On Jun 13, 11:27*am, K1TTT wrote:
On Jun 13, 3:02*pm, Cecil Moore wrote:

On Jun 13, 9:34*am, K1TTT wrote:

why are they (voltages) indeterminate? *i can calculate them, why can't you?

Please tell me how you can calculate an absolute voltage when Z0
is an unknown variable?

the same way you calculate the power to be zero watts. *no need to
know the z0 if the voltage is zero.

Ah, but you said you could calculate "them", meaning at least two
voltages. You have calculated one voltage to be zero. So what is the
value of one of the other voltages when the Z0 is unknown?
--
73, Cecil, w5dxp.com

K1TTT wrote:
On Jun 9, 10:38 pm, Jim Lux wrote:
In fact, the ration between that stored energy and the amount flowing
"through" (i.e. radiated away) is related to the directivity of the
antenna: high directivity antennas have high stored energy (large
magnetic and electric fields): the ratio of stored to radiated energy
is "antenna Q" (analogous to the stored energy in a LC circuit leading
to resonant rise).

So, high directivity = high stored energy = high circulating energy =
high I2R losses.

this is a relationship i haven't heard of before... and would be very
wary of stating so simply.

I should have used arrows rather than equals signs.
But it's basically a manifestation of Chu's idea combined with practical
materials.

Chu proposed the concept relating directivity and stored energy and
physical size. A passively excited multi element array (like a Yagi) has
to transfer energy from element to element to work, and it follows the
characteristics outlined by Chu. And anything with circulating energy
that gets carried by a conductor is going to have high(er) I2R losses
than something that doesn't.


it may be true for a specific type of
antenna, MAYBE Yagi's, MAYBE rhombics or or close coupled wire arrays,
but some of the most directive antennas are parabolic dishes which i
would expect to have very low Q and extremely low losses.

Interesting case there. Loss isn't all that low (typical parabolic
antennas with their feed have an efficiency of 50-70%), although it IS
low compared to the directivity. And, in fact, there's not much stored
energy (so the Q is low). On the other hand a parabolic antenna is
physically very large compared to a wavelength, so the Chu relationship
holds. I'd have to think about whether one can count the energy in the
wave propagating from feed to reflector surface as "stored", but I think
not. Probably only the E and H fields at the reflector surface.


you could
also have an antenna with very high Q, very high i^2r losses, but very
low directivity, so i would be careful about drawing a direct link
between the two.

Yes.. you're right.. the relations set an upper bound on what's
possible.. That is, for a given directivity, you can get either small
size and large stored energy (the Yagi-Uda or W8JK), or large size and
small stored energy (the parabolic reflector and feed). As you note, a
dummy load has very low directivity.

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

Making some assumptions about a sensible implementation for the test, an
interesting test Tom, thanks for the writeup.

One of the interesting propostions emerging in the discussion is that Zs
may be dependent on drive level. Your test setup would be an interesting
one to explore that effect (changing drive level alone, no other adjustment
or change).

In my own tests looking for Pf constant (independent of load changes), I
have noted that I get different results from the IC7000 at different drive
levels. Not surprising, as the gain of the active devices are likely to
change significantly in the upper half of the rated power range, and the
effects of either current or voltage saturation are likely to be manifest
at near rated output, and power control loops at maximum output.

If Zs is dependent on drive level in a significant way, then one must ask
what is the application of Zs in the case of an SSB telephony transmitter.

Owen

On Mon, 14 Jun 2010 11:56:43 -0700 (PDT), K7ITM wrote:

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.

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.

73's
Richard Clark, KB7QHC

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. I dismiss all of your previous comment as a
windup.

Owen

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

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

On 14 jun, 06:01, Owen Duffy wrote:
lu6etj wrote :

...

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

Thanks Owen. I believe I quite understand your kind explanation and
reasons, but I am not sure if I can ask my question well enough
indeed!. I beg your patient.
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.

Thanks again.
Miguel - LU6ETJ

On 12 jun, 10:10, Cecil Moore wrote:
On Jun 11, 11:24*pm, lu6etj wrote:

As a courtesy to me, a foreigner tourist ham, would you mind stop for
a brief moment your more general differences and tell me if you agree
on the behavior of a Thevenin generator with a series resistance of 50
ohms in relation to changes in impedance of a lossless TL predicted by
the Telegrapher's equations solutions in terms of the power dissipated
on the load resistance and series resistence of Thevenin source?
I am pretty serious about this: until today I could not know if you
agree in that!! :)

Miguel, I don't think there is much disagreement about things that are
easily measured, like voltage and current. One solution to the
telegrapher's equations involves forward and reflected waves of
voltage and current. The conventional way of handling power (energy/
unit-time) is to use the voltages and currents to calculate the power
at certain points of interest. The telegrapher's equations do not tell
us *why* the power is what it is and the energy is where it is. To
obtain the why, one must study the behavior of electromagnetic waves.
How does the energy in electromagnetic waves behave? The telegrapher's
equations and Thevenin source do not answer that question.

For instance: Most readers here seem to think that the only phenomenon
that can cause a reversal of direction of energy flow in a
transmission line is a simple EM wave reflection based on the
reflection model. When they cannot explain what is happening using
that model, they throw up their hands and utter crap like, "Reflected
wave energy doesn't slosh back and forth between the load and the
source". But not only does it "slosh back and forth", it sloshes back
and forth at the speed of light in the medium because nothing else is
possible.

These are the people who have allowed their math models to become
their religion. They will not change their minds even when accepted
technical facts are presented. One response was, "Gobblydegook". (sic)

There is another phenomenon, besides a simple reflection, that causes
reflected energy to be redistributed back toward the load and that is
wave cancellation involving two wavefronts. If the two wavefronts are
equal in magnitude and opposite in phase, total wave cancellation is
the result which, in a transmission line, redistributes the wave
energy in the only other direction possible which is, surprise, the
opposite direction. This is a well known, well understood,
mathematically predictable phenomenon that happens all the time in the
field of optics, e.g. at the surface of non-reflective glass. It also
happens all the time in RF transmission lines when a Z0-match is
achieved.

Using the s-parameter equations (phasor math) at a Z0-match point in a
transmission line:

b1 = s11*a1 + s12*a2 = 0 = reflected voltage toward the source
Square this equation to get the reflected power toward the source.

These are the two wavefronts that undergo total wave cancellation,
i.e. total destructive interference.

b2 = s21*a1 + s22*a2 = forward voltage toward the load
s22*a2 is the re-reflection. Square this equation to get the forward
power toward the load.

If one squares both of those equations, one can observe the
interference terms which indicate why and where the energy goes. All
of the energy in s11*a1 and s12*a2 reverses direction at the Z0-match
and flows back toward the load. All the things that Roy is confused
about in his food-for-thought article on forward and reflected power
are easily explained by the power density equation (or by squaring the
s-parameter equations).

Ptot = P1 + P2 + 2*SQRT(P1*P2)*cos(A)
--
73, Cecil, w5dxp.com

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