tuner - feedline - antenna question ?
 

Cecil Moore wrote in news:QeJEh.2909$8x.1740
@newssvr14.news.prodigy.net:

Owen Duffy wrote:
Cecil, it seems that between the two of you, you are constructing a
picture that (in a lossless line for simplicity) if the Bird 43 reads
100W forward and 50 watts reflected, the power radiated (ignoring
antenna ohmic losses) is 100W, but 50W is reflected toward the
transmitter... but that's allright because the 50W will be reflected
by
a Zo matched PA, and energy is conserved on the line.

Please don't insult our intelligence. If the Bird reads

Of course it is nonsense, but it is a logical development based on Jeff's
words "What you are describing could be called 'transmitted' power or
power delivered into a mismatched load, but that it different from
forward power, or the power delivered by the source" and your words "For
systems
Z0-matched by an antenna tuner, the situation becomes trivial to
understand. The reflected energy is re-reflected by the Z0-match provided
by the properly tuned antenna tuner".

The steady state solution of the ratio of V/I at the input to a real
transmission line section (ie lossy) that has a load of some arbitrary
impedance is solved using equations that do not include forward and
reflected power terms. The power at any point is the real part of
V*conjugate(I) at that point, no matter whether it is at the source,
load, line input, output or anywhere along the line.

Owen

tuner - feedline - antenna question ?
 

On Mon, 26 Feb 2007 20:38:00 GMT, Owen Duffy wrote:

The danger in the "power is refelected at a mismatch" explanation, is
that it follows that power reflected at a mismatched antenna flows back
toward the transmitter and is at least partially absorbed in the PA as
heat. Though that is a popular belief, it is not supported by fact.

Hi Owen,

This denies experience.

73's
Richard Clark, KB7QHC

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
Of course it is nonsense, but it is a logical development based on Jeff's
words ...

Please don't blame me for someone else's words.

The irradiance (power) equations from optical engineering
for the combining of electromagnetic power from two EM waves
are accepted as a fact of physics. Do you really think that
the amateur radio community should reject that fact
of physics?
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Richard Clark wrote in
:

On Mon, 26 Feb 2007 20:38:00 GMT, Owen Duffy wrote:

The danger in the "power is refelected at a mismatch" explanation, is
that it follows that power reflected at a mismatched antenna flows back
toward the transmitter and is at least partially absorbed in the PA as
heat. Though that is a popular belief, it is not supported by fact.

Hi Owen,

This denies experience.

Do you mean the experience that the PA may (but not necessarily) run
hotter on other than its rated load impedance?

Could that be exlained without introducing transmission lines and the
reflected power issue by examining how the PA works on a load different
to its rated load?

I suggest that if a PA / line / load situation transforms the actual load
to some arbitrary impedance Z at the PA end of the line, the PA will
peform exactly as if the PA were directly loaded by a lumped constant
load of Z. The explanation of any heating effects or changed operating
voltages is in the effect of the load impedance Z (however it is
obtained) on the PA.

Does that make sense?

Owen

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
I suggest that if a PA / line / load situation transforms the actual load
to some arbitrary impedance Z at the PA end of the line, the PA will
peform exactly as if the PA were directly loaded by a lumped constant
load of Z.

Yes, that is true for the performance of the PA.
Certainly not true for the performance of the
transmission line or antenna.

My favorite quotation by an antenna guru on this
newsgroup is that "a 50 ohm antenna can be replaced
by a 50 ohm resistor without changing anything".
If that were true, we don't need antennas. :-)

I'm going to be away from my computer for 48 hours.
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Cecil Moore wrote in
:

Owen Duffy wrote:
Of course it is nonsense, but it is a logical development based on
Jeff's words ...

Please don't blame me for someone else's words.

A selective partial quotation to misrepesent what was actually written
Cecil!

Owen

tuner - feedline - antenna question ?
 

Cecil Moore wrote in
t:

Owen Duffy wrote:
I suggest that if a PA / line / load situation transforms the actual
load to some arbitrary impedance Z at the PA end of the line, the PA
will peform exactly as if the PA were directly loaded by a lumped
constant load of Z.

Yes, that is true for the performance of the PA.
Certainly not true for the performance of the
transmission line or antenna.


Please explain?

Owen

tuner - feedline - antenna question ?
 

On Mon, 26 Feb 2007 23:24:13 GMT, Owen Duffy wrote:

Could that be exlained without introducing transmission lines and the
reflected power issue by examining how the PA works on a load different
to its rated load?

Hi Owen,

Let's treat this like the Chinese Box problem.

If you didn't know what the load was, could you explain it any
differently? No. Apriori knowledge is not a proof.

73's
Richard Clark, KB7QHC

tuner - feedline - antenna question ?
 

Richard Clark wrote in
:

On Mon, 26 Feb 2007 23:24:13 GMT, Owen Duffy wrote:

Could that be exlained without introducing transmission lines and the
reflected power issue by examining how the PA works on a load different
to its rated load?

Hi Owen,

Let's treat this like the Chinese Box problem.

If you didn't know what the load was, could you explain it any
differently? No. Apriori knowledge is not a proof.

Richard, I content that:
- the power output of the PA; and
- the efficiency of the PA may be (and usually are) sensitive to the load
impedance.

A steady state analysis is usually adequate for most ham radio
applications, though there may be cases where establishment of steady
state brings its own issues. This discussion is about the steady state.

Though it is often asserted that the PA will get hotter as a result of
"reflected power" being dissipated in the dynamic output impedance of the
PA, and that this may / will damage the PA, the power explanation doesn't
work numerically in the general case.

The constrained ratio of V/I is an aspect of the field setup in a
transmission line, and the launching of a reflected wave to reconcile the
load V/I with the constrained (Vf+Vr)/If-Ir) at the load end of the line
is a solution for what happens on the transmission line. At the source
end of the line, (Vf+Vr)/If-Ir) at that point (a function of (Vf+Vr)/If-
Ir at the load end, and the complex propagation coefficient and Zo of the
line) give us the equivalent (complex) impedance seen by the PA, and we
can predict / explain the behaviour of the PA (maximum power out,
efficiency) on that equivalent load. This method of analysis does work
numerically.

Owen

tuner - feedline - antenna question ?
 

On Tue, 27 Feb 2007 01:07:12 GMT, Owen Duffy wrote:

Richard Clark wrote in
Let's treat this like the Chinese Box problem.

If you didn't know what the load was, could you explain it any
differently? No. Apriori knowledge is not a proof.

Richard, I content that:

Contend or offer in contention.

- the power output of the PA; and
- the efficiency of the PA may be (and usually are) sensitive to the load
impedance.

This is not contending nor contention and is content only for a non
sequitur. The line following a tuner exhibits considerable loss (poor
efficiency) that can only occur on the basis of power and mismatch.
You yourself offered in other correspondence that it exceeds cable
attenuation specifications found only in a matching condition. To
suggest that a PA's sensitivity is somehow exhalted in the face of
identical, ordinary behavior of a passive component is hardly
seperable. Consider the simple substitution to your quote:
- the power output at the terminus of the line; and
- the efficiency at the terminus of the line may be (and usually are) sensitive to the load
impedance.

continuing on...
A steady state analysis is usually adequate for most ham radio
applications, though there may be cases where establishment of steady
state brings its own issues. This discussion is about the steady state.

I expressed nothing of transitory behavior.

Though it is often asserted that the PA will get hotter as a result of
"reflected power" being dissipated in the dynamic output impedance of the
PA, and that this may / will damage the PA, the power explanation doesn't
work numerically in the general case.

Heat is the outward proof of power and is always demonstrable in both
specific and general cases. Occurrences of other, significant
radiation from the source (as long as that source physically occupies
a substantially minor region of wavelength) is exceedingly difficult
to achieve.

You don't offer a numerical proof of a general case, and given that
the general case must allow for the specific cases already allowed in
your discussion above - that may be an untenable assertion for you.
Those specific cases are demonstrably caloric and must follow the same
math you suggest.

I suspect you are trying to argue differences by degree (no pun
intended as to heat); but I seriously doubt you can produce the math
to do that. The arguments that flow from that involve what is called
source resistance, and those arguments are legion in this forum (where
naysayers embrace a refusal to accept or name ANY value - a curious
paradox and an engineering nihilism I enjoy to watch).

73's
Richard Clark, KB7QHC