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Antenna Lightning Protection

Discussion in 'Electronic Basics' started by W. eWatson, Sep 19, 2013.

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  1. W. eWatson

    W. eWatson Guest

    I have a mast, rotor and yagi TV antenna on my roof. The antenna is
    probably 15' feet above the roof. It has 12 or so large elements, and a
    similar amount of smaller elements. There are three guy wires. It was
    struck by lightning about eight years ago, and took out the rotor
    control in the house. There was no apparent damage to the antenna it is
    not in use, disconnected from the TV, but the antenna wire goes into the
    house. It is easily the tallest structure around the house, that is, no
    trees accept a tall pine about 80' away, which is close to the height of
    the antenna.

    About the end of August and to mid-Sept. we have occasional electrical
    storms. We had a strong storm near our house 2 weeks ago. My question is
    should I have the antenna taken down or somehow grounded. If the latter
    what's a conventional way to do it? Copper wire from the base of the
    mast down the side of the house to a ground pipe? The antenna is about
    20' from the end of the roof near it. I'm not sure of the material used
    for the mast. It may be aluminum.
     
  2. RobertMacy

    RobertMacy Guest


    I second that. Take it down. To understand why, remember what you just
    described to 'protect' it, that is, make it grounded better?!
    Big ouch.

    Seriously, it's bad enough *IF* you must have that in the air, but to not
    need it and leave it is, ...like an invitation. And believe me. you were
    lucky to only have damaged the rotor last hit.
     
  3. operator jay

    operator jay Guest

    IF you leave it up (which is probably the worse option) then I'd suggest you
    run copper wire from the TOP of the mast, all the way down. Ideally this
    'down conductor' (as some call it) has no sharp bends in it and preferably
    no bends greater than 90 degrees.

    I'm not 100% sure what you mean when you say ground pipe, but I would
    connect the down conductor to a ground rod (10' long rod, steel or copper
    clad steel depending whether your soil eats up unprotected steel, 3/4"
    diameter, pounded straight down into soil until it's top is about a foot
    below ground). Ideally that rod is 2m (or 4m or more) away from your
    house's ground (be that a rod, underground metallic water pipe, or
    whatever). You could then connect the ground rod to your ground system with
    a #6 AWG bare copper wire.

    j
     
  4. W. eWatson

    W. eWatson Guest

    By pipe, I really meant about a six foot copper pipe, 1/2" or so.

    Yes, taking it down the antenna seems a sensible way to go. I'll get
    the fellow who put it together many years ago to remove it.

    To Robert, a bad choice of words to Subject.

    By the way the roof peak is about 60' long, and a roof, lower, is about
    35' long.

    So what's some simple way to protect us from being hit? Someone years
    ago suggested four lightning rods strung out along the peak was a way to
    go, with them all grounded. One end of the line along the peak would go
    down the side of the house to the ground.

    So is there
     
  5. operator jay

    operator jay Guest

    Your reply looks to have gotten cut off.

    If I understand correctly you have a peaked roof on which the peak is
    60'long, and if you rolled down the slope away from the peak, you would go
    over an edge, and drop onto another sloped roof. This lower sloped roof is
    about 35' long, and sloped in the same direction as the higher roof. Also,
    I have been assuming a shingle roof.

    Yes, four lightning rods ("air terminals", probably about 20" tall each)
    along the peak, with a conductor connecting them all, takes care of the
    peak. Then, from the same end of the peak, two conductors could run down
    the slopes from the peak to the edges of the roof (the conductors running
    down from the peak would still be on top of the roof, but near the edge of
    the roof). One conductor would go over the edge of the roof and down to a
    ground electrode. The other conductor would go over the edge of the roof,
    drop to the lower roof, run down the edge of that lower roof to a corner,
    then go over the corner and down to a ground electrode. Those electrodes
    should prbably be interconnected to each other, and to the house's ground.
    The rods should be 2 or 3 feet out from the building.

    I don't recall for sure, but I think you could probably do without the air
    terminals - the conductor running along the peak acts as an "intercepting
    conductor" and takes the lightning hit.

    Take a look at this site, http://www.tlpinc.com/ Browse EVERYTHING under
    "DOC LIBRARY" and I think you'll have a decent feel for what's going on.
    The product catalogs under the doc library not only have the major
    components, but also all the accessories and fittings.

    I have no affiliation with that or any website or manufacturer. I know
    those products and I think that site will be helpful to you.

    Good luck.

    j
     
  6. Bob Masta

    Bob Masta Guest

    I think you need the spiky rods pointing at the sky. The
    purpose of "lightning rods" in this sort of installation is
    not to conduct a hit, but to prevent it in the first place
    by providing a drain for charge build-up. (There is a neat
    high-school science experiment with a Van de Graaff
    generator, where you tape a thumb tack to the globe with the
    point outward... makes a definite "ionic wind" when charged
    up!)

    A system that is actually designed to conduct a strike (like
    the Empire State Building) needs monster buss-bar to handle
    the bazillion (or so) amps. <g>

    Best regards,


    Bob Masta

    DAQARTA v7.40
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, Sound Level Meter
    Frequency Counter, Pitch Track, Pitch-to-MIDI
    FREE Signal Generator, DaqMusic generator
    Science with your sound card!
     
  7. Bill Gill

    Bill Gill Guest

    Actually I just recently read a piece about how lightning
    rods work, and that one said that your explanation is the
    wrong one. They actually do catch lightning strikes, they
    don't discharge the cloud to prevent them.

    Bill
     
  8. Tom Biasi

    Tom Biasi Guest

    1.21 Jigawatts.
     
  9. Massoud

    Massoud Guest

    If there is no tall structure around, why the antenna is 15' high on the
    roof? you dont gain anything (the sight angel may not change more than a
    degree) lower it and let the pine tree get zapped. :)










    --- news://freenews.netfront.net/ - complaints: ---
     
  10. That sounds right.

    I don't think anyone noticed, but a lot of the yagi could/would be
    grounded. The mast would be, the support part could be, which means the
    grounded part is more likely to be hit than the "hot" side. Like you say,
    the lightning will go towards the easiest path, and that would be the
    grounded part of the system.

    That said, a near miss can be almost as fatal, and this does't completely
    rule out a direct hit. YOu'd put lightning arrestors across the feedline.
    In the early days, those were like spark plugs, a short distance for the
    lightning to jump to ground. I'm not sure that really changed, but with
    coax it got package up nicer. You also take precautions, put a neon bulb
    across the receiver's antenna terminals, or now some solid state devie
    that shrots to ground when a sufficiently high voltage hits, yet which
    doesn't cause problems to reception otherwise.

    If the antenna isn't being used, don't let the feedline in the house,
    short it to ground outside.

    Michael
     
  11. Bob Masta

    Bob Masta Guest

    Well, I expect a lot has changed since my '60s
    Electromagnetic Fields EE classes. <g>

    But how do they explain those teeny wires carrying all those
    amps without exploding?

    Best regards,


    Bob Masta

    DAQARTA v7.40
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, Sound Level Meter
    Frequency Counter, Pitch Track, Pitch-to-MIDI
    FREE Signal Generator, DaqMusic generator
    Science with your sound card!
     
  12. Tom Biasi

    Tom Biasi Guest

    Things haven't changed that much Bob. The wires are still not stronger
    than an oak tree.

    Tom
     
  13. Bill Gill

    Bill Gill Guest

    Well, maybe not, but when I visited George Washington's home
    at Mt. Vernon the oak trees had lightning rods.

    Bill
     
  14. Fred Abse

    Fred Abse Guest

    Put there by Ben Franklin?
     
  15. Tom Biasi

    Tom Biasi Guest

    I'm pretty sure they don't want them hit.
     
  16. W. eWatson

    W. eWatson Guest

    I had the entire antenna system taken down about a week ago.
     
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