On Jun 4, 12:18*pm, Richard Clark wrote:
On Thu, 04 Jun 2009 11:47:31 -0700, Jim Lux
wrote:

By the way, the assumption that the run of the mill ham rig has a 50 ohm
resistive output impedance is not necessarily valid.

By the way, this comment above is another assumption in that it lacks
a quantifiable. *I find it offered quite often as a negative assertion
to which the several many posters who offer them never provide an
actual value to prove what the run of the mill ham rig is, much less
is "not."

Actually, I did a casual search for such data, but couldn't find any
for the "run of the mill" solidstate 100W ham rig . There is a fair
amount of data for one tube rig or another). There is some data in
the Moto Ap notes by Granberg, etc, that's reasonably representative,
but it doesn't include the effect of the inevitable LPF on the output.

So, looking at things with which I have practical experience and
measurements.. MMIC amps tend to be be pretty flat over octave
bandwidths, but I don't think they're representative of ham rigs with
either FET or Bipolar output stages (which have to cover multiple
octaves, in any case). Hot microwave FET amps have output impedances
that are anything but 50 ohms, and designing the output networks keeps
lots of RF engineers employed, especially over temperature and device
parameter variation.

I'd love to see some real data for ham rigs.



*Rarer, indeed, is any effort put forward by those posters
to show they have attempted to quantify their own equipment.

Perhaps that's because this is, after all, "rec. radio", as in, nobody
is paying people to comment here, and unless you have a particular
need to know the output Z, it's not worth it to spend the time to
measure it. As previously commented, either you're in the "no tuner"
category, and you tolerate whatever mismatch there is on both ends of
the transmission line, or you have a tuner, and you tune for "best
match", with whatever the output Z is.

For all we know, the folks that complain about not getting a good
match on a Brand X antenna, when everyone else does, have a rig with a
bad match on the output.


As there are posters here who have performed this work, shown their
data, and such data follows conventional design considerations (which
is easily revealed within the page cited athttp://www.wy2u.com/);

Indeed? I'd love to see the data.


then these assumptions dressed in denial are rather unprofound proofs.
As this topic has been visited many times, and as it quickly descends
into equally unsupported claims (although often annotated with vague
references and citations that are quickly demolished); I doubt
anything said here is going to sway those assumptions.


My original contention is that if you're going to measure Antenna Z by
using an autotuner and seeing where it tunes, one of the underlying
assumptions is that the other side of the tuner is 50 ohms.

In reality, having actually done this (e.g. use LDG AT200PC tuners to
measure the mutual impedance matrix of an array), I think the
resolution/step size of the tuner is a bigger problem with the
technique. Given the availability of low cost VNAs for the ham
market, that's a MUCH better solution to measuring antenna impedances.

As an amusing exercise (I anticipate none will tread down this path),
the page athttp://www.wy2u.com/offers a means to test your own rig's
Source Z - if, in fact, you can cope with translating your tuner's
settings into picofarads and nanohenries, and if you can obtain a
known mismatch. *These impediments are Herculean to most,
unfortunately.

Looking at that page, I don't see an obvious link.

Measuring the output Z of the transmitter would be an interesting
exercise.. for microwave circuits, one uses a load-pull setup..

The challenge is, of course, that the amplifier is an active device,
so the output Z probably changes depending on the load. It's not like
an antenna, where the feedpoint Z at a given frequency is pretty much
constant, regardless of the incident power.



73's
Richard Clark, KB7QHC

On Thu, 4 Jun 2009 22:05:00 -0700 (PDT), wrote:

On Jun 4, 12:18*pm, Richard Clark wrote:
On Thu, 04 Jun 2009 11:47:31 -0700, Jim Lux
wrote:

By the way, the assumption that the run of the mill ham rig has a 50 ohm
resistive output impedance is not necessarily valid.

By the way, this comment above is another assumption in that it lacks
a quantifiable. *I find it offered quite often as a negative assertion
to which the several many posters who offer them never provide an
actual value to prove what the run of the mill ham rig is, much less
is "not."

Actually, I did a casual search for such data, but couldn't find any
for the "run of the mill" solidstate 100W ham rig . There is a fair
amount of data for one tube rig or another).

Hi Jim,

Searching and measuring are worlds apart.

There is some data in
the Moto Ap notes by Granberg, etc, that's reasonably representative,
but it doesn't include the effect of the inevitable LPF on the output.

Now, this is the most curious statement of them all. Every LPF that
is mounted in any Ham grade HF rig is designed with both a 50 Ohm
input Z and a 50 Ohm output Z. This is easily verified through the
same page that does the calculations, or through trivial math for the
individual components' Z.

So, looking at things with which I have practical experience and
measurements.. MMIC amps tend to be be pretty flat over octave
bandwidths, but I don't think they're representative of ham rigs with
either FET or Bipolar output stages (which have to cover multiple
octaves, in any case).

Why not? Those same HF rigs have switched LPFs for each octave. This
has been a staple of solid state design for 30+ years. Consult a
schematic.

Hot microwave FET amps have output impedances
that are anything but 50 ohms, and designing the output networks keeps
lots of RF engineers employed, especially over temperature and device
parameter variation.

And for those same 30+ years of HF solid state rigs, their power
transistors have had (and still do) output "native" Z of several Ohms.
This is not a remarkable deviation by the progression to FET, the FET
is simply a different "native" Z with a different transform to get to
the same 50 Ohms. Consult any schematic where the Z transform in the
output transformer is clearly in a Z step-up in the proper ratio. This
stuff has been slam-dunk for decades.

I'd love to see some real data for ham rigs.

Mine (Drake TR-7 and Kenwood TS-430s) exhibit values that vary around
50 Ohms with a low of 35 Ohms and a high of 70 Ohms in the margins.
Those rigs also suffer in those margins. Measurements were done by
pull, by substitution, by looking into the antenna connector with an
RF Bridge and all confirmed by simple reverse design principles.
Variations between any method rarely departed from one another, and
never from the values above. Walt Maxwell has reported his own data
(tube set albeit, but the principles of transformation and exhibited
Source Z are not dependant upon technology).

*Rarer, indeed, is any effort put forward by those posters
to show they have attempted to quantify their own equipment.

Perhaps that's because this is, after all, "rec. radio", as in, nobody
is paying people to comment here, and unless you have a particular
need to know the output Z, it's not worth it to spend the time to
measure it.

This apology condemns the hobby to the lowest common denominator. If
it were meaningful, we would be reading yet another miracle antenna
claim without hint of skeptical enquiry braced with theory, hammered
with models and test gear behind it.

As previously commented, either you're in the "no tuner"
category, and you tolerate whatever mismatch there is on both ends of
the transmission line, or you have a tuner, and you tune for "best
match", with whatever the output Z is.

Every problem is reduced to those two options?

For all we know, the folks that complain about not getting a good
match on a Brand X antenna, when everyone else does, have a rig with a
bad match on the output.

That is arguably so, and my experience described above about operation
in the margins would suggest so. But it would be a very atrocious
Source Z that would lead one to that observation. My experience was
noted only by close examination, not a smoking finals deck. The
complainants experience would argue that the rig is flat out broken
with the drivers pushing 5 or 10 W through incapacitated finals.

More likely the complaining is related to issues outside of the rig.

As there are posters here who have performed this work, shown their
data, and such data follows conventional design considerations (which
is easily revealed within the page cited athttp://www.wy2u.com/);

Indeed? I'd love to see the data.

Op. Cit.

then these assumptions dressed in denial are rather unprofound proofs.
As this topic has been visited many times, and as it quickly descends
into equally unsupported claims (although often annotated with vague
references and citations that are quickly demolished); I doubt
anything said here is going to sway those assumptions.


My original contention is that if you're going to measure Antenna Z by
using an autotuner and seeing where it tunes, one of the underlying
assumptions is that the other side of the tuner is 50 ohms.

In reality, having actually done this (e.g. use LDG AT200PC tuners to
measure the mutual impedance matrix of an array), I think the
resolution/step size of the tuner is a bigger problem with the
technique. Given the availability of low cost VNAs for the ham
market, that's a MUCH better solution to measuring antenna impedances.

As an amusing exercise (I anticipate none will tread down this path),
the page athttp://www.wy2u.com/offers a means to test your own rig's
Source Z - if, in fact, you can cope with translating your tuner's
settings into picofarads and nanohenries, and if you can obtain a
known mismatch. *These impediments are Herculean to most,
unfortunately.

Looking at that page, I don't see an obvious link.

Can you supply a known mismatch? It is inputable at that page;
Can you supply a known C from a tuner that has matched that load? It
is inputable at that page;
Can you supply a known L from a tuner that has matched that load? It
is inputable at that page;
Can you adjust the source Z when the tuner has matched that load? It
is inputable at that page.

This is a substitution method.

These steps reveal the common design criteria for building an LPF for
an output stage. Consult "Filters, Image-Parameter Design" in any
copy of "Reference Data for Radio Engineers." Consult, further,
"Filters, Modern-Network-Theory Design" in the same source. Read the
caption of Fig. 2 in that section:
"The Generator and Load must be considered part of the filter."
In the supporting text:
"The generator and load resistors can be assigned any value
between zero and infinity."
Fig. 25 shows the mathematical impact of Source Z (as R or G) to the
Network response. It also shows the Load Z as a mirror R or G in
symmetry to the source. These commonplace considerations are repeated
in Fig. 27, 28, and 29.

Consult Fig. 34 where both ends can be "interchanged." And repeated
out through Fig. 56.

In the section entitled "Low-Impedance Generator and Load" observe:
"A low impedance generator and/or load may be used with
the above filter by ... an effective turns ratio that transforms
the low impedance to the value required..."

Measuring the output Z of the transmitter would be an interesting
exercise.. for microwave circuits, one uses a load-pull setup..

The challenge is, of course, that the amplifier is an active device,
so the output Z probably changes depending on the load.

I've heard that platitude far too many times. Of course it is an
active device. Of course the output Z changes with load. Do you have
anything more to offer than simple qualitative musings? One could as
easily dream that output Z varies with room temperature, with
humidity, with time of day, with elevation, and if the total of those
variations were capped off with a quantitative measurement of an
accumulated ±10%, then the whole list of objections would get hooted
off the stage. Give me a metric instead of looking under the bed for
spooks.

It's not like
an antenna, where the feedpoint Z at a given frequency is pretty much
constant, regardless of the incident power.

It is also not like a resistor, or a capacitor, or an inductor. Nor
is it like an audio amp or its speaker. The output Z is not like so
many things that to start this list only leads into an infinity of
trivial comparisons that wander the landscape.

So, the output Z is not like the load Z. What significance does that
bring?

On the other hand, I have worked with high power Transistor circuits
that have acted exactly as resistors, inductors, and capacitors and
output Z was exactly like an antenna at a given frequency (or rather
input Z, as one design was an active 100W load).

73's
Richard Clark, KB7QHC

On Jun 5, 12:00*am, Richard Clark wrote:
On Thu, 4 Jun 2009 22:05:00 -0700 (PDT), wrote:
On Jun 4, 12:18*pm, Richard Clark wrote:

Hi Jim,

Searching and measuring are worlds apart.

In the context of discussing on a newsgroup, I'm willing to spend a
few minutes searching. I'm not willing to spend hours measuring.
Others might. I seem to have recalled seeing some data a few years
ago, but I couldn't find it with google.



There is some data in
the Moto Ap notes by Granberg, etc, that's reasonably representative,
but it doesn't include the effect of the inevitable LPF on the output.

Now, this is the most curious statement of them all. *Every LPF that
is mounted in any Ham grade HF rig is designed with both a 50 Ohm
input Z and a 50 Ohm output Z. *This is easily verified through the
same page that does the calculations, or through trivial math for the
individual components' Z.

Uh huh... and all manufacturers use high precision components, and the
impedance at one end of the filter isn't affected by the impedance at
the other end?

My original point is that, barring measurement, you don't KNOW.
(which is sort of your argument too, eh?)



So, looking at things with which I have practical experience and
measurements.. MMIC amps tend to be be pretty flat over octave
bandwidths, but I don't think they're representative of ham rigs with
either FET or Bipolar output stages (which have to cover multiple
octaves, in any case). *

Why not? *

Because the MMICs are a totally different design model. To start
with, they're also Class A, while most ham rigs run Class AB. They
also tend to be "detuned" for broadbanding, at the expense of
efficiency. (not all MMICs are this way.. I'm talking about the MAR-n
series, for instance)

Hot microwave FET amps have output impedances
that are anything but 50 ohms, and designing the output networks keeps
lots of RF engineers employed, especially over temperature and device
parameter variation.

And for those same 30+ years of HF solid state rigs, their power
transistors have had (and still do) output "native" Z of several Ohms.

Would that the active device has a Z that is constant, but it's not.
Sure, the MRF454 data sheet says the output Z is 1+.2j ohms (or
something like that) at 30MHz, but is it still that at 1MHz?

Looking at a more modern power FET for amplifier use, the IXZ210N50L..
There's a whole page of S parameters, and S22 goes from 0.88@-51deg at
2MHz to at 14.32 MHz to at 30 MHz... that's
at Ids =200mA.. bump Ids to 500mA, and the magnitudes stay about the
same, but the phases change, by tens of degrees.

Having actually worked on an amplifier design with similar parts, I
can also say that the datasheet is only a "get you in the ballpark for
the design" tool. The "real parts" (especially when packaged on a
board and attached to the heat sink) are substantially different.

No simple transformer is going to make that look like a constant 50
ohms.

I'd love to see some real data for ham rigs.

Mine (Drake TR-7 and Kenwood TS-430s) exhibit values that vary around
50 Ohms with a low of 35 Ohms and a high of 70 Ohms in the margins.
Those rigs also suffer in those margins. *

so the VSWR looking back from the tuner into your transmitter is
1.4:1? A return loss of around 15dB... what's that work out to... an
error of about 10-15% in the "measuring impedance with a tuner"
technique... not bad, but not great, either, especially stacked up
with the other uncertainties..

Good enough to give a "cross check" on another measurement? Maybe...
if the tuner technique showed I had a load Z of 100+50j, and the MFJ
gave a result of 90 + 40j.. yeah, I'd say it is consistent.



Measurements were done by
pull, by substitution, by looking into the antenna connector with an
RF Bridge and all confirmed by simple reverse design principles.
Variations between any method rarely departed from one another, and
never from the values above. *

Although you have to admit that a 2:1 impedance variation isn't a
particularly outstanding "constant impedance load"


*Rarer, indeed, is any effort put forward by those posters
to show they have attempted to quantify their own equipment.

Perhaps that's because this is, after all, "rec. radio", as in, nobody
is paying people to comment here, and unless you have a particular
need to know the output Z, it's not worth it to spend the time to
measure it. *

This apology condemns the hobby to the lowest common denominator. If
it were meaningful, we would be reading yet another miracle antenna
claim without hint of skeptical enquiry braced with theory, hammered
with models and test gear behind it. *

Not at all.. just because *I* don't want to spend the time measuring
it doesn't mean that the information is of no value to the community.
I would venture that of all the data that hams, collectively, could
measure, this is actually not as useful as some other data.. It just
doesn't have that much impact on day to day operation. Very few hams
adjust their tuner by calculating L and C based on measured data, or
else there wouldn't be a plethora of articles and posts about
"tuning", "pruning", "trimming" and the techniques for doing this, and
arguments about whether a Brand X meter is better than a Brand Y
meter, etc.

Hams, by and large, adjust their tuners by minimizing the reflected
power, and don't much care what the actual component values are. (e.g.
what ham tuner actually has accurate dial calibrations in pF or uH? )

Professionals, on the other hand, do CARE, and do make the
measurements, particularly if they're doing phased arrays, or
designing circuits for mass production, or have to document that their
system will work over wide ranges of temperatures, aging, and other
effects. But, because they're getting *paid* to do it, they're more
than happy to do so. It makes the rest of the job easier.



As previously commented, either you're in the "no tuner"
category, and you tolerate whatever mismatch there is on both ends of
the transmission line, or you have a tuner, and you tune for "best
match", with whatever the output Z is.

Every problem is reduced to those two options?

Obviously not, but I'll bet that it covers over 90% of hamdom (and a
lower percentage of the folks reading this thread).


Looking at that page, I don't see an obvious link.

Can you supply a known mismatch? *It is inputable at that page;

This is a substitution method.

Ahh.. I misunderstood.. I thought you were pointing to process for
doing the measurement and/or some measured data. The cited page is
just the calculator for part of the problem.




Measuring the output Z of the transmitter would be an interesting
exercise.. for microwave circuits, one uses a load-pull setup..

The challenge is, of course, that the amplifier is an active device,
so the output Z probably changes depending on the load. *

I've heard that platitude far too many times. *Of course it is an
active device. *Of course the output Z changes with load. *Do you have
anything more to offer than simple qualitative musings?

Sure.. check out the Ixys data sheet. Plenty of grist for "Z varies
with load and frequency"
Phase of S22 varies 40-50 degrees with Ids. That's in your 10%
ballpark
On the other hand, I have worked with high power Transistor circuits
that have acted exactly as resistors, inductors, and capacitors and
output Z was exactly like an antenna at a given frequency (or rather
input Z, as one design was an active 100W load).


Yes.. but were those run-of-the-mill amateur transceivers? (the
original question).. I have no doubt that it is possible to build
amplifiers with constant Z (to any degree of constancy desired.. heck,
a 1000W amp and a 60db pad gives you a 1mW amplifier with very good
output Z, regardless of what the amp does).

But, does a "designed for mass production and cost target" transmitter
fall into that category?
It's not a published spec
ARRL doesn't measure it when they review rigs

So it's left to someone who cares to do so.

On Fri, 5 Jun 2009 07:18:17 -0700 (PDT), wrote:

Now, this is the most curious statement of them all. *Every LPF that
is mounted in any Ham grade HF rig is designed with both a 50 Ohm
input Z and a 50 Ohm output Z. *This is easily verified through the
same page that does the calculations, or through trivial math for the
individual components' Z.

Uh huh... and all manufacturers use high precision components, and the
impedance at one end of the filter isn't affected by the impedance at
the other end?

Hi Jim,

I haven't the slightest idea why your objection demanding "high
precision components" is necessary. Do you have anything that is
quantifiable to sustain this concern? Give us a Monte Carlo result of
those quantified precisions and their impact on Z.

My original point is that, barring measurement, you don't KNOW.
(which is sort of your argument too, eh?)

Given decades of lock-step design that conforms to accepted practices,
why would anyone have to measure something to KNOW what it is? These
are exceedingly basic considerations that do not demand differential
calculus to get to the first pass approximation. A simple algebraic
approximation is going to be quite good. Measurement will confirm.

You recite Motorola without context, I will fill that gap:
"The network theory for power amplifier design is
well known but is useless unless the designer
has valid input and output impedance data for
the transistor."

Motorola has for years recited at least three different means to
obtain large signal transistor output Z, and has characterized
individual transistors over frequency in charts. I have enumerated
these in the past to no obvious response from other objectors that
Motorola knows what they are doing (even when objectors recited the
exact same references!), but I will proceed once again:
1. Load pull (which satisfies NOT using small signal parameters);
2. Transistor saturation, current, and supply voltage;
3. transition and diffusion capacitances at the collector junction.

This last method responds to your nervous wondering about low
frequency response (UP TO the highest frequency, Z does not undergo
dramatic changes).

I haven't seen a 13.6V, 100W amplifier deck in the last 30 years that
varies one iota from any other - and for good reason: this stuff has
been cookie-cutter design for decades using transistors with known and
optimized characteristics that haven't varied either. Yes, FETs have
emerged in those years, and so have high voltage PNPs and NPNs. Their
contributions have only shifted the design points, not the topology,
nor the matching principles. With absolutely every new component's
introduction, there have been more than sufficient discussion of
matching principles that describe their output Z.

So, looking at things with which I have practical experience and
measurements.. MMIC amps tend to be be pretty flat over octave
bandwidths, but I don't think they're representative of ham rigs with
either FET or Bipolar output stages (which have to cover multiple
octaves, in any case). *

Why not? *

Because the MMICs are a totally different design model. To start
with, they're also Class A, while most ham rigs run Class AB. They
also tend to be "detuned" for broadbanding, at the expense of
efficiency. (not all MMICs are this way.. I'm talking about the MAR-n
series, for instance)

That is not a reason, nor is it different to any great degree. The
same issues dominate both topologies. Further, efficiency is not
always a goal when it contradicts the need for gain; and both may not
satisfy match (as there is more than one form of match: conjugate
match and Z match). I don't suppose you have anything quantitative
here either, do you?

And for those same 30+ years of HF solid state rigs, their power
transistors have had (and still do) output "native" Z of several Ohms.

Would that the active device has a Z that is constant, but it's not.
Sure, the MRF454 data sheet says the output Z is 1+.2j ohms (or
something like that) at 30MHz, but is it still that at 1MHz?

This is another strange objection. You flatly state it is not, but
you are wholly uninformed about it specifically. Your nervousness is
odd with its faltering expectation for performance at what the
industry generally considers to be a very undemanding frequency. Your
question's implied suggestion is: "is the Z for 30MHz the same as the
Z for 29.9MHz?", which from your limited perspective (you are really
reading a rather thin spec sheet) won't answer either. Study
something more encompassing; Motorola has vastly more informed
resources than your meager recitation. A simple browse of half a
dozen transistors from the same production series provides quite
specific details.

My Drake TR-7 uses MRF421s and those transistors are rated at 100W PEP
(my rig is rated at 140-150W CW) where their output resistance varies
from 1.8 Ohm to 1 Ohm over more than 4 octaves. The spec sheets are
more detailed and do not depart from others of that class. As such, I
do not expect your MRF454 would either, but your qualitative
expectations are hard to account for and no parts engineer would cut a
purchase req from them.

Looking at a more modern power FET for amplifier use, the IXZ210N50L..
There's a whole page of S parameters, and S22 goes from 0.88@-51deg at
2MHz to at 14.32 MHz to at 30 MHz... that's
at Ids =200mA.. bump Ids to 500mA, and the magnitudes stay about the
same, but the phases change, by tens of degrees.

Again, Motorola specifically rejects small signal parameterization for
power applications. This is, perhaps, your problem with
characterizing amplifier issues.

Having actually worked on an amplifier design with similar parts, I
can also say that the datasheet is only a "get you in the ballpark for
the design" tool. The "real parts" (especially when packaged on a
board and attached to the heat sink) are substantially different.

I have selected, inspected, and validated transistors to Mil Spec and
found very few wandered from commercial specification. You must
inhabit a very different realm where production lots contain product
that are "substantially different." Do you have some quantification
for "substantially?" Or is this another example of a technician's
shrug?

No simple transformer is going to make that look like a constant 50
ohms.

Ah, are we now down to parsing this to "exactly 50 Ohms" where in your
objections you offer few quantifications? Does 49 Ohms invalidate the
premise and score a home run for the opposing team?

I'd love to see some real data for ham rigs.

Mine (Drake TR-7 and Kenwood TS-430s) exhibit values that vary around
50 Ohms with a low of 35 Ohms and a high of 70 Ohms in the margins.
Those rigs also suffer in those margins. *

so the VSWR looking back from the tuner into your transmitter is
1.4:1? A return loss of around 15dB... what's that work out to... an
error of about 10-15% in the "measuring impedance with a tuner"
technique... not bad, but not great, either, especially stacked up
with the other uncertainties..

Not great? You have already suggested it was unknowable, and others
state it was immaterial. It gives me pause to have given a concrete
result to now find what was unknown is now "uncertain" and what was
immaterial now counts for little at "not great."

Measurements were done by
pull, by substitution, by looking into the antenna connector with an
RF Bridge and all confirmed by simple reverse design principles.
Variations between any method rarely departed from one another, and
never from the values above. *

Although you have to admit that a 2:1 impedance variation isn't a
particularly outstanding "constant impedance load"

This characteristic that is "not particularly outstanding" was
formerly deemed impossible to determine and immaterial by others. I
would say that the gulf that I bridged goes a good deal further than
demurrals such as yours. As for the sudden emergence of the
qualification for "outstanding," that can be obtained if you care to
indulge in quantifying what "outstanding" means to you. Am I being
set up with an impossible goal to satisfy your point? This
performance characteristic that I have published has served an active
market for generations; and that in its own right responds to issues
of "outstanding." The market would respond: "sufficiently so."

As to could it be better? Without a doubt, and again, design would
proceed from knowing the transistor source Z, not "by guess and by
golly." This again goes to conventional design considerations that
were enumerated by H.W. Bode in the late 30s.

just because *I* don't want to spend the time measuring
it doesn't mean that the information is of no value to the community.
I would venture that of all the data that hams, collectively, could
measure, this is actually not as useful as some other data.. It just
doesn't have that much impact on day to day operation.

What a tedious reply in the face of correspondence in other topics
that struggle to pass as intelligent discussion. I wonder why you put
such effort to responding here if this has so little impact, no
relative importance, no relation to design, nor application to "using
a tuner to determine Line Input Impedance" (a fully informed topic of
great impact on day to day operation, isn't it?).

Very few hams
adjust their tuner by calculating L and C based on measured data, or
else there wouldn't be a plethora of articles and posts about
"tuning", "pruning", "trimming" and the techniques for doing this, and
arguments about whether a Brand X meter is better than a Brand Y
meter, etc.

Your comments to the original poster, then, could have been reduced to
one response of one line telling him to abandon his quest by this same
logic.

Hams, by and large, adjust their tuners by minimizing the reflected
power, and don't much care what the actual component values are. (e.g.
what ham tuner actually has accurate dial calibrations in pF or uH? )

Do I need to quote that correspondent's post? And if I did, what
objection would fall from that? another step descending into
intellectual entropy.

Professionals, on the other hand, do CARE,

and Hams do NOT. By this standard, our group would dissolve to the
merits of photons bouncing waves off each other.

Every problem is reduced to those two options?

Obviously not, but I'll bet that it covers over 90% of hamdom (and a
lower percentage of the folks reading this thread).

90% of hamdom - leaving some several many thousands who are interested
is sufficient enough. Not for you? Not enough readers here?
Diminishing the level of discourse is not going to build audience to
that several many thousand potential, will it?

On the other hand, I have worked with high power Transistor circuits
that have acted exactly as resistors, inductors, and capacitors and
output Z was exactly like an antenna at a given frequency (or rather
input Z, as one design was an active 100W load).


Yes.. but were those run-of-the-mill amateur transceivers? (the
original question)..

Yes.. but indeed - how tedious. I have responded to the specific
question; I have responded to the specific component; I am responding
to correlating designs. Every response is rooted in published and
quantified characteristics.

I have no doubt that it is possible to build
amplifiers with constant Z (to any degree of constancy desired.. heck,
a 1000W amp and a 60db pad gives you a 1mW amplifier with very good
output Z, regardless of what the amp does).

Why does your imposed solution have to come with a crippling hit to
efficiency or match? The only inhibition against designing an
amplifier to meet your unquantified expectations is the cost involved,
not loss of efficiency, not loss of match. You said you have
experience in amplifier design, this cannot be such an impossibility
can it?

But, does a "designed for mass production and cost target" transmitter
fall into that category?
It's not a published spec

You mean you haven't read the spec. I have seen this objection too.
When I've offered just such specs, objectors have then recursed back
into how output Z is unknowable and immaterial as if the topic had
never been encountered before.

ARRL doesn't measure it when they review rigs

Now THERE's an authority! Do they measure efficiency?

73's
Richard Clark, KB7QHC

On Jun 5, 1:19*pm, Richard Clark wrote:
On Fri, 5 Jun 2009 07:18:17 -0700 (PDT), wrote:

Uh huh... and all manufacturers use high precision components, and the
impedance at one end of the filter isn't affected by the impedance at
the other end?

Hi Jim,

I haven't the slightest idea why your objection demanding "high
precision components" is necessary. *Do you have anything that is
quantifiable to sustain this concern? *Give us a Monte Carlo result of
those quantified precisions and their impact on Z.

I'm not going to bother. If you care, you can do so, or point to a
published summary, rather than spending hundreds of words reciting how
to do something we both know how to do.

Again.. without published data from the transceiver maker (whether
derived by measurement or analysis, it matters not) or data from
somewhere else, I made the initial assertion that since using the
tuner to measure impedance depended on the source being 50 ohms (or at
least, known Z), one should not blindly assume that a rig has a output
Z of 50 ohms. You provided one set of data for your rig (35 to 70
ohms), which does actually bound the problem, assuming that yours is
representative of the general class. It might be, it might not.
There's no "trivial" (as in spending no more than 5 minutes) way to
know.

For myself, I don't care, today, what my rig's output Z is, because
everything I use it with doesn't care much (e.g. the auto matching
network finds a match, and whether it's matching 50, 30, or 70 ohms,
there's not much difference). If I were doing something different
(measuring Z with a tuner) I would care, and I'd measure it.

Given decades of lock-step design that conforms to accepted practices,
why would anyone have to measure something to KNOW what it is? *

Funny thing, then... there's remarkably little published (as in
findable with google) data on the output impedance of solid state
transmitters. Yes, the designs are pretty cookbook, but there's a
dearth of published test or analysis (I maintain, of course, it's
because nobody really cares much in actual application situations).

For other RF power amp applications (like plasma etchers, RF heating,
etc) there IS data, but those devices aren't ham transmitters.

I did find a couple master's theses that have some data (but over a
very small frequency range around 7MHz) because they used a ham rig as
a source for a bridge scheme of some sort.


Motorola has for years recited at least three different means to
obtain large signal transistor output Z, and has characterized
individual transistors over frequency in charts.
Sure..


And for those same 30+ years of HF solid state rigs, their power
transistors have had (and still do) output "native" Z of several Ohms.

Would that the active device has a Z that is constant, but it's not.
Sure, the MRF454 data sheet says the output Z is 1+.2j ohms (or
something like that) at 30MHz, but is it still that at 1MHz?

Just happened to be a data sheet I have handy... As you say, others
have more data.
(for large signals, no less)


Looking at a more modern power FET for amplifier use, the IXZ210N50L..
There's a whole page of S parameters, and S22 goes from 0.88@-51deg at
2MHz to at 14.32 MHz to at 30 MHz... that's
at Ids =200mA.. bump Ids to 500mA, and the magnitudes stay about the
same, but the phases change, by tens of degrees.

Again, Motorola specifically rejects small signal parameterization for
power applications. *This is, perhaps, your problem with
characterizing amplifier issues.

Those are actually large signal parameters.. that's a 150V transistor
running at several amps drain current.

Again, it just happens to be a datasheet I had laying around.



I have selected, inspected, and validated transistors to Mil Spec and
found very few wandered from commercial specification. *You must
inhabit a very different realm where production lots contain product
that are "substantially different." *Do you have some quantification
for "substantially?" *Or is this another example of a technician's
shrug?

Substantially, as in Output C being off by a factor of more than 2.
But that could also be packaging effects, which are easier to quantify
by experiment than analysis. That's what breadboards are all about.

I would imagine that for parts used in amateur radios, this is all
thoroughly thrashed out, and there would be no big surprises. Just
that the "as implemented" data isn't readily available in 10 minutes
of searching.

No simple transformer is going to make that look like a constant 50
ohms.

Ah, are we now down to parsing this to "exactly 50 Ohms" where in your
objections you offer few quantifications? *Does 49 Ohms invalidate the
premise and score a home run for the opposing team?

Hmm depends on what sort of accuracy you want in your impedance
measurment, eh? If all you care about is 15-20% accuracy, a pretty
big variation will be ok.


I'd love to see some real data for ham rigs.

Mine (Drake TR-7 and Kenwood TS-430s) exhibit values that vary around
50 Ohms with a low of 35 Ohms and a high of 70 Ohms in the margins.
Those rigs also suffer in those margins. *

so the VSWR looking back from the tuner into your transmitter is
1.4:1? * A return loss of around 15dB... what's that work out to... an
error of about 10-15% in the "measuring impedance with a tuner"
technique... *not bad, but not great, either, especially stacked up
with the other uncertainties..

Not great? *You have already suggested it was unknowable,

I never said it was unknowable. I said it wasn't readily available or
known. Clearly one can measure it, and then know it. And now we do,
at least to 1 sig fig sorts of accuracies.. which is better than we
were 24 hours ago.

and others
state it was immaterial. *It gives me pause to have given a concrete
result to now find what was unknown is now "uncertain" and what was
immaterial now counts for little at "not great."

Immaterial in the usual amateur application (feeding a tuner which
feeds a transmission line which feeds an antenna).. not immaterial
when using the tuner to measure Z.



Although you have to admit that a 2:1 impedance variation isn't a
particularly outstanding "constant impedance load"

This characteristic that is "not particularly outstanding" was
formerly deemed impossible to determine and immaterial by others.

You're confusing "data not easily available in 5 minutes on the web"
with "impossible to determine".




Your comments to the original poster, then, could have been reduced to
one response of one line telling him to abandon his quest by this same
logic.

yes, probably.

But, does a "designed for mass production and cost target" transmitter
fall into that category?
It's not a published spec

You mean you haven't read the spec.

--- Hmm. don't see any tolerance on the output impedance spec on my
IC-7000.. page 150 of the manual: Specifications.
All it says is:
Antenna Connector: SO-239x2/50 ohm.

Page 11, where it describes the back panel
Antenna Connector [ANT1][ANT2} Accepts a 50 ohm antenna with a PL-259
connector.

Page 15, provides a recomendation that the load impedance have a SWR
1.5:1, and a boxed warning that at SWR higher than approximately
2.0:1 it drops power.

The service manual isn't much better, although it does have a
calibration procedure for the built in SWR meter, where you attach a
50 ohm dummy load and set to SWR=1, and then 100 ohms and set SWR=2.
That just calibrates the meter, though, it doesn't imply that the
actual output impedance is 50 ohms.


*I have seen this objection too.
When I've offered just such specs, objectors have then recursed back
into how output Z is unknowable and immaterial as if the topic had
never been encountered before.

ARRL doesn't measure it when they review rigs

Now THERE's an authority! *Do they measure efficiency?

At least they do some measurements and they publish their results.

They do measure efficiency, in a round about way (e.g. they measure
output power into a dummy load and they measure DC input power).

jim