[Cialug] [OT] Digital TV

[Zachary Kotlarek]

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.


> 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.

	Zach

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