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Re: Lightning and mast mounted preamps



Hi Joel,

on 3/9/03 5:11 AM, Joel Black at w4jbb@charter.net wrote:

> I'm glad to see someone finally mentioned connecting all your grounds to
> your electrical service ground!  If this is not done, there can be a
> difference of potential (I've seen 12V).  If you know someone who works in
> the electrical utilitiy business (I do telecomm work for an electrical
> utility in the SE), ask them about step-potential.  It's the difference of
> potential between one point on the ground and another.  The company I work
> for says the step potential is about three feet.

Agreed.  And when considering a lightning strike consider some of the facts
as well.  Even in a situation where you have a well grounded tower, the
earth essentially acts as a big, lossy capacitance.  If you receive a
strike, it takes a finite amount of time for the earth to be able to
dissipate that strike energy.  So when the strike hits, it will want to
raise the potential of everything around it.  If the tower is not connected
to the electrical ground and the earth around the tower saturates (ie:
raises to a higher potential), then the remaining strike energy will want to
find somewhere else to go.  Since the earth at the service ground is going
to likely be at some different potential the strike energy will find its way
through your coax, possibly surge arrestor, whatever.  It's trying to
dissipate.  Bad things can happen.  If the grounds are all tied together,
all the potentials rise and fall together.  That way there's no difference
between grounds.

I once was ignorant and thought you should leave the tower unconnected.  I
was told why and it makes sense.  There are guys with huge tower farms on
huge property that don't do this because of the distance and space.  When
they get hit, they generally lose something.
> 
> Hardline should be grounded at the top of the tower, at the bottom, of the
> tower, and when it comes in the building.  After it enters the building, put
> some type of lightning (lightening is what you do to your coffee),
> protection in line with it (whether it be Poly-phaser [what we use at work]
> or the ICE protector Jon mentioned and that I've seen in the Tessco
> catalog).  Run all your grounds to a common point - namely the electrical
> service ground.  BTW, it is all but impossible to put a grounding kit on
> most types of coax (i.e. 9913, 9913F, LMR400, etc.) although I have put it
> on LMR600.  You'll destroy your coax before you get the grounding kit on.
> 

Actually, there is a REALLY easy way to do this.  You buy what's called a
"blitz" bug.  Cable Experts sells them  as Static Arrestors.  I've only seen
them with PL-259's though.  The other thing Bill Hider, N3RR, did was use a
barrel connector as the point where you apply the grounding kit.  He shows
it on his web page.  He used the Andrew Heliax grounding kits on non-heliax
cable.  The barrel and corresponding connectors won't be ruined by the
clamping mechanism.

> Remember, lightning will follow the path of least resistance.  If you're
> depending on the ground in your equipment or your power supply to protect
> your equipment, it's only going to offer the path of least resistance to the
> electrical service ground and, whamo, you've lost, at a minimum, your radio
> equipment.  Your electrical service ground is connected to the neutral that
> comes to your house from the substation which comes from the electrical
> generating plant.  There cannot be a better ground than the one coming from
> the plant - think about it...

Agreed!

73,

Jon
NA9D

-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)

Citizen of the People's Democratic Republik of Illinois

Life Member: ARRL, NRA
Member:  AMSAT, DXCC

http://www.qsl.net/na9d   <- Updated on 1/22/03!!!

"A life lived in fear is a life half lived."


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