Gene, W4SZ wrote:
"However, the physical entities do not have two values at once in the
same time and place."

Richard Harrison wrote:
You can measure each of the two simultaneous constituents with the right
equipment. A Bird Thruline wattmeter uses a directional coupler to
separate forward direction power from reverse direction power. These are
obbtainable at the same time and place anywhere in a 50-ohm coax line.
Individual volts and amps in each direction are easily calcuable from
the powers indicated in each direction.

That's not true.

The directional coupler in a Bird meter samples the across vector
(voltage) from a capacitive divider and adds it to a sample voltage of
the through vector (current) from a current transformer in a
predetermined ratio. After that sum, the output is rectified.

I can place it in a system with NO standing waves and it will show
standing waves. I can place it in a system with standing waves and have
it show NO standing waves. It does not measure standing waves, it
simply measures the ratio and phase of voltage and current at one point
in the transmission line.

There can NEVER be current flowing at that point in two directions at
the same instant of time, and the Bird does not even contain a system
that samples standing waves.

Now I can build a piece of test gear that does directly read standing
waves, but it requires a line sampling lwength of at least 1/4 wl.
Such a device would be totally independent of the actual operating
impedance, and could read either current or voltage.

The Bird meter is NOT that type of unit.

73 Tom

wrote:
I can place it in a system with NO standing waves and it will show
standing waves. I can place it in a system with standing waves and have
it show NO standing waves. It does not measure standing waves, it
simply measures the ratio and phase of voltage and current at one point
in the transmission line.

Yes, but if it is calibrated for 50 ohms and installed in a 50 ohm
environment, it is indeed accurately reporting forward and reflected
power. It is accurately separating the forward wave energy from the
reflected wave energy. If it weren't, Bird would be guilty of false
advertising.
--
73, Cecil http://www.qsl.net/w5dxp

Tom, W8JI wrote:
"The directional coupler in a Bird meter samples the across vector
(voltage) from a capacitive divider and adds it to a sample voltage of
the through vector (current) from a current transformer in a
predetermined ratio.

That`s close. In the cartridges is a loop terminated in a diode.
Capacitive coupling of the loop to the center conductor of the precision
ccoax supplies the voltage sample. Inductive coupling of the loop
supplies the current sample.

I`ve described operation several times here and once in this thread, so
I won`t repeat it.

SWR is easy to get from the forward and reflected indications of the
wattmeter.

VSWR = 1 + sq.rt. (ref. PWR / for. PWR)
Divided by 1 - sq.rt. (ref. PWR / for. PWR)

Bird supplies a family of VSWR lines on a graph of forward power vs.
reflected power for those who would avoid the calculation. They can also
supply a slide-rule to do rhe same.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Tom, W8JI wrote:
"The directional coupler in a Bird meter samples the across vector
(voltage) from a capacitive divider and adds it to a sample voltage of
the through vector (current) from a current transformer in a
predetermined ratio.

That`s close. In the cartridges is a loop terminated in a diode.
Capacitive coupling of the loop to the center conductor of the precision
ccoax supplies the voltage sample. Inductive coupling of the loop
supplies the current sample.

I`ve described operation several times here and once in this thread, so
I won`t repeat it.


We're all agreed on what happens with the Bird's sampling lines and
detector. The only differences arise from each person's attempt to
condense it all into a couple of sentences, and aren't worth arguing
about.

But Richard cuts it too short when he claims that:
A Bird Thruline wattmeter uses a directional coupler to separate
forward direction power from reverse direction power.

That claim confuses two different things: what the line-loop-detector
hardware physically *does*; and what the indicated results *mean*. The
first of these is agreed; the second is not.

The disagreement is entirely about the interpretation - in other words,
it's about the theory about standing and travelling waves. Richard
habitually misses out this step, which makes it look as if the Bird
wattmeter "proves" the physical existence of forward and reverse
travelling waves of power.

It doesn't. Everything that you see printed on the Bird's meter scale,
and in the Bird literature, represents that company's particular
interpretation of theory about waves on transmission lines. The details
of that theory are *not* agreed within this newsgroup, which means that
- to some people - the two halves of Richard's claim do not join up.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian White GM3SEK wrote:
The disagreement is entirely about the interpretation - in other words,
it's about the theory about standing and travelling waves. Richard
habitually misses out this step, which makes it look as if the Bird
wattmeter "proves" the physical existence of forward and reverse
travelling waves of power.

Those are traveling waves of *EM energy* where the power is indicated
at a point as the energy flows through that point. Assuming Z0=50 ohms,
the Bird indicates the number of joules per second flowing toward the
load when the slug is in the forward position. Turning the slug around
causes the Bird to indicate the number of joules per second flowing
toward the source.

The only way to have standing waves of EM energy in a transmission
line is to have two EM waves flowing in opposite directions. I have
asked you before to explain how standing waves develop without the
existence of a forward traveling wave and a rearward traveling wave.
Your silence on that subject has been conspicuous by its absence.
Do standing waves appear by magic?

It doesn't. Everything that you see printed on the Bird's meter scale,
and in the Bird literature, represents that company's particular
interpretation of theory about waves on transmission lines. The details
of that theory are *not* agreed within this newsgroup, which means that
- to some people - the two halves of Richard's claim do not join up.

Are you asserting that Bird is engaging in false advertising?
--
73, Cecil http://www.qsl.net/w5dxp

Ian White GM3SEK wrote:
[SNIP]

The disagreement is entirely about the interpretation - in other words,
it's about the theory about standing and travelling waves. Richard
habitually misses out this step, which makes it look as if the Bird
wattmeter "proves" the physical existence of forward and reverse
travelling waves of power.

It doesn't. Everything that you see printed on the Bird's meter scale,
and in the Bird literature, represents that company's particular
interpretation of theory about waves on transmission lines. The details
of that theory are *not* agreed within this newsgroup, which means that
- to some people - the two halves of Richard's claim do not join up.


Ian, I've not detected this particular disagreement about waves on
transmission lines in the group. I would be most grateful to see a brief
statement of where and how Bird's interpretation of theory is found infirm.

73,

Chuck NT3G

chuck wrote:
Ian White GM3SEK wrote:
[SNIP]
The disagreement is entirely about the interpretation - in other
words, it's about the theory about standing and travelling waves.
Richard habitually misses out this step, which makes it look as if
the Bird wattmeter "proves" the physical existence of forward and
reverse travelling waves of power.
It doesn't. Everything that you see printed on the Bird's meter
scale, and in the Bird literature, represents that company's
particular interpretation of theory about waves on transmission lines.
details of that theory are *not* agreed within this newsgroup, which
means that - to some people - the two halves of Richard's claim do
not join up.


Ian, I've not detected this particular disagreement about waves on
transmission lines in the group. I would be most grateful to see a
brief statement of where and how Bird's interpretation of theory is
found infirm.

The Bird 43 has only one scale calibration: power. Readings on that
scale represent the power delivered to a 50-ohm load when the sensor is
turned to the forward direction. However, the instrument internally
senses only the voltage and current on the line. The "power" reading is
only a calibration, and is only completely meaningful when you use the
instrument in the same circumstances as when it was calibrated.

Now what happens if the load is not exactly 50 ohms? What happens when
you turn the sensor around? You then get some new and different readings
which have to be called "forward power" and "reflected power" - because
"power" is the only thing the Bird's meter scale is calibrated to
indicate.

The Bird Corporation's Application Note "Straight Talk About
Directivity" discusses the meaning of "forward and reflected power"
indications with a mismatched load. That document does not directly
address your question, Chuck, but takes the subject to a further level
of detail about the accuracy of the real-life instrument, and its
limited ability to discriminate between forward and reflected waves.
http://www.bird-electronic.com/app_n...irectivity.pdf

One notable thing about "Straight Talk" is how all the calculations
begin by taking the square root of the power indications. In other
words, all the relative RF power indications from the meter scale are
converted into relative RF voltages, and all the real calculations are
done on the voltages.

Another interesting observation is that if you have a mismatched load,
such that the meter indicates say 93W with the arrow on the sensor
pointing forward and say 23W with the sensor rotated 180deg, then you
would find that 70W is being delivered into the resistive part of the
mismatched load impedance (assuming perfect directivity and no errors of
any other kind).

There are two schools of thought about the physical meaning of all this.

One is that if the meter scale says "power", then there genuinely are
forward and reflected traveling waves of power on the line. In the "93 -
23 = 70W" example, the belief is that there genuinely is a power flow of
93W towards the load, only 70W of which is accepted and 23W is returned.

The other school of thought is that that's not true. The meter may
*read* more "forward power" than is actually being delivered to the
load, but that is a false indication because the instrument is not being
used in the situation for which the power scale was calibrated.
Therefore it is not to be taken at face value - and above all, the
letter "W" on the meter scale does not prove the physical existence of
forward and reflected waves of power.

Every detail about a Bird 43 or similar "directional wattmeter" can be
explained quite simply in terms of travelling waves of voltage and
current. And I do mean every detail - including why a meter that happens
to have been calibrated in "power" will read as it does.

The classic explanation was by Warren Bruene, W5OLY, of the Collins
company. He invented the familiar "Bruene bridge" directional coupler
which samples current through a toroidal transformer, and voltage by a
voltage divider. The principle of the Bird 43 is the same, but the two
separate sampling functions are easier to see in the Bruene bridge.

After a previous incarnation of this debate in 2002, I wrote a 2-page
article which summarised Bruene's original article (from QST, April
1959) and explained the crossover to the Bird sampling technique:
http://www.ifwtech.co.uk/g3sek/in-pr...-of.htm#bruene

An equally good explanation of those same meter readings can be
constructed by regarding the Bruene "bridge" literally as an impedance
bridge. There is no inconsistency between the two approaches - they are
just two different viewpoints looking at the same reality.

On the other hand, we have yet to see an explanation in equivalent
physical detail that is based entirely and exclusively on the viewpoint
of travelling waves of power (with no borrowing from explanations based
on voltage and current).

I am not blaming the Bird Corporation for any of these
misunderstandings. They are simply telling users how to work with the
available "power" markings on the meter scale. The problem is when some
users take them too literally.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Thank you, Ian, for the quick and thorough reply! I look forward to
reading both papers.

73,

Chuck NT3G

On Wed, 12 Apr 2006 16:32:22 +0100, Ian White GM3SEK
wrote:

On the other hand, we have yet to see an explanation in equivalent
physical detail that is based entirely and exclusively on the viewpoint
of travelling waves of power (with no borrowing from explanations based
on voltage and current).

Now Ian,

That is like asking us to explain a speedometer without recourse to
the units for distance and time.

73's
Richard Clark, KB7QHC

On Wed, 12 Apr 2006 16:32:22 +0100, Ian White GM3SEK
wrote:

One is that if the meter scale says "power", then there genuinely are
forward and reflected traveling waves of power on the line. In the "93 -
23 = 70W" example, the belief is that there genuinely is a power flow of
93W towards the load, only 70W of which is accepted and 23W is returned.

The other school of thought is that that's not true. The meter may
*read* more "forward power" than is actually being delivered to the
load, but that is a false indication because the instrument is not being
used in the situation for which the power scale was calibrated.
Therefore it is not to be taken at face value - and above all, the
letter "W" on the meter scale does not prove the physical existence of
forward and reflected waves of power.

Hi Ian,

This argument sets up the first school for failure that is already
admitted to. Your statement from the second school that:
*read* more "forward power" than is actually being delivered to the
load, but that is a false indication
is already admitted to explicitly from the first school:
93W towards the load, only 70W of which is accepted and 23W is returned.
in that the 70W NOT 93W is the correct indication.

The "second" school has nothing to offer on the subject. The
"because" that attends their "discovery" of this error is specious
logic.

The fact remains that when you subtract 23W from the 93W you do find
70W in the load. The second school would have us believe none of the
numbers correlate to power, and yet the results bear out just the
opposite every day.

The second school needs to stay after class.

73's
Richard Clark, KB7QHC