Grounding an Antenna....
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Grounding an Antenna....


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  1. #1
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    Grounding an Antenna....

    is it ever okay to run just an coaxial cable straight from an outside antenna to your TV without ground cables?



    and can you just ground an antenna without having to split the coaxial cable with an grounding block?

  2. #2
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    Per NEC and common sense, no and no.

    In the real world, most DIYers ignore the grounding requirements.
    Jason Fritz likes this.

  3. #3
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    Thread Starter

    So u are saying ..... it okay?

  4. #4
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    Sure... So long as tempting Thor, God of Thunder is your idea of a rollicking good time, that is...

    </sarc>

    You might be able to get away without grounding the antenna for decades, as some people have... or your ungrounded antenna might attract a lightning bolt during the first thunderstorm next spring that results in a catastrophic fire, and maybe even serious injuries or loss of life. Grounding is akin to buying fire-insurance coverage. Statistics say that, all factors being equal, the average single-family structure would burn down only once in 800 years, yet I know of no mortgage lender that will tolerate a borrower going for a single minute without fire insurance.

    In most cases, proper grounding is neither complicated nor expensive. Have a look at the section titled "Grounding outdoor antennas" about three-quarters of the way down this page. It will tell you all you need to know.

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    Vazkey,

    Your question was...
    "is it ever okay to run just an coaxial cable straight from an outside antenna to your TV without ground cables?".
    Answer is...
    Many people do this, but, it's better to ground your system.

    Next question...
    "can you just ground an antenna without having to split the coaxial cable with an grounding block?".
    Answer is...
    Yes you can, but you'd have to Ground one of the Receivers which the Antenna Downlead is connected to. AND, verify continuity (via an Ohm Meter) to a Metal Cold Water Pipe, or Ground Rod for your Electrical Service.

    Now...
    There's no harm in using a Ground Block. They don't insert hardly any resistance to the signal at all.
    Any Block or Wire associated with it, SHOULD be OUTSIDE YOUR HOUSE !
    IF a direct strike hits your Antenna, the sparks could cause a Fire, and if those sparks are in your Attic or other area of your house, BAD things can happen !

    So...
    Ground your Antenna Mount.
    Run/keep that wire outside and down...
    To a Metal Cold Water Pipe, or, a Ground Rod.

    Have a good Day !
    S.W.

  6. #6
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    Since you are in a multiple occupant building, it is more than just polite to ground your antenna. It protects the lives and property of your neighbor.

    That being said I dont have my roof mounted antenna grounded. However I have a giant metal roof and a huge oak tree that stands over the house....whose root system is my lightning rod.

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    Quote Originally Posted by EscapeVelocity View Post
    Since you are in a multiple occupant building, it is more than just polite to ground your antenna. It protects the lives and property of your neighbor.

    That being said I dont have my roof mounted antenna grounded. However I have a giant metal roof and a huge oak tree that stands over the house....whose root system is my lightning rod.
    EV,

    Your "system of grounding" has worked so far, but it sounds more like a problem waiting to happen. Currently, your antenna may be a more attractive target than the tree. Also, a strike on your tree will likely adversely affect your system.

    It is commonly known that one shouldn't seek shelter under tall trees in a lightning storm (because of the likelihood that a tall tree will get struck). If the tree were an effective lightning rod for protection, then we would head for the trees instead of away from the trees. To think that your system is safe is a misconception.

    Many people think that grounding will save them from a lightning strike. It won't save you from a direct strike. It may lessen the damage from a direct strike.

    Grounding helps to avoid a direct strike. Grounding attempts to make your antenna "electrically invisible" to lightning by making it resemble the electrical potential of the earth or ground. Without grounding, your antenna sends up "leaders" just as your tree, and everything gaining charge during a storm. Which leader the lightning chooses to follow is unpredictable.

    Grounding does much more than most people think. Most have discounted grounding as nothing more than satisfying required electrical code.

    Grounding provides a drain for excess EMI and Rf energy that collects on your antenna. As wind blows across your antenna, electrons are shed producing an electrical charge (static charge) that will build up on your antenna causing problems in reception. Unless this excess energy (noise interference) is "drained", it will cause problems. The ground is a drain for unwanted EMI and Rf noise.

    Grounding is especially important in amplified antennae. When amplifying an antenna, an electrical charge is sent to the antenna. This will make your antenna MORE likely to be struck if it is not grounded.

    Grounding reduces noise and increases avoidance of electrical interferences.

    Here is some more:

    Why Ground?

  8. #8
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    Quote Originally Posted by highdefjeff View Post
    Your "system of grounding" has worked so far, but it sounds more like a problem waiting to happen. Currently, your antenna may be a more attractive target than the tree. Also, a strike on your tree will likely adversely affect your system.
    Flashover happens: If a bolt hits the tree, there's little to prevent all or part of the discharge from jumping to an ungrounded antenna. If a coax cable's shield and center conductor offer a low-resistance path to ground, that's where a flashover strike is likely to go.

    Flashover is also the reason why it's not a good idea to hang around big, isolated trees during electrical storms.

  9. #9
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    500 year old Live Oak complete engulfs the house. Trunk is 8 foot wide at the base.

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    Better get to grounding your system!

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    More Grounding info !!

    Here is a nice link on antenna grounding in a question and answer format. I really like the graphic on this page, as it endorses the use of an antenna discharge device, instead of just a simple coaxial grounding block, which IS NOT THE SAME DEVICE !!

    Grounding antenna mast and antenna discharge unit
    WE ARE NOT SHEEPLE !!

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    NEC uses the term "listed antenna discharge unit". I've looked, and cannot find such a product specifically identified as such available for purchase.

    The author of the above referenced article, well known as an expert on the NEC, in another article published on his own website includes the following:

    [810.20] You must provide each conductor of a lead-in from an outdoor antenna with a listed antenna discharge unit (ground block). If you put a discharge unit inside the building, place it nearest the point of entrance-but not near combustible material. You can also place it outside the building, thus eliminating any potential problems stemming from location inside the building.
    [emphasis added]. This particular expert, it appears, accepts that a grounding block meets NEC code requirements.

    The complete text of the referenced article which is a very comprehensive overview of NEC requirements for the grounding of receiving antennas is available at Article 810 - Radio and Television Equipment

    Another article of interest is at http://ecmweb.com/nec/code-basics/el...gnals_crossed/
    Last edited by ProjectSHO89; 07-27-2010 at 04:47 AM.

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    Thank you ProjectSHO89 for catching that! Went right by me!

    I am not aware of any other "antenna discharge unit" (ASIDE from a ground block) to be used in antenna and satellite installations.

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    Digging more into 2008 NEC Sec 810-20.

    A properly grounded grounding block eliminates the requirement for the ADU when used with coax. See listed exception in 810.20 (A).

    810.20 Antenna Discharge unit - Receiving Station

    (A) Where required. Each conductor of a lead-in from an outdoor antenna shall be provided with a listed antenna discharge unit.

    Exception: Where the lead-in conductors are enclosed in a continuous metallic shield that is either grounded with a conductor in accordance with 810.21 or is protected by an antenna discharge unit.


    Last edited by ProjectSHO89; 07-27-2010 at 07:42 AM.

  15. #15
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    There are actually antenna discharge units. They are basically MOVs or gas discharge tubes connected across the coax and connected to ground. Basically they shunt the line to ground if lightning or other surges pass through. Polyphaser and ICE makes them for N and UHF connectors. There may be F connector versions.

    Truth be told, grounding the coax shield at the top and bottom of the antenna and bonding those to the service ground will not only satisfy the NEC but provide decent protection from anything except a direct super strike. I know hams whose towers are hit multiple times per year with zero damage. I ground my tower at the top and bottom using the Andrew ground kits as well as F connector ground blocks at the top and bottom. I also have an extensive ground field with #2 wire and 36 ground rods spaced 16ft apart. I followed the instructions from the Motorola book. Overkill for the average TV antenna of course, but I don't have the average TV antenna.

    For most people just ground the top and bottom and connect to the service ground. Get enough insurance to cover the rest.
    Last edited by n2rj; 07-27-2010 at 04:45 PM.
    Ryan, N2RJ

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    This firm has some models of these devices, but they don't seem to carry one with F-type connectors. These are plasma gas discharge units that a somewhat expensive, but well below the cost of a plasma or large LCD TV, and most likely less than the average home owners deductible if a claim had to be filed on a high end TDV.

    Cables, Coaxial Cable, Cable Connectors, Adapters, Attenuators, Microwave Parts - Pasternack Enterprises. This company gears towards the broadcast industry and offers bulk purchase prices, but they will sell to the public.
    WE ARE NOT SHEEPLE !!

  17. #17
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    I have bought arrestors from Industrial Communication Engineers (ICE) as well. They will sell you a complete kit which includes one or more discharge units (arrestors), a SPG bar and conductive grease. Get an 8ft ground rod from your local supply house, some #2 wire and you are golden.

    Industrial Communication Engineers, LTD.

    They have one that comes in "F" connector 75 ohm, up to 1GHz which is perfect for OTA antennas and cable TV. Downside is that it's 38 bucks. But it is pretty good. They also carry TVRO and DBS impulse suppressors.

    Impulse Suppresors | Arrestors

    Polyphaser also has 75 ohm arrestors:

    http://www.polyphaser.com/Products/prod/coax/75ohm/

    I use polyphaser at my house for the ham stuff. I will get one for the TV antenna soon.

    Other useful lightning links:

    National Lightning Safety Institute (NLSI)

    Very nice series of lightning protection articles courtesy of ARRL, applicable to ham radio stations but also useful for TV antennas, especially those on towers and other high support structures - Link

    If you can, cadwelding your ground wires and ground rod is the absolute best way to keep them low resistance.
    Last edited by n2rj; 07-28-2010 at 06:42 AM.
    Ryan, N2RJ

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  18. #18
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    Currently I am using an 8 bay Bowtie antenna between 45 to 50 feet up. I have the coax going to a grounding block and I am running about 3 feet of 8 gauge copper wire to a grounding rod. Here is my question. The grounding rod I am running to, has been there for about 40 years or better. Is there a simple way I can test that ground? I live right next a river, so I suspect the soil is good for ground. Is there a simple way to test my grounding rod? And if I replace the grounding rod, any suggestions? Do I want to go with a copper or aluminum rod? And how long of a rod? Thanks in advance for any help.

  19. #19
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    Testing a grounding rod has to be done with a Megger or similar instrument. You can't just do it with a multimeter. Any electrician should be able to help you unless you have your own megger. Basically you want to do a ground resistance test. Frankly unless your rod has been corroded it is likely fine. Moist soil does help but is not critical.

    I would recommend a copper clad rod. Aluminum is too soft and I haven't seen many Aluminum ground rods. I have seen galvanized rods as well. Those are OK but may not last as long as a good copper clad rod.
    Ryan, N2RJ

    Extra class certified antenna NUT

  20. #20
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    Thanks Ryan. I am paranoid about that ground. The grounding rod was part of the original antenna system on this house. I reused the ground rod and a portion of the old mast, but I don't see any signs of corrosion, I used a wired brush to scrape the area I put the clamp on and the copper appeared with little work, so I suspect it is probably fine. The old system was 2 low band VHF yagi's stack with a 300 ohm lead, at least what was left of it. Thank again.

 

 

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