Apparently, Michaels described in "Technical Correspondence" in QST
NOV 1997 a method for calculating loss on a mismatched line.

I don't have the article, and haven't been able to find it on the net,
so I am working from references to it that I have seen, mainly in
Usenet.

Apparently, the method involves calculation of a factor (let's call it
MR) as MR=|(Zl-Zo*)/(Zl+Zo)|, and the line loss between two points is
given by 10*log((1-MR1**2)/(1-MR2**2)) where MR1 and MR2 are the
values for MR at points 1 and 2.

I have compared the results of this on lines with Xo0 and high VSWR,
and the results are identical to calcuating the loss by subtraction of
Real(VI*) at point 1 from Real(VI*) at point 2.

Has anyone a link to, or a reference to the derivation of the formula?

Owen
--

On Wed, 06 Jul 2005 22:07:41 GMT, Owen wrote:


Apparently, the method involves calculation of a factor (let's call it
MR) as MR=|(Zl-Zo*)/(Zl+Zo)|, and the line loss between two points is
given by 10*log((1-MR1**2)/(1-MR2**2)) where MR1 and MR2 are the
values for MR at points 1 and 2.

Sorry, that gives the additional loss "due to SWR" which has to be
added to the matched line loss to obtain the total loss between points
1 and 2.

Zl in the formulas is the impedance (V/I) at the point where MR is
calculated.

Owen
--

"Owen" wrote in message
...
On Wed, 06 Jul 2005 22:07:41 GMT, Owen wrote:


Apparently, the method involves calculation of a factor (let's call it
MR) as MR=|(Zl-Zo*)/(Zl+Zo)|, and the line loss between two points is
given by 10*log((1-MR1**2)/(1-MR2**2)) where MR1 and MR2 are the
values for MR at points 1 and 2.

Sorry, that gives the additional loss "due to SWR" which has to be
added to the matched line loss to obtain the total loss between points
1 and 2.

Zl in the formulas is the impedance (V/I) at the point where MR is
calculated.

Owen

Well, Owen, you might take a look at Appendix 8 of Reflections 2, which can
be found on my web site at w2du.com. Click on 'Read Appendices from
Reflections 2', the click on Appendix 8. I think what you'll see there will
be of interest.

Walt, W2DU

On Wed, 6 Jul 2005 18:32:50 -0400, "Walter Maxwell"
wrote:

Well, Owen, you might take a look at Appendix 8 of Reflections 2, which can
be found on my web site at w2du.com. Click on 'Read Appendices from
Reflections 2', the click on Appendix 8. I think what you'll see there will
be of interest.

Thanks Walt. I had a look at it, and although it doesn't state as
much, isn't it correct only for distortionless lines (Xo=0)?
Owen
--

Owen,

Your formula is too short to be anything but an approximation. It may
be a very good approximation. On the other hand it may contain
exactly the same errors as whatever you may have checked it against.

The exact formula is exceedingly involved and occupies about half a
dozen lines of source code in new program SWRARGUE which by
coincidence I have just placed in my website.

You can check your formula against my program. Let us know how you get
on.
----
Reg, G4FGQ

---------------------------------------------------------------

"Owen" wrote in message
...

Apparently, Michaels described in "Technical Correspondence" in QST
NOV 1997 a method for calculating loss on a mismatched line.

I don't have the article, and haven't been able to find it on the
net,
so I am working from references to it that I have seen, mainly in
Usenet.

Apparently, the method involves calculation of a factor (let's call
it
MR) as MR=|(Zl-Zo*)/(Zl+Zo)|, and the line loss between two points
is
given by 10*log((1-MR1**2)/(1-MR2**2)) where MR1 and MR2 are the
values for MR at points 1 and 2.

I have compared the results of this on lines with Xo0 and high
VSWR,
and the results are identical to calcuating the loss by subtraction
of
Real(VI*) at point 1 from Real(VI*) at point 2.

Has anyone a link to, or a reference to the derivation of the
formula?

Owen
--

On Wed, 6 Jul 2005 23:48:53 +0000 (UTC), "Reg Edwards"
wrote:

Owen,

Your formula is too short to be anything but an approximation. It may
be a very good approximation. On the other hand it may contain
exactly the same errors as whatever you may have checked it against.

The exact formula is exceedingly involved and occupies about half a
dozen lines of source code in new program SWRARGUE which by
coincidence I have just placed in my website.

I have calculated the loss using P=Real(V*I*) at the two points, and
it is long winded. Michaels approach produces the same result, and the
coding is more elegant, probably faster to calculate. He is a SK, so I
can't ask him, but in the hope that it is well known, someone might
know of the derivation.


You can check your formula against my program. Let us know how you get
on.

Your calculator does not allow complex Zo does it? Doesn't that mean
it assumes a distortionless line. I am calculating loss in the general
case.

Thanks...

Owen

--

"Owen" wrote in message
...
On Wed, 6 Jul 2005 18:32:50 -0400, "Walter Maxwell"
wrote:

Well, Owen, you might take a look at Appendix 8 of Reflections 2, which
can
be found on my web site at w2du.com. Click on 'Read Appendices from
Reflections 2', the click on Appendix 8. I think what you'll see there
will
be of interest.

Thanks Walt. I had a look at it, and although it doesn't state as
much, isn't it correct only for distortionless lines (Xo=0)?
Owen

As I understand it, Owen, a line has to be lossless for Xo to be 0, while
distortionless lines have loss but have equal series R and shunt G. All
lines that I've measured have a small negative X, that would be zero if the
line were lossless. So I'd have to say that the material in Appendix is is
correct for standard lines. Distortionless lines are normally found only in
long-distance phone lines used at voice frequencies, not RF. Or am I missing
something?

Walt,W2DU

Owen:

Right of you to be cautious of that wise and crafty old brit.

Not only has he survived in this den of treacherous and particularly
vicious hams--he has THRIVED--this is quite suspicious in itself!

However, most often you will find there is true wisdom in his words
and programs... and it is of a highly practical nature. He is a
welcomed resource here...

John

"Owen" wrote in message
...
On Wed, 6 Jul 2005 23:48:53 +0000 (UTC), "Reg Edwards"
wrote:

Owen,

Your formula is too short to be anything but an approximation. It
may
be a very good approximation. On the other hand it may contain
exactly the same errors as whatever you may have checked it against.

The exact formula is exceedingly involved and occupies about half a
dozen lines of source code in new program SWRARGUE which by
coincidence I have just placed in my website.

I have calculated the loss using P=Real(V*I*) at the two points, and
it is long winded. Michaels approach produces the same result, and
the
coding is more elegant, probably faster to calculate. He is a SK, so
I
can't ask him, but in the hope that it is well known, someone might
know of the derivation.


You can check your formula against my program. Let us know how you
get
on.

Your calculator does not allow complex Zo does it? Doesn't that mean
it assumes a distortionless line. I am calculating loss in the
general
case.

Thanks...

Owen

--

On Wed, 06 Jul 2005 22:27:08 GMT, Owen wrote:

On Wed, 06 Jul 2005 22:07:41 GMT, Owen wrote:


Apparently, the method involves calculation of a factor (let's call it
MR) as MR=|(Zl-Zo*)/(Zl+Zo)|, and the line loss between two points is
given by 10*log((1-MR1**2)/(1-MR2**2)) where MR1 and MR2 are the
values for MR at points 1 and 2.

Sorry, that gives the additional loss "due to SWR" which has to be
added to the matched line loss to obtain the total loss between points
1 and 2.

Zl in the formulas is the impedance (V/I) at the point where MR is
calculated.

I think "Computation of Impedance and Efficiency of Transmission Line
with High Standing-Wave Ratio", W.W. Macalpine, Transactions of the
AIEE, vol. 72, pp 334-339; July, 1953 might be of interest to you.

The same reference is used as the basis for the section
"Transformation of Impedance on Lines With Highh SWR" in the ITT
handbook.

On Wed, 6 Jul 2005 20:06:13 -0400, "Walter Maxwell"
wrote:


As I understand it, Owen, a line has to be lossless for Xo to be 0, while
distortionless lines have loss but have equal series R and shunt G. All

Walt, I learnt that a distortionless line is one where attenuation and
phase velocity are constant for all frequencies, and that requires
that R/XL=G/XC in the RLGC model of a lines characteristics, and the
result is that Zo is purely real.

A lossless line is a special case of a distortionless line.

lines that I've measured have a small negative X, that would be zero if the
line were lossless. So I'd have to say that the material in Appendix is is
correct for standard lines. Distortionless lines are normally found only in
long-distance phone lines used at voice frequencies, not RF. Or am I missing
something?

If you like, I am saying your approach is valid for lossless lines, it
is also valid for all distortionless lines, but I think it is not
accurate for lines in the general case because it isn't correct if
Xo!=0.

Owen
--