Cecil Moore wrote:

Someone reported being able to hear each individual large
snowflake. Could be that the amount of charge in a large
snowflake or a large piece of dust is magnitudes higher than
in a drop of rain, which I assume is the charge you are talking
about above. In any case, a very large number of particles
hitting around the same time could have a cumulative effect.
I personally have never heard P-static from rain but I think
I have seen it remembered on the bandscope on my IC-756PRO.

This study found that 20% of the observed charges were greater than 1.6
pC. Or, 80% were below 1.6 pC. At least it doesn't contradict your
hypothesis.

http://adsabs.harvard.edu/abs/1981PhDT.......149B
Collection of Electric Charge Information on Snowflakes in the Field.

73,

Chuck

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chuck wrote:
This study found that 20% of the observed charges were greater than 1.6
pC. Or, 80% were below 1.6 pC. At least it doesn't contradict your
hypothesis.

Let me make it clear that virtually all of my precipitation
static experience has been with wind-blown dust in the
Arizona desert with absolutely no personal experience
with snow static and very little with rain static. All I
know about snow and rain static is what I have read and
heard. Here in East Texas, rain is usually preceded by
lightning so precipitation noise from rain is hard to
detect. I think I saw it on the bandscope display of my
IC-756PRO the other day, didn't see any lightning or
hear any thunder but, of course, I can't say for certain.

However, I can say with certainty that precipitation static
from wind-blown dust can exist on a low humidity clear-sky
day and was somewhat proportional to wind speed. Changing
over from a bare-wire dipole to an insulated folded dipole
reduced the problem to a tolerable level. The folded dipole
was less noisy on dry windy days than a bare-wire dipole with
a 4:1 voltage balun (DC short) on the feedline. I can't swear
that corona didn't exist during receive, but I never saw any
glow at night even when I was transmitting 500 watts. Corona
should be less of a problem in low humidity like Arizona.
--
73, Cecil http://www.w5dxp.com

chuck wrote:
This study found that 20% of the observed charges were greater than 1.6
pC. Or, 80% were below 1.6 pC. At least it doesn't contradict your
hypothesis.

One other thought based on Richard C's comments:
Your calculation didn't take reflections in a resonant
antenna system into account which could cause the maximum
voltage to be a couple of magnitudes larger at the antinodes.
That assumes the burst of RF from the discharge is a few
cycles long at the resonant frequency. As an IEEE paper
says, resonance can cause "voltage magnification by coherent
spatial modes".
--
73, Cecil http://www.w5dxp.com

OK, lets try to model the fundamental phenomena we're talking about and
try to understand them in terms of simple electrostatic principles.

We start with these assumptions:

1. Vertical antenna of length l
2. Antenna grounded at base
3. Ideal RF current sensor at base (i.e., receiver)
4. Complete absence of electrostatic fields except from #5 below
5. A single negative charge Q that can be moved from infinity to actual
contact with the antenna.
6. Electromagnetic effects of a moving charge are not considered; they
do exist, of course, so reader beware.

We start by placing the charge Q at infinity so that there is no net
charge on the antenna.

As Q is brought near the antenna, its field will cause a redistribution
of charges on the antenna. Because the antenna is connected to the earth
at its base, a negative charge will flow into the earth from the
antenna. This will result in the antenna having a net positive charge Q'
such that |Q'||Q| (i.e., the closer the charge is to the antenna, the
smaller the difference between Q' and Q, and in the limit, they are
equal). The negative charge flowing to earth causes a current to be
detected by the RF current sensor at the base of the antenna.

As the charge moves closer and ultimately touches the antenna,
a movement of exactly -Q into the earth is completed, with the result
that the antenna once again has a net charge of zero and from the moment
of impact, no further charge redistributions or currents take place.

Note that in this model, the signal we hear is actually generated by the
approach of the charge, rather than by its actual physical presence on
the antenna. (Consider the effect of insulated wire with this model.)

This is the specific mechanism in the model by which a charge colliding
with the antenna causes a quantifiable current in the receiver. Our
objective is to get a handle on the waveshape (risetime, peak, etc.) of
this current; i.e., can it be detected by a receiver as a noise impulse?

The waveshape of the current pulse will be determined mainly by 1) the
magnitude of the charge; 2) the time required for the charge
redistribution to propagate through the antenna; and 3) the velocity
with which the charge approaches the antenna. We know the magnitude of
the charge by construction and assume propagation of the charge
redistribution (i.e., we are not talking about charge carrier drift) at
the speed of light.

The critical element, of course, is the velocity of the charge as it
approaches the antenna. The lower its velocity, the longer the risetime
of the induced current pulse. If Q is attached to a snowflake with a
velocity of one mile per hour, the current peak will be quite low
because the charge redistribution will occur over a relatively long time
period.

But if we assume the charge velocity is so high that the other factors
establish risetime, we can estimate some of the interesting pulse
parameters.

For example, if the antenna is conveniently 1/100 mile long and Q = 1
pC, we get a peak current on the order of 20 uA. If our receiver front
end is 50 ohms, that peak current would generate a 1 mV peak voltage
pulse with a negligible risetime. (Please check my arithmetic) I think
the model shows this to be the highest peak current attainable (under
quite unrealistic assumptions).

If the rise-time of the current pulse depends on the particle's
velocity, then it is not clear how that pulse's peak amplitude can be
increased. I'm not persuaded that resonance is relevant, particularly
since so much of the noise we are discussing is very broadband.

We can explore the number of charges that must arrive in some time
window to achieve a given combined pulse magnitude at the receiver.

First, however, someone who has not forgotten his math and physics
should algebraically relate pulse risetime and peak value to charge
velocity. Then we would have an indication of the detectability of a
single charge striking an antenna. We could predict the magnitude of the
charge and/or the velocity needed to achieve some specified signal level
at the input of the receiver. This relationship has not yet been
presented and without it, understanding of the possibility of
non-coronal precipitation static remains elusive.

Are there other approaches to quantitative demonstrations out there?
Does someone have an alternative model of how a charge striking an
antenna is translated into a detectable signal?

Have fun!

73,
Chuck



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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.
--
73, Cecil http://www.w5dxp.com

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? ;-)

73,

Chuck









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chuck wrote:
What is elusive is how the charges get changed into a
detectable signal.

Yes, there's a broad range of possible explanations.
One interesting theory is that uncharged particles
rubbing against an uncharged antenna results in a
triboelectric effect that, after contact, leaves the
antenna and particles with opposite charges. You might
call it the relativity theory of charged particles. :-)

Will you tell me again how we know that non-coronal p-static exists?

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?

In 1939, another C. Moore, W9LZX, solved the corona
problem at HCJB in Quito, Ecuador by inventing the
cubical quad antenna. Describing the problem with the
Yagi beam: "Gigantic corona discharges sprang full-
blown from the tips of the driven element and directors,
standing out in mid-air and burning with a wicked hiss
and crackle. The heavy industrial aluminum tubing used
for the elements of the doomed beam glowed with the
heat of the arc and turned incandescent at the tips.
Large molten chunks of aluminum dropped to the ground
as the inexorable fire slowly consumed the antenna. The
corona discharges were so loud and so intense that they
could be seen and heard singing and burning a quarter-
mile away from the station."

So Clarence Moore invented the cubical quad to solve
the corona problem. One must admit that the cubical
quad at least reduced the corona problem by many
magnitudes during transmit. One must also admit that
the corona problem during receive is magnitudes below
the problem during transmit. At some level, the air
ceases to be ionized and corona ceases to exist, by
definition. What can we conclude by applying the
principle of antenna transmit/receive reciprocity?

Comparing the Yagi to the cubical quad is similar to
comparing a single-wire 1/2WL dipole to a full-wave loop.
The ground referenced loop with its rounded corners
certainly reduces the corona threshold level. It is
possible that the loop is quieter *because* it is below
the corona threshold and the single-wire dipole is not.
Can we hear p-static on a full-wave loop? Yes, I have
heard it on a clear-sky, low-humidity, windy day in the
Arizona desert. Did it occur without ionization of the
air? There probably were no points (pun intended) in the
system conducive to corona discharge.

Obviously a qualitative argument rather than a quantitative
one but possibly valid nonetheless based on the Quito
experience.
--
73, Cecil http://www.w5dxp.com

"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.

"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.

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