"Jeff" wrote in
.com:

The so called "forward power" and "reflected power" are notional
values, but not actual power "components". The only power is the
average rate at which energy passes a point, and it is in one
direction or the other.

I am sorry, but I disagree, forward power is real and can be measured,
or if you wish separated out with a circulator or isolator. 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.

Jeff,

You dropped a number of terms he
- 'transmitted' power;
- power delivered into a mismatched load;
- forward power;
- power delivered by the source;

The power delivered to a load (of any kind) from a lossless transmission
line section, is the same as the power delivered by the source. In the
case of the lossy line, then the line characteristics and load impedance
also need to be taken into account to calculate the power lost in the
line section, and it is not as simple as using up a dB/100' rating in a
table (unless the line is matched).

You assertion that you have travelling forward and reflected power waves
on the transmission line runs into a problem when you try to analyse the
combination of both at a point (eg the input to the line) as power
doesn't combine vectorially.

When you devise configurations with circulators, isolaters, directional
couplers, hybrids etc to "trap and reroute" reflected power, you have
probably changed the nature of the load on a line section and that
accounts for why the reflected power seems to have been isolated from
forward power.

Owen

"
The power delivered to a load (of any kind) from a lossless transmission
line section, is the same as the power delivered by the source.

So it is your contention that power is not reflected at a mismatch. The wave
certainly is so the power contained in the reflected portion must be as
well.

You assertion that you have travelling forward and reflected power waves
on the transmission line runs into a problem when you try to analyse the
combination of both at a point (eg the input to the line) as power
doesn't combine vectorially.

I was not trying to analyse the combination of any wave on the line ("power"
waves, whatever they may be, or anything else), I was merely noting that you
can quantify and measure the power contained the both the forward and
reflected waves and they are real quantities.

Jeff

Jeff wrote:
I was not trying to analyse the combination of any wave on the line ("power"
waves, whatever they may be, or anything else), I was merely noting that you
can quantify and measure the power contained the both the forward and
reflected waves and they are real quantities.

The joules/sec are real quantities but whether joules/sec
is power depends upon the definition of "power". Some say
the joules/sec in a reflected wave is not power and they
produce a definition of "power" from a physics book to
prove it, i.e. no work done. To satisfy the purists you
may need to change your statement to: "I was merely noting
that you can quantify and measure the joules/sec contained
in both the forward and reflected waves and they are real
quantities."
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
The joules/sec are real quantities but whether joules/sec
is power depends upon the definition of "power".

In our case here on the internet, it depends on whether or not you
choose to equate 'units of power' with the definition of power.

73 ac6xg

Jim Kelley wrote:

Cecil Moore wrote:
The joules/sec are real quantities but whether joules/sec
is power depends upon the definition of "power".

In our case here on the internet, it depends on whether or not you
choose to equate 'units of power' with the definition of power.

Most engineers equate the units of power to power, i.e.
joules/sec = watts and so does the IEEE dictionary. But I
am content to assert that the joules in the joules per
second of a reflected wave is real energy. Do you disagree?
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Jim Kelley wrote:
Most engineers equate the units of power to power, i.e.
joules/sec = watts and so does the IEEE dictionary.

I can't speak for most engineers, but I think the first time I saw it
was in high school physics, and of course later in engineering school.
That was about 35 years ago. I think of it a fundamental concept -
one that I happen to understand very well. Not unlike the
relationship between Joules and electron-volts.

But I
am content to assert that the joules in the joules per
second of a reflected wave is real energy. Do you disagree?

I don't agree that the terms power and energy become interchangeable
by virtue of the fact that their units can both be expressed with the
word Joule in them. One can find himself making unrealistic
predictions if he is not precise in his application of the ideas which
underlie these terms.

73, ac6xg

Jim Kelley wrote:
I don't agree that the terms power and energy become interchangeable by
virtue of the fact that their units can both be expressed with the word
Joule in them.

That's why I am willing to switch from the words "Reflected
Power" to "Reflected Energy" and measure that energy flow
past a point on a transmission line in joules/second.
Thus "power" and "watts" are dropped from the discussion
along with any semantic disagreements over the definitions
of those words.

So the question is: With a forward RF energy flow of 200
joules/sec and a reverse RF energy flow of 100 joules/sec,
would you agree that there is 300 joules of energy existing
in a lossless one-second long transmission line? i.e. exactly
the amount of energy required to support the forward RF
energy wave and the reflected RF energy wave.

Or if the above transmission line is one microsecond long,
that 300 microjoules of energy exists in the line, i.e.
exactly the amount of energy required to support the
forward RF energy wave and the reflected RF energy wave.
--
73, Cecil, http://www.qsl.net/w5dxp

"Jeff" wrote in
.com:


"
The power delivered to a load (of any kind) from a lossless
transmission line section, is the same as the power delivered by the
source.

So it is your contention that power is not reflected at a mismatch.
The wave certainly is so the power contained in the reflected portion
must be as well.

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.

The power at a point in a transmission line is P=real(V*conjugate(I)).
This expands to four terms, and people arbitrarily allocate the terms
forward power and reflected power to just two of the four terms because
they happen to be VfIf and VrIr.


You assertion that you have travelling forward and reflected power
waves on the transmission line runs into a problem when you try to
analyse the combination of both at a point (eg the input to the line)
as power doesn't combine vectorially.

I was not trying to analyse the combination of any wave on the line
("power" waves, whatever they may be, or anything else), I was merely
noting that you can quantify and measure the power contained the both
the forward and reflected waves and they are real quantities.

The Bird 43 does not measure power directly, it responds to Vf or Vr
components at a point as explained in the article I quoted. The article
deals with the conditions under which readings can be converted to power,
and whether forward power or reverse power are of themselves meaninful.

If you have read it and disagree, then thats ok. If you can identify
flaws in the article, constructive feedback is welcome.

Owen

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.

That only applies to mismatched systems. 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. It's all explained in my energy
analysis article at: http://www.w5dxp.com/energy.htm
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote in
:

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.

That only applies to mismatched systems. 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. It's all explained in my energy
analysis article at: http://www.w5dxp.com/energy.htm

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.

The reality is that the Bird responds to Vf and Vr (depending on the
orientation of the slug), and in the special case where the sampler is
calibrated to respond to |Vf| and |Vr| for a purely real ratio of V/I
(Zn=Rn+j0 which is 50+j0 in the case of the '43), on the line at the
point of the sampler, then the average power passing that point is a
single number, it is |Vf|^2/Rn-|Vr|^2/Rn. The foward and reflected power
readings are not meaningful in themselves, but you can deconstruct rho,
and (knowing Zn) |Vf| and |Vr| from them.

Owen