folded dipoles
 

On Sat, 23 Dec 2006 10:02:20 -0500, chuck wrote:

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.

Hi Chuck,

The author wasn't particularly interested in the electrification as he
was the conduction and subsequent discharge. In actuality, what is
described as exogenous electrification is no different from
autogenous. The air currents described simply convect smaller
particles as has been described in subsequent years in other aviation
material starting with "Atmospheric Electricity," Chalmers, J.A. -
1967; or earlier with "The Fair Weather Atmospheric Electric Potential
and its Gradient," Clark, J.F. 1958.

Normal convection builds up a charge stratification on the order of
190 V/m at ground level, but declines to half that a mile up. At that
same mile altitude (above ground level) charge density increases
1000%.

Needless to say, aircraft at different altitudes in identical, clement
weather are subject to vastly different fields.

73's
Richard Clark, KB7QHC

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Richard Clark wrote:


Hi Chuck,

The author wasn't particularly interested in the electrification as he
was the conduction and subsequent discharge. In actuality, what is
described as exogenous electrification is no different from
autogenous. The air currents described simply convect smaller
particles as has been described in subsequent years in other aviation
material starting with "Atmospheric Electricity," Chalmers, J.A. -
1967; or earlier with "The Fair Weather Atmospheric Electric Potential
and its Gradient," Clark, J.F. 1958.

Normal convection builds up a charge stratification on the order of
190 V/m at ground level, but declines to half that a mile up. At that
same mile altitude (above ground level) charge density increases
1000%.

Needless to say, aircraft at different altitudes in identical, clement
weather are subject to vastly different fields.

73's
Richard Clark, KB7QHC

Hi Richard,

Thanks for the second opinion and additional information. I agree with
your interpretation.

73,

Chuck

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folded dipoles
 

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

Exactly. Thank you, Cecil. There are many physical mechanisms for
generating natural electrical noise. Ask any radio astronomer.

73, Jim AC6XG

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Cecil Moore wrote:

.. . .


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


Hi Cecil,

Though I must seem to be coveting the dead-horse-beating trophy, have
you found an explanation of how the relatively low average currents that
charged precipitation imparts to an antenna cause static? My back of the
envelope calcs showed nanovolt-level signals at the receiver from this
current. Clearly, adding charges could eventually result in a corona,
but how does the typical current density found in a storm result in
measurable (i.e., readily detectable) signals at the receiver front-end
when no coronas are present? As I asked in an earlier post, is there a
relaxation mechanism somewhere in the antenna/receiver system? Where?
What determines its time constants?

Are the reported current densities wrong (i.e., not representative of
the conditions under which non-coronal p-static is typically developed)?
Is p-static somehow anomalous in that it is not found in all storms with
charged precipitation?

The coronal mechanism is understandable to me, but the non-coronal
p-static leaves me needing a better explanation than I have been able to
find.

A special thanks to you for helping to keep the group lively and
interesting, Cecil!

73,

Chuck
NT3G




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Here's a link to a brief Navy document (gotta be true!) that gives a
simple overview of noise. It claims coronal discharges are the principal
cause of precipitation static. No mention, however, of any other,
non-principal causes.

http://www.globalsecurity.org/milita...14030_ch10.pdf
14030_ch10.pdf (application/pdf Object)

Evidently, aircraft encounter current densities between 50-300 A/square
meter, while typical current densities near the ground from charged
precipitation are on the order of 1 uA/square meter. That's quite a few
orders of magnitude difference.

http://www.jya.com/mil-std-464.htm
MIL-STD-464


Chuck

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On Sun, 24 Dec 2006 08:31:56 -0500, chuck wrote:

My back of the
envelope calcs showed nanovolt-level signals at the receiver from this
current.

Hi Chuck,

From the nature of your questions that follow, your envelope appears
to be insufficient to cover the topic.

Clearly, adding charges could eventually result in a corona,
but how does the typical current density found in a storm result in
measurable (i.e., readily detectable) signals at the receiver front-end
when no coronas are present? As I asked in an earlier post, is there a
relaxation mechanism somewhere in the antenna/receiver system? Where?
What determines its time constants?

There are two mechanisms at work, and they are classically the source
and the load. The source imparts an impulse, the load provides a
complex response. Any impulse's origin is the arrival of a charge.
The load (the antenna feeding the receiver) is very large in
comparison to the volume of charge arriving and all impulses are not
coherent.

Your nano-volt determination appears to neglect the accumulation of
charges which, in turn, does not take into account the reactance of
the load (there has to be a considerable mismatch involved here).

73's
Richard Clark, KB7QHC

folded dipoles
 

chuck wrote:
Though I must seem to be coveting the dead-horse-beating trophy, have
you found an explanation of how the relatively low average currents that
charged precipitation imparts to an antenna cause static? My back of the
envelope calcs showed nanovolt-level signals at the receiver from this
current.

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

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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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Cecil Moore wrote:
...

Makes you wish we could shoot 'em through a darn cloud chamber! grin

Regards,
JS

folded dipoles
 

Richard Clark wrote:

There are two mechanisms at work, and they are classically the source
and the load. The source imparts an impulse, the load provides a
complex response. Any impulse's origin is the arrival of a charge.
The load (the antenna feeding the receiver) is very large in
comparison to the volume of charge arriving and all impulses are not
coherent.

Your nano-volt determination appears to neglect the accumulation of
charges which, in turn, does not take into account the reactance of
the load (there has to be a considerable mismatch involved here).

73's
Richard Clark, KB7QHC

I'm not sure of the numbers involved, but as someone who has lived in a
300 inch of snow per season and storms with up to 10 inch/hour plus high
winds, that snow static is real and a real pain in the ass. It makes
small pops as it hits, and eventually you will hear a large amount of
noise apparently from discharge. Dependant on antenna type, etc.

I have no experience with dust.

tom
K0TAR