"chuck" wrote in message
...
Cecil Moore wrote:
chuck wrote:
... understanding of the possibility of
non-coronal precipitation static remains elusive.

Please note that human understanding is not
necessary for something to exist and denying
its existence because of a lack of understanding
doesn't make it go away. It is what it is.

Nicely said, Cecil.

Hope you didn't get the impression I was denying the existence of
non-coronal p-static, or attempting to make it go away. But I hope you'll
agree that to be detected in a receiver, the static has to have a certain
amplitude. We know what that amplitude is and we know the kinds of charges
scientists have measured on precipitation as well as typical current
densities. What is elusive is how the charges get changed into a
detectable signal. Hardly metaphysics, and no more intended to attain
Human Understanding than the application of Ohm's law! ;-)

Actually, I was trying to provide a basis or framework within which
non-coronal static could be analyzed. Except for the unfortunate paragraph
with hypothetical numbers (the sad result of an embarrassing senior
moment) the rest seems a reasonable start.

Will you tell me again how we know that non-coronal p-static exists?
Without that information we need to say "It is what it is iff it exists",
no? ;-)

i have a feeling that what you will find is that the individual charges on
drops, flakes, and dust is too small to be detected by a normal amateur
receiver. However, the electric field that must accompany them is what
generates the corona effects that can be heard. Just think about it, how do
small particles get charged without also generating a larger bulk field?
The effect that charges the particles, be it dry friction from wind on dust,
or freezing and convection in clouds (any cloud, not just those with enough
charge to generate lightning) is not an individual particle effect, it
happens to many, many particles at once which cumulatively create a much
larger electric field than any one of them alone could create. And while
the charge transfer of small drops striking a conductor may not be enough to
stimulate a receiver the corona caused by the accumulated field over the
whole height of the structure can be significant.

"Cecil Moore" wrote in message
. ..
chuck wrote:
What is elusive is how the charges get changed into a detectable signal.

By definition, corona requires ionization of the air
which requires a certain current through the air, i.e.
at least a small arc. The question is, can p-static
exist and be heard below the corona threshold?

corona is not an 'arc', an arc is normally between two conductors. corona
is a local cascade breakdown in air as electrons are accelerated enough so
that when they colide with another molecule of the air they can knock off
more electrons. That is why there is a threshold voltage for corona
inception, below a given field strength the electrons can't gain enough
energy to sustain the breakdown. note that the shape of the conductor is
very important in this process also, a blunt smooth surface will produce
smaller fields and have a higher inception voltage than a sharp point
because the field gets concentrated more around the point and thus requires
a lower voltage to start corona breakdown.

What can we conclude by applying the
principle of antenna transmit/receive reciprocity?

in this case, nothing. the tx problem was because the rf voltage at the
antenna tips was high enough to cause corona on a massive scale. rf voltage
on a receiving antenna is miniscule and so can not be the source of
corona... this means other sources, not related to rf and the intended use
of the structure as an antenna, are the cause.

Dave wrote:
However, the electric field that must accompany them is what
generates the corona effects that can be heard.

Wouldn't the whole sky glow at night like the
Northern Lights if the entire dust cloud was
ionizing the air to the corona threshold?

The fair weather current doesn't meet the
corona threshold so how could corona occur
with a rounded full-wave loop under fair
weather conditions?
--
73, Cecil http://www.w5dxp.com

Dave wrote:
note that the shape of the conductor is
very important in this process also, a blunt smooth surface will produce
smaller fields and have a higher inception voltage than a sharp point
because the field gets concentrated more around the point and thus requires
a lower voltage to start corona breakdown.

So the sharp ends of a single-wire dipole would be more
conducive to corona than would a rounded full-wave loop.
Would you say that an antenna without corona is quieter
than an antenna with corona?
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
m...
Dave wrote:
However, the electric field that must accompany them is what generates
the corona effects that can be heard.

Wouldn't the whole sky glow at night like the
Northern Lights if the entire dust cloud was
ionizing the air to the corona threshold?

no, the field in the air is below the threshold. it is the concentrated
field around objects that cause the field to exceed the threshold.


The fair weather current doesn't meet the
corona threshold so how could corona occur
with a rounded full-wave loop under fair
weather conditions?

the fair weather current and the field that drives it is fairly small, not
normally enough to cause corona or we would be hearing it all the time.

"Cecil Moore" wrote in message
...
Dave wrote:
note that the shape of the conductor is very important in this process
also, a blunt smooth surface will produce smaller fields and have a
higher inception voltage than a sharp point because the field gets
concentrated more around the point and thus requires a lower voltage to
start corona breakdown.

So the sharp ends of a single-wire dipole would be more
conducive to corona than would a rounded full-wave loop.
Would you say that an antenna without corona is quieter
than an antenna with corona?

of course. we see that here all the time, the top antenna of a stack can be
very noisy with corona, but those lower down on the tower (even though they
are getting hit by the same rain/snow) are quiet.

Dave wrote:

i have a feeling that what you will find is that the individual charges on
drops, flakes, and dust is too small to be detected by a normal amateur
receiver. However, the electric field that must accompany them is what
generates the corona effects that can be heard. Just think about it, how do
small particles get charged without also generating a larger bulk field?
The effect that charges the particles, be it dry friction from wind on dust,
or freezing and convection in clouds (any cloud, not just those with enough
charge to generate lightning) is not an individual particle effect, it
happens to many, many particles at once which cumulatively create a much
larger electric field than any one of them alone could create. And while
the charge transfer of small drops striking a conductor may not be enough to
stimulate a receiver the corona caused by the accumulated field over the
whole height of the structure can be significant.


Charges can be accumulated on objects so as to produce a corona
breakdown in many ways. I think this is one of our fundamental starting
points and hopefully, was never in question. The separation of charges
can be accomplished by a variety of techniques, not all well-understood.

A moving cloud of charged particles can induce very large charges into a
grounded conductor. A sufficient concentration of charge at pointed
components of the conductor will produce a corona. The corona plainly
radiates "noise" that is detected by our receivers.

There is less certainty about whether an ungrounded conductor (say, an
unattached wire) can be made to produce a corona via electrostatic
induction. As I wrote in an earlier post in this thread, an ungrounded
conductor cannot be charged by an external field, but the distribution
of charges preexisting on the conductor can be affected by the field,
perhaps causing coronal discharges. I recall writing that uneven
discharges of the positive and negative "ends" of the conductor could
even leave the conductor with a net charge.

Your points are good ones, Dave, and worth keeping in mind.

73,

Chuck


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"chuck" wrote in message
...
Dave wrote:

i have a feeling that what you will find is that the individual charges
on drops, flakes, and dust is too small to be detected by a normal
amateur receiver. However, the electric field that must accompany them
is what generates the corona effects that can be heard. Just think about
it, how do small particles get charged without also generating a larger
bulk field? The effect that charges the particles, be it dry friction
from wind on dust, or freezing and convection in clouds (any cloud, not
just those with enough charge to generate lightning) is not an individual
particle effect, it happens to many, many particles at once which
cumulatively create a much larger electric field than any one of them
alone could create. And while the charge transfer of small drops
striking a conductor may not be enough to stimulate a receiver the corona
caused by the accumulated field over the whole height of the structure
can be significant.
Charges can be accumulated on objects so as to produce a corona breakdown
in many ways. I think this is one of our fundamental starting points and
hopefully, was never in question. The separation of charges can be
accomplished by a variety of techniques, not all well-understood.

A moving cloud of charged particles can induce very large charges into a
grounded conductor. A sufficient concentration of charge at pointed
components of the conductor will produce a corona. The corona plainly
radiates "noise" that is detected by our receivers.

There is less certainty about whether an ungrounded conductor (say, an
unattached wire) can be made to produce a corona via electrostatic
induction. As I wrote in an earlier post in this thread, an ungrounded
conductor cannot be charged by an external field, but the distribution of
charges preexisting on the conductor can be affected by the field, perhaps
causing coronal discharges. I recall writing that uneven discharges of the
positive and negative "ends" of the conductor could even leave the
conductor with a net charge.

Your points are good ones, Dave, and worth keeping in mind.

floating conductors can definitely create corona. this can be seen in
corona camera pictures of power line insulators and other hardware that is
insulated but still in the high field near a power line. even water drops
on insulators can cause corona in a very strong field. and even if you get
away from power line stuff, a leyden jar has an insulated conductor and it
can obviously be charged, as can aircraft... and if they accumulate enough
charge they can cause corona.

Dave wrote:
"chuck" wrote in message
...
Dave wrote:

i have a feeling that what you will find is that the individual charges
on drops, flakes, and dust is too small to be detected by a normal
amateur receiver. However, the electric field that must accompany them
is what generates the corona effects that can be heard. Just think about
it, how do small particles get charged without also generating a larger
bulk field? The effect that charges the particles, be it dry friction
from wind on dust, or freezing and convection in clouds (any cloud, not
just those with enough charge to generate lightning) is not an individual
particle effect, it happens to many, many particles at once which
cumulatively create a much larger electric field than any one of them
alone could create. And while the charge transfer of small drops
striking a conductor may not be enough to stimulate a receiver the corona
caused by the accumulated field over the whole height of the structure
can be significant.
Charges can be accumulated on objects so as to produce a corona breakdown
in many ways. I think this is one of our fundamental starting points and
hopefully, was never in question. The separation of charges can be
accomplished by a variety of techniques, not all well-understood.

A moving cloud of charged particles can induce very large charges into a
grounded conductor. A sufficient concentration of charge at pointed
components of the conductor will produce a corona. The corona plainly
radiates "noise" that is detected by our receivers.

There is less certainty about whether an ungrounded conductor (say, an
unattached wire) can be made to produce a corona via electrostatic
induction. As I wrote in an earlier post in this thread, an ungrounded
conductor cannot be charged by an external field, but the distribution of
charges preexisting on the conductor can be affected by the field, perhaps
causing coronal discharges. I recall writing that uneven discharges of the
positive and negative "ends" of the conductor could even leave the
conductor with a net charge.

Your points are good ones, Dave, and worth keeping in mind.

floating conductors can definitely create corona. this can be seen in
corona camera pictures of power line insulators and other hardware that is
insulated but still in the high field near a power line. even water drops
on insulators can cause corona in a very strong field. and even if you get
away from power line stuff, a leyden jar has an insulated conductor and it
can obviously be charged, as can aircraft... and if they accumulate enough
charge they can cause corona.



Hi Dave,

A leyden jar is, of course, a capacitor. It is charged by grounding the
outside, applying a charge to the inside conductor, and then removing
the ground. Hope I didn't cause anyone to suspect that a capacitor could
not be charged that way.

Recall that in electrostatic induction, we always ground the conductor,
bring a field near it, and then remove the ground connection. A net
charge then remains on the conductor even after the inducing field is
moved away.

Aircraft can be and are regularly charged by the triboelectric effect.
The issue I raised is whether they can be given a net charge by
immersion in an electric field.

I also tried to explain that it is possible for a floating conductor to
produce a coronal discharge without that conductor having a net charge,
and followed with the suggestion that the act of producing a
differential coronal discharge might itself result in a net charge on
the conductor, but the corona can be produced by the field even when the
conductor is not charged. Your power line example may be a good example
of coronal discharge of a floating conductor in a strong field, but we
probably don't know if it ever had a net charge on it due to the field.

Hope this clarifies my thoughts a little. ;-)

73,

Chuck




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On Mon, 25 Dec 2006 23:10:00 -0600, Cecil Moore
wrote:

chuck wrote:
... understanding of the possibility of
non-coronal precipitation static remains elusive.

Please note that human understanding is not
necessary for something to exist and denying
its existence because of a lack of understanding
doesn't make it go away. It is what it is.

Amen, Cecil!

Anyone who has lived in central Texas and is an active ham has
experienced all sorts of extraordinary noises....corona discharges,
precipitation static, and others.... which can be experienced on a
clear day, cloudy day, rainy day, dusty day....though I would hasten
to add that the most dramatic noise performances occurred with an
approaching weather front of some kind and *are* probably corona
discharges. Other noises that I experienced while trying to work DX
were not so easily identifiable as corona.

I haven't experienced the same noises here in Virginia. Here, I get
little in the way of warning, other than normal crashes of static,
before hearing a loud *bang* of thunder indicating that I should
disconnect aerials and vacate the shack!.

One other empirical data point...all of the above mentioned noises
were *dramatically* reduced when switching from plumbers-delight, yagi
antennas to closed loop, cubical quads. Always. Despite the fact
that many have insisted that quads aren't "quieter" than yagis, it's
my story and I'm sticking to it. I use yagis now. If I lived in
Texas, I would probably be using quads again.

73,

Ken K4XL


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