Rain "static" on a dipole ... what causes it

[Joe Fitter BV/N0IAT]

Been meaning to ask this question for a while now..

I notice that my 2 element spider quad, and a 20 meter dipole both
exhibit s-9 rain induced static. The static is not like static
crashes, but a constant s-9 noise. No NB is able to cure this
problem. The 3 element, aluminum yagi does not experience this
kind of static. It makes no difference whether the clouds are
charged electrically, or, if it is just a constant steady rain.

When the rain stops...so too does the noise.

So, now for the $2 question: why does this happen?

I suspect the HF yagi is matched via gamma match or some other approach
that puts the entire driven element at dc ground. I know the dipole is
not shunt to ground, nor is the quad. Am I getting close?

or, some other near vicinity item is creating the static only when
the rain falls and getting into the quad and dipole but not effecting
the aluminum yagi.

Any ideas?

Joe

[R. Bruce Winchell]

Joe,
I'd be willing to bet that the wire on your quad and dipole are of the
open stranded variety. The corrosion along the length of the wire will
increasingly worsen and the corrosion becomes a zillion little capacitors
that stores static energy from friction and atmospheric
electrical activity. When this discharges, you get noise. The rain may
have a different ionic polarization and this makes the entire situation
worse. Recommend you go to solid enameled wire on your quad and an
insulated wire on your dipole. This stops the corrosion effect. RF does
not "see" the insulation or enamel. 73 KC8ARO Bruce

[W8JI Tom]

Hi Joe,

In article <4ep58c$3...@tilde.csc.ti.com>, Joe Fitter BV/N0IAT
<joe...@transend.com.tw> writes:

>So, now for the $2 question: why does this happen?
>
>I suspect the HF yagi is matched via gamma match or some other approach
>that puts the entire driven element at dc ground. I know the dipole is
>not shunt to ground, nor is the quad. Am I getting close?

If the noise is a high pitiched sizzle that gets worse and the pops and
disappears when lighting flashes, it is from corona discharge. Tiny
streamers trail from your antenna into the air. This is most noticable
with high antennas using thin or pointed conductors. Sharp point increase
the charge concentration and increase the occurance of streamers (or
corona) in a storm.

The cure is blunt, thick conductors and keeping the antenna close to the
ground. Thick unbroken insulation will also help distribute the charge.

>or, some other near vicinity item is creating the static only when
>the rain falls and getting into the quad and dipole but not effecting
>the aluminum yagi.
>

That's possible, or perhaps it's because the yagi is a thicker and
smoother conductor. Less voltage gradient (charge concentration at sharp
points), less corona.

73 Tom

[Joe]

Hi Bruce, Thanks for the tip. Actually, the Quad and the Dipole are
both made from insulated stranded copper wire. Interesting bit on
the stranded versus solid wire, though. Perhaps this is occuring even
though the wire is insulated by black and red pvc. I'll try changing
the wire and see what happens.

Thanks,

Joe