"Dave" wrote in message
...

"Ian White, G3SEK" wrote in message
news
Dave wrote:

"Reg Edwards" wrote in message
...

Reflected power is a mere fiction. Power which is not radiated from
an
antenna never actually arrives there. In fact it never leaves the
transmitter.

but, but, but, i can SEE reflected power! it shows on my TDR, i can
see
ghosts in video from it, i can measure it, i can catch it in a
circulator!
how can it be fiction?!?!?!

You aren't being literal-minded enough. When you claim to "see" and
"measure" reflected power, you're applying theories that assume it
exists. You are not proving that it does exist.

What shows on your TDR, as ghosts on your TV, and also on a slotted
line, is the interaction between forward and reflected voltage waves.
Likewise a circulator (or a directional coupler) processes the voltage
and current waves. I've yet to see a fully detailed functional
explanation of any of those devices in terms of power waves alone.

That is because "forward and reflected power waves" is a derivative
concept. It depends on concepts of voltage and current waves for its
existence; but it doesn't add anything useful that we didn't already
know.

i know that, i was just trying to get in all the bogus arguments before
anyone else did. 'power waves' are a concept invented to simplify some
concepts, but instead they just hide the important details. we have been
over and over that on here in the past and always end up in the same
place,
i was just hoping to skip right to the end.


maybe if i had learned to use smileys it would have helped.... what is the
sarcastic one?? something like ;-^ or something like that??

If this old mind recalls correctly a TV station with an undesireable SWR
will not transmit a clear image to its viewers because the delayed
re-reflection arrives at the TV set later and casues a ghost or smear.
Could you please explain the "Reflected power is a mere fiction." and the
smear or ghost?

tnx
Hank WD5JFR
"Reg Edwards" wrote in message
...

"Richard Clark" wrote:
What you describe as reflection and re-reflection occurs between the
mismatched antenna and the tuner that has been adjusted to minimize
power returned to the transmitter. The sole function of the tuner is
to keep this power from being dissipated by the transmitter (common
experience of arcing, denoting a voltage reflection, or thermal
runaway, denoting a current reflection). The "virtual" reflection
(offered by the tuner) is generally know as the complex conjugate of
the remote load, seen at the near end of the line through which it is
returning. This means that the line transforms the phase and
amplitude of the reflection, and the tuner's job is to invert that
relationship to counteract it, and return it to the antenna.

There are both wave descriptions of this process, and lumped circuit
equivalents. Both work, and both describe the same process from
different points of view. One does not negate the other's validity
(unless, of course, you attempt to mix the points of view and demand
consistency in terms - a frequent rhetorical trap here).

There will no doubt be a flurry of denials to this simple example with
contortions of logic to match. As for the math, you will find it by
the reams, once you've been overwhelmed with the arcana of hyperbolic
descriptions of a novel physics that have to proceed its proof.

Keep your eye on how your literal points in your question go abandoned
with these arcane theories.

73's
Richard Clark, KB7QHC
====================================

Dear Richard, you are confusing the matter even further, if that were
possible.

The only saving grace about your tedius message is that you yourself
eventually realise what a load of overcomplicated nonsense it is.

Reflected power is a mere fiction. Power which is not radiated from an
antenna never actually arrives there. In fact it never leaves the
transmitter.

All the power which leaves the transmiter is radiated except for that
which
is lost in the line. It has nowhere else to go!

But for the existence of so-called SWR meters, the words 'forward and
reflected power' would never enter people's vocabularies. For the few who
become involved with such matters, the misleading fiction also appears in
the language of mathematics.

Names have to be invented in order to discuss mathematical equations in
plain English. But there's no reason why they should be propagated, just
to
confuse, into the real World.

The sole purpose of an SWR meter is to indicate whether or not the
transmitter is loaded with 50 ohms.
----
Reg, G4FGQ

Henry Kolesnik wrote:

I know that any power not dissipated by an antenna is reflected back to the
transmitter. Then the transmitter "reflects" this reflection back to
antenna, ad nauseum until its all gone. I also know that a short or an open
is required to reflect power and I'm searching for which it is, an open or a
short. I'm inclined to think it's a virtual open but I'm at a loss to
understand that and I wonder if someone has a good explanation or analogy
and some math wouldn't hurt.

Hank, EM reflections are covered on this web page.

http://www.mellesgriot.com/products/optics/oc_2_1.htm

In particular: "Clearly, if the wavelength of the incident light and the
thickness of the film are such that a phase difference exists between
reflections of p, then reflected wavefronts interfere destructively, and
overall reflected intensity is a minimum. If the two reflections are of
equal amplitude, then this amplitude (and hence intensity) minimum will
be zero."

"In the absence of absorption or scatter, the principle of conservation of
energy indicates all "lost" reflected intensity will appear as enhanced
intensity in the transmitted beam. The sum of the reflected and transmitted
beam intensities is always equal to the incident intensity. This important
fact has been confirmed experimentally."

In order for (rearward-traveling) "reflected intensity" to "appear as
(forward-traveling) enhanced intensity in the transmitted beam", the
momentum of that (rearward-traveling) intensity must change directions.
Thus, it appears that total destructive interference between two rearward-
traveling reflected waves in a transmission line will reverse the direction
of momentum of the energy in those canceled reflected waves.

We need to change a few of your statements:

Any power not dissipated or radiated by an antenna is reflected back.
"Dissipation" means EM energy transformed into heat, according to
the IEEE Dictionary.

The transmitter/tuner end will not re-reflect 100% of the reflected energy
unless there exists a short, open, pure reactance, or "total destructive
interference" as explained in _Optics_, by Hecht.

Besides a short or an open, a purely reactive impedance will cause
100% energy reflection. Apparently, so will "total destructive
interference". Quoting from _Microwave_Transmission_, by J. C. Slater:

"The method of eliminating reflections is based on the interference
between waves. ... The fundamental principle behind the elimination
of reflections is then to have each reflected wave canceled by another
wave of equal amplitude and opposite phase."

That's pretty clear. We get one set of rearward-traveling reflections
at the match point. We get another set of rearward-traveling reflections
at the antenna. If these two sets of reflections are equal in magnitude
and opposite in phase at the match point, they cancel each other and the
rearward-traveling momentum energy in those two waves is conserved by
changing direction to become part of a forward-traveling wave.
--
73, Cecil http://www.qsl.net/w5dxp



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"Dave" wrote in message
...

"Reg Edwards" wrote in message
...

Reflected power is a mere fiction. Power which is not radiated from an
antenna never actually arrives there. In fact it never leaves the
transmitter.

but, but, but, i can SEE reflected power! it shows on my TDR, i can see
ghosts in video from it, i can measure it, i can catch it in a circulator!
how can it be fiction?!?!?!


Clearly there is reflected power. Just don't take the SWR meter too
literally. It does not actually measure power, but the scale has been fudged
so it indicates the correct power if the load is equal to some design value.
I can see a long thread here.

Tam/WB2TT

Richard Clark wrote:
As for the math, you will find it by
the reams, once you've been overwhelmed with the arcana of hyperbolic
descriptions of a novel physics that have to proceed its proof.

A scattering parameter analysis, described in HP Application Note
95-1 (available on the web) is ideal for analyzing what happens
at a match point in a typical ham radio antenna system.

b1 = s11(a1) + s12(a2)

b2 = s21(a1) + s22(a2)

b1 is the net forward voltage, b2 is the net reflected voltage
a1 is the incident forward voltage, a2 is the incident reflected voltage

Quoting from HP AN 95-1: Another advantage of s-parameters springs
from the simple relationship between the variables a1, a2, b1, and
b2, and various power waves:

|a1|^2 = Power incident on the input of the network.
(forward power incident on the match point)

|a2|^2 = Power reflected from the load.

|b1|^2 = Power reflected from the input port of the network.
(power reflected from the match point back toward the source)

|b2|^2 = Power incident on the load.

The previous four equations show that s-parameters are simply
related to power gain and mismatch loss, quantities which are
often of more interest than the corresponding voltage functions.

|s11|^2 = Power reflected from the network input divided by
power incident on the network input

|s22|^2 = Power reflected from the network output divided by
power incident on the network output

|s21|^2 = Power delivered to a Z0 load divided by power available
from a Z0 source

|s12|^2 = Reverse transducer power gain with Z0 load and source

End quote.

b2 is the voltage reflected back toward the source and

b2 = s21(a1) + s22(a2)

It should be obvious that b2 cannot be zero unless there exists
total destructive interference between s21(a1) and s22(a2), i.e.
s21(a1) is equal in magnitude and opposite in phase to s22(a2).
--
73, Cecil http://www.qsl.net/w5dxp



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"Tam/WB2TT" wrote in message
...
Clearly there is reflected power. Just don't take the SWR meter too
literally. It does not actually measure power, but the scale has been
fudged
so it indicates the correct power if the load is equal to some design
value.
I can see a long thread here.

see my last replies to this thread... i'm done... cecil and reg are back and
will undoubtedly re-hash optical methods and conjugate matches till the
server dies... as for me, this thread is now over.

Reg Edwards wrote:
Reflected power is a mere fiction. Power which is not radiated from an
antenna never actually arrives there. In fact it never leaves the
transmitter.

Therefore, radar cannot work since it relies upon reflected
joules/second. Mirrors also cannot work since there is an ExB
amount of power in those reflections.

Reg, for a 291.5 ohm antenna to accept 100 watts requires the forward
power to the antenna to be 200 watts. 100 watts is accepted by the
antenna and 100 watts is rejected by the antenna. 200 watts to the
antenna is routinely accomplished by a 100 watt ham transmitter and
a Z0-match provided by a tuner.

This is exactly like a partially silvered mirror that reflects half
the irradiance and allows half the irradiance through.

Assume a one second long lossless unterminated transmission line.
Pour 1000 watts into it for one second. During the next second, we
disconnect the line from the source and you grab the two wires, one
in each hand. Then tell us whether reflected power exists or not.
--
73, Cecil http://www.qsl.net/w5dxp



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Dave wrote:
That is because "forward and reflected power waves" is a derivative
concept. It depends on concepts of voltage and current waves for its
existence; but it doesn't add anything useful that we didn't already
know.

i know that, i was just trying to get in all the bogus arguments before
anyone else did.

Oh... in that case: "Well done - a noble effort, sir!"

(You forgot to mention the slotted line, which mercifully saved you from
a perfect score :-)

'power waves' are a concept invented to simplify some
concepts, but instead they just hide the important details. we have been
over and over that on here in the past and always end up in the same
place,
i was just hoping to skip right to the end.


What, in this newsgroup?


maybe if i had learned to use smileys it would have helped.... what is
the sarcastic one?? something like ;-^ or something like that??

Sorry I missed the deliberate irony on your part, Dave, but the same
things have often been said here in total seriousness. And here we go
again...


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian White, G3SEK wrote:
After the first microsecond the transmitter is operating into a
steady-state load impedance. The only *useful* question then is: "Given
that particular value of load impedance, how much power can my
transmitter generate?" But that isn't an antenna/transmission-line
problem at all - the answer lies in the transmitter, and *only* the
transmitter.

Using 200 ft. of unterminated RG-58 on 440 MHz, the transmitter
sees close to 50 ohms and can deliver its full rated power into
the coax with no antenna. Therefore, I seriously doubt that your
question above is the "only *useful* question".
--
73, Cecil http://www.qsl.net/w5dxp



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"Cecil Moore" wrote in message
...
Henry Kolesnik wrote:

I know that any power not dissipated by an antenna is reflected back to
the
transmitter. Then the transmitter "reflects" this reflection back to
antenna, ad nauseum until its all gone. I also know that a short or an
open
is required to reflect power and I'm searching for which it is, an open
or a
short. I'm inclined to think it's a virtual open but I'm at a loss to
understand that and I wonder if someone has a good explanation or
analogy
and some math wouldn't hurt.

Hank, EM reflections are covered on this web page.

http://www.mellesgriot.com/products/optics/oc_2_1.htm

In particular: "Clearly, if the wavelength of the incident light and the
thickness of the film are such that a phase difference exists between
reflections of p, then reflected wavefronts interfere destructively, and
overall reflected intensity is a minimum. If the two reflections are of
equal amplitude, then this amplitude (and hence intensity) minimum will
be zero."

"In the absence of absorption or scatter, the principle of conservation of
energy indicates all "lost" reflected intensity will appear as enhanced
intensity in the transmitted beam. The sum of the reflected and
transmitted
beam intensities is always equal to the incident intensity. This important
fact has been confirmed experimentally."

In order for (rearward-traveling) "reflected intensity" to "appear as
(forward-traveling) enhanced intensity in the transmitted beam", the
momentum of that (rearward-traveling) intensity must change directions.
Thus, it appears that total destructive interference between two rearward-
traveling reflected waves in a transmission line will reverse the
direction
of momentum of the energy in those canceled reflected waves.

We need to change a few of your statements:

Any power not dissipated or radiated by an antenna is reflected back.
"Dissipation" means EM energy transformed into heat, according to
the IEEE Dictionary.

The transmitter/tuner end will not re-reflect 100% of the reflected energy
unless there exists a short, open, pure reactance, or "total destructive
interference" as explained in _Optics_, by Hecht.

Besides a short or an open, a purely reactive impedance will cause
100% energy reflection. Apparently, so will "total destructive
interference". Quoting from _Microwave_Transmission_, by J. C. Slater:

"The method of eliminating reflections is based on the interference
between waves. ... The fundamental principle behind the elimination
of reflections is then to have each reflected wave canceled by another
wave of equal amplitude and opposite phase."

That's pretty clear. We get one set of rearward-traveling reflections
at the match point. We get another set of rearward-traveling reflections
at the antenna. If these two sets of reflections are equal in magnitude
and opposite in phase at the match point, they cancel each other and the
rearward-traveling momentum energy in those two waves is conserved by
changing direction to become part of a forward-traveling wave.
--
73, Cecil http://www.qsl.net/w5dxp
Cecil,

I am not quite sure what you are saying. But, I ran a SPICE simulation of
the following:
1V 1MHz source with resistor R0 feeding a 50 Ohm 250 ns transmission line
shorted at the far end. Independent of R0, in steady state the voltage at
the input end of the transmission line will be 1V. The effect of R0 is to
limit how long it takes to reach steady state. For R0 = 50 Ohms, it is one
cycle; for R0 = 500 Ohms, it is about 8 cycles, as eyeballed off the
waveform display.