[TowerTalk] Rain static

[Jim Lux]

At 10:48 PM 8/31/2005, Michael Tope wrote:

>----- Original Message ----- From: "Jim Lux" <jimlux at earthlink.net>
>
>>Here's a question.  Is the pitch of the musical note constant regardless of
>>where you are tuned within a band?  That is, is the signal RF, or just AF
>>impulses that are broadband RF.
>
>Jim,
>
>The percipitation noise that I have heard has always been broadband
>RF impulses (e.g. pitch doesn't change with VFO frequency).


That would be consistent with charged drops (or snowflakes or dust 
particles) that hit the "thing" and steadily deposit charge.  The voltage 
builds up, and periodically discharges.

In airplanes (which use AM radios), this is the general mechanism for P-static.
The "static dissipating wicks" you see at the ends of the wings are an 
attempt to reduce the problem by making many small discharges, a long way 
from the radio antenna, rather than periodic big discharges.

The "frequency" of the discharges (I've head it audibly as a buzzing sound) 
is related to the charging rate, which in turn is going to be some sort of 
complex combination of the particle rate and the amount of charge on each 
particle, which is exceedingly difficult to predict.

For instance, the charge on rain drops can vary pretty substantially, 
depending on what part of the storm they came from, or even in a 
non-electrified storm, depending on the droplet size (which limits the 
maximum charge) and how far they fell.

There are people who actually build toys to measure this kind of think.  A 
wire outside connected to a NE2 neon bulb with the other terminal of the 
NE2 grounded.  It blinks periodically, with the blink rate proportional to 
the charging rate.

I'll pose the question to someone at work who actually knows a lot about 
droplet electrification and see if he has a plausible explanation for Tom's 
observation about higher antennas having more problems than low antennas.


>Mike, W4EF.....................................