On 6/11/12 10:31 PM, Hal Murray wrote:
albertson.ch...@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?
-----------
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? 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.
http://www.amazon.com/The-Art-Science-Lightning-Protection/dp/052187811X
Martin Uman and his collaborator Rakov have probably forgotten more
about lightning than everyone on this list collectively knows about it.
This one is a bit pricey still, but is the definitive tome.
A Dover Press version of Uman's "The Lightning Discharge" is <$20, and
well worth the investment if you're interested in lightning.
Ronald Standler's book "Protection of Electronic Circuits from
Overvoltages" is a great source on overvoltage protection in general.
$20 in paperback. Lots of useful information on how to design/purchase
transient suppression for all kinds of signals. And surprising
information on how certain kinds of techniques can actually make things
worse.
One wants to be careful about texts published by manufacturers of
protection equipment. Yes, they typically have valid information, but
it *is* coming from a source which wants you to "buy more stuff", so
they tend to be a bit more conservative (more protection = better, even
if the physics doesn't support it). That said, much of the high quality
peer reviewed research on things like lightning rods (aka "air
terminals") does come from companies making such things.
Also, there are several pubs out there widely distributed aimed at
applications like FAA Control Towers or high reliability 24/7 land
mobile radio. The recommendations in those books may prove to be
somewhat of overkill for a couple reasons: most amateurs don't need
that level of protection; the suggestions aren't always supported by the
physics, but are there because "they don't hurt", triggering the "nobody
got fired for buying IBM mainframes" phenomenon... if it's small
differential cost, why not do it, because if we don't do it, and
something goes wrong, we'll be blamed.
Legality wise
Nat Elec Code (aka NFPA70) has bonding and grounding requirements. Art
250 on grounding, Arts in the 800s on antennas. Expensive ($80-100) if
you buy it, but since it forms the basis for California's Title 24
(State Electrical Code), a scanned version is online at
https://public.resource.org/. The antenna grounding stuff doesn't
change very much, so an older code found at a used book store might also
work.
NFPA780 is the lightning protection code.
IEEE 1100 - The Emerald Book - is very useful on grounding, transient
protection, etc. issues in general. Pretty expensive.. find it in a library.
http://standards.ieee.org/findstds/standard/1100-2005.html
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