On Mar 21, 3:06 pm, (Richard Harrison)
wrote:
Bird says of its Model 43 Wattmeter: "Experience using the "Thruline"
Wattmeter for transmitter tune-up, antenna matching, etc. (i.e. on
operating problems), shows that the power ratio is as useful in practice
as the VSWR."

One can see reflected power disappear at the transmitter terminals as a
match is made to the transmitter load. That eliminates stress on the
transmitter from reverse power.

I suggest that a more accurate description would read:
"One can see the indication on meter go to zero at the transmitter
terminals as the match is made to the transmitter load".

The scale on the meter could be labelled "furlongs per fortnight" and
this would still be true.

After exploring alternative explanations for the various phenomena,
the explorer will be ready to understand what a directional wattmeter
really measures (as opposed to what its meter scale claims to
indicate)
and truly understand what inferences can be correctly made from its
indications.

Reverse power is as real as its Bird Wattmeter indication.

I absolutely agree with this.

....Keith

Keith Dysart wrote:

On Mar 21, 3:06 pm, (Richard Harrison)
wrote:

Bird says of its Model 43 Wattmeter: "Experience using the "Thruline"
Wattmeter for transmitter tune-up, antenna matching, etc. (i.e. on
operating problems), shows that the power ratio is as useful in practice
as the VSWR."

One can see reflected power disappear at the transmitter terminals as a
match is made to the transmitter load. That eliminates stress on the
transmitter from reverse power.

I suggest that a more accurate description would read:
"One can see the indication on meter go to zero at the transmitter
terminals as the match is made to the transmitter load".

Then, you have never matched with a reflection. Without the experience,
how can you make a claim? You have not made the observation yet you
claim what it 'should' be.

On Mar 21, 4:30 pm, Dan Bloomquist wrote:
Keith Dysart wrote:
On Mar 21, 3:06 pm, (Richard Harrison)
wrote:

Bird says of its Model 43 Wattmeter: "Experience using the "Thruline"
Wattmeter for transmitter tune-up, antenna matching, etc. (i.e. on
operating problems), shows that the power ratio is as useful in practice
as the VSWR."

One can see reflected power disappear at the transmitter terminals as a
match is made to the transmitter load. That eliminates stress on the
transmitter from reverse power.

I suggest that a more accurate description would read:
"One can see the indication on the meter go to zero at the transmitter
terminals as the match is made to the transmitter load".

Then, you have never matched with a reflection. Without the experience,
how can you make a claim? You have not made the observation yet you
claim what it 'should' be.

I may have misunderstood, but I thought that when Richard said "see
reflected power disappear" he was observing the Bird Wattmeter
mentioned
in his previous paragraph and watching its indication go to zero. If
this
is not what was meant, then I need elaboration.

Otherwise, I think I said the same as Richard in different (and,
arguably
more precise) words.

....Keith

Keith Dysart wrote:

On Mar 21, 4:30 pm, Dan Bloomquist wrote:

Keith Dysart wrote:

On Mar 21, 3:06 pm, (Richard Harrison)
wrote:

Bird says of its Model 43 Wattmeter: "Experience using the "Thruline"
Wattmeter for transmitter tune-up, antenna matching, etc. (i.e. on
operating problems), shows that the power ratio is as useful in practice
as the VSWR."

One can see reflected power disappear at the transmitter terminals as a
match is made to the transmitter load. That eliminates stress on the
transmitter from reverse power.

I suggest that a more accurate description would read:
"One can see the indication on the meter go to zero at the transmitter
terminals as the match is made to the transmitter load".

Then, you have never matched with a reflection. Without the experience,
how can you make a claim? You have not made the observation yet you
claim what it 'should' be.


I may have misunderstood, but I thought that when Richard said "see
reflected power disappear" he was observing the Bird Wattmeter
mentioned
in his previous paragraph and watching its indication go to zero. If
this
is not what was meant, then I need elaboration.

My mistake. You both said something that is not what happens. I will
assume you are looking for no reflection between a transmitter and a
transmatch. But the source to a transmission line is on the other side
of that transmatch. You will most certainly see a reflected wave if the
end of that transmission line is not terminated into purely 50 ohm load.

Otherwise, I think I said the same as Richard in different (and,
arguably
more precise) words.

I see that. But neither is the case. If you are matching a transmitter
to mis-matched line, the reflection does not go to zero. In fact, the
reflection is a function of the line and termination and is constant.
Nothing you do at the transmitter can change it.


...Keith

Best, Dan.

On Mar 21, 5:24 pm, Dan Bloomquist wrote:
Keith Dysart wrote:
On Mar 21, 4:30 pm, Dan Bloomquist wrote:

Keith Dysart wrote:

On Mar 21, 3:06 pm, (Richard Harrison)
wrote:

Bird says of its Model 43 Wattmeter: "Experience using the "Thruline"
Wattmeter for transmitter tune-up, antenna matching, etc. (i.e. on
operating problems), shows that the power ratio is as useful in practice
as the VSWR."

One can see reflected power disappear at the transmitter terminals as a
match is made to the transmitter load. That eliminates stress on the
transmitter from reverse power.

I suggest that a more accurate description would read:
"One can see the indication on the meter go to zero at the transmitter
terminals as the match is made to the transmitter load".

Then, you have never matched with a reflection. Without the experience,
how can you make a claim? You have not made the observation yet you
claim what it 'should' be.

I may have misunderstood, but I thought that when Richard said "see
reflected power disappear" he was observing the Bird Wattmeter
mentioned
in his previous paragraph and watching its indication go to zero. If
this
is not what was meant, then I need elaboration.

My mistake. You both said something that is not what happens. I will
assume you are looking for no reflection between a transmitter and a
transmatch. But the source to a transmission line is on the other side
of that transmatch. You will most certainly see a reflected wave if the
end of that transmission line is not terminated into purely 50 ohm load.

Otherwise, I think I said the same as Richard in different (and,
arguably
more precise) words.

I see that. But neither is the case. If you are matching a transmitter
to mis-matched line, the reflection does not go to zero. In fact, the
reflection is a function of the line and termination and is constant.
Nothing you do at the transmitter can change it.



...Keith

Best, Dan

I agree with what you say.

I had made the leap that Richard's configuration was transmitter,
Bird, matching
device as that seemed to be the only way that an adjustment could
bring
the meter on the Bird to zero. If this was not the intended
configuration
then I am completely confused and Richard will need to clarify his
intent.

....Keith

"Keith Dysart" wrote in news:1174507951.363436.150330
@y66g2000hsf.googlegroups.com:

....
The scale on the meter could be labelled "furlongs per fortnight" and
this would still be true.

After exploring alternative explanations for the various phenomena,
the explorer will be ready to understand what a directional wattmeter
really measures (as opposed to what its meter scale claims to
indicate)
and truly understand what inferences can be correctly made from its
indications.

Keith,

I drafted an article exploring the operation of a Breune type directional
wattmeter, it is at http://www.vk1od.net/VSWR/VSWRMeter.htm . The Bird 43
responds in the same way, but from a different sampler construction.

The article gives a simple derivation of the meter response, and deals
with the legitimacy of scaling the instrument in Watts.

If one takes measurements with the instrument, it is true that the power
at a point is "forward power" less "reflected power", and the
manufacturer has scaled the instrument in Watts to facilitate that
calculation, but that does not imply that the value of "forward power" or
"reflected power" has any stand alone value, the ratio of the two is
meaningful, the difference of the two is meaningful, but one alone is
meaningless.

To illustrate the lack of stand-alone value of the "forward power"
reading, one could place two such instruments, one calibrated for 50 ohm
and another calibrated for 100 ohm in tandem at the tx, and then a load.
The two instruments will indicate different "forward power" and different
"reflected power".

Notwithstanding the fact that the "forward power" and "reflected power"
readings are each not of stand alone, the difference between "forward
power" and "reflected power" has meaning and will be the same for each
instrument.

I agree with you that a lack of understanding of the instrument can be
used to prop up bogus explanations and concepts, even leading to people
citing the Bird 43 user manual like it was a respected and authoritative
text.

Owen

Owen Duffy wrote in
:

Notwithstanding the fact that the "forward power" and "reflected
power" readings are each not of stand alone, the difference between
"forward power" and "reflected power" has meaning and will be the same
for each instrument.

That reads better with the missing word supplied:

Notwithstanding the fact that the "forward power" and "reflected power"
readings are each not of stand alone meaning, the difference between
"forward power" and "reflected power" has meaning and will be the same for
each instrument.

Would any poster in this thread who doesn't "believe in" reflected
power kindly explain how a transmission line can fail upstream of a
serious mismatch anywhere along the the length of that line. If that
doesn't result from the sum of forward and reflected voltage/current,
then (IYO) what is the reason such failures?

Don't think that this doesn't occur. I've seen it many times, and had
to find and replace the molten and arced-over components that
resulted.

RF

"Richard Fry" wrote in news:1174511497.343920.155080
@e1g2000hsg.googlegroups.com:

Would any poster in this thread who doesn't "believe in" reflected
power kindly explain how a transmission line can fail upstream of a
serious mismatch anywhere along the the length of that line. If that
doesn't result from the sum of forward and reflected voltage/current,
then (IYO) what is the reason such failures?

Without making any admissions about my beliefs...

A transmission line with mismatched load can be described in terms of
travelling waves, and the voltage and current at a point on the line can
be calculated from the forward and reflected waves.

The voltage at the point may be higher than under matched conditions for
the same load power, and that may cause insulation breakdown.

The current at the point may be higher than under matched conditions for
the same load power, and that would cause higher loss in conductors and
may result in damage.

Don't think that this doesn't occur. I've seen it many times, and had
to find and replace the molten and arced-over components that
resulted.

None of these explanations require designating "reflected power" at a
point, or implying that it is the energy in "reflected power" that is
totally and solely responsible for the physical damage.

Owen

"Owen Duffy" wrote
None of these explanations require designating "reflected power"
at a point, or implying that it is the energy in "reflected power"
that is totally and solely responsible for the physical damage.
___________

I guess you are relying on the fact that there will be no reflected r-f
voltage/
current if there is no incident voltage/current? And no argument, there.

But of course, it is the vector sum of ALL of these that may cause the
transmission line/network/tx failure(s) mentioned in my relevant posts
in this thread.

And so that does NOT prove that reflected power/voltage/current
does not exist, or is unimportant in an r-f system design.

The specifications of a transmission line or other r-f network or circuit
can be chosen with due engineering care to be rated for a defined incident
power applied to a load with a given mismatch to a specific Zo, and with
respect to the carrier frequency, the modulation thereon, the ambient air
temperature/pressure, solar illumination, line pressurization, and other
operating parameters.

These realities are commonly recogniz(s)ed and incorporated by most
commercial designers/evaluators of r-f transmission systems, and as a result
pose no significant problems to them and/or their clients.

But none of this means that r-f reflections do not, may not, or can not
exist -- whether in "ham" systems, or otherwise.

RF

PS: Please edit my email address in replies here so that
it can't accurately be picked up by spammers. I get enough
spam already. Gracias.