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

--

My program assumes line Zo is purely resistive. But at HF it is
practically impossible to tell the difference in line loss between an
angle of 0 degrees and 1 degree which is the range of Zo angles
involved.

I have the exact formula for any line but its far too complicated to
write here.

I didn't use it in my program as it would have meant another input
value for no useful purpose.
----
Reg

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

"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, 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.

Dear Reg,

I do not believe in coincidence (that's how we knew when the 2nd
airplane flew into the World Trade Center, that it was not an
accident.)



Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html

"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

In my first edition of "Paul and Nasar", p 335, dealing with lossy
transmission lines; there is a footnote as follows:

For the interested reader, a very thorough discussion of the derivation the
transmission-line equations is given in R. B. Adler, L. J. Chu, and R. M.
Fano , "Electromagnetic Energy Transmission and Radiation", Wiley, New York,
1960, chap. 9.

I have never seen the reference, so cannot comment, but may be available in
a university library. Wonder if that is the Fano in "Fano's limit".

73,

Frank

Owen wrote:
"Has anuypne a link to or reference to derivation of the formula?"

My 19th edition of the ARRL Antenna Book treats additional power loss
due to SWR on page 24-10.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote in message
...
Owen wrote:
"Has anuypne a link to or reference to derivation of the formula?"

My 19th edition of the ARRL Antenna Book treats additional power
loss
due to SWR on page 24-10.

Best regards, Richard Harrison, KB5WZI

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

On this subject the only hope of discovering the exact loss on a line
with SWR is to do an exact complex mathematical analyis for yourseslf
and hope you don't make any mistakes.

For starters, the calculated curves shown in ARRL publications over
the years, as plagiarised by the RSGB, are in error. But they are near
enough not to lose any sleep about.

Why the importance attatched to this line feature I can't imagine.
---
Reg.

On Thu, 7 Jul 2005 11:23:24 -0500, (Richard
Harrison) wrote:

Owen wrote:
"Has anuypne a link to or reference to derivation of the formula?"

My 19th edition of the ARRL Antenna Book treats additional power loss
due to SWR on page 24-10.

Richard, I have an 18th edition, and the formula it gives does not
factor in the angle of the reflection, and so is an approximation.

I don't know if that applies to the 19th edition.

Back to my original post, I was not in search of a formula for an
exact solution, nor a reason to want an exact solution, but rather
whether anyone has seen the derivation of Michaels formula quoted in
QST Nov 97.

Thanks for your help.

Owen

--

"Owen" wrote in message
...
On Thu, 7 Jul 2005 11:23:24 -0500, (Richard
Harrison) wrote:

Owen wrote:
"Has anuypne a link to or reference to derivation of the formula?"

My 19th edition of the ARRL Antenna Book treats additional power loss
due to SWR on page 24-10.

Richard, I have an 18th edition, and the formula it gives does not
factor in the angle of the reflection, and so is an approximation.

I don't know if that applies to the 19th edition.

Back to my original post, I was not in search of a formula for an
exact solution, nor a reason to want an exact solution, but rather
whether anyone has seen the derivation of Michaels formula quoted in
QST Nov 97.

Thanks for your help.

Owen

Well, Owen, if you believe the expressions I presented in Reflections 2 are
approximate, then why do I get the correct answers?

Walt, W2DU

On Thu, 7 Jul 2005 18:46:36 -0400, "Walter Maxwell"
wrote:


Well, Owen, if you believe the expressions I presented in Reflections 2 are
approximate, then why do I get the correct answers?

It seems to me that the method requires that rho is not greater than
one (otherwise the denominator (1-rho2**2) becomes negative, which is
a nonsense). This hints that it does not apply in the general case
where rho *can* be greater than 1, and is therefore probably limited
to cases of distorionless line (Xo=0).

To avoid publishing "ugly" maths here, I have put a page up at
http://www.vk1od.net/temp/reflection.htm with a bunch of expressions
for conditions on the modelled line, including functions for power
flow at an arbitrary point, Loss calculated from powerflow at two
points and loss based on your loss formula + matched line loss.

The graphs show the loss from point x to the load, x is 0 at the load
and negative toward the source.

The algorithms produce quite different results. If I ignore Xo (ie
force Zo to be real), then both algorithms produce the same results.

Have I made a mistake in the maths, or in modelling the scenario?

Owen
--

"Owen" wrote in message
...
On Thu, 7 Jul 2005 18:46:36 -0400, "Walter Maxwell"
wrote:


Well, Owen, if you believe the expressions I presented in Reflections 2
are
approximate, then why do I get the correct answers?

It seems to me that the method requires that rho is not greater than
one (otherwise the denominator (1-rho2**2) becomes negative, which is
a nonsense). This hints that it does not apply in the general case
where rho *can* be greater than 1, and is therefore probably limited
to cases of distorionless line (Xo=0).

To avoid publishing "ugly" maths here, I have put a page up at
http://www.vk1od.net/temp/reflection.htm with a bunch of expressions
for conditions on the modelled line, including functions for power
flow at an arbitrary point, Loss calculated from powerflow at two
points and loss based on your loss formula + matched line loss.

The graphs show the loss from point x to the load, x is 0 at the load
and negative toward the source.

The algorithms produce quite different results. If I ignore Xo (ie
force Zo to be real), then both algorithms produce the same results.

Have I made a mistake in the maths, or in modelling the scenario?

Owen

Thanks for responding, Owen, but I'm going to be otherwise occupied until
Saturday, so the fact that I don't respond immediately doesn't mean that I'm
ignoring you.

Walt