On 9/7/2011 11:47 AM, Richard Clark wrote:
On Wed, 07 Sep 2011 10:48:55 -0700, Jim
wrote:

but just the clear sky current could provide some charging.

There is a earth-sky current in the femtoamperes per cm² that has a
constant potential gradient on the order of 600V/m (or something like
that). This current is the return path for all lightning strike
charge transfers, world-wide.

a few pA/sq meter and a kV/meter field is how I always remember it (in
round numbers) It's small, that's true.


Few dipoles are co-planar, parallel wrt ground.

Actually, humidity doesn't affect the charging all that much. What
humidity affects is the leakage current across dirty insulators.

Which could easily overwhelm this femtoampere charge where a gigaOhm
leakage is trivial (zealous Hams using teflon technology?).

Well.. Consider a 20 meter long wire hanging 10 meters above the
ground (half a 80m dipole) so now you're talking tens of pA, 100 Meg
isolation isn't hard to get with clean insulators. That 20 m wire is
like a 850 pF capacitor. If assume, say, 25 pA charging current, you
get a volt every 42 seconds. After half an hour or so, you're up to 40
volts or so..

Granted it's not a lot of Joules.. (heck, probably not even a microjoule)..

So fair weather charging isn't likely to kill your MFJ..

Back to the dust/rain/induction charging, which can certainly get the
levels needed.