pez wrote:

| wrote:
| As has been aptly demonstrated in another thread, it does
| not work for lines with complex Z0.

Could you tell me please in which thread?

Seems he is talking about that third power term in Chipman's
equation, the one caused by the resonance effect between the
feedline's Z0 reactance and the load's reactance.
--
73, Cecil http://www.qsl.net/w5dxp



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Reg Edwards wrote:

A so-called directional wattmeter or SWR meter merely responds to the
magnitude of a reflection coefficient usually, but not necessarily, relative
to 50 + j0 ohms. Half of the information, the angle, is discarded without
being aware of its existence.


Not exactly correct.

The phase information is not displayed explicitly
on a scaler instrument like the Bird meter, but
phase is definitely involved in the principles of
operation of the directional coupler.

Very seldom, if ever, do we care a feather or a
fig what the exact phase value is, but the
directional coupler is not balanced unless the
phase is zero.

All automatic antenna tuners utilize this fact.

Bill W0IYH

Reg Edwards wrote:
A so-called directional wattmeter or SWR meter merely responds to the
magnitude of a reflection coefficient
[...]
Just a little box containing assumptions, preconceived notions,
suppositions, ambiguitiues and a lot of imagination.

The box responds only to the voltage and the current on the line. Those
are the only *physical* things it responds to. All the rest is about
ideas.

The basic design of the instrument is inspired by the idea of forward
and reflected V and I waves, and the idea of the reflection
coefficient. The circuit is designed so that the meter displays the
magnitude of the reflection coefficient on a linear scale.

The further *calibration* of the meter scale in terms of SWR and
forward/reflected power is then inspired(?) by yet more ideas - which
Reg so aptly describes as a mix of "assumptions, preconceived notions,
suppositions, ambiguities and a lot of imagination."


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

"William E. Sabin" wrote Reg Edwards wrote:

A so-called directional wattmeter or SWR meter merely responds to the
magnitude of a reflection coefficient usually, but not necessarily,
relative
to 50 + j0 ohms. Half of the information, the angle, is discarded
without
being aware of its existence.


Not exactly correct.

The phase information is not displayed explicitly
on a scaler instrument like the Bird meter, but
phase is definitely involved in the principles of
operation of the directional coupler.

Very seldom, if ever, do we care a feather or a
fig what the exact phase value is, but the
directional coupler is not balanced unless the
phase is zero.

All automatic antenna tuners utilize this fact.

Bill W0IYH

===================================

Bill, why the unnecessarily complications?

It is possible to imagine the so-called SWR meter is telling you the
imaginary value of the SWR on a non-existent transmission line. But it's
hardly of educational value when novices, even experienced engineers, are
trying to understand what the reading really means. It's as confusing and
as untruthful as Blair.

Why don't we accept the simple fact that the meter tells us only whether the
transmitter is loaded with a resistance of a particular value or not. Which
is no more nor less than what the instrument on the front panel of your
transceiver is provided for.

Then we can forget all about SWR, fwd and reflected power, until needed on
real ines. Change the name of the meter to TLI.
---
Reg, G4FGQ

"Reg Edwards" wrote in message
...
It is possible to imagine the so-called SWR meter is telling you the
imaginary value of the SWR on a non-existent transmission line. But it's
hardly of educational value when novices, even experienced engineers, are
trying to understand what the reading really means. It's as confusing and
as untruthful as Blair.

Why don't we accept the simple fact that the meter tells us only whether
the
transmitter is loaded with a resistance of a particular value or not.
Which
is no more nor less than what the instrument on the front panel of your
transceiver is provided for.

Then we can forget all about SWR, fwd and reflected power, until needed on
real ines. Change the name of the meter to TLI.
---
Reg, G4FGQ

Amen to that. I turned down the power on my transmitter, and measured P
forward and P rev while feeding about 100 feet of unterminated 9913. I then
REMOVED the coax; i.e. there was nothing connected to the output side of the
meter. Still measured the same Pf and Pr. (Daiwa meter)

Tam/WB2TT

Yet you've found it impossible to explain, either numerically or in
equation form, which "power wave" these "interference terms" belongs to,
or how this "interference" comes about in your model of superposing,
traveling power waves.

The explanation is indeed simple -- as long as you can continue to avoid
explaining it.

Roy Lewallen, W7EL

Cecil Moore wrote:
wrote:

Regardless of whether there is an alternative explanation,
you should reject the reflected power model because....
In general, IT DOES NOT WORK.


In general, our feedline losses are low enough that it does
work. In general on HF, we are dealing with near-resistive
Z0's and Z0-matched systems.

As has been aptly demonstrated in another thread, it does
not work for lines with complex Z0.


Actually it does. All one has to do is take the power interference
terms into account.
. . .

Tarmo Tammaru wrote:
Amen to that. I turned down the power on my transmitter, and measured P
forward and P rev while feeding about 100 feet of unterminated 9913. I then
REMOVED the coax; i.e. there was nothing connected to the output side of the
meter. Still measured the same Pf and Pr. (Daiwa meter)

Of course, you were simply getting a same-cycle reflection. The reflected
wave model is consistent. If the open-circuit is at the transmitter terminal,
all the power is reflected immediately.
--
73, Cecil http://www.qsl.net/w5dxp



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Roy Lewallen wrote:

Yet you've found it impossible to explain, either numerically or in
equation form, which "power wave" these "interference terms" belongs to,
or how this "interference" comes about in your model of superposing,
traveling power waves.

For the record, I don't superpose things that lack phase. But if you
turn on two 100 watt light bulbs, don't you double the light output?
This stuff is all explained in _Optics_, by Hecht.

The explanation is indeed simple -- as long as you can continue to avoid
explaining it.

It is all explained in Chipman's "Transmission Lines". Please take the time
to read it and understand it. Just as the voltage and current increase depending
upon the 'Q' of a resonant circuit, the same thing happens with reactive
transmission lines. I am not going to waste my time explaining such an easy
concept. You probably can simulate the situation by drawing the dividing
plane between the cap and the resistor in the following circuit.
|
RF source----//----capacitor---|---resistor------inductor-------+
| | |
+-------//----------------|--------------------------------+
|
plane

The voltage across the capacitor or inductor, depending upon the 'Q' of
the circuit, can be greater than the RF source voltage. You can add 1WL
of transmission line at the '//' point without changing anything. In this
case, the energy exchanged between the capacitor and inductor travels through
the resistor and contributes to power dissipation in the radiation resistance
(if that is what that resistance is). Like I said before, it's a no-brainer.
Once I read Chipman's explanation, it was as clear as day.
--
73, Cecil http://www.qsl.net/w5dxp



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"Scientists" are also human too, and tend to want to disregard or not
even
try to measure data that may contradict their models. This makes them
feel
comfortable that they are "right".

I completely agree.

So can you overcome your "tend[ancy] to want to disregard or
not even try to measure data that may contradict their models."?

...Keith



I'll think about it after you tell us what you get when you measure the
end of the inductor.


Slick

Keith wrote:
"Scientists are usually interested in producing models which will allow
them to predict the behaviour of the real world.

True. Models must be adjusted to reality, not the other way around. But,
once the model is verified it becomes useful.

You don`t have to measure the area of a rectangle with a planimeter once
you know that area is the product of the length and width of the
rectangle.

Best regards, Richard Harrison, KB5WZI