Where does it go? (mismatched power)
 

On Sun, 13 Jun 2010 21:53:35 GMT, Owen Duffy wrote:

I have made an error here, Walt reports Pf=95W, Pr=20W, and on that basis
rho^2=0.211. The discrepency in rho is not discussed in the paper.

This needs to be put into the perspective of my last post too, as it
will impact your rho.
Pf = 90 to 100W,
Pr = 15 to 25W

73's
Richard Clark, KB7QHC

Where does it go? (mismatched power)
 

Richard Clark wrote in
:

Understanding what is available at Walt's bench, Pf could be off by
5W or 5%. The 0 reading also suffers the same 5W indeterminacy if it
is measured on the same scale (assuming he is using a Bird wattmeter
with a 100W slug).


Richard,

You can wax on all you like, and try as hard as you like, but if the
source was exactly Zs=50+j0, then the Bird 43 reading for Pf should be
exactly the same.

RF measurement is as you note, fraught with problems, but here is a
relatively simple case. Walt reported that he adjusted the radio on a 50
ohm load, measured Pf and Pr, then substituted another load, no other
changes and reported a 5% reduction in Pf.

I will leave you to arguing wether Walt's observed 5% reduction is of any
value.

Anyone who accepts that a competent measurement technician, competently
using the Bird 43, can reasonably discern a 5% reduction in Pf when it
should be 0% if Zs=50+j0, might question whether that observation
supports the proposition that Zs=50+j0.

Owen

Where does it go? (mismatched power)
 

On Jun 13, 10:04*pm, Owen Duffy wrote:
Richard Clark wrote :

Understanding what is available at *Walt's bench, Pf could be off by
5W or 5%. *The 0 reading also suffers the same 5W indeterminacy if it
is measured on the same scale (assuming he is using a Bird wattmeter
with a 100W slug).

Richard,

You can wax on all you like, and try as hard as you like, but if the
source was exactly Zs=50+j0, then the Bird 43 reading for Pf should be
exactly the same.

RF measurement is as you note, fraught with problems, but here is a
relatively simple case. Walt reported that he adjusted the radio on a 50
ohm load, measured Pf and Pr, then substituted another load, no other
changes and reported a 5% reduction in Pf.

I will leave you to arguing wether Walt's observed 5% reduction is of any
value.

Anyone who accepts that a competent measurement technician, competently
using the Bird 43, can reasonably discern a 5% reduction in Pf when it
should be 0% if Zs=50+j0, might question whether that observation
supports the proposition that Zs=50+j0.

Owen

Owen, I don't understand where you found a 5% drop in power when you
say it should have been 0%. A 5% drop from what value to what value?
Where did you find that data? If you're referring to 100w Pf with the
50 + j0 load and then the 95w Pf the mismatched load, you've got to
understand that the source was now delivering only 75w, and the 20w of
reflected power added to the 75w = 95w. These are two separate
measurements--the first a stand-alone value and the second the sum of
two values. Is this a point you overlooked?

Walt

Where does it go? (mismatched power)
 

walt wrote in
:

Owen, I don't understand where you found a 5% drop in power when you
say it should have been 0%. A 5% drop from what value to what value?

Hello Walt,

I wrote an article with the mathematical development for the fact that Pf
(as indicated by a properly calibrated directional wattmeter such as the
Bird 43) is independent of load impedance if and only if the Thevenin
source impedance is 50+j0 ohms. The article is at http://vk1od.net/blog/?
p=1028 .

This provides the basis for a simple go/nogo test for the hypothesis that
a particular transmitter, under particular conditions, exibits Zs=50+j0.

Where did you find that data? If you're referring to 100w Pf with the
50 + j0 load and then the 95w Pf the mismatched load, you've got to
understand that the source was now delivering only 75w, and the 20w of
reflected power added to the 75w = 95w. These are two separate
measurements--the first a stand-alone value and the second the sum of
two values. Is this a point you overlooked?

The source is Ch 19a where you report Pf=100, Pr=0 in Step 1; and Pf=95
and Pr=20 in Step 8. I am only interested in the relative values of Pf in
Step 1 (VSWR(50)=1) and Step 8 (VSWR(50)=3).

I conceded in another post that within reasonable expectations of error,
and considering the load case (VSWR(50)=3), that Zs under those
conditions and subject to only one load test is probably very close to 50
+j0, but probably not exactly.

In one test that I conducted with a range of loads, the drop in Pf was up
to 21% with VSWR(50)=1.5, but it varied with different VSWR(50)=1.5 load
angles. Whilst some values supported the proposition that Zs=50+j0,
others indicated that it was significantly different. Zs did not appear
to be constant, it appeared to be load dependent to some extent.

Going back to your case, if the source was 50+j0, we should expect Pf=
100, and if we trust your readings from the Bird 43 as characterising the
load to have rho^2=21%, we would expect the power delivered to the load
to be 78.9W rather than 75W, and error of 0.2dB. Not a large error, but
hard to account for entirely as instrument error.

In the measurements of an IC7000 that I made, the measured output power
on one VSWR(50)=1.5 load was 82.5W when it would have been 104.6W had the
source been 50+j0, an error of 0.8dB. I opined that this test did not
support the proposition that Zs was not 50+j0

Owen

Where does it go? (mismatched power)
 

Owen Duffy wrote in
:

....
In the measurements of an IC7000 that I made, the measured output
power on one VSWR(50)=1.5 load was 82.5W when it would have been
104.6W had the source been 50+j0, an error of 0.8dB. I opined that
this test did not support the proposition that Zs was not 50+j0

Too many "nots", isn't there?

It should read:

I opined that this test did not support the proposition that Zs was 50+j0.

Apologies, Owen.

Where does it go? (mismatched power)
 

On Mon, 14 Jun 2010 02:04:46 GMT, Owen Duffy wrote:

Anyone who accepts that a competent measurement technician, competently
using the Bird 43, can reasonably discern a 5% reduction in Pf when it
should be 0% if Zs=50+j0, might question whether that observation
supports the proposition that Zs=50+j0.

On Mon, 14 Jun 2010 04:18:02 GMT, Owen Duffy wrote:
if we trust your readings ...
Not a large error, but hard to account for entirely as instrument error.

Hi Owen,

Questions, emphatic competency, and reasonableness all in the space of
one sentence. I can see the well where you drew the literary "wax
on."

I will leave you to arguing wether Walt's observed 5% reduction is of any
value.

The follow-on discussion between you and Walt obviously reveals
sufficient value.

73's
Richard Clark, KB7QHC

Where does it go? (mismatched power)
 

On 13 jun, 21:27, Owen Duffy wrote:
lu6etj wrote :

...

I should tell owen he was inadvertently moving towards a logical
bifurcation's fallacy because is not absolutely true that Thevenin
theorem can not be used to calculate -for example- circuit efficience.
There are an exception to this limitation = It can be used to
efficience calculations when disconnecting the load in the original
circuit the dissipated power is null.

Miguel, when I said "cannot" I was of course meaning in the general case,
as most readers would understand.

Obviously there are cases where the efficiency calculations will be
correct, the obvious one being where the Thevnin equivalent is identical
to the original network.

If you want to make inferences about a source solely on the basis of its
Thevenin equivalent, you are on dangerous ground because you will not
always be correct.

People making the inference for example, that Zeq of a certain source
cannot be 50+j0 because the conversion efficiency of that source with a
50+j0 load is greater than 50% are wrong.

Owen

Hello Owen, OK at your comment I understand, here my apologies =

In earlier post I write:
"The final Thevenin circuit is an idealization built with an ideal
voltage source in series with an ideal resistor. This new idealized
circuit It is a new born entity whose properties are now fully
described for these only two idealized circuit elements. These are
the
virtues and the defects of reductionist models :("

And in the first post I was thinking about Thevenin resulting scheme
ceases to represent fully the original circuit and place the problem
in a more elementary and different situation that a real world
transmitter, enabling a clear answer to much simpler scheme for the
behavior of standing waves in such elementary context. And I thought
it was pretty clear beacuse was clear enough in my mind... :)
When one write in his own language, normally think is communicating
very well the idea in his mind, until notice his partner take it in
another way! Difficult is multiplied when you are trying communicate
to a mind that also thinks in a different language...!
Later I realized that having formulated in terms of a simple generator
in series with a resistor would not have generated a false
interpretation and not difficult the flow of ideas.

I sincerely believe (correct me if I am wrong) this newsgroup does not
seems make (do?) efforts enough (sufficient?) to totally (completely?)
solve the more simpler cases before skip to more advanced and
sofisticated considerations on more complex systems.
For example: do you (*) recognize Roy Lewallen late example in "Food
for tought" assuming (or conceding that) as not representing a real
rig but a simple constant voltage source in series with a resistor, at
least? to give some credit to his ideas Until now, I could not
know...
(*) I do not know how clearly denote plural in "do you"

73 Miguel - LU6ETJ.
Here 04:46 LT - I am not responsible for anything written by me :)

Where does it go? (mismatched power)
 

lu6etj wrote in
:

....
For example: do you (*) recognize Roy Lewallen late example in "Food
for tought" assuming (or conceding that) as not representing a real
rig but a simple constant voltage source in series with a resistor, at
least? to give some credit to his ideas Until now, I could not
know...

In that article, Roy says "My commercial amateur HF transceiver is
probably typical of modern rigs in that it produces a constant forward
average power into varying load impedances—provided the impedance isn’t
extreme enough to cause the rig to severely cut back its power output."

Assuming that "constant forward average power" means 'as would be
indicated on a directional wattmeter calibrated for Z=50+j0', if that is
true for all load impedances that Pf is constant (within limits), then it
is evidence that Zs=50+j0 (within those limits).

He goes on to say "It turns out that a linear model of my transmitter
(without a transmatch) over its non-shutdown range is very simple—it’s
just a voltage source in series with a resistance." Subject to the
conditions I stated in the previous paragraph, that is correct, but that
whilst that model can be used to determine behaviour of the external
load, there are limits to the inferences that can be drawn about the
internals of the transmitter, including as mentioned in earlier posts,
internal dissipation and efficiency. Roy acknowledges that in the next
paragraph. Only a mischief maker would represent Roy as meaning
otherwise.

From my own experience, I don't agree that HF ham rigs typically produce
constant Pf into varying loads. Walt's transmitter measurements that we
are discussing do not show constant Pf, though the change is fairly
small. But this is a practical measurement project for yourself, don't be
put off by the attempts to discredit measurements with anything but
traceable calibration.

(*) I do not know how clearly denote plural in "do you"

I am not the expert that others are on English language, and we speak a
version of English closer to the English here... but "you" is plural and
singular (but if followed by a verb, it is treated as plural eg "you are
correct"), and you could say to a group "do you agree", though some
people may say "do you all agree" or "do y'all agree", though those might
be seen as asking each member of the group rather than collectively.

Owen

Where does it go? (mismatched power)
 

On Jun 13, 11:19*am, Keith Dysart wrote:
Was your disingenuity deliberate?

No, it was non-existent. The source I referred to was Roy's *specified
source* in his food-for-thought article on forward and reflected
power. Roy used his *specified source* to do his power calculations.
Contrary to what you asserted, Roy certainly did "make an inference
about the internal dissipation of the source". The fact that Roy's
*specified source* doesn't resemble a ham transmitter is irrelevant.
--
73, Cecil, w5dxp.com

Where does it go? (mismatched power)
 

On Jun 13, 11:26*am, K1TTT wrote:
because they use the newer 'fields and waves in communication
electronics' by ramo, whinnery, and van duzer that uses reflection
coefficients and calculates voltages, currents, electric and magnetic
fields.

I've got a copy of the 3rd edition of that very book. S-parameters are
covered on page 540 so my question remains. Why don't RF engineers
read the book?
--
73, Cecil, w5dxp.com