Topband: corona noise

[Tom W8JI]

> What is "a lot taller"?
>

I can't answer that question specifically. It varies with e-field conditions 
and the type of antennas and structures.

The corona is a micro power noise generator so it radiates noise, and the 
target has to neutralize the field near other points so they don't break 
into corona.

> Would an aluminum or steel (or combination) mast extension with pointed 
> tip, extending say 10-20 feet above the top beam -- let's say one for 
> 20m -- help to reduce corona discharge noise in the top beam?
>

It should. I always put a sacrificial vertical of some type above my 
antennas for that reason, and to keep lightning off antenna element tips. 
The "rule of guess" I use is the target I use is over twice the antenna 
element radius length above the antenna. It seems to work here.

When we took Bill Fisher's antennas down at his mountain QTH, his top 
antennas had element tips eaten up from lightning and corona. Antenna 
elements just 10-20 feet lower were clean.

I played with this stuff a great deal in Ohio because my old two-way 
business had marine repeaters along the lake. Corona noise, right when ships 
and other services needed communications the most, could be severely 
hampered by p-static. Sharp points, like frayed ends of guylines, aggravated 
noise problems when antenna were around the guyline. I could climb the 
towers and hear the frayed or splayed guyline ends making the exact same 
acoustical noise pitch as the RF noise bothering antennas.

The only way to cure it is to stop the corona (which means it moves 
somewhere else, usually) through rounded ends or by adding a taller leak or 
target that is away from the antenna. Changing antenna types, grounds or 
grounding, DC feedline paths....none of that actually helped. The repeater 
systems had DC grounded hi-Q cavities, and noise was exactly the same with 
or without the cans. The same is true here at the house, where antenna with 
or without element grounding are all basically the same, although I do 
mitigate internal cable voltage buildup.

73 Tom