The power explanation
 

Cecil, W5DXP wroote:
"What is the dissipation in the generator using a Norton source?"

According to page 76 of Terman`s 1955 opus:
"Alternatively, a load impedance may be matched to a source of power in
such a way as to make the power delivered to the load a maximum (the
available power of the power source). This is accomplished by making the
load impedance the conjugate of the generator impedance as defined by
Thevenin`s theorem."

On page 75 Terman labels a Norton diagram: "Equivalent Arrangement".

Equivalence means the open-circuit voltage and short-circuit current are
the same whichever diagram represents the power source.

The power dissipated in the source under matched conditions depends not
on the diagramatic representation, but upon how much of the internal
resistance of the source behaves as a resistor does, and how much is
"dissipationless resistance". It`s real, but makes no heat. If it were
fictional, final amplifiers would be limited to 50% efficiency. We all
know many R-F amplifiers have discontinuous input power
which allows efficiencies much in excess of 50%.

Best regards, Richard Harrison. KB5WZI

The power explanation
 

On Fri, 02 Mar 2007 07:04:32 GMT, Owen Duffy wrote:

I find negative propositions a bit oblique, what DOES it imply?

I was responding to your words:

"I will at this point re quote Chipman to roughly this scenario (being
more general, he didn't specify the reflection).

"At the signal source end of the line ... none of the power
reflected by the terminal load impedance is re-reflected on
returning to the input end of the line."
The ellipsis reveals that the source Z matches the line Z."

I disagree that the conditions that exist in the steady state at the
source end of the line imply in the general case, matching in the Jacobi
Maximum Power Transfer Theoram sense.

Hi Owen,

This is still oblique. Are you speaking of the conditions you created
(for either instance in this thread)? Or that Chipman created to
illustrate his figure? Or through a loose reference to me? Or
perhaps it is compounded in the missing preceding comma for a
parenthetical "in the general case?"

If the last serves, and to the point of obliquity, when did the JMPTT
show up and who are you disagreeing with?

73's
Richard Clark, KB7QHC

The power explanation
 

On 2 Mar 2007 05:27:13 -0800, "Denny" wrote:



Ya know, all the bits sent on to the great bit bucket in the sky
during this 'discussion' could have been avoided by simply reading
Walt Maxwell's "Reflections" until you understand it...
denny / k8do

Hi Denny,

I am to presume you are adding bits to the bit bucket then? Your own
answer to any of Owen's examples would have trumped hoary advice.

73's
Richard Clark, KB7QHC

The power explanation
 

Cecil Moore wrote in news:fuWFh.3131$M65.1761
@newssvr21.news.prodigy.net:

Cecil Moore wrote:
Owen Duffy wrote:
This simple example that shows that existence of "reflected power" on
a transmission line does not necessarily result in some or all of the
"reflected power" being dissipated in the generator.

I will leave it to Cecil to take to confuse this simple example with
some photon based complication.

No photons necessary, Owen. You are using a Thevenin
equivalent source.

What is the dissipation in the generator using a Norton
source?

The existence of cases that show that dissipation in the source does not
necessarily increase due to VSWR on the transmission line does not
support the assertion that "VSWR causes reflected power that is
dissipated in the source". One sound case is enough to disprove the
generality.

Sure, transforming the source to a Norton equivalent would produce an
answer, and in this case a different answer for what happens inside the
generator. That Norton equivalent source with half wave s/c line will
also produce zero dissipation in the source.

Cecil, it appears your motive is to create confusion to divert attention
from the cases that are inconsistent with the assertion that "VSWR causes
reflected power that is dissipated in the source".

I have no difficulty with the statement "a transmitter is usually
specified to work over a limited range of load impedances (often
specified as a maximum VSWR at the transmitter terminals), the user
should expect it works properly over that range and should understand
that operation outside of that range may expose it to voltages or
currents (consequent heat), that may cause permanent damage". This advice
can be given to a six hour ham without telling them any lies, but
imparting the knowledge that they need to operate safely.

The explanation expressed / supported by some here that "we use ATUs to
cause total re-reflection of power "reflected" from the antenna so
protecting the PA" is a nonsense explanation of how the ATU protects the
PA from the effects of a poor load.


Owen

The power explanation
 

Owen Duffy wrote:
Cecil, it appears your motive is to create confusion to divert attention
from the cases that are inconsistent with the assertion that "VSWR causes
reflected power that is dissipated in the source".

Appearances can be deceiving. My motive is to uncover facts
and I agree with virtually everything you have said.

My personal opinion is that from 0% to 100% of reflected
power can be dissipated in the source depending upon the
relative phase of the incident reflected wave and the
configuration of the source. It can be argued that if the
source sees an infinite or zero impedance, then all of the
source power is reflected at the source output. This, of
course, would be a same-cycle reflection, something that
also occurs at the mismatched load.

By convention, any power same-cycle reflected at the source
output was never generated to start with - one of the original
copouts.

Since the great majority of amateur transmitters are
looking into a Z0-match resulting in total destructive
interference in the direction of the source, IMO, this
subject is pretty much moot. That's why I poke fun at it.

All one has to do to calculate the reflected power
dissipated in the source is to understand the constructive
and destructive interference occurring at the source
output terminal. This is easier said than done.
--
73, Cecil http://www.w5dxp.com

The power explanation
 

Owen Duffy wrote:
Richard Clark wrote in
:

On Fri, 02 Mar 2007 06:16:15 GMT, Owen Duffy wrote:

that does not imply matching in
the Jacobi Maximum Power Transfer Theoram sense.

-um, OK-

I find negative propositions a bit oblique, what DOES it imply?

I was responding to your words:

"I will at this point re quote Chipman to roughly this scenario (being
more general, he didn't specify the reflection).

"At the signal source end of the line ... none of the power
reflected by the terminal load impedance is re-reflected on
returning to the input end of the line."
The ellipsis reveals that the source Z matches the line Z."


The confusion arises out of Richard's misleading quotation, which is out
of context and includes an inaccurate final sentence ("The ellipsis
reveals...") added by Richard himself.

The context in Chipman's book is specifically about the scale of
"reflection loss" as found alongside a Smith chart. Reflection loss is
the power delivered into a mismatched (reflecting) load impedance,
relative to the power that would have been delivered into a matched
(non-reflecting) load.

Chipman points out that "The concept is directly applicable only to
transmission-line circuits of the form shown in Fig 9-26, in which the
source impedance is equal to the characteristic impedance of the line."

In more detailed analysis, he explains why the definition of reflection
loss only holds good if there is no further re-reflection at the source,
so the "reflection loss" scale on the Smith chart can only be used in
cases where the source impedance Zs is equal to Zo of the line.

Richard's comment that "The ellipsis reveals that the source Z matches
the line Z" is misleading, for that isn't at all what Chipman was
saying. Chipman makes it perfectly clear that this section is dealing
with a special case, which only applies if Zs has deliberately been made
equal to Zo. Most of the rest of the book deals with the more general
case where Zs is NOT necessarily equal to Zo.

However, that special case often does apply to signal generators and
similar test equipment. If the RF output comes through an attenuator
that has a design impedance of Zo, and if the attenuation is large
enough, this creates a good approximation to a source of impedance Zo.
Then the reflection loss concept becomes valid.




--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

The power explanation
 

On Sat, 3 Mar 2007 00:10:21 +0000, Ian White GM3SEK
wrote:

The confusion arises out of Richard's misleading quotation,

blah blah blah blah blah

Hi Ian,

I have restrained the afterburners until 1200 GMT (seeing as you are
undoubtedly in bed) so that you can fully read the entire side thread
and discover the complete botch you've made in an attempt to weakly
persuade the group that a transmitter could never absorb the energy of
a reflected wave.

That was your point for this chain of accusation, wasn't it, or were
the accusations a solitary pleasure? (I hope you opt for the first,
or other explanation.) I don't expect any apologies so that I can
enjoy a dish that is best eaten cold (re-heated actually). ;-)

73's
Richard Clark, KB7QHC

The power explanation
 

On Fri, 02 Mar 2007 20:37:22 -0800, Richard Clark
wrote:

until 1200 GMT

"Don't talk to me about a man's being able to talk sense;
everyone can talk sense. Can he talk nonsense?"

The power explanation
 

On Mar 3, 4:37 am, Richard Clark wrote:
On Sat, 3 Mar 2007 00:10:21 +0000, Ian White GM3SEK

wrote:
The confusion arises out of Richard's misleading quotation,

blah blah blah blah blah

Hi Ian,

I have restrained the afterburners until 1200 GMT (seeing as you are
undoubtedly in bed) so that you can fully read the entire side thread
and discover the complete botch you've made in an attempt to weakly
persuade the group that a transmitter could never absorb the energy of
a reflected wave.

That was your point for this chain of accusation, wasn't it, or were
the accusations a solitary pleasure? (I hope you opt for the first,
or other explanation.) I don't expect any apologies so that I can
enjoy a dish that is best eaten cold (re-heated actually). ;-)

73's
Richard Clark, KB7QHC

I'm in a hotel in Jax, FL, unable to use my routine connections to
rraa, so I'm learning my way around in unknown territory here, and
hope to make a post that will appear.

I've been reading this thread with interest, but the discussions
appear to be only academically related. On the other hand, I've made
measurements that prove the sailent points of these academic
discussions. These measurements were made since those reported in
Reflections 2, and will appear in Reflections 3. However, they are
available on my web page at www.w2du.com. Go to 'Preview of Chapters
from Reflections 3' and click on Chapter 19A.

You may want to disregard the first portion of the chapter, which is
an epilog to Bruene's fiction concerning the conjugate match. The
pertinent portion here is that which reports in detail the step-by-
step procedure in measuring the output impedance of a Kenwood TS-830S
transceiver feeding a reactive-impedance load.

With a careful review of these steps I'm sure you'll find empirical
proof of the academics appearing in the previous posts.

Walt, W2DU

The power explanation
 

On Wed, 28 Feb 2007 20:35:27 GMT, Owen Duffy wrote:

Breaking out of the previous thread to explore the "power explanation" in
a steady state situation:

The scenario for discussion is a transmitter connected to a half wave of
600 ohm lossless transmission line connected to an antenna with a
feedpoint impedance of 70+j0.

The transmitter is rated for 100W output, 100W is developed in the 70 ohm
load, the VSWR on the transmission line is 8.6, the "forward power"
(meaning Vf^2/Zo) on the transmission line is 267W, the "reflected
power" (meaning Vr^2/Zo) on the transmission line is 167W, the DC input
power to the transmitter is 200W.

The questions a

Is there any internal inconsistency in the scenario characterisation, if
so, identify / explain?

What is the heat dissipated in the transmitter (and why)?

What part of the "reflected power" of 167W is dissipated in the
transmitter (and why)?

Owen

Hi All,

Per recent correspondence from Walt Maxwell, he has asked me to post
his contribution:

Hi Richard,

I'm in a hotel in Jacksonville, away from my home computer, and at
this time I can't access the rraa to send, can only receive, so I'm
asking for your help.

I've been reading the posts on this thread and find it interesting.
However, it's been only discussed academically. On the other hand,
I've made measurements that prove the results described, measurements
made since those reported in Reflections 2.

I'd like for you to alert the posters on this thread to see Chapter
19A that will appear in Reflections 3, which is available for download
from my web page at www.w2du.com. The entire chapter was written as a
final epilogue to Bruene's fiction, but the portion pertinent to the
thread is in the last portion of the chapter concerning the
measurements made using a Kenwood TS-830S. Therein lies
the proof.

It would be nice if you could post the entire portion of the
measurements section, but that probably wouldn't work, because of
special characters used in Word that wouldn't appear in the text.
Anyway, I'd like for the posters to know that experimental proof
exists to support the claims made in the thread.

Thanks, Richard,

Walt


73's
Richard Clark, KB7QHC