Loading Coils; was : Vincent antenna
 

On Thu, 29 Nov 2007 18:26:56 GMT, Cecil Moore
wrote:
More mooching validation. You guys could collect more nickels if you
learned to doff your caps instead of engaging in your incessant
muttering.
The same could have been said of Galileo.

OK, so you believe that Galileo was a muttering mooch and you desire
association with him in that context. Don't get singed.

Do you suggest that technical absurdities go unchallenged?

Has that challenge never occurred, or simply not in this week? You
are just blocking the sidewalk and mooching for validation.

While we are dropping the names of Italian notables, enjoy my Bonfire
of the Vanities as you have already brought your marshmallows.

73's
Girolamo Savonarola

Loading Coils; was : Vincent antenna
 

That is his "obvious" explanation. He should remove that from his webpage as
it is rather embarassing. Given that the magnetic field moves at the speed
of light, there will be no equipment in any hamshack that will measure the
delta between the field affecting coils spaced 1mm apart vs coils spaced
10mm apart or 1000mm apart.



I should think that many hams have things that can measure 3 ns (1000mm
light time), particularly in a repetitive system. That's one cycle at
300 MHz, or 36 degrees at 30 MHz.


Systems that rely on nulling or matching, with a variable line
stretcher, for instance, can do this fairly well.

For example of a measurement technique, say one put a LED in series with
the turn at one end, and another at the other end, along with enough DC
bias current to make sure they both stay lit, with the RF current
essentially modulating the brightness (Hmm. the LED has parasitic terms,
and you'd need a fast one.. but that's the general idea).

You could then observe the two LEDs with some system that compares the
modulated signal from the two in a nulling arrangement (for instance,
put an optical chopper wheel in front of one light path), then adjust
relative lengths of the optical paths (with a moving mirror).

Or, what about using a H field probe (i.e. something like a Rogowski
coil), fed back to a measurement system using resistive leads (377
ohms/square) that don't perturb the field.

If you have a LOT of RF power available for the test, you could use the
Faraday or Kerr effect to measure the magnetic field too.. Flint glass
has a Verdet constant of 0.11 radians/(Tesla*mm).
Rotation(radians) = V*B*l

Say your probe is 1mm long, and you can reliably measure a rotation of
0.11 radian (5-6 degrees), you'd need a field of 1 T, which is fairly high.
Biot-Savart is B=4piE-7*I/(2pi R) = 2E-7 *I/R
Say your probe is 1mm (1E-3m), to get 1T you'd need 1/2E-4 amps (5kA)..



Anyway... a sufficiently clever amateur probably does have equipment in
their shack that could be cobbled together to make this sort of
measurement, without needing exotic measurement gear.

(Mind you, having a fast sampling scope would make it easy).

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Tom Donaly wrote:
Many people over the years have done just fine loading their antennas
with lumped inductors.

That's not the point of this discussion, Tom. The
only question that needs to be answered here is:
Can a 2" dia, 100 T, 10" long loading coil have
a delay of 3 nS through it at 4 MHz? Do you support
such a technical absurdity? The Corum IEEE white
paper suggests that delay is in error by a magnitude.

All of the boundary test conditions given in Corum's
IEEE white paper are satisfied by a 75m bugcatcher
loading coil. There is no reason to believe that
the underlying principles of physics do not apply.
In fact, the diagram of the 1/4WL resonant system
looks exactly like a base loading coil, stinger,
and top hat as is used for 75m mobile operation.

Do you really believe that an antenna + loading coil has
to be a quarter wave long to resonate?
73,
Tom Donaly, KA6RUH

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Richard Clark wrote:
More mooching validation. You guys could collect more nickels if you
learned to doff your caps instead of engaging in your incessant
muttering.

The same could have been said of Galileo. Do you
suggest that technical absurdities go unchallenged?

You're not Galileo.
73,
Tom Donaly, KA6RUH

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Gene Fuller wrote:
Second, your analysis is utter rot! Are you suggesting that if the
coil can be made resonant at some frequency, and then you cut it in
half, that it still behaves the same?

No, it behaves approximately like half of the original
coil tending to have approximately the same Z0 and VF as
the original coil. The phase shift through the coil will
tend to be approximately 1/2 of the original phase shift -
not exact because of end effects.

Let's say we have a 1/4WL helical antenna with an obvious
phase shift of 90 degrees. If we cut that helical in half,
it is likely to have a phase shift of approximately 45
degrees, nowhere near the 4.5 degrees that W8JI has
"measured".

If we add a stinger to the above half-coil, we will have
a base-loaded antenna. The phase shift will be relatively
close to 45 degrees at the same frequency. The stinger
contributes another few degrees. The impedance discontinuity
between the coil and stinger contributes the rest of the
90 degrees of electrical length.

"Utter rot" is a pretty good description of this. Your problem is
that you've become so enamored of your little reflection theory that
you insist that only a set of transmission lines 90 degrees in total
length can resonate. Too bad your education isn't complete or you'd know
this isn't so.
73,
Tom Donaly, KA6RUH

Loading Coils; was : Vincent antenna
 

On 29 Nov, 08:36, Cecil Moore wrote:
Roy Lewallen wrote:
I see Cecil's temporarily run out of steam on his alternative theories
of transmission line operation and so has fallen back to his equally
imaginative pseudo-science of loading coils. I made and posted careful
measurements on this group long ago of a physically small coil to refute
some of the stranger claims being made.

Well, the subject was 75m bugcatcher loading coils", so your
choice of a "physically small coil" was already somewhat of
a straw man.

And Roy, you made the same mental blunder in your measurements
that Tom made. I have explained it to you before and you have
so far refused to listen or even read my postings so here it
is once again. Everyone is invited to think about what I am
saying and agree or attempt to refute it. Point by point:

A 1/4WL monopole over ground is known to be 90 degrees long.
The phase of the current changes by only a few degrees from
feedpoint to tip. How much phase shift (delay) in the current
would we measure in 30 degrees of a monopole? Answer: Only
one or two degrees. Why is there only a small number of degrees
of phase shift (delay) in the current in 30 degrees of monopole?
Because it is *standing-wave current* that is being used for
the measurement and the phase barely changes over the entire
monopole length.

EZNEC agrees. A 1/4WL monopole has 5.67 degrees of phase shift
in the current from segment 1 to segment 33 even though the
antenna is 90 degrees long and therefore has an inherent delay
of 90 degrees from feedpoint to tip. Standing-wave current
cannot be used to measure the delay through a wire.

So can that same *standing-wave current* be used to measure
the phase shift (delay) through a coil? Answer: No, standing
wave current cannot be used to measure the phase shift (delay)
through a wire or through a coil because the phase hardly
changes no matter how long is the delay through the coil or
through the wire (assuming coil and wire are 1/2WL).

Roy and Tom both used standing-wave current to try to measure
the delay through a coil. Such an attempt is doomed to failure
for obvious reasons and is a violation of the scientific method.

STANDING WAVE CURRENT CANNOT BE USED TO MEASURE PHASE SHIFTS
IN A WIRE OR IN A COIL BECAUSE STANDING WAVE CURRENT HAS
ESSENTIALLY NO PHASE SHIFT! THERE IS NO PHASE INFORMATION
IN STANDING WAVES!

There is absolutely no correlation between the phase of
standing-wave current and the delay through a coil or
through a wire.

What is the phase shift through a coil at self-resonance?
Answer: It is known to be 90 degrees at the first self-
resonant frequency, i.e. 180 degrees end-to-end.

What is the measured phase shift through that self-resonant
coil at the self-resonant frequency using standing-wave
current? Answer: That measured phase shift will be very
close to zero, nowhere near the known 90 degrees.
--
73, Cecil http://www.w5dxp.com

IF the coil windings are all exposed then I agree with you Cecil
But a dead horse will never get upregardless of the amount of
whipping.
Regards
Art

Loading Coils; was : Vincent antenna
 

Jim Kelley wrote:
From what is written there it's not possible to know exactly what he
measured.

Please read the rest of the material on his web site
concerning current flow through loading coils. He
made many more assertions and "measurements" using
standing-wave current.

I have no idea what 'standing wave current phase shift' is supposed to
mean. Standing waves obviously don't propagate, so naturally there
wouldn't be a propagation delay associated with them.

My point exactly yet standing-wave current is what
both W8JI and W7EL used to "measure" the phase shift
through a loading coil. It is exactly my point that
there is no phase shift associated with standing-
wave current in a coil or in a wire so it CANNOT
be used to "measure" phase shift. There is NO
phase information in the current used for the
W8JI and W7EL measurements. They both apparently
thought they were measuring traveling-wave currents
when the currents were actually overwhelmingly
standing-wave currents.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Jim Lux wrote:
I should think that many hams have things that can measure 3 ns (1000mm
light time), particularly in a repetitive system. That's one cycle at
300 MHz, or 36 degrees at 30 MHz.

The referenced W8JI 3 nS "measurement" was the delay
in a 2' dia, 100 T, 10" long loading coil on 4 MHz,
i.e. 4.5 degrees.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Tom Donaly wrote:

What is the characteristic impedance of Tom's coil?


A few thousand ohms. Use equation 50 at:

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

What's your formula for the velocity factor of Tom's coil? Is it from
the same Tesla coil crackpot you quoted in previous posts?


Do you reject all IEEE white papers? The formula
is equation 32.


Ahem...I'm quite familiar with that paper from work with Tesla coils,
and I have had some conversations a few years ago with Jim Corum.

That's a conference paper, so I wouldn't vouch for it's extensive peer
review.

The Corum's analysis is an attempt to fit transmission line behavior to
what is essentially a lumped system (Tesla coils can be very well
modeled as lumped systems). While the model is certainly valid within
their stated limitations, the real question that arises is "why". A
useful model makes useful predictions, and simple lumped models make
adequate predictions of tesla coil performance.

However, their analysis might have value for higher frequencies, where
the coil is a bigger fraction of a freespace wavelength. A typical
tesla coil runs at a few hundred kHz (lambda= 10-20 km), and a
positively huge one might have a secondary perhaps 2-3 meters long (i.e.
the coil is 1/10,000th wavelength long.
Furthermore, people HAVE made current measurements at the top and bottom
of a large tesla coil and found very small phase differences, indicating
that there is little or no deviation from a lumped model. One might
want to look at
http://www.abelian.demon.co.uk/tssp/

Compare this to a loading coil that is 30 cm long on an antenna for
40m: 1:120th wavelength.

Loading Coils; was : Vincent antenna
 

John Smith wrote:
Cecil Moore wrote:

AI4QJ wrote:

That is his "obvious" explanation. He should remove that from his
webpage as it is rather embarassing.


W8JI made a gross error in his measurement and
then tried to rationalize the impossible result.


Cecil:

How would you have like to be working at NASA, with this group; And, you
were the one responsible for not coverting kilometers to miles and
SMACKING that spacecraft we lost into Mars? ;-)


It wasn't km and miles, it was pounds and newtons AND
the error was that Lockheed Martin supplied the thrust data in pounds,
unlike the contractual requirement to supply it in Newtons (which is
what we at JPL have used for decades). The error wasn't caught because
the absolute magnitude of the force is very small, so the differences
from predict to observation were on the order of the measurement
uncertainty. (We're talking measuring the velocity to mm/sec and range
to mm, when its at Mars.)
I'd venture that anyone would find measuring distances to 1 part in 1E12
challenging...





Crud, I've volunteered on serving on those soup-lines, would hate to
have seen ya' there. chuckle

Regards,
JS