Antonio Vernucci wrote:
The extra power measured at the receiver is obviously "created" at the
expense of power taken away from other regions of the space (according
to the transmit antenna pattern).

Too fundamental to deserve further discussions!

Almost everyone knows what occurs in free space -
constructive interference in the direction of
greater gain and destructive interference in the
direction of lesser gain. But my posting was not
about free space. I thank you for your input so
far but please now extend those EM wave concepts
to transmission lines.

Everyone doesn't agree that constructive and
destructive interference also happens at a Z0-
match point in a transmission line with reflections.
That is the topic that needs "further discussions".

Just as constructive interference functions to
increase antenna gain in one direction while
destructive interference functions to decrease
antenna gain in another direction, in a transmission
line at a Z0-match point, constructive interference
functions to increase the energy flow toward the
load while destructive interference functions to
decrease the energy flow toward the source.

Antonio, please don't bow out now. You are apparently
one of the few posters who fully understands interference.
--
73, Cecil http://www.w5dxp.com

Just as constructive interference functions to
increase antenna gain in one direction while
destructive interference functions to decrease
antenna gain in another direction, in a transmission
line at a Z0-match point, constructive interference
functions to increase the energy flow toward the
load while destructive interference functions to
decrease the energy flow toward the source.

I cannot follow your reasoning as I cannot understand what is a "Z0-match
point".

In my understanding:
- if the transmission line end is mismatched, in no point impedance can be equal
to Z0.
- conversely if the transmission line end is matched, impedance is equal to Z0
in all points. But there is no reflected wave and hence no energy flow toward
the source

Then, your "Z0-match point" must be something else which I cannot figure out.

73
Tony I0JX

Tony, I0JX wrote:
"Then, your "Zo-matchpoint" must be comething else which I cannot figure
out."

I`ll guess with Tony that in a made-up case of a 50-ohm antenna and a
50-ohm transmitter connected by a 1/2-wavelength of 300-ohm twinlead, we
have a Zo-match to 50-ohms because the twin-lead, mismatched at both
ends, still looks to source and load like 50-ohms.

Best regards, Richard Harrison, KB5WZI

Antonio Vernucci wrote:
I cannot follow your reasoning as I cannot understand what is a
"Z0-match point".

A Z0-match is defined in my ARRL Antenna Book.

Then, your "Z0-match point" must be something else which I cannot figure
out.

Here is an example of a Z0-match to 50 ohms at point '+':

XMTR--50 ohm coax---+---1/2 WL 300 ohm feedline---50 ohm load

The SWR on the 300 ohm feedline is 6:1. The SWR on the 50
ohm coax is 1:1. What happens to the energy and momentum
of the reflected waves on the 300 ohm feedline? Seems
obvious that there is destructive interference toward
the XMTR and constructive interference toward the load.
--
73, Cecil http://www.w5dxp.com

A Z0-match is defined in my ARRL Antenna Book.

Sorry, I have that book, but I do not remember where it is.

Here is an example of a Z0-match to 50 ohms at point '+':

XMTR--50 ohm coax---+---1/2 WL 300 ohm feedline---50 ohm load


OK, understood.

The SWR on the 300 ohm feedline is 6:1. The SWR on the 50
ohm coax is 1:1. What happens to the energy and momentum
of the reflected waves on the 300 ohm feedline? Seems
obvious that there is destructive interference toward
the XMTR and constructive interference toward the load.

I am not sure on whether I am able to correctly interpret your statement. My
understanding is:

- reflected power does not reach the transmitter, as it is fully reflected back
toward the load
- such re-reflected power reaches the load, where it is partially absorbed (thus
contributing to the total power delivered to the load) and partially reflected
back once more

Probably this is what you call destructive interference at the trasmitter and
constructive interference at the load.

The fact that reflected power is fully re-reflected to the load does not seem to
be appreciated by everyone. Many people still attribute their transmitter power
transistors failure to reflected power burning them. The failure is instead
clearly due to malfunctioning or poor design of the SWR protection circuit that:
- does not keep the collector voltage within its maximum allowable value when
load impedance is too high
- does not keep the collector current and the junction temperature within their
maximum allowable values when load impedance is too low

73

Tony I0JX

Antonio Vernucci wrote:
- reflected power does not reach the transmitter, as it is fully
reflected back toward the load

The re-reflection is associated with destructive interference
toward the source and an equal magnitude of constructive
interference toward the load. The energy in the canceled
reflected waves is redistributed to a region that allows
constructive interference to occur, i.e. in the opposite
direction to the direction of reflected wave cancellation
toward the source.

Probably this is what you call destructive interference at the
trasmitter and constructive interference at the load.

At a Z0-match *point*, destructive interference *toward* the
transmitter and constructive interference *toward* the load.

It is akin to the passive elements of a Yagi causing
destructive interference to the rear and constructive
interference toward the front. What is the front/back
ratio of a Z0-match? :-)
--
73, Cecil http://www.w5dxp.com

Cecil, W5DXP wrote:
"Antonio, please don`t bow out now."

Why is a principle so trivial as superposition worth a thread in this
newsgroup?

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Why is a principle so trivial as superposition worth a thread in this
newsgroup?

Because most of the posters to this newsgroup do not
know what happens to the energy in the waves during
superposition inside a transmission line. They seem
to understand superposition in free space but not
inside a transmission line. Maxwell's laws are the
same for EM waves in free space and inside a
transmission line.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
et...
Richard Harrison wrote:
Why is a principle so trivial as superposition worth a thread in this
newsgroup?

Because most of the posters to this newsgroup do not
know what happens to the energy in the waves during
superposition inside a transmission line. They seem
to understand superposition in free space but not
inside a transmission line. Maxwell's laws are the
same for EM waves in free space and inside a
transmission line.
--
73, Cecil http://www.w5dxp.com

"Sal M. Onella" wrote in message
...

"Cecil Moore" wrote in message
et...
Richard Harrison wrote:
Why is a principle so trivial as superposition worth a thread in this
newsgroup?

Because most of the posters to this newsgroup do not
know what happens to the energy in the waves during
superposition inside a transmission line. They seem
to understand superposition in free space but not
inside a transmission line. Maxwell's laws are the
same for EM waves in free space and inside a
transmission line.
--
73, Cecil http://www.w5dxp.com



Sorry for the blank post, above, -- double-click-itis set in.

I like 90% of these technical discussions. I'm a curious person by nature
but I don't always know what doors to pull open, so it's nice when a good
door is held open for me.

73
"Sal"
(KD6VKW)