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