On Tue, 15 Jun 2010 01:40:16 GMT, Owen Duffy wrote:

Richard Clark wrote in
:


Comparing to my table of results for my own TS430S, with similar
initical conditions, that is well within the range of measurements I
have taken.

After all the goading about toleranced figures and "vacant adjectives",
this is what you contibute.

C'mon Owen,

I have posted my results several times before. I don't think either
of us expected they made a ripple of notice then, but now this one
does when it is confirmed at another bench? I'm flattered.

I dismiss all of your previous comment as a windup.

Golly.

73's
Richard Clark, KB7QHC

lu6etj wrote in
:

....
I am not interested yet to make questions about real rigs, but reduce
at first only one specific problem at the most simple theorical model
I can think: an ideal constant voltage source in series with an ideal
resistence loaded at first with simple resistive loads connected
directly and late via ideal lossless TL of differents simple
wavelenghts 1/2, 1/4, 1/8 (I have formed idea about this, but I am not
interested in my concept but your concept about it).
For example, I want to know if you (all) would predict identical Rs
and Rl dissipation in that reduced and theorical context with direct
and remotely connected loads (vinculated via TL).

To this point K1TTT -seem to me- tell me you all would agree to settle
the problem with Telegrapher's equations to obtain TL input Z and then
apply simple circuit theory solution to calculate Rs-Rl dissipation
(before begin Thevenin misleading issue).
I do not want to advance more from here for fear to complicate the
question with my translation.

Yes, if you are looking for a steady state solution, that is a valid
solution, and almost the easiest solution.

If you are using lossless lines, then the solution can be simpler than the
Telegrapher's Equation which uses hyperbolic trig functions. Simple trig
functions suffice if the line is lossless... but of course, the hyperbolic
functions will also work.

The reason I said "almost the easiest solution" above is that a trig based
simplification of the Telegrapher's Equation is simpler than the hyperbolic
Telegrapher's equation.

Implicit in this is that for the steady state, it doesn't matter how an
external network dictates V/I (Z) at the source/load terminals, whether or
not transmission lines are involved, or their length, the power delivered
by the source to its immediate load is determined by Veq, Zeq of the
source, and Zl of the load.

If an experiment indicates othewise, the experiment is flawed (eg something
is wrong with the assumed values for circuit components, measurement error
etc).

Taking Walt's example, he connected three 50 ohms loads in parallel, then
attached a nominal 50 ohm line of 13.5° electrical length. If you use TLLC
(http://www.vk1od.net/calc/tl/tllc.php) to solve this problem at 4MHz using
RG213 (though I don't know what he used), Zin is 17.78+j10.58. A lossless
solution will have very slightly lower R. Walt measured 17.98 + j8.77 which
suggests that the load at the end of the 50 ohm line was not exactly
16.6667+j0, or the line a little shorter, Zo off spec etc.

Whilst the above focuses on steady state analysis, understand that steady
state analysis is not appropriate for some types of transmitters, but for
systems where the transmission line propagation delay is small compared the
the highest modulating frequency, steady state analysis should be adequate.

Owen

On Mon, 14 Jun 2010 19:00:47 -0700 (PDT), walt wrote:

I'm hungering to learn of the setup and procedure you used, because
I'd like to know what reflection mechanism gave a return signal that
could be discriminated from the 70w output signal from the
transceiver.

Hi Walt,

For every hundred pundits there is at least one bench worker that is
more productive than them all. Of course I am being facetious, it is
probably closer to a thousand.

In the SARL Forums at:
http://www.sarl.org.za
search for the 19/04/2009 posting by ZS6BIM with the thread name:
Measuring the Output Impedance of a 100W Class AB HF Linear Amplifier
Plenty of data and charted and screen shots of O'scopes.

A very intriguing use of directional couplers (much as I would expect
Tom to have done). It seems to me I've directed you to similar work
(the rat-race-like method seems familiar to our email discussion some
dozen years ago).

The writer had the cojones to use his vector voltmeter at the
transmitter's antenna terminal. Back in 1997 I used my GR bridge to
look down the throat of the fire breathing dragon (TS430S) while it
was asleep and got similar results:
10 MHz 74 Ohms
14 MHz 74 Ohms
18 MHz 60 Ohms
21 MHz 37 Ohms
25 MHz 35 Ohms
28 MHz 48 Ohms
29 MHz 70 Ohms

73's
Richard Clark, KB7QHC

On Jun 14, 9:00*pm, walt wrote:
In his Nov 1991 QST article Warren Bruene, W5OLY, used what I believe
is a similar procedure, in which he claims he measured the Rs that he
called the 'source impedance' of the RF amp. *He used his measurements
in asserting that because his Rs didn't equal RL there could be no
conjugate match when the source is an RF power amp. I have never
believed his procedure and measurements were valid, and I still don't.

IMO, the error that Bruene made is similar in concept to the some of
the errors being made here in this thread. Many people assume that a
simple reflection is the only way to change the direction and momentum
of an EM wave in a transmission line. In "Reflections", Sec 4.3,
Reflection Mechanics of Stub Matching, you describe the role of wave
cancellation associated with interference as a mechanism for
redistributing reflected energy back toward the load. You said, "Wave
interference between these two complimentary waves at the stub point
causes a cancellation of energy flow in the direction toward the
generator." It seems obvious to me that your "virtual short"
reflection at a Z0-match point is a combination of ordinary wave
reflection and interference patterns adding up to zero energy flowing
toward the source. Obviously, interference can also happen inside a
source.

Redistribution of energy can occur associated with destructive/
constructive interference inside the source and has an effect on the V/
I ratios, i.e. on the impedances. Bruene's pinging method completely
ignores the role of interference at the source. The Z = (Vfor+Vref)/
(Ifor+Iref) impedance for coherent waves may be a completely different
value than for the non-coherent pinging waves.
--
73, Cecil, w5dxp.com

On Jun 15, 1:30*am, lu6etj wrote:
Sorry and thanks Cecil I do not see this kind answer (I still using
normal Google groups reader and loss tracking of your message).
Tomorrow I will analize it with care, now is late here but I do not
want delay my aknowledge.

Miguel, some posters here don't seem to realize that your questions
involve a source like the one specified by w7el in his foot-for-
thought article. That source may bear little resemblance to an actual
ham transmitter but it is the one w7el specified and it can be easily
analyzed for source resistor dissipation and tracking of the reflected
energy.
--
73, Cecil, w5dxp.com

On 15 jun, 05:49, K7ITM wrote:
On Jun 14, 7:00*pm, walt wrote:



On Jun 14, 2:56*pm, K7ITM wrote:

On Jun 13, 11:42*pm, Owen Duffy wrote:

Owen Duffy wrote :

...

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.

I suppose this will be buried where nobody will read it...

I realized that with the nice instrument-grade directional couplers
that came with a new 100W RF power amplifier, and with the other
equipment on my bench, I can measure RF amplifier/transmitter source
impedance relatively easily and with good accuracy. *I strongly
suspect the accuracy will be limited first by how well the setup of
the transmitter/amplifier can be duplicated, and not by the
measurement instruments.

I won't go through the whole test setup, but just say that
substituting an open or short for the connection to the transmitter
yields the expected amplitude return signal, and terminating the line
in a precision 50 ohm calibration standard yields a 47dB return loss,
for the frequency I was measuring (nominally 7MHz, for this first
measurement). *The measurement involves sending a signal offset from
the nominal transmitter frequency by a few Hertz at about -20dBm
toward the transmitter, and looking at what comes back.

Measuring a Kenwood TS520S, set up for about 70 watts output, ALC
disabled, operating as a linear amplifier somewhat (about 30 watts)
below its maximum output: *result is 56+j16 ohms at the output UHF
connector on the TS520S. *That's about 1.4:1 SWR, and at some point
along a lossless line, that's equivalent to about 70+j0 ohms: *not
terribly close to 50 ohms. *I'm not going to bother with a detailed
error analysis presentation, but I'm confident that the amplitude of
the return loss is accurate within 0.1dB, and the phase angle within
10 degrees, to better than 99% probability.

I may make some more measurements with different amplifier setups and
at different frequencies, but for now, that's it...

Cheers,
Tom

Tom, you stated earlier that you measured the source impedance of a
TS520S transceiver by inserting a somewhat off-resonance signal into
the output terminals when the rig was delivering 70 watts, and the
source impedance was measured as 56+j16 ohms. However, you chose not
to describe the setup or the procedure for obtaining this data.

I'm hungering to learn of the setup and procedure you used, because
I'd like to know what reflection mechanism gave a return signal that
could be discriminated from the 70w output signal from the
transceiver.

In his Nov 1991 QST article Warren Bruene, W5OLY, used what I believe
is a similar procedure, in which he claims he measured the Rs that he
called the 'source impedance' of the RF amp. *He used his measurements
in asserting that because his Rs didn't equal RL there could be no
conjugate match when the source is an RF power amp. I have never
believed his procedure and measurements were valid, and I still don't.
So if your setup in any way resembles what Bruene presented in his QST
article I would like to know how you can justify a procedure that
involves inserting an off-set frequency signal rearward into an
operating RF power amp *to determine the source impedance.

Walt, W2DU

OK...

So let's consider making a load-pull measurement of source impedance.
Since we're trying to resolve both resistance and reactance, we need
to change the load in at least two directions that have a degree of
orthogonality. *But we could also change the load over a range of
values. *For example, we could connect a 51+j0 load directly to the
output port we're trying to measure, and then connect it through
varying lengths of 50.0 ohm lossless coax. *45 electrical degrees of
line would shift the phase of the 51 ohm load so it looks instead like
49.99-j0.99 ohms. *90 electrical degrees shifts the 51 ohm load to
49.02+j0 ohms, and so forth. *Measurements of the varying amplitude
output with those loads will give us enough information to resolve the
source resistance and reactance and open-circuit voltage.

For a 51 ohm load on a 50 ohm line, the reflection coefficient
magnitude is 1/100, so if the transmitter is putting out 100Vrms
forward, the reverse is 1Vrms.

Now consider a method to change the line length that doesn't use
individual sections that have to be patched in and out, but rather
uses a "trombone" section that, in theory anyway, could range from
zero length to essentially infinite length. *Picture that trombone
section getting longer at a fixed rate, so now the load is rotating
around a circle on the linear reflection coefficient plane (which is,
by the way, exactly the same plane the Smith chart is plotted on); the
circle is centered at zero and is a constant 1/100 amplitude, with
linearly varying phase. *So the 1Vrms reverse wave on the line of the
100Vrms forward example arrives back at the amplifier at continuously
varying phase. *Imagine that the phase shift is 360 degrees in 1/100
of a second. *Now note that the reverse wave corresponds _exactly_ to
a wave offset in frequency from the forward wave by 100Hz. *If the
line is continuously lengthening, the offset is negative; if the line
is shortening instead, the offset is positive.

Now, from the point of view of the amplifier, can that scenario be
distinguished from one in which I have a perfect 50 ohm load that
absorbs all the transmitter's output, and a method to introduce a
"reverse" 1.00Vrms wave into the line at a frequency that's offset
from the transmitter's output by 100Hz?

If you believe that the amplifier can distinguish between those two
scenarios, I fear we have nothing more to discuss.

Cheers,
Tom

Hello Tom,

The method of constant varying phase of a mismatch to determine output
impedance I use in my simulation also (because it saves me time). I
use a second source with some frequency offset instead of the trombone
as you described (the trombone I cannot implement easily in my pspice
package).

When you change the phase very slowly, a soft power supply may change
voltage during the slow variation (as a load change may result in a DC
supply current change). When the difference frequency is sufficiently
high (for example 200 Hz or more), the electrolytics will keep the
supply voltage constant during all phase "steps". Therefore there may
be slight difference between measurement with a set of loads with
increasing phase and the RF injection method (for example with vector
analyzer).

I checked the injection method in simulation for linear circuits (with
both real and complex output impedance), linear active circuits, and
power circuits. I couldn’t find any flaw in the method. So I think
your reasoning is valid.

Some results applicable to PAs, inclusive the implementation in
simulation are in: http://www.tetech.nl/divers/PA_impedance.pdf. Note
that I determine the reflected voltage by means of interference with
the amplifier's output signal (envelope detection) as this saves me
from making a narrow band filter that results in very long run times.

I am now simulating a circuit with 6146 valve and pi-filter output (50
Ohms) and I will add it to the document.

Best regards,

Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me

Richard Fry wrote:

If reflected power is fictitious, and the number wavelengths of
transmission line of any random impedance compared to the load
connected to it makes no difference in the load seen by the
transmitter, the output power produced by the transmitter, and the
power dissipated in the far-end termination, then what is the reason
you chose a 1/2 wavelength of transmission line in your quoted post?

RF

I chose that length so that the transmission line would have no effect
on the impedance seen by the transmitter. As I've said many times, and
you've continually disagreed with, increased dissipation and/or damage
at the transmitter is due to the impedance it sees, and not by
"reflected power". The example I gave keeps the transmitter load
impedance constant while changing the "reflected power". And it shows
that neither the transmitter nor the load see any changes in dissipation.

If I had chosen a different length line, then changing its Z0 would have
changed the impedance seen by the transmitter, which would have changed
its efficiency by an amount which could have been determined only with
additional knowledge about its characteristics. But replacing the
transmission line with a lumped impedance transforming network would
have exactly the same effect on the transmitter, again illustrating that
the only important factor is the impedance the transmitter sees and not
the "reflected power" in the line it's connected to.

This posting is being made, though, for the benefit of other readers.
I've explained this many times to you before with no noticeable effect
on your understanding.

Roy Lewallen, W7EL

Richard Fry wrote:
On Jun 11, 12:29 pm, Richard Fry wrote:

If reflected power is fictitious, etc

Followup: Those denying the existence of reflected signals within an
antenna system may wish to view the measurement of such signals, at
the link below.

http://i62.photobucket.com/albums/h8...easurement.gif

RF

Thanks, but I've designed TDR systems and prepared and given classes on
the topic.

Roy Lewallen, W7EL

Owen Duffy wrote:
lu6etj wrote in news:da3e5147-cad8-47f9-9784-
:

...
OK. Thank you very much. This clarify so much the issue to me. Please,
another question: On the same system-example, who does not agree with
the notion that the reflected power is never dissipated in Thevenin
Rs? (I am referring to habitual posters in these threads, of course)


Thevenin's theorem says nothing of what happens inside the source (eg
dissipation), or how the source may be implemented.
. . .

Cecil has used this fact as a convenient way of avoiding confrontation
with the illustrations given in my "food for thought" essays. However,
those models aren't claimed to be Thevenin equivalents of anything. They
are just simple models consisting of an ideal source and a perfect
resistance, as used in may circuit analysis textbooks to illustrate
basic electrical circuit operation. The dissipation in the resistance is
clearly not related to "reflected power", and the reflected power
"theories" being promoted here fail to explain the relationship between
the dissipation in the resistor and "reflected power". I contend that if
an analytical method fails to correctly predict the dissipation in such
a simple case, it can't be trusted to predict the dissipation in other
cases, and has underlying logical flaws. For all the fluff about
photons, optics, non-dissipative sources, and the like, I have yet to
see an equation that relates the dissipation in the resistance in one of
those painfully simple circuits to the "reflected power" in the
transmission line it's connected to.

Roy Lewallen, W7EL

lu6etj wrote:

R. R. Well... I forget to say the more important = For the sake of
the advance of the topic please do replace "Thevenin circuit" in my
original question for "an ideal constant voltage source in series with
an ideal resistance" equivalent only to itself :)

Thank you, that's exactly what I've tried to do. But calling all such
simple circuits "Thevenin equivalents" is a convenient way to avoid
having to explain the phenomena they illustrate. So that has been the
tactic of some of the "reflected power" proponents.

Roy Lewallen, W7EL