tuner - feedline - antenna question ?
 

Owen Duffy wrote:
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.

But it does combine according to the following formula
which is the irradiance equation from the field of
optics.

Ptot = P1 + P2 + 2*SQRT(P1*P2)cos(A)

where 'A' is the angle between V1 and V2 and V1 is
the voltage associated with P1 and V2 is the voltage
associated with P2.

The first time I saw this equation was in Dr. Best's
Nov/Dec 2001 QEX article on Transmissions Lines. It
really does work for "adding" the two powers in two
coherent waves.
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

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

tuner - feedline - antenna question ?
 

Cecil Moore wrote in
:

Owen Duffy wrote:
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.

But it does combine according to the following formula
which is the irradiance equation from the field of
optics.

Ptot = P1 + P2 + 2*SQRT(P1*P2)cos(A)

where 'A' is the angle between V1 and V2 and V1 is
the voltage associated with P1 and V2 is the voltage
associated with P2.

Cecil,

A is not a property of P1 or P2, and cannot be derived from them. I
maintain that you cannot vectorially combine P1 and P2.

Owen

tuner - feedline - antenna question ?
 

"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

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
A is not a property of P1 or P2, and cannot be derived from them. I
maintain that you cannot vectorially combine P1 and P2.

P1 is a property of V1^2/Z0, A is a property of V1.
P2 is a property of V2^2/Z0, A is a property of V2.
There is an unbroken chain of cause and effect.
It is true that one cannot directly vectorially
combine P1 and P2 because P1 and P2 are not vectors.

However, the ability to combine the P1 and P2 of
coherent EM waves dates back to before you were born.
Optical engineers didn't have the luxury of being
able to measure the phase angles. All they could
measure was the total amplitude. Please don't try
to tell us that their total amplitude measurements
were wrong throughout the 20th century and are
still wrong in the 21st century.

The rules for combining P1 and P2 when they are
coherent are known as the irradiance equations in
optics. Dr. Best applied them to RF quantities.
Please reference "Optics", by Hecht, 4th edition,
page 388 and Dr. Best's, "Wave Mechanics of Transmission
Lines, Part 3: ..." in the Nov/Dec 2001 issue of "QEX".
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

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

tuner - feedline - antenna question ?
 

Cecil Moore wrote in news:wnIEh.2899$8x.278
@newssvr14.news.prodigy.net:

Owen Duffy wrote:
A is not a property of P1 or P2, and cannot be derived from them. I
maintain that you cannot vectorially combine P1 and P2.

....
It is true that one cannot directly vectorially
combine P1 and P2 because P1 and P2 are not vectors.

Thanks

....

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
Cecil Moore wrote in news:wnIEh.2899$8x.278
It is true that one cannot directly vectorially
combine P1 and P2 because P1 and P2 are not vectors.

Thanks

That doesn't mean that there are not valid rules for
combining P1 and P2. Optical engineers have been doing
it for decades. RF engineers seem to lag behind.

You seemed to be questioning the validity of the power
combination equation. Have you changed your mind?
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

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

tuner - feedline - antenna question ?
 

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
100w forward and 50w reflected, the power radiated by
the antenna is 50w, neglecting losses.

Pload = Pfor - Pref

The situation at the output of a lossless tuner is:

Pfor = Psource + Pref

Please honor the conservation of energy principle in your
postings.
--
73, Cecil http://www.w5dxp.com