[Cialug] [OT] Digital TV

[Tim Wilson]

On Mon, May 4, 2009 at 3:49 PM, Zachary Kotlarek <zach at kotlarek.com> wrote:

>
> On May 4, 2009, at 3:38 PM, Tim Wilson wrote:
>
>  've heard that what you have to protect against the most is not lightning,
>> but static electricity.  Wind blowing particles across the antenna can build
>> up static electricity, which will travel down the wire and into your
>> sensitive components.  I've had installers tell me that if (in my case) the
>> dish were to get a direct strike, the lightning would likely travel the
>> cable, regardless of grounding.  I don't know if that's true, but more than
>> one person has told me this.  My guess is that in the case of a direct
>> strike, enough electricity would still flow through the cable to fry
>> components.
>>
>
>
> I think that's probably true -- there's a good chance a direct strike will
> blow out your electronics no matter what. But hopefully you can mitigate the
> damage and go from "my VCR exploded and started the house on fire" to "the
> VCR blew a few capacitors and needs to be replaced". And there's certainly a
> better chance your equipment will survive if the line is properly grounded
> than if it's not.


Oh yeah, I'm definitely for grounding, I'm just saying that a lightning
strike could still take out your equipment.  Don't count on nearby objects
attracting the lightning.  There still might be enough of a charge left in
the air to zap your gadgets.



>
>
>
>  I've also heard to put a gentle curve in the cable coming down from the
>> antenna similar to a drip curve.  The thought is, lightning (or at least
>> some of it) will travel in a straight line, and will not follow the curve.
>>
>
>
> That's about inductance. You're supposed to install grounding wires with no
> small-radius turns to minimize the inductance of the grounding path. There's
> a very large, near-instantaneous current change related to a lightning
> strike, so even minor curves can have a large impact on the effectiveness of
> a grounding wire. There's probably some benefit to adding inductance to the
> signal wire, but I don't know that it would provide any practical amount of
> protection beyond the existing high impedance of the signal path versus the
> grounding path.


I was meaning a curve in the actual cable, not the grounding wire.  Like a
half-loop, where the cable comes down, and curves back up with a gentle
radius.  But I guess the same could work for grounding wires.


>
>        Zach
>
>
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-- 
Tim
Required reading: http://bccplease.com/
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