can you possibly deny..."

doesn't seem to me the language of convicing arguments, much less proof,
from either side. They seem more a sign of the posters frustration, but
not otherwise convincing.

My guess is that this discussion will not converge on a convincing
outcome.

If the past is any indicator, just when agreement of two or three people
looks likely, someone will inject some noise like lets start dealing with
time domain and transient issues to prove that steady state analysis is
invalid in the practical sense, or this needs a photon explanation with
reference to a text no one is likely to have. It as though those posters
intended to wreck logical development and conclusion. Ah, but that is
USENET!

The basis of the assertion that a PA is naturally or magically conjugate
matched as a necessary consequence of adjustment or design for maximum
power output is based on an leveraging the Maximum Power Transfer Theorem
which depends on a linear source. I don't recall seeing experimental
results to convincingly demonstrate that the PA is a linear source,
though I have seen those that suggest otherwise. If the source cannot be
proven to be sufficiently close to a linear source, then the basis for
arguing the implicit conjugate match dissolves.

No one has yet come up with a quantitative proof that in the general case
PAs of all kinds have an equivalent source impedance the conjugate of
their load, nor convincing experiments that would place bounds on the
reflection coefficient looking into the PA for practical transmitters.

No one has demonstrated that using equivalent impedances etc is not a
valid analysis of the steady state behaviour.

Owen

Cecil Moore wrote:
Richard Harrison wrote:
Terman says on page 96 of his 1955 opus:
"The reflected wave is identical with the incident wave except that it
is traveling toward the generator."

Gene needs to tell us how the TV modulation that
causes ghosting makes its predictable round trips
to the source and back without the aid of the
reverse traveling wave.

Cecil,

It is interesting that you can be so precise at times and so sloppy at
other times. I very carefully limited my discussion to steady state
conditions, which is what everyone is already talking about in this
case. You then conveniently inject modulation into the mix, completely
ignoring what I said.

Do the math and show us how my comment is in error. Add the two
traveling waves and see if you get the summation to be precisely a
standing wave plus a residual forward traveling wave. Go back and reread
your quoted references and try to figure out if anything I said is
different from your gurus.

73,
Gene
W4SZ

Gene, W4SZ wrote:
"No need to account for any mythical power in the reflected waves."

My dictionary defines reflected power as:
"The power flowing back to the generator from the load."

Maximum power theorem is defined as:
"The maximum power will be absorbed by one network from another joined
to it at two terminals, when the impedance of the receiving network is
varied, if the impedances (looking into the two networks at the
junction) are conjugates of each other."

Clearly a generator (transmitter) connected to a load through a lossless
line sees Zo of the line as its load until the instant that reflected
power returns to the generator from the load.
Suppose the round-trip delay of the line makes the reflected voltage
exactly in phase with the transmitter output. further suppose the
reflection was total so that the reflected voltage exactly equals the
transmitter output. In this special case, we might as well be connecting
identical battery cells in parallel. No current is going to flow. The
generator is seeing infinite impedance.

What is the generator load that extracts maximum power from a
transmitter? A conjugately matched load, of course. To determine the
impedance of a transmitter, one only needs to find the load which
extracts maximum power. The transmitter impedance is its conjugate.

Best regards, Richard Harrison, KB5WZI

On Mar 22, 12:31 pm, (Richard Harrison)
wrote:

What is the generator load that extracts maximum power from a
transmitter? A conjugately matched load, of course. To determine the
impedance of a transmitter, one only needs to find the load which
extracts maximum power. The transmitter impedance is its conjugate.

Best regards, Richard Harrison, KB5WZI

We have a new signal generator here at the Labs, but it came without
any documentation. We've been hoping to find out more about it, and
your suggestion gave us a clue for a test to try. We have a limited
set of loads, only from 40 to 60 ohms, but we can add some known
reactance in series with that. When we put an accurate 50 ohm load on
the generator, we measured exactly 1 watt with our accurate RF power
meter. When we changed the load to 40 ohms, the power went up to
1.238 watts, and with a 60 ohm load, it was .839 watts. When we add
reactance, either capacitive or inductive, the power goes down, so
we're pretty sure the generator output doesn't look reactive. Beaker
is having a little trouble with the math on this one. Could you help
him out? What sort of output impedance does this generator have?

Oh, and we thought to do another experiment. While the generator was
operating, we sent a short burst of RF down a 50 ohm transmission line
to the generator's output. Because the power measurements seem to say
the generator's output resistance is very low, we thought we would see
a return pulse, delayed by the round-trip time down the 15 meters of
high-quality cable. But we didn't see any echo. What could be going
on? We double-checked everything, and even looked into the line next
to the generator with a high impedance probe. We can see the burst
going in there, but still nothing comes back.

From the labs,
Dr. Honeydew

On Mar 20, 3:37 pm, Walter Maxwell wrote:
One of the issues discussed in this thread that Owen originated concerned whether or not reflected power
enters the power amp and dissipates as heat in the plates of the amp. Some of the posters apparently are
unable to appreciate that the reflected power does not cause heating of the amp, unless the reflected power
detunes the amp and the amp is left detuned from resonance, which of course is not the correct manner of
operating the amp.

In the last post of the original thread I presented the details of an experiment I performed (one of many
using the same procedure) on a Kenwood TS-830S transceiver that proves how and why reflected power in no way
causes heating of the amp when the amp is properly adjusted in the presence of the reflected power.

Usually, such a presentation as in the last post in that thread evokes a great deal of response, as for
example, Art Unwin's. So I'm somewhat surprised, and a little disappointed that my post has resulted in total
silence. Have my efforts in helping to solve the problem gone for naught?

Walt, W2DU

I have followed this thread with interest There are some who seem to
dispute the existance of reflected power and its ability to do damage.
My answear is that reflected power can certainly do so any one want to
run a completly detuned antenna to prove me wrong may do so at their
expence and risk. as to it causing heat in the amp of course not the
extra work that the amp has to do to "push" the signal to the antenna
does. if a semiconductive device is over worked then it will produce
heat.
The old thermonic valves are far more tolerant than semiconductors.
mike M0DMD

wrote:
I have followed this thread with interest There are some who seem to
dispute the existance of reflected power and its ability to do damage.
My answear is that reflected power can certainly do so any one want to
run a completly detuned antenna to prove me wrong may do so at their
expence and risk.

Reflected power doing damage is an overly simplistic
way of viewing things. The reflected wave is capable
of causing damage without giving up any of its energy.
It is not the energy in the reflected wave, per se,
that causes the damage. It is the interference pattern
established by superposition of the forward wave and
the reflected wave that causes the damage.

If the reflected voltage arrives back at the source
in phase with the forward voltage, that constructive
voltage interference can cause an over-voltage condition
that blows the finals. This over-voltage condition actually
reduces the dissipation in the finals because it is
accompanied by a destructive interference, reduced-current
condition. The finals are actually cooler than normal
when the over-voltage begins to fry them.

Of course, a Thevenin equivalent source doesn't suffer
from an over-voltage problem. Power consumption within
a Thevenin equivalent source actually decreases during
constructive interference between the forward and
reflected voltages.

If the reflected current arrives back at the source
in phase with the forward current, the result can
be an over-current condition which can indeed cause
over-heating and failure.

What happens in the finals depends upon the phase
of the reflected wave. Solid-state finals are
usually protected from both over-voltage and
over-current by detecting the SWR. A fold-back SWR
limit of 3:1 limits both the ratios of Vmax/Vmin
and Imax/Imin to 3:1.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:


Reflected power doing damage is an overly simplistic
way of viewing things. The reflected wave is capable
of causing damage without giving up any of its energy.
It is not the energy in the reflected wave, per se,
that causes the damage. It is the interference pattern
established by superposition of the forward wave and
the reflected wave that causes the damage.

If the reflected voltage arrives back at the source
in phase with the forward voltage, that constructive
voltage interference can cause an over-voltage condition
that blows the finals. This over-voltage condition actually
reduces the dissipation in the finals because it is
accompanied by a destructive interference, reduced-current
condition. The finals are actually cooler than normal
when the over-voltage begins to fry them.


Cecil,

Ya know, it is possible to simply add and subtract voltages. It is not
required to determine an "interference pattern". Solid state electronics
are damaged by high voltage or high power dissipation (or both). No
"interference patterns" required.

Perhaps the manufacturers could add exactly the correct length of
transmission line inside the transceivers so that the wrong kind of
interference could never occur at the finals.

8-)

73,
Gene
W4SZ

Gene Fuller wrote:
Ya know, it is possible to simply add and subtract voltages. It is not
required to determine an "interference pattern".

It is absolutely necessary to understand the interference
patterns if one wants to track the energy through the
system.
--
73, Cecil http://www.w5dxp.com

On 20 Mar, 08:37, Walter Maxwell wrote:
One of the issues discussed in this thread that Owen originated concerned whether or not reflected power
enters the power amp and dissipates as heat in the plates of the amp. Some of the posters apparently are
unable to appreciate that the reflected power does not cause heating of the amp, unless the reflected power
detunes the amp and the amp is left detuned from resonance, which of course is not the correct manner of
operating the amp.

In the last post of the original thread I presented the details of an experiment I performed (one of many
using the same procedure) on a Kenwood TS-830S transceiver that proves how and why reflected power in no way
causes heating of the amp when the amp is properly adjusted in the presence of the reflected power.

Usually, such a presentation as in the last post in that thread evokes a great deal of response, as for
example, Art Unwin's. So I'm somewhat surprised, and a little disappointed that my post has resulted in total
silence. Have my efforts in helping to solve the problem gone for naught?

Walt, W2DU

Walt you got your wish, over 100 posts and still coming. How many
postings is it going to take to not only read what you said and also
the hard part
understand what you are saying? Only you can answer whether your help
to solve the problem has gone for naught. Maybe at 200 postings you
will feel a bit better about things but I doubt it. But I must thank
you as you have greatly decreased the number ugly postings in my
direction so please keep it up.
Regards
Art
Art