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Thread: Lightning Arrestor for Ladder Line Feed

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  1. #11
    Join Date
    Jul 2006
    Location
    Montana
    Posts
    3,270

    Default

    It is my understanding Lightning Arrestors only protect your equipment from near-by lightning strikes, not direct hits.

    A direct hit will vaporize the ladder line and any simple "lightning arrestors" you have in line with it. All that's left is a small stream of ionized plasma where the ladder line used to be. This stream of plasma acts as a conduit for the rest of the lightning to ground into your radios. Trying to protect your radios from a direct strike with a simple lightning arrestor is like relying on a sheet of bubble wrap around your car to be your only protection in a head-on freeway crash.

    Lightning arrestors do work very well in keeping stray voltage from nearby strikes from getting to your equipment. If a small, tiny fraction of nearby lightning strike finds your antenna, the arrestor will keep it at bay.
    Last edited by KE7HQY; 03-12-2010 at 02:31 AM.

  2. #12
    Join Date
    Jul 2006
    Location
    Montana
    Posts
    3,270

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    The easiest, cheapest solution to deal with direct lightning strikes is to have a way to physically disconnect the feedline and have a "pigtail" you can throw out in the grass. For me, I installed coaxial "bulkhead" through my wall. This allows me to easily unscrew the coax and throw it out into the yard when a lightning storm is nearby. For a twinlead, two wingnuts for a quick disconnect would do the job. Note, this doesn't ensure anything. It simply minimizes the chance that the direct strike will get to your radio. If you're really concerned, disconnect the radio and put it in a metal filing cabinet.

    It is interesting to learn how the pros deal with direct strikes, like to a cell tower or AM/FM broadcast antenna. Here is a good paper on the subject:

    http://awapps.commscope.com/search/d...spx?docid=7882

  3. #13

    Default

    Please be aware that the actual "device" used, (Lightning arrestor, Switch, spark plug gap, Etc) Is close to the LEAST important part of any lightning protection system.

    MUCH more important is the proper grounding and bonding of all ground systems. (Decent grounding is LOTS more than just running a skinny wire out to a single ground rod)

    If you "disconnect" wires (A very dangerous practice when a storm is nearby)
    Be SURE to either properly ground those disconnected lines OR remove them far from the building! To simply leave a disconnected line laying about on the floor is about like leaving a stick of dynamite on the floor!

    I much prefer some type of grounding switch if you do not plan to operate while the storm is overhead, Or if you do plan to operate during storms like many of us do, I.C.E. (Industrial Communications Engineers) has good products at a reasonable price:

    http://www.iceradioproducts.com/impulse1.html#2


    For some tips on lightning protection on a budget:

    http://www.scribd.com/doc/14868226/l...deron-a-budget

  4. #14

    Default

    Two thoughts;-

    Back in the earlier days of Radio,many thousands of outside antennas were

    used by the general public,without any thought of lightning protection.

    OK, these were Tube Receivers,& you could buy knife switches with built-in

    spark gaps & other such junk,but a farmer in the backblocks of Western

    Australia, (Or Kansas for that matter),was usually more concerned with

    getting as much wire in the air as he could,to receive Radio Broadcasts

    from,usually a fair distance away.

    Lightning protection was rarely thought about.

    Even Hams,who might well have had higher antenna structures,didn't worry

    that much.

    Obviously, Solid State equipment is more fragile,but lightning damage is

    relatively rare.


    Secondly,twin feeders normally feed an antenna which is at least nominally

    balanced to earth,so the possibility of doing something along the lines of a

    earth for lightning induced transients is there.

    A large Inductor from each leg to earth is a possibility.

    The problem would probably be getting enough reactance to not affect the

    wanted signal,& not have too much reactance & resistance to be a good

    earth.

    Of course,a folded dipole could in theory be earthed at its centre,without

    affecting the balance.


    Now,as I've disagreed with the general consensus,I'll put on my fireproof

    suit!


    73, VK6ZGO
    Last edited by VK6ZGO; 03-16-2010 at 07:46 AM. Reason: Tidy up

  5. #15

    Default Spark Plugs

    Take a look here:
    http://webpages.charter.net/aj8mh-ra...ebookind1.html

    The pictures were taken in Texas. Since moving to Michigan, I've had to mount the ground plate 3 feet above ground to keep it out of the snow. I run #6 wire to my ground rod.

    73,
    Joe

  6. #16

    Default

    Even if the idea was patented, using spark plugs for "lightning protection" has been around since at least the late 1920s and since the "olde tyme" length of a patent was 14 years (now 20 years) the patent would have long expired.

    One thing that you can do to prevent the effects of static electricity "build up" is to put non inductive resistors to ground from each side of the feedline. Values between 47K and 100K are very common and the effect on the feedline cannot really be measured without some very accurate test equipment.

    Glen, K9STH

  7. #17
    Join Date
    Nov 2004
    Location
    41, Cecelia Terrace, Pittsfield, MA 01201
    Posts
    2

    Default I.C.E. Makes arrestors for open-wire/ladder line

    http://www.iceradioproducts.com/impulse1.html

    I have used their coaxial arrestors for some years now. Very well
    constructed.
    You might want to look into Their Open wire Arrestor.
    73
    NJ1T (The deaf DXer)

  8. #18
    Join Date
    Oct 2003
    Location
    Middle Georgia USA
    Posts
    7,722

    Default

    There are inherent design problems with ladder line lightning arrestors.

    Pay attention to what KJM posted. The lightning arrestor is one of the least important parts of the system!!!

    On bands where the doublet antenna reaches the highest impedance, ladder line voltage might be 2000 volts or more to ground at a kilowatt. At 100 watts plan on 650 volts or so.

    Any lightning gap that will pass that voltage OUT will pass that voltage in. That won't be much protection for a solid state rig or a tuner.


    Best idea with ladder line is clearly to disconnect if you can get a big enough gap and ground the line to a good panel ground. My choice would be a knife switch on a good entrance panel like coax would normally use, or to disconnect and throw it outside away from the house.

    I think anything else is mostly kidding yourself.

    73 Tom

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