Topband: Rain static

[Guy Olinger K2AV]

A morph on the original subject.

Rain static on stacked beams on a tower is often reported with this
pattern:  Rain static on the top beam is high, whereas it is low or
non-existent on the lower.  Since the upper beam can hardly shield the
lower beam from getting wet in the rain, it cannot be that the drops are
charged.

Even if they are charged at height, while they are falling, they are in
constant contact with saturated air and will equalize on the way down.  Try
to maintain static charge on an object in steam from a hot shower.

When high beam yes, low beam no, rain static is being observed....

What is differentiating the two beams is the characteristic of high voltage
opposite charges to accumulate charge on the structure which is closest to
the opposite source of charge, e.g. sky in this discussion.  Thus the upper
beam, being closest to the sky on a complex conductive structure (tower and
all its stuff) will be carrying the charge.  The raindrop is neutral, and
at touching, accumulates a tiny charge from the metal, which because of our
oh-so-sensitive receivers is audible.

Another aspect of this system is that for purposes of creating static, the
tower must be grounded by some method (usually true unless specifically
insulated), to allow the flow of opposite charge from the ground to the
highest metallic system, which in turn must not be effectively insulated
from the tower or from directly touching the rain.

Complete insulation from the rain will minimize static on beverages, as
*sometimes* does forest high overhead, as the charge max is well overhead.
Loblolly pine in my little forest seems highly conductive.  Lightning
selects the loblollies.  Nine of the last ten dead trees I have had cut
down are lightning struck loblollies, lightning-selected out of a mix of
loblolly, oak, poplar, maple, sweet gum, etc. The other was a poplar 30
feet higher than the rest of the crown.

If the method of feed and termination does not allow the beverage (either
kind) to see ground, then there is no way for the earth charge to migrate
to the beverage wire, the wire will not charge the drops at contact, and it
will be silent.

My 160 3/8 wave inverted L (up 95, out 105) is isolated by the high voltage
isolation transformer (double polyimide plus teflon sleeve) from any
charging ground, and most of the wire is PE insulated #12 stranded.  The
FCP is at 8-10 feet, 90 feet below the area tree crown.  Three separate
methods of isolation are at work.

My tribander, at the other end of the lot on the tower, gets rain/snow
static a-plenty. The driven element has a DC path to "local" ground via the
feedline.  It has a bead balun that came with the beam, nothing that
isolates DC.

The wire/aluminum is the villain, not the raindrop. The raindrop was just
minding its own business floating down until it got zapped by a pesky piece
of antenna.

73, Guy

On Thu, Jun 13, 2013 at 11:42 AM, K9AY <k9ay at k9ay.com> wrote:

> All of my bare wire Beverages experience rain or snow static. Those with
> insulated wire -- whether BoG or above ground -- do not. Snowflakes and
> raindrops take on a charge in the clouds and discharge on contact with a
> conductor. Snow static seems to be consistently bad; rain varies.
>
> Gary
> K9AY
>
>
>
> From: "Bruce" <k1fz at myfairpoint.net>
> To: <topband at contesting.com>
> Subject: Topband: BOG antenna
>
> Noticed many storms have caused rain static on every ham antenna except my
> BOG. The BOG was very quiet and hearing stations in its normal manner.. I
> did hear a slight trace of something in there, one time when the noise was
> screaming on other antennas. Another local 160 meter DXer reported similar
> reception on his BOG.  Wonder how many others have observed the same?
>
> Thanks in advance,
> 73
> Bruce-K1FZ
> All good topband ops know how to put up a beverage at night.
> _________________
> Topband Reflector
>