[time-nuts] Thunderbolt cabling questions

Chris Albertson albertson.chris at gmail.com
Tue Jun 12 06:36:01 UTC 2012


On Mon, Jun 11, 2012 at 10:31 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
>
> albertson.chris at gmail.com said:
>> But you know what?  If you simply place an automotive "puck" type GPS
>> antenna on your roof you have to do the same thing.  It must be grounded the
>> same way, same lightening protection and so on.   So in the end you may as
>> well put up a professional looking and permanent  steel mast.  It is not
>> that much more work.
>
> What about putting a skylight high on the roof and putting the antenna up in
> it?
>
> What's magic about inside vs outside the roof/skylight envelope?

If the skylight is transparent to radio frequency then it might work.
But many times low emisivity glass (tat means the modern energy
savings type) has metallic coatings that attenuate radio signals.

Also from inside the skylight can you see the horizon all around for
360 dregs.  for that to happen the skylight must be taller than the
peak of the roof.  That would be an unusual skylight
>
> -----------
>
> I have a large pine tree out front.  It's roughly 3x the height of my (one
> story) house.  What are the chances of any lightning hitting my house rather
> than the tree?

A direct strick is not required.  What if the lightening hit a power
pole down the block?  there would still be a huge electric field and
the potential between the antenna and ground would be huge and there
would be current.   If the lightening hit the antenna there is nothing
you can do, grounding will not help.  What he prepared for is the much
more likely chance of a nearby strike.

Here is "The Book"
http://members.rennlist.org/warren/LightningProtectionAndGrounding.pdf



 What if I put an antenna on the top of my house so the tree
> is only 2x the height of my antenna?
>
> Of course, that depends on how far the tree is from my house.  Not far.  Call
> it 45 degrees from the back of my house to the top of the tree.  An antenna
> on the top of my house would probably be below that sight line.
>
> Is there a good book or URL on lightning vs antennas?  Again, I'm interested
> in both the technical issues as well as the local zoning/legal issues.

The local building code almost always reads "do what NEC says".  In
other words few cities will invest the time and $$$ to write their own
code and will defer to the Nation Electric Code.  Technically the most
sites papers are all for universities in Florida.
>
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
>
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-- 

Chris Albertson
Redondo Beach, California



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