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Author Topic: Ladder line Lighting protection  (Read 7830 times)
N4HRA
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Posts: 282




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« on: May 15, 2011, 07:20:06 AM »

Question: I am trying to figure out how to add lighting protection to my ladder line that feeds my dipole antenna.

I think I have a solution: The ladder line comes into the attic end gable to a SGE 239 ATU.
I am thinking placing a Transi-Trap Surge protection  on the coax at the ATU and then  run the ground wire approx 20ft down to a 12 ft ground rod

I would like comments on the method please

Thank you
Lew
N4HRA
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NN4RH
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Posts: 328




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« Reply #1 on: May 15, 2011, 08:17:19 AM »

Best that you make sure you have enough homeowners insurance before you do that.

Things should be grounded or disconnected outside.

http://www.arrl.org/lightning-protection


There are some commercial balanced line surge protectors out there, but I don't know how good they are.

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

http://www.thewireman.com/ground.html

Plus there's a number of ad-hoc approaches if you google for balanced line lightning protection.



« Last Edit: May 15, 2011, 08:21:36 AM by NN4RH » Logged
K4SAV
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Posts: 1847




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« Reply #2 on: May 15, 2011, 04:03:20 PM »

You can add some amount of protection from some induced currents and voltages on a ladderline dipole, however that may not be enough to save your rig from damage.   Protection from a direct lightning strike is probably more trouble than you are willing to go to, and may be impossible depending on space and resources available to rebuild your antenna system.  Ladder line cannot carry lightning current.  It will simple evaporate.  When that happens, there is no way to control the lightning path.  With the ladderline entering the house thru the attic, you should hope the antenna never takes a direct hit.

The ICE open wire suppressors are for lines with impedances of 300 to 600 ohms.  That means an open wire line with a matched antenna (300 to 600 ohm antenna).  A ladderline fed dipole with no matching devices at the antenna doesn't qualify.  A line with high SWR could trigger the suppressor depending on power level and where the suppressor is located.  I don't know what level of voltage the ICE suppressors pass, but on a 600 ohm line at 1KW PEP (rated for the unit), it has to be very high and will be greater than that which will damage a receiver (even passing thru a tuner in the reverse direction).  So this kind of protection does not guarantee no damage.  

A better surge suppressor for a ladderline fed dipole would be some kind of disconnect between the ladderline and tuner.  The ladderline should then be connected to ground.  This of course offers no protection at all for a direct hit.

Jerry, K4SAV
« Last Edit: May 15, 2011, 04:13:19 PM by K4SAV » Logged
KB9CRY
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« Reply #3 on: May 15, 2011, 04:57:24 PM »

You can add some amount of protection from some induced currents and voltages on a ladderline dipole, however that may not be enough to save your rig from damage.   Protection from a direct lightning strike is probably more trouble than you are willing to go to, and may be impossible depending on space and resources available to rebuild your antenna system.  Ladder line cannot carry lightning current.  It will simple evaporate.  When that happens, there is no way to control the lightning path.  With the ladderline entering the house thru the attic, you should hope the antenna never takes a direct hit.

The ICE open wire suppressors are for lines with impedances of 300 to 600 ohms.  That means an open wire line with a matched antenna (300 to 600 ohm antenna).  A ladderline fed dipole with no matching devices at the antenna doesn't qualify.  A line with high SWR could trigger the suppressor depending on power level and where the suppressor is located.  I don't know what level of voltage the ICE suppressors pass, but on a 600 ohm line at 1KW PEP (rated for the unit), it has to be very high and will be greater than that which will damage a receiver (even passing thru a tuner in the reverse direction).  So this kind of protection does not guarantee no damage.  

A better surge suppressor for a ladderline fed dipole would be some kind of disconnect between the ladderline and tuner.  The ladderline should then be connected to ground.  This of course offers no protection at all for a direct hit.

Jerry, K4SAV




Ditto what he said....TransiTraps are Cr....
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N4KC
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« Reply #4 on: May 16, 2011, 10:52:44 AM »

Always looking for the simple solution, but I just use banana plugs and disconnect the feedline outside the house.  Of course, you have to remember to do that!  And it does not offer protection against static buildup during dust storms or storms that sneak up on you and the local TV meteorologist if you leave it hooked up.  I did use surplus telephone company two-plug versions, but I can't seem to find those anymore.  And the tiny screws tended to rust and you could not get the wire disconnected if you needed to change the length of the feedline.  I am using a mish-mash now, including some Radio Shack audio versions that have a big set of screw-down hickies that clamp down on the conductors.

There have been a couple of times when a middle-of-the-night clap of thunder woke me up and I found myself outside barefoot and in my PJs, disconnecting the feedline in the dark while standing in rainwater, remembering I am holding onto 500 feet of copper wire!

73,

Don Keith N4KC
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N4HRA
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« Reply #5 on: May 17, 2011, 03:36:42 AM »

I thank you all for the response to my question,
I will most likely run the ladder line down to the ground post, install the ATU their
and then run the coax back up to the attic.
my ham shack is at the other end of the house and this is the only way I can get the coax in/out

73
Lew
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NN4RH
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« Reply #6 on: May 17, 2011, 04:34:15 AM »

Always looking for the simple solution, but I just use banana plugs and disconnect the feedline outside the house.  Of course, you have to remember to do that! 

Yeah, that's what I did when I had a parallel feedline for awhile. I had a second set of banana jacks attached to a nearby ground rod so I could ground the feedline.
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KD5VHF
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« Reply #7 on: May 17, 2011, 06:32:00 AM »

Always looking for the simple solution, but I just use banana plugs and disconnect the feedline outside the house.  Of course, you have to remember to do that! 

Yeah, that's what I did when I had a parallel feedline for awhile. I had a second set of banana jacks attached to a nearby ground rod so I could ground the feedline.

I used to connect my wires to a ground rod also. They got "HIT" and destroyed the antenna and feed line. I then realized by connecting the antenna to a ground rod that I made the antenna into a very nice large lightning rod!
I now simply disconnect the wires and let them hang in the air ;-)
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KE4JOY
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« Reply #8 on: May 17, 2011, 07:20:16 AM »

Wait you guys think that because the antenna is not grounded it is not suceptable to surge current?
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KE3WD
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« Reply #9 on: May 17, 2011, 07:24:06 AM »

Wait you guys think that because the antenna is not grounded it is not suceptable to surge current?

The grounded wire would be a low impedance path to ground.  Ohm's law should explain the rest. 


73
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KE3WD
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« Reply #10 on: May 17, 2011, 07:25:53 AM »

Old Timers used an open frame DPDT knife switch to disconnect ladder line from the shack equipment. 


73
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KE4JOY
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« Reply #11 on: May 17, 2011, 07:49:33 AM »

Old Timers used an open frame DPDT knife switch to disconnect ladder line from the shack equipment. 


73

Usually that knife switch would connect the antenna to ground when not in use.

Yes I know that a grounded antenna has a lower impedance path. I am just saying when you hang a wire or a chunk of aluminum up high grounded or not it can still be subjected to surge current. Hopefully it wont arc over to something that IS grounded.

A direct strike and all bets are off grounded or not.
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