To: <towertalk@contesting.com>
> Date: Tue, 05 May 1998 00:03:23 +0000
> From: David Robbins <k1ttt@berkshire.net>
Hi Dave ,
> > create a smooth ball made out of an ion cloud...and noise from audio
> > to light.... in the process of making the little cloud.
>
> true, but exactly what is the spectrum of this noise. if you know
> of a good reference or paper on this i would like to get it.
Reference paper? If you stand there you can hear the corona...if you
look at night you can see it...if you turn on a receiver it
covers ELF to light.
An arc is an ideal broadband noise source ( besides being a boat
that smell like animals).
> to the tips of elements of decent size yagis. if i get a chance i'll
> try to put in a simple model to see how far out from a vertical mast
> the field is significantly affected, but i expect it is a fairly short
> distance.
The force acting between two charges is directly proportional to the
the product of the two charges and inversely proportional to the
distance between them. That's a pretty simple rule. The mast should
have a large effect in a cone extending down with a radius twice its
height at the base. Tuck your antenna in or even anywhere near
that cone, and field gradient will be greatly reduced.
> 1. the sharp points would have lower energy discharges, the
> objects they are exciting are much shorter than a resonant antenna
> would be (assuming a porcupine vs an hf yagi, it may be different
> at uhf), and they are some distance away from the yagi.
Maybe so, but IMHO it would be better to have no corona at all, than
to have an intentional broadband noise source coupled to a poor
"antenna".
It isn't the frequency of the small element tips or whiskers you are
"calling" the antenna that matters. The antenna is actually the
entire structure...tower and all... since currents are common mode
as opposed to differential mode currents used to excite our
traditional intentional radiators. If that were a factor, it would
mean corona from the small pins that traditionally corrode and arc
arc in bell insulators would not affect one hundred sixty meters as
much as UHF. We know that isn't true.
> 2. allowing the yagi itself to go into corona
would probably lead to
> higher energy discharges to start with, the pulses generated are
> directly exciting a resonant structure, and they are of course much
> closer to the antenna.
True. And the worse place for corona would be at the tips, where the
high impedance discharge is coupled to the high impedance antenna
tips.
> I am definately not convinced yet, but i am beginning to understand
> the idea behind intentional corona sources.
It seems to me the problem is incorrectly visualizing the high
electric field that extends for miles and miles as something that can
be neutralized by a tiny little area with a small ion cloud.
We seem to totally ignore the ion cloud is very range limited and
the resulting change outside that area is absolutely no different
than if the "cloud" was replaced by a sphere of the same shape.
Actually the sphere would be better, because it has no charge
deterioration with distance away from the center of the sphere, where
the ion cloud would be most intense at the noise generating whiskers
and rapidly diminish in effect as you move away.
IMO it's unwise to install any intentional noise generator near the
antenna, especially when a smooth ball can have exactly the same
effect on the electric field without generating intentional undesired
corona noise.
73, Tom W8JI
w8ji.tom@MCIONE.com
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