Dave wrote:


the noise is caused by corona on the antenna due to the electric field
between the ground and cloud. this field can be many thousands of kv per
meter which is enough to cause sharp points and tips of elements to generate
corona which makes the hiss and pop noises.



Hi Dave,

Yeah, that's another hypothesis. One might even be led to reason that
insulation would prevent these corona discharges. Yet, it is quite easy
to charge a grounded antenna (completely insulated) with the electric
field that exists between the ground and clouds (or air masses).

So we have at least two candidate causes for what is called by some
"precipitation static": charged particles physically impinging on the
antenna wire; and electrostatically induced charges that produce corona
discharges. Are there others? Can both processes occur simultaneously?
Are the two processes simply different paths to the same end: corona
discharges?

Do we have a way to test these competing hypotheses?

73,

Chuck

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


the noise is caused by corona on the antenna due to the electric field
between the ground and cloud. this field can be many thousands of kv per
meter which is enough to cause sharp points and tips of elements to
generate corona which makes the hiss and pop noises.



Hi Dave,

Yeah, that's another hypothesis. One might even be led to reason that
insulation would prevent these corona discharges. Yet, it is quite easy to
charge a grounded antenna (completely insulated) with the electric field
that exists between the ground and clouds (or air masses).

So we have at least two candidate causes for what is called by some
"precipitation static": charged particles physically impinging on the
antenna wire; and electrostatically induced charges that produce corona
discharges. Are there others? Can both processes occur simultaneously? Are
the two processes simply different paths to the same end: corona
discharges?

Do we have a way to test these competing hypotheses?

the easiest test is done for us, all we have to do is observe.
'precipitation' static can occur without rain or snow, and it sounds exactly
like the noise when there is rain or snow... so i say the corona effect is
the major cause and any effect from charged particles is secondary and much
smaller.

chuck wrote:
Dave wrote:


the noise is caused by corona on the antenna due to the electric field
between the ground and cloud. this field can be many thousands of kv
per meter which is enough to cause sharp points and tips of elements
to generate corona which makes the hiss and pop noises.



Hi Dave,

Yeah, that's another hypothesis. One might even be led to reason that
insulation would prevent these corona discharges. Yet, it is quite easy
to charge a grounded antenna (completely insulated) with the electric
field that exists between the ground and clouds (or air masses).

So we have at least two candidate causes for what is called by some
"precipitation static": charged particles physically impinging on the
antenna wire; and electrostatically induced charges that produce corona
discharges. Are there others? Can both processes occur simultaneously?
Are the two processes simply different paths to the same end: corona
discharges?

Do we have a way to test these competing hypotheses?

73,

Chuck

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You can easily charge up an insulator with a static charge. A comb is
usually made out of an insulating material. Run one through some hair
and it will pick up small pieces of paper. (I use my wife's hair.)
Secondly, particles don't have to be charged to create a charge on
an antenna. They just have to touch it and be pulled off. Google
triboelectricity. (I think I spelled that right. If I didn't, ask
Cecil how it's spelled. He knows.) Yes, there is more than one way to
charge an object to the point of creating corona discharge. Make a
small Van de Graf generator and try that. You also might want to
charge up an insulator (your comb), touch it to your antenna, and
measure how much charge was actually transferred to the antenna.
Discharging insulators is sometimes difficult because they're, well,
insulators and charge doesn't move around on them readily. Sometimes
you have to use Polonium 210, or a torch, or a specially built
fan to accomplish this. (You can buy a Polonium brush. The manufacturer
warns against taking it apart to see how it works, though.)

Make a homemade field mill and measure the earth's electric field
during a time when there's corona discharge from your antenna. A large
natural electric field from a big, honking thundercloud could easily
cause coronal discharge on your antenna under those circumstances.
There are lots of things a dedicated amateur can do to measure static
electricity, and, if he doesn't get killed, the effort is worth it.
Just making up theories out of the clear blue, however, without any
attempt to test them, is just a waste of time.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:


You can easily charge up an insulator with a static charge. A comb is
usually made out of an insulating material. Run one through some hair
and it will pick up small pieces of paper. (I use my wife's hair.)
Secondly, particles don't have to be charged to create a charge on
an antenna. They just have to touch it and be pulled off. Google
triboelectricity. (I think I spelled that right. If I didn't, ask
Cecil how it's spelled. He knows.) Yes, there is more than one way to
charge an object to the point of creating corona discharge. Make a
small Van de Graf generator and try that. You also might want to
charge up an insulator (your comb), touch it to your antenna, and
measure how much charge was actually transferred to the antenna.
Discharging insulators is sometimes difficult because they're, well,
insulators and charge doesn't move around on them readily. Sometimes
you have to use Polonium 210, or a torch, or a specially built
fan to accomplish this. (You can buy a Polonium brush. The manufacturer
warns against taking it apart to see how it works, though.)

Make a homemade field mill and measure the earth's electric field
during a time when there's corona discharge from your antenna. A large
natural electric field from a big, honking thundercloud could easily
cause coronal discharge on your antenna under those circumstances.
There are lots of things a dedicated amateur can do to measure static
electricity, and, if he doesn't get killed, the effort is worth it.
Just making up theories out of the clear blue, however, without any
attempt to test them, is just a waste of time.
73,
Tom Donaly, KA6RUH

Hi Tom,

Don't know toward whom your post was directed, but I'll comment anyway
--if that's OK. ;-)

I'm quite comfortable with your statements on electrostatics. Regarding
theories and testing, however, there is perhaps more to be said. A lot
of anecdotal evidence of p-static has been described, more or less
roughly, in the group. That's really great. But before meaningful tests
can be designed, I think an attempt at understanding the mechanisms
behind the various p-static reports should be explored. A big part of
the problem is that we probably can't cause the p-static to appear on
command in our testing laboratories! Moreover, we are pulling stuff out
of the air if we believe all reported cases of p-static arise from
similar conditions. In more blunt language, I most humbly suggest we
seem to be having difficulty understanding what is going on and I hope
that the more it is discussed the more likely we can achieve closure.

We have, if I am following correctly, at least two suggested causes for
the observed phenomena. Charge impingement and electrostatic induction.
Yeah, they're both electrostatic actions, but very different. They can
even occur simultaneously, which adds additional complication. Moreover,
we're concerned with an electrodynamic consequence (a current in the
receiver input circuit) of some electrostatic event(s).

It is beginning to appear that in some minds, these two explanations are
merging: both can cause coronal discharges. I am somewhat skeptical
about the induction mechanism, at least in the case of an insulated
wire. Here is why: if the field is strong enough to cause coronal
discharge of an insulated conductor, it will also cause coronal
discharge of almost everything in the vicinity. I think a very strong
field would be required for that to occur, surely much more than 10
KV/meter. Didn't W8JI describe something like that with discharges from
trees?

Electrostatic induction will not generally transfer a charge to an
ungrounded conductor. It will simply redistribute the free charges
thereon so as to render the net field within the conductor zero. In
other words, only charged object(s) brought into direct contact with the
conductor will impart a charge. An electroscope comes to mind: bringing
a charged comb near the electroscope will cause the leaves to fly
outward, but no charge is transferred; the comb (i.e., its field) merely
redistributes the charges preexisting on the electroscope.

For a grounded wire antenna (even one grounded through the 50 ohm input
impedance of the receiver), there is a vast supply of charges that can
be "induced" by charged clouds into the conductor from the earth itself.
All the free charges in the wire (rather than 50%(?) of them in the
insulated case?) may make coronal discharges possible at lesser field
strengths.

I hope we can continue to kick this around.

73,
Chuck NT3G




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chuck wrote:
So we have at least two candidate causes for what is called by some
"precipitation static": charged particles physically impinging on the
antenna wire; and electrostatically induced charges that produce corona
discharges.

Precipitation static requires static transferred from charged
particles of rain, snow, or dust. Corona requires the ionization
of air. These two phenomena can exist together or separately.
Ionization of air requires a certain threshold. Precipitation
static can exist either below or that threshold or be the cause
of the corona. Corona can exist in the absence of precipitation
static. There are other kinds of static, e.g. propagating EM
static from numerous sources.
--
73, Cecil, w5dxp.com

chuck wrote:

Hi Tom,

Don't know toward whom your post was directed, but I'll comment anyway
--if that's OK. ;-)

I'm quite comfortable with your statements on electrostatics. Regarding
theories and testing, however, there is perhaps more to be said. A lot
of anecdotal evidence of p-static has been described, more or less
roughly, in the group. That's really great. But before meaningful tests
can be designed, I think an attempt at understanding the mechanisms
behind the various p-static reports should be explored. A big part of
the problem is that we probably can't cause the p-static to appear on
command in our testing laboratories! Moreover, we are pulling stuff out
of the air if we believe all reported cases of p-static arise from
similar conditions. In more blunt language, I most humbly suggest we
seem to be having difficulty understanding what is going on and I hope
that the more it is discussed the more likely we can achieve closure.

We have, if I am following correctly, at least two suggested causes for
the observed phenomena. Charge impingement and electrostatic induction.
Yeah, they're both electrostatic actions, but very different. They can
even occur simultaneously, which adds additional complication. Moreover,
we're concerned with an electrodynamic consequence (a current in the
receiver input circuit) of some electrostatic event(s).

It is beginning to appear that in some minds, these two explanations are
merging: both can cause coronal discharges. I am somewhat skeptical
about the induction mechanism, at least in the case of an insulated
wire. Here is why: if the field is strong enough to cause coronal
discharge of an insulated conductor, it will also cause coronal
discharge of almost everything in the vicinity. I think a very strong
field would be required for that to occur, surely much more than 10
KV/meter. Didn't W8JI describe something like that with discharges from
trees?

Electrostatic induction will not generally transfer a charge to an
ungrounded conductor. It will simply redistribute the free charges
thereon so as to render the net field within the conductor zero. In
other words, only charged object(s) brought into direct contact with the
conductor will impart a charge. An electroscope comes to mind: bringing
a charged comb near the electroscope will cause the leaves to fly
outward, but no charge is transferred; the comb (i.e., its field) merely
redistributes the charges preexisting on the electroscope.

For a grounded wire antenna (even one grounded through the 50 ohm input
impedance of the receiver), there is a vast supply of charges that can
be "induced" by charged clouds into the conductor from the earth itself.
All the free charges in the wire (rather than 50%(?) of them in the
insulated case?) may make coronal discharges possible at lesser field
strengths.

I hope we can continue to kick this around.

73,
Chuck NT3G




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Hi Chuck,
Read "Meteorological Aspects of Precipitation Static" By
Lieutenant Robert C, Edwards, U.S.N.R., and Captain George W. Brock,
U.S.A.A.F. from the Journal of Meteorology, Vol. 1, Number 4,
December, 1945. If you Google "Precipitation Static" you can
find a pdf file of it. They actually went up in three different
airplanes, an RB-37, a B-25D, and a B-17G and did some measurements.
You might be interested in their methods and conclusions.
73,
Tom Donaly, KA6RUH

Cecil Moore wrote:

chuck wrote:

So we have at least two candidate causes for what is called by some
"precipitation static": charged particles physically impinging on the
antenna wire; and electrostatically induced charges that produce corona
discharges.


Precipitation static requires static transferred from charged
particles of rain, snow, or dust. Corona requires the ionization
of air. These two phenomena can exist together or separately.
Ionization of air requires a certain threshold. Precipitation
static can exist either below or that threshold or be the cause
of the corona. Corona can exist in the absence of precipitation
static. There are other kinds of static, e.g. propagating EM
static from numerous sources.
--
73, Cecil, w5dxp.com


Many declarative sentences, Cecil, but you're wrong, as usual.
When are you going to actually do some meaningful experiments to
find out whether you're right or not?
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:


Hi Chuck,
Read "Meteorological Aspects of Precipitation Static" By
Lieutenant Robert C, Edwards, U.S.N.R., and Captain George W. Brock,
U.S.A.A.F. from the Journal of Meteorology, Vol. 1, Number 4,
December, 1945. If you Google "Precipitation Static" you can
find a pdf file of it. They actually went up in three different
airplanes, an RB-37, a B-25D, and a B-17G and did some measurements.
You might be interested in their methods and conclusions.
73,
Tom Donaly, KA6RUH

Hi Tom,

Thanks for the reference. Quite an interesting article.

My one problem with it after a quick reading is their
autogenous/exogenous electrification dichotomy. More particularly, their
notion of exogenous electrification, which " . . . occurs when an
aircraft flies through electric fields previously established by a
charge separation in the free atmosphere."

Not sure it is important to the physics exactly how the electric field
was established, but taking the airplane to be an isolated conductor in
an electric field, I wonder how "electrification" can take place.

Perhaps 60 years ago we used different terminology, but electrification
usually refers to contact charge separation. Since there is no assumed
contact with charged particles in the exogenous electrification mode,
electrification may be a misnomer today. As I suggested in an earlier
post, all an electric field can do to an isolated conductor is
redistribute the charges preexisting on the conductor. Of course if the
redistribution of charges leads to coronal discharges favoring either
the positive or negative "end" of the plane, then the plane could
acquire a non-zero net charge (i.e., be electrified). The authors don't
give a hint that this is what was envisioned, though.

I'd appreciate comments on whether such a thing as "exogenous
electrification" as described by the authors makes sense to anyone else.

73.

Chuck
NT3G


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On Sat, 23 Dec 2006 03:38:18 GMT, "Tom Donaly"
wrote:

Cecil Moore wrote:
propagating EM static
--
you're wrong, as usual.

Hi Tom,

But always entertaining if you haven't heard the joke before [rare].

73's
Richard Clark, KB7QHC

Tom Donaly wrote:
Many declarative sentences, Cecil, but you're wrong, as usual.
When are you going to actually do some meaningful experiments to
find out whether you're right or not?

Where are your experiments that prove you right and me
wrong? Where are your references for such?

All the experimentation has already been done by others,
Tom, and pretty well documented in publications available
on the web including a host of governmental and university
publications so I would be wasting my time. It is possible
that I misunderstood something but impossible that there
has not been enough experimentation. Wishing that all static
is caused by ionization of the air is just a pipe dream. There
would probably never be enough precipitation static on a
well-designed folded dipole to result in ionization of the air
but certainly enough to hear in a receiver.
--
73, Cecil, w5dxp.com