On Thu, 25 Nov 2004 20:20:32 GMT, (Robert Lay
W9DMK) wrote:

Bob,

You might want to look at this paper:

http://users.triconet.org/wesandlinda/AIEE_High_Swr.pdf



|Various authors provide curves or formula for computing the "total
|loss" in transmission lines, as opposed to the "matched-line" loss.
|Specifically, The ARRL Antenna Book gives an equation in Chapter 24
|that seems to give results consistent with other sources (See the
|details at the end of this posting). However, there seems to be a
|fundamental flaw in the way in which the equation is applied.
|
|In essence, the equation provides a loss factor which is a function of
|the matched-loss attenuation and the absolute reflection coefficient.
|The matched-loss attenuation is the value normally expressed in dB per
|100 ft. and shown in tables or shown in logarithmic plots as a
|function of frequency. The reflection coefficient is introduced into
|the expression in order to increase the total losses as the SWR on the
|line increases.
|
|After calculating a total loss factor it is applied to lines of any
|length based on the reflection coefficient at the load. In my opinion,
|it makes no sense whatsoever to provide an expression that is to
|determine the losses per unit length on a line and have it based on
|the reflection coefficient at the end of the line. If there is a
|mismatched load, and if the line has losses, then it follows that the
|SWR will become lower and lower the further we are from the
|termination. That being the case, would it not make more sense to say
|that the "additional" losses would be much higher at the load end of
|the line, where the SWR is high, than at great distance from the load,
|where the SWR is significantly lower? In fact, if the line is long
|enough, we know that the SWR approaches 1:1, and in a line with an SWR
|of 1:1 there should be no additional losses above the matched-line
|losses.
|
|Nonetheless, with that non-sensical approach, the numerical examples
|shown at the referenced page and also in a later article on the
|subject of Highly Reactive Loads makes it quite clear that the loss
|factor is applied uniformly to the entire length of line.
|
|If we take the expression for the total loss and apply it to small
|increments of line wherein the SWR is relatively constant, then it not
|only makes more sense, but it also predicts noticeably less total loss
|in longer lines.
|
|I have embarked on careful measurements of lines severely mismatched
|(quarter wave open circuit stubs), and I can find no correlation
|between my measurements and the values predicted by the "total loss"
|equation. My measurements always show very low losses in comparison to
|the model.
|
|I would be interested in corresponding with anyone who has other
|models for line losses, or anyone who has made measurements on
|quarter-wave stubs.
|
|##########Equation and data taken directly from The ARRL Antenna Book,
|17th Ed., page 24-9 ###############
|(Eq 10) Total Loss (dB) = 10 log [ {(Alpha * Alpha - (AbsRho *
|AbsRho)} / {Alpha * (1- (AbsRho * AbsRho)) } ]
|
|where
|
| Alpha = 10^(ML/10) = matched-line loss ratio
|
| AbsRho = (SWR - 1) / (SWR + 1)
|
|where
| ML = the matched-line loss for particular length of line, in
|dB
|
| SWR = SWR at load end of line
|
|The text then goes on with a numeric example using a 150 ft. length of
|RG-213 coax that is terminated in a 4:1 mismatch (SWR = 4:1, AbsRho =
|0.6) at 14.2 MHz. The calculations for total line loss, per the above
|equation, results in a total line loss of 2.107 dB.
|
|
|
|
|Bob, W9DMK, Dahlgren, VA
|http://www.qsl.net/w9dmk

On Thu, 25 Nov 2004 20:51:16 -0700, Wes Stewart
wrote:

On Thu, 25 Nov 2004 20:20:32 GMT, (Robert Lay
W9DMK) wrote:

Bob,

You might want to look at this paper:

http://users.triconet.org/wesandlinda/AIEE_High_Swr.pdf


Dear Wes,

I have downloaded the pdf file and printed it out. It's tough reading.
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. It's more like "return loss", which is also
not a true "loss" in my thinking. In other words, it seems that the
"Additional Losses Due to SWR" are not losses at all, but are simply a
measure of the power that "could" have been delivered to the load were
it not for the mis-match.
Bob, W9DMK, Dahlgren, VA
http://www.qsl.net/w9dmk

On Fri, 26 Nov 2004 16:12:34 GMT, (Robert Lay
W9DMK) wrote:

|On Thu, 25 Nov 2004 20:51:16 -0700, Wes Stewart
|wrote:
|
|On Thu, 25 Nov 2004 20:20:32 GMT, (Robert Lay
|W9DMK) wrote:
|
|Bob,
|
|You might want to look at this paper:
|
|http://users.triconet.org/wesandlinda/AIEE_High_Swr.pdf
|
|
|Dear Wes,
|
|I have downloaded the pdf file and printed it out. It's tough reading.

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


|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.

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.

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

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

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.


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

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.

For your 1/4WL open stub on 10.6 MHz, with a stub impedance of 0.57 ohms,
I calculate total losses of about 0.2 dB.
--
73, Cecil http://www.qsl.net/w5dxp

On Sun, 28 Nov 2004 09:38:28 -0600, Cecil Moore
wrote:

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.

For your 1/4WL open stub on 10.6 MHz, with a stub impedance of 0.57 ohms,
I calculate total losses of about 0.2 dB.
--
73, Cecil http://www.qsl.net/w5dxp

Dear Cecil,

I hope I'm not misinterpreting your values - I assume that you are
starting with a theoretical open circuit and a theoretical RG-8 line
and calculating a theoretical impedance seen looking into that line of
0.57 + j 0. From that you then calculate a theoretical 0.2 dB. When I
say calculate, I assume that you may instead by using a nomogram.
Anyway, based on all of that being the situation up to but not
including the loss figure, when I take the 0.57 + j0 and calculate the
SWR as 87.7 I get a loss more like .05 dB, theoretically, so I'm not
sure in what ways we are coming up with these numbers. I can explain
exactly how I got mine, which was via measurements followed by a
theoretical cacluation of loss based on the two SWR's formula which is
built into all Smith Charts.

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

Robert Lay W9DMK wrote:
..For your 1/4WL open stub on 10.6 MHz, with a stub impedance of 0.57 ohms,
I calculate total losses of about 0.2 dB.

I hope I'm not misinterpreting your values - I assume that you are
starting with a theoretical open circuit and a theoretical RG-8 line
and calculating a theoretical impedance seen looking into that line of
0.57 + j 0. From that you then calculate a theoretical 0.2 dB. When I
say calculate, I assume that you may instead by using a nomogram.

Not using a nomogram but everything is 100% theoretical. It doesn't
matter what line is being used as long as it's Z0 is 50 ohms. Matched
line loss didn't enter into my calculations. It's only total loss.

Anyway, based on all of that being the situation up to but not
including the loss figure, when I take the 0.57 + j0 and calculate the
SWR as 87.7 I get a loss more like .05 dB, theoretically, so I'm not
sure in what ways we are coming up with these numbers.

Is that the additional loss due to SWR or the total loss? My theoretical
loss is total loss and the matched line loss need not be known. The
measured resistance of the resonant stub is all one needs to know besides
Z0.

I can explain
exactly how I got mine, which was via measurements followed by a
theoretical cacluation of loss based on the two SWR's formula which is
built into all Smith Charts.

I can't remember where the following formula came from. I think it
was from an RF guru at Intel, but I can't be sure. I have a hand-
written notebook of useful formulas covering 25 years but I didn't
record where they all came from.

The formula for theoretical TOTAL losses in a *resonant* stub:

Total loss = 10*log{[(Z0-R)/(Z0+R)]^2}

where R is the measured resistance of the resonant stub and Z0
is the characteristic impedance of the stub material. You can
see the [(Z0-R)/(Z0+R)]^2 term is akin to a virtual rho^2 at
the mouth of the stub. Since rho^2 = Pref/Pfor, the losses in
the stub are equivalent to the losses in an equivalent resistance
equal to the measured virtual resistance at the mouth of the stub.
--
73, Cecil http://www.qsl.net/w5dxp

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

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.

Hi Bob,

I've let this simmer for a while, but I have to return to this because
you've erred in interpretation of this particular page and those
particular subjects. They are entirely caloric losses, not what you
dismiss as the myth of mismatch loss.

You need only review the math offered to observe they use the
conventional "real" line loss and add more "real" line loss in
proportion to the reflections at either one or two interfaces. The
equations are quite literal to this and explicitly state:
A0 = normal attenuation of line

If you want deeper math, one source can be found in Chipman's (as
unread as any here) "Transmission Lines."

This is yet another of my references that attend to my recent, short
thread on the nature of power determination error, and mismatched
loads AND sources. In fact ALL of these references I've offered
explicitly describe that the source MUST be matched for ANY of these
equations about transmission lines bandied about to accurately offer
true answers. The naive presumptions that Source Z is immaterial to
the outcome of analysis is quite widespread here.

Chipman offers the rigorous math that attends explicitly to the Smith
Chart loss nomograph you reference elsewhere in this thread. If you
lack access to this work, I can munge up the equations here for you.
I will add, this math is for "lossless" lines, as is the implication
of the Smith Chart nomograph; but it only requires you to add that in
for yourself by restructuring the math to include loss. At that level
of granularity, it won't be pretty; but you can rest assured it will
be complete.

73's
Richard Clark, KB7QHC

On Sun, 28 Nov 2004 18:41:44 GMT, Richard Clark
wrote:

|On Sat, 27 Nov 2004 21:43:14 GMT, (Robert Lay
|W9DMK) wrote:
|
| 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.
|
|Hi Bob,
|
|I've let this simmer for a while, but I have to return to this because
|you've erred in interpretation of this particular page and those
|particular subjects. They are entirely caloric losses, not what you
|dismiss as the myth of mismatch loss.
|
|You need only review the math offered to observe they use the
|conventional "real" line loss and add more "real" line loss in
|proportion to the reflections at either one or two interfaces. The
|equations are quite literal to this and explicitly state:
| A0 = normal attenuation of line
|
|If you want deeper math, one source can be found in Chipman's (as
|unread as any here) "Transmission Lines."
|
|This is yet another of my references that attend to my recent, short
|thread on the nature of power determination error, and mismatched
|loads AND sources. In fact ALL of these references I've offered
|explicitly describe that the source MUST be matched for ANY of these
|equations about transmission lines bandied about to accurately offer
|true answers. The naive presumptions that Source Z is immaterial to
|the outcome of analysis is quite widespread here.
|
|Chipman offers the rigorous math that attends explicitly to the Smith
|Chart loss nomograph you reference elsewhere in this thread. If you
|lack access to this work, I can munge up the equations here for you.

Richard,

If you wouild cite the pages to which you refer, I would gladly scan
then to pdf and post them for all to reference.

Wes


|I will add, this math is for "lossless" lines, as is the implication
|of the Smith Chart nomograph; but it only requires you to add that in
|for yourself by restructuring the math to include loss. At that level
|of granularity, it won't be pretty; but you can rest assured it will
|be complete.
|
|73's
|Richard Clark, KB7QHC

On Sun, 28 Nov 2004 16:53:59 -0700, Wes Stewart
wrote:

If you wouild cite the pages to which you refer, I would gladly scan
then to pdf and post them for all to reference.

Hi Wes,

The math is on the bottom of pg. 203 which is supporting Fig. 9-26.

There is also a section entitled 8.8 Multiple reflections on ppg
174...176.

Then there is the specific math of fully specified matches at both
ends, that is at the source and the load, found in Fig. 10-7 that is
supported by discussion on ppg. 225...227.

All of this bears on discussion around and about the necessary
treatment of the Z of the Source, but I haven't supplied all the
citations within this one reference by any means.

Thanx, Wes. You needn't do all these scans. The group needs to do
their own heavy lifting to escape their naivety about source Z.

73's
Richard Clark, KB7QHC