[TowerTalk] Info for all

[Jim Lux]

I assume that these bits of "fur" are near the top of the tower?
They would fit in the general class of "static dissipators" having very 
small radii of curvature (compared to, say, the end of the antenna element) 
and, so, having very low breakdown voltages, making it easy to bleed off 
charge as corona discharge.  You'll see this kind of approach used on 
airplanes to bleed of "P-static", which is actually charge that builds up 
on the plane's (conductive) body as it hits charged raindrops and cloud 
particles.  It's also a nifty demo on something like a Van deGraaff 
generator, where you can show that the maximum terminal voltage is reduced 
(lots of frequent little sparks as opposed to infrequent big ones).

Consider though, that the tower as a whole should be grounded solidly (for 
a variety of reasons), so the real question is whether trying to make a 
lower resistance connection from ground to "air" is worth doing.  There 
won't be significant "impact charging" from charged dust or raindrops 
hitting the tower, and any such charging will rapidly be conducted to ground.

As far as lightning prevention goes it's uncertain whether sharp pointed 
airterminals (or static dissipators) help or hurt.... One theory holds that 
the sharp points on the air terminal help dissipate the relative charge and 
prevent a substantial leader from developing... Another holds that the 
sharp points can spray ions into the air where they form a semiconductive 
cloud... Yet another theory talks about changing the electric field 
distribution around the object, and therefore changing the likely path of 
lightning.

The real problem is that it is mind bendingly difficult to get good, 
repeatable, scientific data on the efficacy of such things.  Creating a 
realistic E-field in the lab is very non trivial (it's not just a matter of 
hooking up a big Marx bank.. the rise time and shape of the field are very 
different than that of the usual impulse source... Marxes are used to 
simulate the waveform AFTER the lightning has connected) There are some 
researchers at Erico in Australia who were developing test setups for just 
this problem.

If you try and do field experiments, there are so many confounding other 
effects that it's hard to get unambiguous data, even with A/B type 
comparisons, except perhaps over many years at one location. Perhaps the 
Langmuir Lab has published some data.

It all probably comes down to: It won't hurt..


At 02:11 PM 9/15/2003 -0700, Jim W7RY wrote:
>IMHO...
>
>Many schools of thought on this theory of static dissipation... Most
>determine that it does not help.
>
>I don't know how many more appendages you could have on an amateur
>tower.....With multiple single band beam antennas or a single multi-band
>beam You have quite a large amount of surface area...
>
>With this in mind... How would this theory work?
>
>73
>Jim W7RY
>
>
>
>----- Original Message -----
>From: <KB2HUK at aol.com>
>To: <towertalk at contesting.com>
>Sent: Monday, September 15, 2003 11:41 AM
>Subject: [TowerTalk] Info for all
>
>
> > Hello , I just picked up a little hint today I would like to pass along to
> > everyone.  Most of you experienced tower techs may already know this .
>To help
> > disapate static and lessen the chance of a lighting hit try using stranded
> > welding cable ( it containes many strands ) connected to the legs of the
>tower
> > and then spread out the strands like a umbrella so any static on the tower
>leg
> > has a place to go .   Please correct me if I am wrong on this as I am not
>a
> > tech and I may have mis quoted the source.  I hope I got this right and
>can help
> > someone .   John
> > _______________________________________________
> >
> > See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
>questions and ask for Sherman, W2FLA.
> >
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> >
> >
>
>
>_______________________________________________
>
>See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless 
>Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with 
>any questions and ask for Sherman, W2FLA.
>
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