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.
tnx
Hank WD5JFR

On Sun, 23 May 2004 02:07:13 GMT, "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.
tnx
Hank WD5JFR


Hi Hank,

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

"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

On Sun, 23 May 2004 05:57:28 +0000 (UTC), "Reg Edwards"
wrote:
Dear Richard, you are confusing the matter even further, if that were
possible.

Old Son,

Have I stolen your thunder?

Like the pendulum with a dull and meagre swing, your predictable
observations on this subject return to an unremarkable SWR, a topic
never raised without the old wife discovering it under her bed....

Does the following strike a bell?
A QUOTATION:

"When you can measure what you are speaking about and express it in numbers
you know something about it. But when you cannot measure it, when you cannot
express it in numbers, your knowledge is of a meagre and unsatisfactory
kind. It may be the beginning of knowledge but you have scarcely in your
thoughts advanced to the state of science."

You have never offered a scintilla of quantized discussion to the
matter. If you can summon up a respectable treatise that would make
lord kelvinator proud, then maybe we would have something of actual
substance to discuss. We can start with any of a number of my own -
if, of course, you want to advance to the state of science. Forgive
this last bit of presumption if you are simply trolling again. That,
too, has its own entertainment merit and I am glad to correspond in
kind. :-)

73's
Richard Clark, KB7QHC

Richard Clark wrote:
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

I agree with that last statement - and we can take it a step further.

Each description can do things that the other one can't; no argument
about that. But in cases where both descriptions should be valid, then
they *must* agree.

This is a basic cross-check that should always be applied... but
regrettably isn't.


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

Reg Edwards wrote:

Reflected power is a mere fiction.

Fiction may not be the right word, but reflected power is certainly a
*useless* thing to calculate.

Power which is not radiated from an antenna never actually arrives
there. In fact it never leaves the transmitter.

Agreed.

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.

As far as the transmitter is concerned, it doesn't matter how that
particular value of load impedance was created. There are several ways
to create a specified value of (R +/-jX), and whichever way it's done,
the transmitter will deliver exactly the power.


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

"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?!?!?!

Reg:

Consider a signal generator connected through a circulator to the input of a
slotted line. The circulator provides a constant impedance to the signal
generator no matter what impedance is connected to the output port of the
circulator. Now, if your quote below is true, please explain the standing
wave pattern measured via the slotted line probe whenever the slotted line
itself is terminated in other than its characteristic impedance.

Also ponder this scenario. A transmitter is adjusted to deliver the maximum
output power of which it is capable (limited by its power supply) into a 50
ohm transmission line several wavelengths long, terminated in a 50 ohm
antenna. The transmission line is just barely rated to handle the power
delivered by the transmitter under these conditions.

Now something fails within the antenna, and its input Z rises to 2000 ohms.
If the transmitter has no protective circuits to shut it down, it will
continue to generate power, and the transmission line will arc/burn. Of
course, so might the tx output circuits, but let's say they are "very
robust," and the tx continues to operate.

What is the source of the additional power causing the line failure? The tx
already was delivering all the power it could before the failure, so it
isn't coming from there.

RF

Visit http://rfry.org for FM broadcast RF system papers.

____________________

"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.

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.


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

"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.