Dish reflector
 

On Apr 30, 11:26*pm, Jim Kelley wrote:
But when there is a change in the amplitude of the
standing wave in x, and I max is known, then determining the shift in
phase from the equation is a no brainer, Cecil.

Jim,

I'm still reading, trying to understand the various arguments being
put forward!

One thing I'm not clear about is your response to Cecil's point about
phase measurements along a standing wave.

Please correct me if I've got any of this wrong: I'm picturing a half-
wave antenna with a current standing wave in the shape of a (half)
sine wave. My understanding is that if I could observe the current at
a particular point along the antenna its amplitude would vary
sinusoidally with time, and its peak amplitude would be determined by
its distance from the centre of the antenna (and of course by the peak
amplitude of the current at the centre).

If I could observe the current at several points along the antenna
they would all be in-phase, in the sense that they would all reach
peak amplitude at the same time, and cross zero at the same time. The
only thing that would distinguish them would be the peak amplitude.

Cecil seems to be saying that, in a system like the one I've
described, measuring the relative phase of the currents at two points
along the antenna tells you nothing about their (electrical) distance
apart. If I've misinterpreted him, I'm sure cecil will correct me!

Given that the currents all along the antenna are in-phase, Cecil's
point seems so obvious - what am I missing? Or do you actually agree
this point and I've misunderstood your position?

Regards,
Steve

Dish reflector
 

Jim Kelley wrote:
But when there is a change in the amplitude of the
standing wave in x, and I max is known, then determining the shift in
phase from the equation is a no brainer, Cecil.

Exactly! You and I are agreed that the *amplitude* holds
the key to the phase shift *through a straight wire* so
you are preaching to the choir. The phase of the total
current on a standing-wave antenna is unrelated to the
delay through the loading coil.

Unfortunately, the current "bulge" through a loading
coil causes an error in the simple "no-brainer"
calculation that you are suggesting. Some other method
of determining the phase-shift/delay through a coil is
needed.

That other method is to load the loading coil with
its characteristic impedance and measure the phase
shift in the resulting traveling wave.

For instance, in the coil426.EZ file from my web
page, the current at the bottom of the coil is
1.0168 amps at 0.00 degrees. The current at the
top of the coil is 0.8179 amps at -0.06 degrees.
The maximum current in the middle of the coil
is 1.1092 amps at -0.04 degrees.

The total current equation through a loading coil
is not a simple cosine function like it is through
a thin-wire. Determining the actual delay through a
loading coil is apparently NOT a no brainer.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Dish reflector
 

On May 1, 12:58*am, wrote:
On Apr 30, 11:26*pm, Jim Kelley wrote:

But when there is a change in the amplitude of the
standing wave in x, and I max is known, then determining the shift in
phase from the equation is a no brainer, Cecil.

Jim,

I'm still reading, trying to understand the various arguments being
put forward!

One thing I'm not clear about is your response to Cecil's point about
phase measurements along a standing wave.

Please correct me if I've got any of this wrong: I'm picturing a half-
wave antenna with a current standing wave in the shape of a (half)
sine wave. My understanding is that if I could observe the current at
a particular point along the antenna its amplitude would vary
sinusoidally with time, and its peak amplitude would be determined by
its distance from the centre of the antenna (and of course by the peak
amplitude of the current at the centre).

If I could observe the current at several points along the antenna
they would all be in-phase, in the sense that they would all reach
peak amplitude at the same time, and cross zero at the same time. The
only thing that would distinguish them would be the peak amplitude.

Cecil seems to be saying that, in a system like the one I've
described, measuring the relative phase of the currents at two points
along the antenna tells you nothing about their (electrical) distance
apart. If I've misinterpreted him, I'm sure cecil will correct me!

Given that the currents all along the antenna are in-phase, Cecil's
point seems so obvious - what am I missing? Or do you actually agree
this point and I've misunderstood your position?

Regards,
Steve

Hi Steve,

Yes, I think you have it right. But there's more to it. Typically we
wouldn't measure the amplitude of the standing wave envelope. We
would make a measurement of either the forward or the reflected
traveling wave, which are phase delayed along the antenna. Cecil seems
to believe that he has cornered the market on making such
measurements. Although he has proposed an interesting method for
making the measurement, others have also made it using conventional
techniques. But he lambasts them, unfairly and incorrectly. I guess
you had to be there. :-)

Thanks,

ac6xg

Dish reflector
 

Jim Kelley wrote:
Typically we
wouldn't measure the amplitude of the standing wave envelope.

That is where you are mistaken. The total current on a
standing-wave antenna is primarily standing wave current.
What you are saying is that we wouldn't typically measure
the total current. On the contrary, total current is exactly
what we would typically measure and is exactly what w7el
measured. That's why he measured a negligible phase shift.

We would make a measurement of either the forward or the reflected
traveling wave, which are phase delayed along the antenna.

I'm sorry, but that is a false statement. Measuring the forward
or reflected traveling wave, which is less than 10% of the
total energy on the antenna, is exactly what is the problem.

Traveling waves on standing-wave antennas are very hard to
separate and measure. Exactly how do you propose to separate
the forward wave from the reflected wave while preserving the
amplitude and phase of each?

Hint: w7el used the total current for his "measurements".
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Dish reflector
 

Cecil Moore wrote:
I'm sorry, but that is a false statement. Measuring the forward
or reflected traveling wave, which is less than 10% of the
total energy on the antenna, is exactly what is the problem.

Let me amend that statement which is misleading.

The standing wave current on a standing wave antenna,
which w7el used for his measurements, accounts for 90+%
of the total current. He essentially measured total
current, not traveling wave current.

I think if you contacted Roy directly, he will admit
that fact.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Dish reflector
 

Cecil Moore wrote:

We would make a measurement of either the forward or the reflected
traveling wave, which are phase delayed along the antenna.

I'm sorry, but that is a false statement. Measuring the forward
or reflected traveling wave, which is less than 10% of the
total energy on the antenna, is exactly what is the problem.

Hmmmm. Perhaps I misspoke. I should have said that's what I usually
measure when I want to know how much power my antenna is radiating. I
guess I don't actually know for sure what other people usually measure.
But if they have a Bird wattmeter for example, that's what they usually
measure too.

ac6xg

Dish reflector
 

Jim Kelley wrote:
Cecil Moore wrote:

We would make a measurement of either the forward or the reflected
traveling wave, which are phase delayed along the antenna.

I'm sorry, but that is a false statement. Measuring the forward
or reflected traveling wave, which is less than 10% of the
total energy *on the antenna*, is exactly what is the problem.

Hmmmm. Perhaps I misspoke. I should have said that's what I usually
measure when I want to know how much power my antenna is radiating. I
guess I don't actually know for sure what other people usually measure.
But if they have a Bird wattmeter for example, that's what they usually
measure too.

The context, as proved by your first posting above is
measurements "along the antenna". Why do you need to divert
the issue by changing the context in midstream? Why can't
you just discuss things in context?

A Bird wattmeter will not work "along the antenna". Contrary
to what you assert above, *nobody* uses a Bird wattmeter
"along the antenna" to measure anything. A Bird wattmeter
is a 4-terminal device requiring a reference which doesn't
exist "along the antenna".

The only measurements that have been made "along the antenna"
are total current measurements. Seems the only way to measure
forward traveling waves "along the antenna" is to use a
traveling wave antenna like a terminated rhombic.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Dish reflector
 

On Fri, 01 May 2009 11:15:11 -0700, Jim Kelley
wrote:

Cecil Moore wrote:

We would make a measurement of either the forward or the reflected
traveling wave, which are phase delayed along the antenna.

I'm sorry, but that is a false statement. Measuring the forward
or reflected traveling wave, which is less than 10% of the
total energy on the antenna, is exactly what is the problem.

Hmmmm. Perhaps I misspoke. I should have said that's what I usually
measure when I want to know how much power my antenna is radiating. I
guess I don't actually know for sure what other people usually measure.
But if they have a Bird wattmeter for example, that's what they usually
measure too.

Hi Jim,

For the sake of Steve's interest, it would be fair to point out that
no one measures current along the antenna, but many measure the
current INTO the antenna (it is/was, in fact, the preferred method for
FCC power measurements of AM Band transmitters). And by measuring
current INTO the antenna, with it tuned as a resistive load, there is
no issue of reflection. Beyond the feed point, conventional teachings
inform the FCC of expected performance.

Not that Jim has suggested it, but I find it extremely unlikely that
anyone uses a Bird Wattmeter to measure current along the length of an
antenna (of any size or in any state of match) - however, the
electronics of the Bird (and more so the Bruene SWR bridge) could make
it achievable.... except.

Except the lead making the remote measurement would introduce a
significant error as it would inhabit the fields and disturb them.

Another method is the in-line current meter with a meter readout. Then
that meter is read through binoculars. Years back, such a method was
used to kick-start a manufactured controversy which embers now
struggle for oxygen in the ashes of this thread. You will recognize
the flicker of that spark with one word: phase.

Steve, the elements of this discussion you find lacking clarity (in
what would seem an ordinary observation to you) are leveraged meanings
that are the prelude to a larger proof (sic). To follow it, you would
have to suspend your inclination to question odd re-definitions of
perfectly understood concepts and invented terms that "supplement"
conventional science. If you refuse to suspend your judgment and ask
a question along the way, chances are that trolley will jump the
tracks. Otherwise, how could something so ordinary take 300 posts to
arrive nowhere?

73's
Richard Clark, KB7QHC

Dish reflector
 

Cecil Moore wrote:
Jim Kelley wrote:
Cecil Moore wrote:

We would make a measurement of either the forward or the reflected
traveling wave, which are phase delayed along the antenna.

I'm sorry, but that is a false statement. Measuring the forward
or reflected traveling wave, which is less than 10% of the
total energy *on the antenna*, is exactly what is the problem.

Hmmmm. Perhaps I misspoke. I should have said that's what I usually
measure when I want to know how much power my antenna is radiating. I
guess I don't actually know for sure what other people usually measure.
But if they have a Bird wattmeter for example, that's what they
usually measure too.

The context, as proved by your first posting above is
measurements "along the antenna". Why do you need to divert
the issue by changing the context in midstream? Why can't
you just discuss things in context?

A Bird wattmeter will not work "along the antenna". Contrary
to what you assert above, *nobody* uses a Bird wattmeter
"along the antenna" to measure anything. A Bird wattmeter
is a 4-terminal device requiring a reference which doesn't
exist "along the antenna".

The only measurements that have been made "along the antenna"
are total current measurements. Seems the only way to measure
forward traveling waves "along the antenna" is to use a
traveling wave antenna like a terminated rhombic.

Yes, bla bla bla, whine, etc.

Here is a photograph of a directional wattmeter converted to measure
current on W8JI's web page.

http://www.w8ji.com/building_a_current_meter.htm

ac6xg

Dish reflector
 

Jim & Richard,

I guess I'll retire gracefully because I'm not privy to the "history"
between individuals on this Forum and I'm now not even sure when
answers are to be taken seriously or as a joke.

Jim's most recent posting is a good example. We were talking about
measuring current along a dipole. I assumed that would mean measuring
the standing-wave current, but Jim introduced the notion of measuring
travelling wave currents. When challenged as to how we might do that,
we got a URL pointing us to a simple standing wave meter - it
certainly can't discriminate Forward and Reverse.

From other postings I've read I take Jim to be a pretty knowledgeable
guy - so this has to be a wind-up, right?

Steve