Cecil Moore wrote:

. . .
The IEEE Definitions are what engineers abide by. . .

If you believe that, you haven't had much contact with real, working
engineers.

In my experience, the IEEE definitions are often way out of step with
common usage by working engineers. Nearly none in my acquaintance look
to it as an authoritative source. A useful guideline, perhaps, at most.
I can easily see three causes for the deficiency:

1. The IEEE Dictionary covers an extremely wide variety of rapidly
evolving specialties, including power, digital, fields, control systems,
fiber optics, electronics, EMC, and on and on. It would be extremely
difficult to cover all these disparate specialties accurately and in
depth without a huge amount of input from working engineers in each
specialty.
2. As far as I can tell, the Dictionary is put together by volunteers,
which limits the time and effort which can applied to it.
3. The active membership of the IEEE largely comprises academics rather
than working engineers. Academics are a poor source of information about
common usage by working engineers. And, working engineers don't tend to
"abide by" the dictates of academics, in my experience.

I don't have a recent copy of the IEEE Dictionary, but think and hope
it's improved over the years. But I'm certain it hasn't come anywhere
close to the point at which it's something "engineers" "abide by".

Roy Lewallen, W7EL

On Sat, 27 Nov 2004 21:43:14 GMT, (Robert Lay
W9DMK) wrote:

On Fri, 26 Nov 2004 10:57:25 -0700, Wes Stewart
wrote:


Yes. But the ITT Reference Data For Radio Engineers uses this paper
as a reference.

If you have Mathcad, a sheet that implements some of the equations was
included as a reference in my Balanced Transmission line paper.

http://users.triconet.org/wesandlinda/LineCalc.mcd


Dear Wes,

I was happy to find that the MacAlpine paper is the first part of
Chapter 22 of the ITT Handbook, as the latter is much more readable.

I did not pick up on the MathCad files, because I do not have MathCd -
however, the material from MacAlpine and Ricardi have answered most of
my concerns.


|I hope that MacAlpine agrees with what Dave and Richard are telling
|me, because their responses seem to be correct and are exactly what I
|was afraid of - that I've been sucked into another example of the
|strange terminology used to describe "losses".
|
|I have always thought of "loss" as a conversion to another form of
|energy (typically heat energy) which is lost from the system.
|Apparently, the kind of "loss" being described in the example that I
|gave is not a loss at all.

I was premature in those two paragraphs, above. I can see now that the
Additional Losses Due to SWR really are dissipative and are unrelated
to the "Mismatch Losses" and "Transducer Losses" defined on page 22-12
of the ITT Handbook, 5th Ed.


Yes it is. A simple-minded way of looking at it is if the SWR is
greater than unity then increased current is flowing in the line. The
line has resistive loss, so the I^2*R loss increases. The current
isn't constant (there is a current standing ratio, ISWR, just like a
VSWR) so there are peaks and valleys in the current and as you have
figured out, the longer the line and the higher its nominal loss, the
lower the ISWR is at the line input.

My interpretation of your "Yes it is." is that you mean that the
Additional Losses Due to SWR are truly heat losses and are due to the
ohmic losses in the hot spots of the line. Then we agree on that
point. Your paragraph above is much more succinct than the papers by
MacAlpine and Ricardi, but it certainly tells the story.

So the loss per unit length is non-linear and varies with distance
from the mismatch, but it is a real dissipative loss.

I don't know that I would have used the term "non-linear", but I would
certainly agree that it varies along the line in accordance with the
current loops.

For those interested in the loss in the shorted or open stub case,
maybe this will be of interest:
http://users.triconet.org/wesandlind...ching_Loss.pdf

I took that pdf and added it to the collection. There were several
things about that paper that filled-in gaps of detail in MacAlpine.
However, neither paper gives us much hope for a simple model of these
losses. Nonetheless, it makes hash out of the material in The ARRL
Antenna Book. In all fairness, the Antenna Book cannot cover all
aspects of these topics in detail. Unfortunately, the material in the
Antenna Book is, in my opinion, very misleading in several specific
areas, as follows:
- The Antenna Book gives only one expression for Total Line
Loss (combining ML loss and the Additional Loss Due to SWR). If we
accept Macalpine's model, there are different relationships for the
range of SWR from 0 to 6 and for the range from 6 upwards.
- Antenna Book does not explain that the hot spots are very
localized and that the additional losses can be quite dependant upon
the length of the line in wavelengths. For example, the losses in a
segment of line less than 1/3 wavelength might be insignificant in
comparison with a segment of line greater than 1/3 wavelength simply
because the shorter segment may not contain a hot spot. In other
words, one cannot apply the Antenna Book equations, blindly, because
of several factors that are not even mentioned, and for short line
segments it is quite possible that there would be no signicant losses
due to SWR.
- The most misleading information in The Antenna Book is on
pages 24-11 and 24-12 where it is shown that a 100 foot RG-213
feedline will suffer 25 dB of Additional Loss Due to SWR at 1.83 MHz
because of the very short antenna. I believe that when the equations
from the ITT Handbook are used instead, that the actual losses will be
far, far less.

Just today, I made a careful measurement on an RG-8/U line of 5.33
meters length at 30 MHz and terminated with a 4700 + j 0 load. The
Matched Line Loss of that line at 30 MHz is 0.9 dB per 100 feet, and
its Velocity Factor is between 0.75 and 0.80 The input impedance was
actually measured at 2.45 -j15 ohms for an SWR at the input of 22.25.
The SWR at the load end was 94. Those two SWR's establish a total loss
on the line of 0.15 dB. If one were to blindly apply the formula in
The Antenna Book on page 24-9, the result obtained would be 4.323 dB.


I have finally resolved this problem. The last paragraph, immediately
above, represents the problem that I have been unable to reconcile
until now.

Surprisingly, it was not until today that I finally made a computation
of the input power to the line for the configuration above.
Specifically, I was able to compute the voltage and current at the
input to the line that would produce a 100 volt reference voltage
across the 4700 ohm line. That is the obvious thing that had to be
done in order to establish a reference power for purposes of computing
losses. That calculation resulted in an applied voltage at the line
input of 29.2 volts at angle -171.5 degrees and a current of 1.917
amps at -90.78 degrees. Computing power into the line as E*Icos(theta)
= 9.024 watts. The power delivered to the load is 100 volts squared
divided by 4700 ohms, which is 2.127 watts.

Therefore the efficiency is 23.6% and the losses in the line are 6.275
dB. In all fairness, I did have to change one assumption in the data
above. I had to revise my attenuation value of 0.9 dB per 100 ft.
upwards to a value of 1.72 dB per 100 ft. in order to get my measured
impedance at the line input to be consistent with that line impedance,
length, load value and velocity factor.

Up until today, I could not see the losses being that high. In fact,
everything that I used to compute losses based on the measurements
above told me that the losses were on the order of 0.3 dB or less,
depending on which foolish method I was using. The method that really
sucked me in was the method based on two SWR readings - one at the
load and one at the input. That method, gives either 0.15 dB or 0.3
dB, depending upon whether you believe the scale at the bottom of the
Smith Chart or whether you believe the nomograms on pages 22-7 or 22-8
of the ITT Reference Data for Radio Engineers, 5th Edition.

So, once I tackled it head on and just did the brute force, obvious
calculation, I got a loss figure that exactly corresponds to the
losses predicted in The ARRL Antenna Book, 17th Edition, page 24-9.

So, I hope everyone had fun and learned something in the process. I
know I did.

73,

Bob, W9DMK, Dahlgren, VA
http://www.qsl.net/w9dmk

Cecil Moore wrote:
Of course,
the disciplines of physics and engineering are certainly at
odds with one another.

That is nothing but an excuse for your own sloppy thinking.

When it comes down to fundamentals, physics and engineering must always
agree exactly - because they are both working with the same physical
reality. That is a bedrock principle, known and shared by all competent
physicists and all competent engineers.

There's a reason why they call these subjects "disciplines", you know.
Reality sets hard rules that you have to follow - or else you'll get it
wrong.

The only differences between physics and engineering are the
acknowledged and clearly understood approximations that each side has to
apply in order to follow its own particular interests. Physics is most
interested in knowing things, while engineering is most interested in
doing things - but neither to the exclusion of the other.

If your ideas cannot make the physics and engineering approaches agree,
it means that your ideas are wrong. That is a simple and completely
reliable test.

And it's strictly *your* problem.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Roy Lewallen wrote:
Cecil Moore wrote:
The IEEE Definitions are what engineers abide by. . .

If you believe that, you haven't had much contact with real, working
engineers.

What dictionary do "real, working engineers" use? A language
without a dictionary is a disaster waiting to happen.
--
73, Cecil http://www.qsl.net/w5dxp

Ian White, G3SEK wrote:
If your ideas cannot make the physics and engineering approaches agree,
it means that your ideas are wrong.

If you believe physicists and engineers agree on everything, you are
living in never-never land. It's difficult to find two physicists
who agree on everything - or two engineers. Witness the arguments
on this newsgroup.

Ian, there are 13 definitions of "efficiency" in the IEEE Dictionary,
each associated with a different engineering discipline. And that's
not counting the definitions of "efficiency" that exist in the
world of pure physics. Anyone who thinks a word has one and only
one definition that everyone agrees upon and encompasses all subjects
and all fields is clearly out of touch with reality.

For instance, I point to the definition of "power" in the IEEE
dictionary. Some posters on this newsgroup disagree with that definition
and that's from people who had the same textbook as I did in college.
Since that's the case, then of course, some of the ideas of engineering
and physics will disagree. "Power" for a power engineer working at a
power generating plant measuring megajoules/sec in a transmission line
simply does not have the same definition as "power" for a physics professor.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil A. Moore wrote:
"Power" for a power engineer working at a
power generating plant measuring megajoules/sec in a transmission line
simply does not have the same definition as "power" for a physics professor.

"Power" is just a single word, so it certainly does have to carry
several different shades of usage.

My point is that the competent engineer and the competent physics
professor understand that their different usages are still completely
consistent at a fundamental level.

I don't believe you understand the discipline that that need for
consistency imposes.



--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

"Ian White, G3SEK" wrote in message
...
Cecil A. Moore wrote:
"Power" for a power engineer working at a
power generating plant measuring megajoules/sec in a transmission line
simply does not have the same definition as "power" for a physics
professor.

"Power" is just a single word, so it certainly does have to carry several
different shades of usage.

My point is that the competent engineer and the competent physics
professor understand that their different usages are still completely
consistent at a fundamental level.

I don't believe you understand the discipline that that need for
consistency imposes.

Cecil's back at it, I see.



--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Sat, 04 Dec 2004 05:24:33 GMT, (Robert Lay
W9DMK) wrote:

Just today, I made a careful measurement on an RG-8/U line of 5.33
meters length at 30 MHz and terminated with a 4700 + j 0 load. The
Matched Line Loss of that line at 30 MHz is 0.9 dB per 100 feet, and
its Velocity Factor is between 0.75 and 0.80 The input impedance was
actually measured at 2.45 -j15 ohms for an SWR at the input of 22.25.
The SWR at the load end was 94. Those two SWR's establish a total loss
on the line of 0.15 dB. If one were to blindly apply the formula in
The Antenna Book on page 24-9, the result obtained would be 4.323 dB.

Surprisingly, it was not until today that I finally made a computation
of the input power to the line for the configuration above.
Specifically, I was able to compute the voltage and current at the
input to the line that would produce a 100 volt reference voltage
across the 4700 ohm line. That is the obvious thing that had to be
done in order to establish a reference power for purposes of computing
losses. That calculation resulted in an applied voltage at the line
input of 29.2 volts at angle -171.5 degrees and a current of 1.917
amps at -90.78 degrees. Computing power into the line as E*Icos(theta)
= 9.024 watts. The power delivered to the load is 100 volts squared
divided by 4700 ohms, which is 2.127 watts.

Therefore the efficiency is 23.6% and the losses in the line are 6.275
dB. In all fairness, I did have to change one assumption in the data
above. I had to revise my attenuation value of 0.9 dB per 100 ft.
upwards to a value of 1.72 dB per 100 ft. in order to get my measured
impedance at the line input to be consistent with that line impedance,
length, load value and velocity factor.

Hi Bob,

I notice that true to form, all the response in this thread were not
to your bench results. I trust you will appreciate hard
correspondence rather than the fluff.

The one thing (actually there are several) I noted was your having to
double the presumed line loss to make the numbers come out. Given
this injection (or removal) of 100% (or %50) of error, it stands to
reason that your bench, method or instruments need a attention.

The details as I've sifted from the postings:
Cable type = Columbia's number 1198 - not 9913.
Open circuit stub length = 5.334 meters
Frequency = 10.6 MHz,
Input Z = 0.57 + j 0.3 ohms.

The above details appear to have shifted in mid-stream to:
Cable type = RG-8/U line
stub length = 5.334 meters
Frequency = 30.0 MHz,
Open end termination = 4700 + j 0
Input Z = 2.45 -j15

I will skip the determinations of loss and SWR as being problematic as
you indicate and simply go with your observations noted above, and
summarized he
Open end Vtermination = 100V @ 0°
Open end Itermination = 0.0213A @ 0°
Fed end Vinput = 29.2V @ -171.5°
Fed end Iinput = 1.917A @ -90.78°

I was puzzled to see what was initially a resonant stub now measured
with an extremely high Reactance until I re-scanned the material to
note the tripling of frequency.

What caught my eye was this load and certainly your leap of faith that
it was wholly resistive, especially at HF for its size. This would be
extremely unlikely even in a standards lab.

To make a measurement, the rule of thumb is to have instrumentation
whose precision and accuracy exceeds the goal of measuring an unknown
by 5 to 10 times. For really difficult tests (and RF is classic in
that regard) 3 times is often the best you can achieve.

Let's look at that 4700 Ohm resistance. It demands that any
instrumentation support a paralleling load of no less than 23.5K Ohms
to 47K Ohms, or worst case, 14K Ohms. Let's simply ask about the
family lineage of that 4700 Ohm resistance. It sounds suspiciously
like a common (hopefully) carbon composition resistor.

If so, such beasties are rare if it is of the commercial variety, to
not exhibit reactances due to spiral cut value trimming, or an
end-to-end capacitance. Let's just say that you obtained a remarkable
resistor, but it cannot escape this common parasitic capacitance which
for the garden variety resistor amounts to 1.5pF.

At 30 MHz, this 1.5pF capacitance represents a reactance of 3.5K Ohm.
This rather sweeps aside your specification for the load and replaces
it with 4700 -j3537 Ohms. This is a big time source of error and does
not even come close to the 3X requirement for the lowest accuracy.
Worse yet, you haven't even added the bridging impedance of your
measuring device which is certain to be on par, if not worse (you
haven't identified your instrumentation).

Hope you are still looking forward to more fun. ;-)

73's
Richard Clark, KB7QHC

On Sat, 04 Dec 2004 18:40:20 GMT, Richard Clark
wrote:

At 30 MHz, this 1.5pF capacitance represents a reactance of 3.5K Ohm.
This rather sweeps aside your specification for the load and replaces
it with 4700 -j3537 Ohms.

Actually 1700 -j2258 Ohms

As you can see, this is the reason why open stubs are avoided.
"Knowing" the parasitic capacitance is problematic. The fringing
effect at the end is difficult to manage whereas a short is much
simpler to define and implement.

73's
Richard Clark, KB7QHC

(PS : You can't deal with reflections without involving Distance,
Velocity,
Place and Time.)

======================================

Just an addition -

You can't deal with Reflections without involving Distance, Velocity,
ECHO's, Place, and, above all, TIME.

Attempted steady-state analyses reduce to non-sense without involving TIME.

But it is a simple matter to relate power levels, one to another, dB-wise or
otherwise, at different PLACES and TIME.

All you guru's, old wives and experts on forward and reflected powers, real
or imaginary, should bear this basic, elementary stuff in mind.

Whatever happened to your primay education?

Power, work and energy are intimately related to TIME.

The self-educated kids living in South American underground Rio sewers,
subjected to culling by armed police, reduced to making a precarious living
be selling laced cigarettes, can do better.

But don't worry about it. Just continue taking your viagra. As for me,
tonight I'm on white, dry, Bordeaux, best consumed within six months of
purchase. And the French know what they are talking about.
----
Reg.