Ian White, G3SEK wrote:
Let me turn the question around, Cecil: can you explain in detail how
any directional coupler gets its directional properties, using *only*
your concepts of power waves?

Sure, P=V*I and V/I=Z0 for both forward waves and reflected waves. The
angle between the voltage and current is always zero degrees or 180 degrees
for any traveling wave. The ratio of voltage to current is always Z0 for
any traveling wave.
--
73, Cecil http://www.qsl.net/w5dxp



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Ian White wrote:

1. The Bird "wattmeter" does not in fact sense power. At the detailed
level, it senses voltages and currents in its internal transmission
line, and then sums and subtracts them to give RF voltages that the
diode detects. I repeat, there is no sensing of power as such, and no
detection of power as such.

My point is that all directional couplers DO work by sensing forward and
reflected waves of voltage and current BUT NOT WAVES OF POWER.

The inner workings of every directional coupler can be explained
*completely* in terms of waves of voltage and current. That includes
resistive bridges, Bruene bridges and parallel-line couplers (of which
the coupler in the Bird is a sub-class). They all work because E and I
waves are phasors, and the construction of the coupler makes them add in
one direction and subtract in the other. There's an example of a
detailed analysis, about the Bruene bridge but applicable in principle
to other types as well, at:
http://www.ifwtech.co.uk/g3sek/in-pr...-of.htm#bruene

Waveguide directional couplers work in very similar ways, but have to be
analysed in terms of forward and reflected E and H fields. That kind of
explanation also works for a waveguide circulator, the difference being
that some of the fields are inside a magnetic medium. A coaxial
circulator is more complex because it involves voltages and currents on
the line part and also E and H fields in the magnetic medium, but the
principle is the same.

This is all standard stuff that has been known for decades. Forward and
reflected waves of V and I (or E and H) give a complete explanation of
the directional properties of all such devices.

Let me turn the question around, Cecil: can you explain in detail how
any directional coupler gets its directional properties, using *only*
your concepts of power waves?

Ian is precisely correct when he says power meters such as the Bird, or
Bruene's Directional Wattmeter DO NOT sense power, they sense only voltage
and current. The meter indicating the power is simply calibrated to indicate
the E^2/Zo power flowing in the characteristic impedance, Zo, of the line.
E^2/Zo = power, and that expression was used to calibrate the meter scale in
terms of the voltage and current propagating in either direction. See Page
3-16 in Reflections 1 and Page 3-15 in Reflections 2, taken from Warren
Bruene's QST article, April 1958, Ref 38 in Reflection.

Walt, W2DU

Ian, G3SEK wrote:
"What are those V`s and I`s doing in your reply?"

Cecil is right on target. Power is VxI. The Bird takes carefully
balanced samples of V&I. In the incident wave the samples are in-phase.
In the reflected wave the samples are 180-degrees out-of-phase. By
exactly balancing the two samples, the reflected wave cancels. Only the
incident wave is sensed. To sense the reflected wave only, the polarity
of one of the two samples is switched.

I am now more dangerous. Until today, I had never seen one of Kraus`
books. I now own the third edition of "Antennas (for all applications)".
Kraus says there are "fundamental" units and "secondary" units. The
"Ampere" is a fundamental unit. All secondary units can be derived from
the fundamental units.

In the Bird, the given is a 50-ohm line. Power is 50(I)(I), since I=E/R
= E/50, and E = 50(I) = V.

Power = EI

The Bird is accurate enough using a sample of E and a sample of I and
scaling to determine power. Multiplication is just scaling or the number
of times you repeat a number in an addition column. In the Bird, scaling
is an electrical adjustment.

Best regards, Richard Harrison, KB5WZI

Ian, G3SEK wrote:
"1. The Bird "wattmeter" does not in fact sense power. At the detailed
level, it senses voltages and currents in its internal transmission
line---."

Since the ratio of voltage to current in either direction is always Zo,
all you need are voltage and current samples of one direction at a time.

The Bird is not alone in determining power from such voltage and current
samples. The dynamometer does too.

A d-c meter is useless on a-c because the needle tries to move first one
way then the other as the a-c current through it alternates. Inertia
keeps the indication on a-c close to zero.

The dynamometer eliminates the flicker and gives an appropriate
deflection on a-c. It does this by replacing the d-c meter`s permanent
magnet with an a-c coil. This is arranged to torque the needle upscale
no matter whch direction the current takes through the coils. The
moveable coil is always deflected the same way by interaction with the
fixed coil.

It is simple to calibrate a dynamometer for power and feed current
through one coil and place volts across the other. It senses volts and
amps but it reads out power, as does the Bird wattmeter.

Best regards, Richard Harrison, KB5WZI

Ian White, G3SEK wrote:
I believe that I'm asking a question that your theories of power waves
are fundamentally incapable of answering... but that's a problem for you
and your theories, not for me.

Quoting from the article on my web page:

"Note that this is NOT a new and different method of system analysis.
The only purpose of this paper is to illustrate how to track the
energy at an impedance discontinuity point in a transmission line."

It does so by recognizing destructive interference between two phasor
voltages when the relative phase angle is greater than 90 degrees and
the constructive interference between two phasor voltages when the
relative phase angle is less than 90 degrees.

There are lots of questions that cannot be answered by any discussion
of power only. My *ONLY* purpose is to track the energy components
which is in addition to standard system analysis. There is absolutely
no conflict between the two subjects. The energy components are always
associated with voltages and currents.
--
73, Cecil http://www.qsl.net/w5dxp



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Richard Harrison wrote:
Ian, G3SEK wrote:
"What are those V`s and I`s doing in your reply?"

Cecil is right on target. Power is VxI. The Bird takes carefully
balanced samples of V&I. In the incident wave the samples are in-phase.
In the reflected wave the samples are 180-degrees out-of-phase. By
exactly balancing the two samples, the reflected wave cancels. Only the
incident wave is sensed. To sense the reflected wave only, the polarity
of one of the two samples is switched.

Correct. I have said that, or near, several times in this and preceding
threads. An article saying the same has been on my web site for almost a
year.

I am now more dangerous. Until today, I had never seen one of Kraus`
books. I now own the third edition of "Antennas (for all applications)".
Kraus says there are "fundamental" units and "secondary" units. The
"Ampere" is a fundamental unit. All secondary units can be derived from
the fundamental units.

That is of course true... but if you believe it relevant to this
discussion, you are indeed much more dangerous.

In the Bird, the given is a 50-ohm line. Power is 50(I)(I), since I=E/R
= E/50, and E = 50(I) = V.

Power = EI

The Bird is accurate enough using a sample of E and a sample of I and
scaling to determine power.

As you yourself say, the Bird senses current and voltage samples; and
these are then added (forward) or subtracted (reverse). There is no
physical mechanism inside the Bird by which E x I multiplication takes
place, so power is not directly sensed or measured.

Multiplication is just scaling or the number
of times you repeat a number in an addition column.

That is a kindergarten concept that only works for integers (how do you
repeat a number 3.14159 times?) and anyway, it physically does not
happen inside a Bird.

In the Bird, scaling
is an electrical adjustment.

No, the meter scale comes from an external calibration.


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

Richard Harrison wrote:

It is simple to calibrate a dynamometer for power and feed current
through one coil and place volts across the other. It senses volts and
amps but it reads out power,

Correct...

as does the Bird wattmeter.

Wrong. The Bird has no second meter coil, and no other physical
mechanism to multiply the E sample by the I sample.

As Walt says (thank you, sir) the Bird is *calibrated* in terms of power
using a matched load.

I've made my point. There's an Internet abbreviation called
IAFWAFIAWMWQ... so I'll be wise, and quit.


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

On Sat, 26 Jul 2003 22:31:38 -0500, W5DXP
wrote:
Ian White, G3SEK wrote:
I believe that I'm asking a question that your theories of power waves
are fundamentally incapable of answering... but that's a problem for you
and your theories, not for me.

Quoting from the article on my web page:

:-)

On Sun, 27 Jul 2003 07:49:22 +0100, "Ian White, G3SEK"
wrote:
As you yourself say, the Bird senses current and voltage samples; and
these are then added (forward) or subtracted (reverse). There is no
physical mechanism inside the Bird by which E x I multiplication takes
place, so power is not directly sensed or measured.

In the Bird, scaling
is an electrical adjustment.

No, the meter scale comes from an external calibration.


Hi Ian,

If you boil down power to heat, it still takes the scale on a
thermometer to confirm the magnitude. Scales are a form of
quantifying into scientific rigor the qualitative utterances of "not
much power," "some power," "more power," "a lot of power...." Denying
that multiplication is performed through the observance of established
boundary conditions and the movement of a coil in a magnetic field
(the resulting torsion which easily conforms to evidence of power) by
nay-saying is not compelling argument.

I've seen antennas described as "transducers" and with this current
side-topic, the Bird Wattmeter is more so such a transducer in its
translation of electrical power to physical power. The Bird Wattmeter
consumes power at a known ratio to the applied power. Ratios are one
of the simplest and most resolved quantities to confirm. There is
very little, short of serious physical abuse, that can disturb this
ratio (such as overpowering the line to create breakdowns such that
there are destructive arcs or fusing current). Efficiency aside (that
power lost to resistors within the sensing circuit), power of a known
ratio magnitude is invested in the needle's angular deflection and
holding it against spring tension. Newton would easily accept this as
"Power." It is basically what he called the ballistic pendulum.

If one cannot measure Power with a Bird Wattmeter, then prayer is the
only solution to the enigma of its reckoning. If you have issue with
the systemic failures that abound in Power determination, then argue
the cause not the instrument. I have described in the past how Power
determination can be upset drastically in the face of measurements
performed between two mismatches (both the source and the load); but
it is not the fault of the instrument in the Power determination's
failure. No other instrument nor method (short of acknowledging the
indeterminacy of phase) will improve over sure failure.

73's
Richard Clark, KB7QHC

Ian, G3SEK wrote:
"No, the meter scale comes from external calibration."

Who said it didn`t?

The scale is mass produced. In the Bird element, a resistor is selected,
in some elements it is a variable resistor, called the "calibration
resistor". A suitable replacement is the Helitrim 7138 mini variable.

See "Calobration and Repair for Bird Wattmeter Elements, page 48, April
1989, 73 Amateur Radio.

Best regards, Richard Harrison, KB5WZI