(Robert Lay W9DMK) wrote:
Yes, I believe it does - that is, it makes perfect sense to have a low
resistance and to have a near zero reactive component. What does not
make sense is that the high SWR is supposed to produce outrageous
losses. I don't see values that I can interpret as high losses - quite
the opposite. Maybe I just don't interpret it correctly, but I would
expect it to be several ohms - not 0.57 ohms.

Hi Bob, I'm still at my relatives' house posting through Google. I'll
expand on this when I get back to my computer.

Those equations in The ARRL Antenna Book (15th Edition) make an assumption
that may or may not be true - I don't know. What they are assuming is that
the losses are due to the additional power associated with high SWR. In
general, if the forward power is 100w for the matched case and the sum
of the forward and reflected power is 300w for the unmatched case, the
losses will be three times higher for the unmatched case. That seems a
reasonable assumption. However, rho at the shorted or open end of a stub
is equal to |1| so rho^2 will be equal to 1. That puts (1-rho^2) = 0 in
the denominator of the equation and makes the addditional losses undefined.

In fact, and this is where it gets ridiculous, the examples in the
ARRL Antenna Book would lead me to believe that the above quarter wave
line would exhibit 20 dB of total losses. In order to get those
numbers the SWR at the load of say 8000 would have to decrease to
1.01:1 at the source end in order to account for 20 dB in losses. (See
the example on page 24-9 of the 17th Edition.)

Here's an example. Assume 100w is delivered to the load for both the
matched and unmatched conditions. Assume 3dB matched line loss in the
transmission line. Assume an SWR of 5.83:1 (rho=0.707) at the load for
the mismatched condition.

Forward 200w------------3dB loss-------------Matched Load 100w


Forward 400w------------3dB loss-------------Mismatched Load 100w
Reflected 50w both Forward 200w
directions Reflected 100w

The equations gives an additional loss of 5.44dB. This is based on an
assumption that the losses are directly proportional to forward power
plus reflected power.

Remember that at the mouth of the stub, the impedance is equal to
(Vf + Vr)/(If + Ir) so, knowing the Z0, that should allow you to
calculate those four values existing at the mouth of the stub. From
that, you can calculate the total losses. More when I get back.
--
73, Cecil, W5DXP

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

Keep in mind that real ohmic and dielectric losses measured in watts depend
upon sqrt(SWR). Thus, the higher the SWR (load mismatch) the greater the
I^2R losses in the conductors and similarly in the dielectric.

So, to me, a non-unity SWR connotes real power loss measurable in watts and
attributable to well-known loss mechanisms.

Of course, any real power lost in the line materials represents power not
delivered to the load, so this fits somewhat with the viewpoint that
Line Loss is in fact the magnitude of power undelivered to the load due to
the mismatch. But, I think that we are looking at real watts of loss here.

Another confusing factor is that one is usually interested in the total loss
attributable to the use of a mismatched line and not especially in how that
loss is distributed along the line from load to source. But there are
applications where the loss distribution with line length is of concern. An
example is the case of a complex Zo with rho unity in which the majority
of the power loss occurs in the section of the line nearest the load and
decreases toward the source. In that case of probably limited application,
the line nearest the load might be required to handle more power than that
further toward the source.

A somewhat related example concerns the W2DU balun in which is it observed
that the beads nearest the mismatched load endure the largest heat
dissipation and are commonly larger that the remainder further toward the
source.

However, since complex Zo is an issue of magnitude usually only at low r-f
and more so at audio frequencies, this is seldom a practical consideration.

Thanks for bringing this topic to light, Bob. Like most engineers, I have
been guilty of looking at "line loss" as a monolithic phenomenon and not
being concerned with the micro-structure of its distribution.

--
73, George W5YR
Fairview, TX

http://www.w5yr.com


"Robert Lay W9DMK" wrote in message
...
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

Modeling a free space dipole made from a lossless conductor, 100 ft in
length, at 1.8 MHz shows an input impedance of 6.694 - j1621 Ohms. As
expected the radiation efficiency is 100%.

Adding 300 ft of 600 Ohm, 6" spaced, copper open wire transmission line
degrades the radiation efficiency to 16.75 %. The result, therefore
indicates a transmission line loss of 7.76 dB. The input impedance is
calculated as 11 - j619.7 Ohms.

The ARRL, DOS based program, "TL" computes, for 300 ft of 600 Ohm line
terminated with 6.694 - j1621 Ohms, a loss of 8.19 dB, and an input
impedance of 18.35 - j805 Ohms.

Realizing that 6" spaced, #14 AWG, is not exactly 600 Ohms, and NEC's
computation of parallel wire transmission lines is not 100% accurate; the
results do seem to confirm the validity of the ARRL's program.

Another interesting experiment with the ARRL's program also seems to verify
its accuracy:

RG8, 1000 ft, frequency 100 MHz. Matched line loss = 24.82 dB.
Load impedance 1 - j1000 Ohms. Total line loss = 61.82 dB.
The program computes the input impedance to by: 50.3 - j0.2 Ohms.

73,

Frank


"George, W5YR" wrote in message
...
Keep in mind that real ohmic and dielectric losses measured in watts
depend
upon sqrt(SWR). Thus, the higher the SWR (load mismatch) the greater the
I^2R losses in the conductors and similarly in the dielectric.

So, to me, a non-unity SWR connotes real power loss measurable in watts
and
attributable to well-known loss mechanisms.

Of course, any real power lost in the line materials represents power not
delivered to the load, so this fits somewhat with the viewpoint that
Line Loss is in fact the magnitude of power undelivered to the load due to
the mismatch. But, I think that we are looking at real watts of loss here.

Another confusing factor is that one is usually interested in the total
loss
attributable to the use of a mismatched line and not especially in how
that
loss is distributed along the line from load to source. But there are
applications where the loss distribution with line length is of concern.
An
example is the case of a complex Zo with rho unity in which the majority
of the power loss occurs in the section of the line nearest the load and
decreases toward the source. In that case of probably limited application,
the line nearest the load might be required to handle more power than that
further toward the source.

A somewhat related example concerns the W2DU balun in which is it observed
that the beads nearest the mismatched load endure the largest heat
dissipation and are commonly larger that the remainder further toward the
source.

However, since complex Zo is an issue of magnitude usually only at low r-f
and more so at audio frequencies, this is seldom a practical
consideration.

Thanks for bringing this topic to light, Bob. Like most engineers, I have
been guilty of looking at "line loss" as a monolithic phenomenon and not
being concerned with the micro-structure of its distribution.

--
73, George W5YR
Fairview, TX

http://www.w5yr.com


"Robert Lay W9DMK" wrote in message
...
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 07:33:04 GMT, Richard Clark
wrote:

.....snip
Reference Data for Radio Engineers, "Mismatch and Transducer Loss,"
"One End Mismatched," pg. 22-12:
Transducer Loss = A0 + 10 · log (Pm/P) decibels
where
A0 = normal attenuation of the line
Pm = power that would be delivered were system matched
P = power delivered to the load

Of particular note is that this is one of my references as to the
nature of Source Z which is often neglected in academic treatments
with the presumption that the engineer has already been schooled in
the nature of Real sources (this may shock some complaisant readers
here). However, this citation offers that explicit lesson in figure
10 and makes use of this commonplace characteristic in illustrations
of Mismatch Uncertainty. They go as far as to explicitly offer a
section entitled "Generator and Load Mismatched." You may wish to
review this treatment as it offers the math that would present the
most loss available in a line, above and beyond the typical charts
offered for line loss (which are confined to both ends being matched).

Dear Richard,

I'm finally ready to comment on the above - it is my great fortune to
be blessed with copies of both the Fourth and Fifth Editions of the
ITT Handbook.

I studied over the first 13 pages of Chapter 22 and found that, just
as Wes said, it's entirely the work of MacAlpine as published in 1953.

I went over Equations (1) through (4) in the Mismatch section very
carefully and found no heartburn with anything in that section. This
is NOT to say that I LIKE it, but I do understand it and have no
problem with the math model and the figures. My problems with the two
mismatch topics is simply that I just don't like to call it a loss
when energy that COULD have been delivered to the load does NOT get
delivered to the load as a result of mismatch. For me, lost energy in
a transmission line problem is energy actually lost in the
transmission line, not energy that is being lost elsewhere as a result
of the transmission line not being matched properly. I realize that
I'm probably alone in that thinking, but I like to feel that such
terms as efficiency and losses should be associated strongly with the
item under evaluation, namely the transmission line, and not the
ancillary equipment which feed it or terminate it. Those items get
their own hearings relative to efficiency and losses and those
evaluations do not require the presence of the transmission line. In
fact, those items are usually evaluated as to their performance in
ways that do not in any way relate to how well some transmission line
is or is not working.

However, this is not the nub of the problem that I was encountering -
a problem which has now been partly resolved. At least I think I have
a far, far better understanding of the problem now than I had a few
days ago. The problem centers on the Additional Losses Due to SWR and
how to model them. Since it is, perhaps, more appropriate to continue
that topic under the responses from Wes, I will not go into it here.

I want to thank you and Wes, both, for leading me to Chapter 22 - it
is much more readable than MacAlpine's original paper.

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

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

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

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