[mythtv-users] OT: DIY Antennas in the attic, is a ground necessary?

[Simon Hobson]

Tom Flair wrote:

>My concern is whether or not I should be concerned with grounding 
>out the antenna since it will be in the attic and what I would 
>connect the ground to on the antenna itself.

The simple method is just strip off a short length of the outside 
insulation, and use a suitable sized metal P clip to connect to the 
outer screen - and then hook this to the main earthing point in the 
house. This will provide some limited protection, but won't stop any 
surge down the inner conductor.

For that you'd want to cut the cable and fit an inline surge 
protector - these have a spark gap (or possibly transorbs) so that 
high voltages on the inner core can jump across to the case, and then 
down an earthing cable.
As a DIY measure, you could probably get away with one of the spark 
gap surge protectors used on phone lines - over here in the UK, 
business installations normally use Krone punchdown terminals with 
the facility to plug in a protection magazine.
https://secure.nimans.net/product_info.aspx?product_id=742ea5c2-4fbd-11d7-b2a0-00b0d0225691
https://secure.nimans.net/product_info.aspx?product_id=742ea556-4fbd-11d7-b2a0-00b0d0225691
These are two pole protectors, so you'd only need to use centre and 
one end pin.

Any earth needs to be both thick and short. To the very steeply 
rising signal of a lightning surge, a piece of wire looks like an 
inductor with a significant impedance - so ideally you need a really 
short cable (measured in inches, not feet). Also, for full 
protection, you should arrange that EVERY cable that comes into the 
house comes in via the same point, and tie all their surge 
protections to one bolt and then to an earthing point or earth rod. 
You'll still get surges remaining, but they'll be common mode to all 
equipment & services in the house and damage is less likely.
-- 
Simon Hobson

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