Richard Clark wrote:
This is an amusing irony of where you have found power where you have
always posited there is none, and where you have rejected there is
power when it has been shown to exist. Each example exposes your lack
of experience in the scale of the error and its relation to the
equipment measuring it.

In exactly the same way that forward power can exceed generated
power in a 1/4WL matching section of transmission line, so can
the forward irradiance in 1/4WL of thin film exceed the forward
irradiance in the air before incidence. That you are still so
terribly confused about such a simple fact of light physics is sad.
You obviously don't understand the information on the Melles-Groit
web page. http://www.mellesgriot.com/products/optics/oc_2_1.htm
Please study it until you understand it.
--
73, Cecil http://www.qsl.net/w5dxp

Richard Clark wrote:

As the last "thin-film" comment reveals, it
has always been about how one mind can encompass two contradictory
positions (total cancellation - non total cancellation) about the same
mechanism (a quarterwave matching section).

In other words: A Troll.

If the incident irradiance is a single frequency coherent signal,
the requirement for TOTAL CANCELLATION OF REFLECTIONS is still
that the index of refraction of the 1/4WL thin-film be the square
root of the medium upon which it is deposited. QED
--
73, Cecil http://www.qsl.net/w5dxp

On Fri, 14 Oct 2005 16:22:39 GMT, Cecil Moore wrote:


It was previously reported that the path through the Bird
is 40mm. The path through the Bird is actually about five

Cecil,

If you are referring to my statement in another thread, it was that
the sampling element is about 40mm inside the 50 ohm Thruline section
(ie that there is about 40mm of 50 ohm transmission line between the
Bird 43 terminals and the sampling element), not as you have stated
above.

Owen
--

Jim Kelley wrote:
I think it might also be interesting to discuss the instance in which
the Bird is interfaced with a real halfwave section.

If the Bird is inserted at a point where the net voltage divided
by the net current is equal to 50, apparently a 50 ohm Z0-match
is achieved at that point and any length of lossless 50 ohm coax
can be inserted without altering the forward/reflected conditions
in the adjacent transmission lines.
--
73, Cecil http://www.qsl.net/w5dxp

Owen Duffy wrote:

On Fri, 14 Oct 2005 16:22:39 GMT, Cecil Moore wrote:
It was previously reported that the path through the Bird
is 40mm. The path through the Bird is actually about five

If you are referring to my statement in another thread, it was that
the sampling element is about 40mm inside the 50 ohm Thruline section
(ie that there is about 40mm of 50 ohm transmission line between the
Bird 43 terminals and the sampling element), not as you have stated
above.

I'm sorry, Owen, I took your statement to mean that the total length
of path through the Bird is 40mm (1.5") which is not enough length
to force a 50 ohm environment. I downloaded the Bird manual this
morning and discovered that, unlike an MFJ, the path through the Bird
is about 5 inches and coaxial. I apologize to Bird and you Bird
experts for that bad assumption.
--
73, Cecil http://www.qsl.net/w5dxp

That explains why my new tuner failed to work. I have a rotary switch that
selects 40mm of 50, 75,300, 450, and 600 ohm coax. I thought it should match
anything! Now I see I have to go to 5" lengths. I should know better than to
build anything before all the errata sheets are in.

I can use some additional diversion as almost all the soldering iron burns
have healed.

"Cecil Moore" wrote in message
m...
Owen Duffy wrote:

On Fri, 14 Oct 2005 16:22:39 GMT, Cecil Moore wrote:
It was previously reported that the path through the Bird
is 40mm. The path through the Bird is actually about five

If you are referring to my statement in another thread, it was that
the sampling element is about 40mm inside the 50 ohm Thruline section
(ie that there is about 40mm of 50 ohm transmission line between the
Bird 43 terminals and the sampling element), not as you have stated
above.

I'm sorry, Owen, I took your statement to mean that the total length
of path through the Bird is 40mm (1.5") which is not enough length
to force a 50 ohm environment. I downloaded the Bird manual this
morning and discovered that, unlike an MFJ, the path through the Bird
is about 5 inches and coaxial. I apologize to Bird and you Bird
experts for that bad assumption.
--
73, Cecil http://www.qsl.net/w5dxp

On Wed, 12 Oct 2005 22:09:51 GMT, Owen Duffy wrote:

The myth: Measurements with a Bird 43 of the conditions on the
Thruline section are invalid unless it has some minimum length of 50
ohm line on both sides of itself.


All,

Can I offer the suggestion that the key to understanding why this is
so, it to understand the sampler.

I don't have the detail of the physical and electrical parameters of
the Bird sampler, however I suspect that like so many other
reflectometers, it comes down to a device that samples independently
the net current and the net voltage associated with any travelling
waves, and those RF samples are in proportion and phase relationship
that when algebraicly added and rectified, they produce a DC voltage
that is proportional to the power flow in one direction only (provided
that Zo is real). The proportions calibrate the instrument for a
specific V/I ratio.

Apart from mentioning that Zo must be real, and I will address that in
another thread, Zo in the region where the sample is unimportant to
the "proportion and phase relationship..." bit. Zo of the through line
is important only to the extent that you would generally:
- not want a significant transformation of impedance between the load
terminals and the calibrated sensor at that calibrated V/I ratio.
- not want a significant transformation of impedance between the
generator and load terminals at that calibrated V/I ratio to minimise
disruption to the system being measured.

Everyday we use instruments to measure something, somewhere and apply
that knowledge to infer something else, somewhere else using
appropriate other knowledge. For example, you might measure the
voltage drop across a cathode resistor and make some reasonable
inference about anode current using appropriate other knowledge.
Making measurements with a Bird 43 in one place and inferring the
situation somewhere else using appropriate other knowledge is
reasonable.

For example, I may have an antenna system (say a loop) that uses a
transmission line transformer (TLT) to transform the loop terminal Z
to 50 ohms. I can attach the generator end of the TLT to the Bird 43,
attach the Bird 43 via 50 ohm cable to a transceiver that is rated for
a nominal 50+j0 ohm load, and proceed to adjust the antenna / TLT for
zero reflected power indication on the Bird 43 knowing that I can
reasonably infer that the load presented to the transceiver will be
approximately 50+j0 ohms using the knowledge that Bird readings
indicate Z at that point is 50+j0 and there will be insignificant
transformation on the 50 ohm cable to the transceiver. This is a
proper and sound application of the instrument.

Did I get that wrong?

Did I need to mention environments?

Owen
--

THERE ARE ABOUT 4.17 WATTS OF REFLECTED ENERGY FLOWING BACK THROUGH THE
BIRD AND THE BIRD COMPLETELY IGNORES IT. So the Bird is not even yielding
valid readings for forward and reflected power through itself. That's
exactly what I have been saying all along. If it were calibrated for
75 ohms, it would indicate the correct values.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil, With a 1/2 wl of 75 ohm line terminated with 50 ohms at both
the source and load end, the 4.17 watts reflected energy does not flow
back thru the Bird. With 100 watts incident on the source (Bird), 100
watts will be either radiated, or consumed as heat at the load end.
4.17 will be reflected back to the source. When it reaches the source,
a portion will be reflected back towards the load, and a portion
consumed as heat. ect. The small portion consumed by heat might
account for the 1/2 needle deflection Owen observed on reflected power.
4.17 watts does not flow back thru the Bird as reflected power, and
the Bird, of course acknowledges. I don't think the Bird ignores that.
I acknowledge that the Bird does not report the actual forward/reverse
power in this example
Gary N4AST

On 14 Oct 2005 16:07:44 -0700, wrote:

I don't think the Bird ignores that.

Hi Gary,

And none but one does.

I acknowledge that the Bird does not report the actual forward/reverse
power in this example

And this responds to a fabricated question.

Who would approach a Bird and expect it to in the first place? A lid.
This is like complaining that your speedometer doesn't report the
actual speed of the car passing you. Having said that, an entire
thread of correspondence could grow to show adapters and cables
between the two cars "could" contrive to make that happen, and then
the topic drift would blame the erroneous name of speedometer, when it
is only a highway-to-tire traction indicator - HTTTI.

If I were back in the calibration business, this stuff would be like
gold being pushed across the counter.
"It doesn't work when I put it into an out-of-spec system,
could you check the accuracy against a known load?"

I suppose most of the filthy lucre has been absorbed into either Iraq
or FEMA contracts.

73's
Richard Clark, KB7QHC

On Fri, 14 Oct 2005 21:23:25 GMT, Owen Duffy wrote:


that when algebraicly added and rectified, they produce a DC voltage
that is proportional to the power flow in one direction only (provided
that Zo is real). The proportions calibrate the instrument for a

Sorry, that should be:

"that when algebraicly added and rectified, they produce a DC voltage
that is proportional to the square root of power flow in one direction
only (provided that Zo is real). The proportions calibrate the
instrument for a..."

Owen
--