[Cialug] [OT] Digital TV

Mon May 4 15:38:06 CDT 2009

On Mon, May 4, 2009 at 3:10 PM, <murraymckee at wellsfargo.com> wrote:

> It is 100' of line across the attic, down to the basement, across the
> basement ceiling, and back up to the living room.
>
> I've heard of amplified antennas but not of amps in the line from a
> standard antenna.  Where does one look for them?  I've talked to both Best
> Buy and Radio Shack about the problem and they suggested the amplified
> antenna, but putting it in the living room, not in the attic.  It would seem
> to me to make more sense to put it in the attic.

I bought a line amplifier years ago from Radio Shack.  In my setup, my
downstairs Tivo feeds multiple TVs.  I use the house TV cable for that.
Instead of plugging that into the "in", I hook it up to the "out".  Of
course, with feeding more than 1 TV and having a run of more than a few
feet, I decided to amplify the signal.  And yes, I amplify the signal as
close to the origination as possible.

>
> There is a lightening arrester cable coming down the gable of the roof a
> few feet from where I anticipate bringing the coax cable into the attic.  I
> could jumper from the block over to that.  I'll have to recheck where it
> goes into the ground.  I haven't looked at it intentionally in years.
>
> I have a cell phone tower not too far from the house and I expect it will
> attract the vast majority of the lightening in the area so I expect my house
> will be pretty safe, but I don't want to loose all my electrical equipment
> just to prove a point.

I'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'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.
Again, nothing to back this up, but if you're trying to protect your
components, does it really hurt anything?

>
>
> Murray McKee
> Operating Systems Engineer
> WFFIS - Wells Fargo Financial Information Systems
> 800 Walnut Street
> MAC F4030-037
> Des Moines, IA 50309-3605
> WORK (515)557-6127 Cell (NEW) (515) 343-6630  FAX (515) 557-6046
> MurrayMcKee at WellsFargo.com
> "This message may contain confidential and / or privileged information.  If
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>
> -----Original Message-----
> From: cialug-bounces at cialug.org [mailto:cialug-bounces at cialug.org] On
> Behalf Of Zachary Kotlarek
> Sent: Monday, May 04, 2009 2:15 PM
> To: Central Iowa Linux Users Group
> Subject: Re: [Cialug] [OT] Digital TV
>
>
> On May 4, 2009, at 12:33 PM, <murraymckee at wellsfargo.com> <
> murraymckee at wellsfargo.com
>  > wrote:
>
> > There is a 4 way splitter in the living room with one line going to
> > each of the two DTV boxes, one to the VCR, and one to the TV.
>
>
> I am not a radio engineer, but my (non-DTV) experience fighting with a
> roof-mounted rotary UHF mast suggests that 4 legs without an amp is
> probably optimistic -- RG-6 has a loss of about 1 dB per 20 feet, and
> a 4-way splitter likely has a loss of 7-8 dB. You might consider
> replacing the splitter with a distribution amp or adding a pre-amp to
> the antenna feed.
>
>
> > How does one ground the antenna so that lightening doesn't get
> > transferred to the DTV box / VCR / TV etc.?
>
>
> Start with a grounding block between the antenna and the entrance to
> your house -- a grounding block is essentially a female-female coax
> gender-changer where the shield is tied to a screw:
>        http://www.sadoun.com/Sat/Products/Accessories/RECDSV70.jpg
>
> Attach that screw to a standard ground rod (or other suitable
> grounding device) as close to the antenna as is practicable using a
> heavy gauge wire with no small-radius turns -- essentially the same
> procedure you'd use for a lightning rod. I believe the NEC always says
> you should connect the new ground rod to your breaker box, and I'm
> sure there are other rules about wire and antenna placement that you
> should follow if you want to do things right.
>
>        Zach
>
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-- 
Tim
Required reading: http://bccplease.com/
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