I have just had several glasses of Australian Zonte's Footstep wine.
I can recommend it. Its name can be traced back to a marsupial which
replaced the dinosaurs.

Transmission lines, which even the dinosaurs knew nothing about, are
associated with losses of one sort and another. But there is one sort
of loss which is never mentioned in discussions on this newsgroup. It
is reflection loss.

Reflection loss is sometimes known as mismatch loss.

It is that loss which occurs in the load impedance because it is not
matched to the line impedance Zo. When the line is not matched there
is a reflection of amps and volts back towards the generator.

The reflected volts and amps, in conjunction with the existing volts
and amps, present to the generator an impedance which causes it to
deliver to the line exactly the power in the load plus the power lost
in the line. That this occurs is quite obvious.

When calculated, the power lost in the line automatically takes into
account the increase in loss due to SWR which occurs on the line due
to the mismatch of the load.

But the most important parameter is not the SWR but the reflection
coefficient, Gamma.

Gamma = ( Zt - Zo ) / ( Zt + Zo ).

The loss in the load due to reflection is given by

Reflection Loss = 4.343 * Ln( 1 - Square( G ) ) decibels.

where G is the magnitude of the reflection coefficient which is easy
to measure.
----
Reg.

Reg Edwards wrote:
The reflected volts and amps, in conjunction with the existing volts
and amps, present to the generator an impedance which causes it to
deliver to the line exactly the power in the load plus the power lost
in the line. That this occurs is quite obvious.

A tuner will present the designed-for impedance to the
generator and thus develops reflection gain that neutralizes,
to varying degrees, the reflection loss at the load.
--
73, Cecil http://www.qsl.net/w5dxp

On Sun, 5 Mar 2006 03:29:51 +0000 (UTC), "Reg Edwards"
wrote:

I have just had several glasses of Australian Zonte's Footstep wine.
I can recommend it. Its name can be traced back to a marsupial which
replaced the dinosaurs.

That's really well-aged wine.


Transmission lines, which even the dinosaurs knew nothing about, are
associated with losses of one sort and another. But there is one sort
of loss which is never mentioned in discussions on this newsgroup. It
is reflection loss.

Never mentioned??? You must have tipped too many and nodded off.

[snipped]

Perhaps he's lost in his reflections.

ORIGINAL MESSAGE:

Reg Edwards wrote:

I have just had several glasses of Australian Zonte's Footstep wine.
I can recommend it. Its name can be traced back to a marsupial which
replaced the dinosaurs.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I love the Aussie sense of humor. Who else would name a marsupial
"Footstep"?

Bill, W6WRT

Reg, G4FGQ wrote:
"The most important parameter is not SWR but the reflection coefficient,
Gamma."

My age is about the same as Reg`s. I have 4 children and 6
grandchildren, and am a veteran of WW-2, but doubt that adds to my
credibility. Neither does the beer I had with dinner add authority to
what I write. I have a degree in Electrical Engineering, but Americans
and probably Brits too view this credential with suspicion. It did open
the door to good jobs.

Reg expresses disdain for "bibles" such as Terman or Kraus but their
writings have endured the test of time and are proved by countless
experiments.

On page 99 of Terman`s 1955 edition of "Electronic and Radio
Engineering" (my textbook was an earlier edition) is found the formula
to convert the reflection coefficient into SWR or vice versa. These two
parameters are innexorably locked together by formulas (4-22a) and
(4-22b).

There really is no need to rename the ubiquituos SWR meter as Reg has
recommended. This really requires no comment as it isn`t about to
happen.

Best regards, Richard Harrison, KB5WZI

On Mon, 6 Mar 2006 02:34:06 -0600, (Richard
Harrison) wrote:


On page 99 of Terman`s 1955 edition of "Electronic and Radio
Engineering" (my textbook was an earlier edition) is found the formula
to convert the reflection coefficient into SWR or vice versa. These two
parameters are innexorably locked together by formulas (4-22a) and
(4-22b).

Richard, formula 4-22b calculates the magnitude of the reflection
coefficient from SWR. It is not possible to calculate the reflection
coefficient (as you say) in the general sense since you lack the phase
information.

Owen
--

Owen Duffy wrote:
"Richard, formula 4-22b calculates the magnitude of the reflection
coefficient from SWR, it is not possible to calculate the reflection
coefficient (as you say) in the general case since you lack phase
information."

Phase information is not needed. It is true that the reflection
coefficient is a vector ratio of the reflected voltage to the incident
voltage at the load but this does not affect conversion of the
reflection coefficient to the SWR.

Reactance at the load has the same effect as adding a same-impedance
line (of particular length) between the generator and load. This only
shifts the SWR pattern on the line, but in a practical line has no
effect on the minima and maxima on the line.

SWR is simply the ratio of the maximmum amplitude to the minimum
amplitude of voltage (or current) on the line in a particular region of
the line. A maximum is displaced by 1/4-wave from a minimum.

Phase information is irrelevant to conversion between reflection
coefficient and SWR. That`s why Terman didn`t include it.

Best regards, Richard Harrison, KB5WZI

On Mon, 6 Mar 2006 04:49:53 -0600, (Richard
Harrison) wrote:



Richard,

You originally stated:

On page 99 of Terman`s 1955 edition of "Electronic and Radio
Engineering" (my textbook was an earlier edition) is found the formula
to convert the reflection coefficient into SWR or vice versa. These
two parameters are innexorably locked together by formulas (4-22a) and
(4-22b).

You are squirming away from the accuracy of your assertion that Terman
calculates reflection coefficient from SWR, ie the "or vice versa" in
your statement.

The reflection coefficient is a complex number with magnitude and
phase, as you acknowledge when you later say "It is true that the
reflection coefficient is a vector ratio of the reflected voltage to
the incident voltage at the load".

In formula 4-22b of my copy of Terman, the term on the lhs is |rho|,
which is the magnitude of the reflection coefficient.

No, you cannot calculate the reflection coefficient from SWR alone,
but you can calculate the magnitude alone, but that is less
information than the reflection coefficient.

To illustrate, and as you know, the reflection coefficient at a point
can be used with the line propagation constants to calculate the
impedance at another point on the line. You cannot do that with the
magnitude of the reflection coefficient.

You have misrepresented Terman, he does not calculate the reflection
coefficient from SWR (at least not in my copy).

Owen
--

Owen Duffy wrote:
"In formula 4-22b of my copy of Terman, the term on the lhs is Irhol
which is the magnitude of the reflection coefficient."

In my copy, 4-22b gives the "absolute value" of the reflection
coefficient (it is embraced with bars) which I believe means the
"absolute value" of a number or a symbol without reference to its
algebraic sign.

(4-22b):
+or- reflection coefficient=
SWR-1 / SWR+1

These formulas, (4-22a) and 4-22b) aren`t just theory. They are
constantly put to use. A derivation which uses the sq rt of the ratio of
refllected power to forward power for the reflection coefficient appears
on page 23 of my Bird Model 43 Directional Thruline Wattmeter Manual.:
SWR = 1+reflection coefficient / 1-reflection coefficient
(Same as 4-22a)

Transmission lines are special because they enforce Zo. That is, in
either direction of travel, when you apply a voltage to the low-loss
line, the current which results is locked in-phase with the applied
voltage. In other words, Zo is a resistance.

Best regards, Richard Harrison, KB5WZI