Reflection Loss
 

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.

Reflection Loss
 

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

Reflection Loss
 

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]

Reflection Loss
 

Perhaps he's lost in his reflections.

Reflection Loss
 

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

Reflection Loss
 

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

Reflection Loss
 

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
--

Reflection Loss
 

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

Reflection Loss
 

"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, I'm afraid your worship of Terman has let you down.

The two parameters are NOT inexorably locked together.

SWR can be calculated from the Reflection Coefficient. But half of
the information is then lost and gone for ever.

And so, NOT vice-versa!
---
Reg.

Reflection Loss
 

Dear Richard,

You must have a very extensive library.

By the way, it is NOT Terman or his books which I disdain.

It is the TREATMENT, by his readers, of his books as Bibles which I
disdain.

The situation is on a par with the more modern, unjustifyable,
absolute confidence placed in computer programs and pocket calculators
by their users.

Computer programs have authors. How much confidence can be placed in
THEM is what matters.

Amongst my exceedingly small collection of books is one of Terman's.
It was printed during WW2. I bought it, second hand, just after the
war. 60 years back I learned, critically, a lot from it. Nowadays I
refer to it every few months when searching for something about which
to write another computer program. So the book is still quite
valuable as a comprehensible collection of topics.

I have nothing from Kraus. I know of him only from the frequency at
which he is referred to by bible worshippers on this newsgroup.

I have read about B,L & E. They are the famous trio who left the site
without bothering to measure ground resistivity. Their boss should
have sent them back. Who was HE? He must have known what they were
up to less than THEY did.

Being a WW2 veteran I'm pleased to meet you. The experience, like
mine, was educational. And I'm sure you have a sense of humour
similar to mine. ;o)
----
Regards, Reg, G4FGQ.