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 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 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

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

Reg, G4FGQ wrote:
"The active device generally behaves as a current source."

As Reg also wrote:
"I can`t imagine why this conversation has continued for so many years
by more or less the same group of experts."

Agreed! Reg seems to have answered his own question.The same people
recite the same arguments in hopes their view of reality will be
accepted. Fat chance! Time has inured them.

Reg has faithfully proposed constant-current behaviour from all vacuum
valves and transistors as I recall. I agree that most of these devices
have extremely high plate ond collector resistances as linear
amplifiers. Current through them is almost constant regardless of anode
voltage.

As most transmitter power amplifiers exceed 50% efficiency by a good
margin, these devices are not operating as Class-A linear amplifiers.
They instead operate as HF switches. These are turned-off most of every
cycle and are only on for short pulses. Harmonics and other noise is
cleaned up by output filters. It`s the only thing which makes the output
linear.

During the output device`s conduction, its saturation volts are very low
and its current is very high, giving the device a very low impedance
while switched-on. You may not infer a low impedance from the d-c volts
and amps feeding the final amplifier. These are the averages, almost, of
the device amps. The device saturation volts sre what counts toward its
dissipation and loss. The transmitter usually has no built-in indicator
of saturation voltage. It wouldn`t read much anyway.Device
impedance depends mostly on its ratio of off to on times. This is a form
of lossless resistance. Dissipation is zero in a sewitched-off device.
The d-c volts and amps are related to the output device(s) internal
impedances used as a switch when the transmitter output is considered. A
high voltage and a low current accompany a high internal impedance but
they won`t be nearly so high as the spec sheet plate or collector
resistances.

We have d-c power input to the amplifier. We can measure HF power
output. The difference is dissipation, but loss resistance does not
represent the total source resistance because we have non-dissipative
resistance in the device off-times.

There have been measurements of transmitter internal output impedances
which indicated that they did indeed match their loads. I have not done
it myself but have no reason to doubt the reports.

Best regards, Richard Harrison, KB5WZI