Antenna and Lightning
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Antenna and Lightning
Looking to put a recieve antenna up in the atic of our new home ans run coax to a wall plate. What precations and steps should I take to make sure its storm safe and to eliminate the possiblilty of lightning striking it and burning my house down.
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thebigphish
- Posts: 1477
- Joined: Sat Nov 29, 2003 10:10 pm
- What radios do you own?: AM/FM
Re: Antenna and Lightning
If it's "in the attic", it will be appreciably no more an attractor for lightning than the highest point on your house.
"How do you plan to outwit Death?"
"With a knight and bishop combination; I will destroy his flank." --Antonious Block
"With a knight and bishop combination; I will destroy his flank." --Antonious Block
Re: Antenna and Lightning
"If it's "in the attic", it will be appreciably no more an attractor for lightning than the highest point on your house."
True but missing the point: IF you take a hit (and houses ARE struck by lightning all the time), the lightning will see that antenna as a dandy path to ground, and much of the strike energy will flow down that antenna.
Basically, the ARRL guidelines are your friends here. To keep it simple:
1) Nice HEAVY ground wire, bonded to the antenna, and run OUTSIDE the house as much as possible. Connect it TO THE SAME GROUND POINT AS YOUR ELECTRICAL SERVICE ENTRY!
2) Nice Transi-Trap or Polyphaser suppressor on the feedline to your radio, again, with a GOOD ground line.
You want the main ground OUTSIDE the house, because when the lightning hits, LOTS of amps will flow through that copper. There will be a HELL of a magnetic field around that wire, and it WILL want to move - you want it moving OUTSIDE. It will also possibly vaporise - if that happens, it will be as though you had detonator cord instead of copper. You want that blast wave OUTSIDE the house where it can dissipate.
You want to keep everything you can at the same potential - hence tying onto the same service ground as the electrical system. You DON'T want a big potential difference between the house ground wires and the antenna ground - that's what causes the lightning to jump to the house wires.
True but missing the point: IF you take a hit (and houses ARE struck by lightning all the time), the lightning will see that antenna as a dandy path to ground, and much of the strike energy will flow down that antenna.
Basically, the ARRL guidelines are your friends here. To keep it simple:
1) Nice HEAVY ground wire, bonded to the antenna, and run OUTSIDE the house as much as possible. Connect it TO THE SAME GROUND POINT AS YOUR ELECTRICAL SERVICE ENTRY!
2) Nice Transi-Trap or Polyphaser suppressor on the feedline to your radio, again, with a GOOD ground line.
You want the main ground OUTSIDE the house, because when the lightning hits, LOTS of amps will flow through that copper. There will be a HELL of a magnetic field around that wire, and it WILL want to move - you want it moving OUTSIDE. It will also possibly vaporise - if that happens, it will be as though you had detonator cord instead of copper. You want that blast wave OUTSIDE the house where it can dissipate.
You want to keep everything you can at the same potential - hence tying onto the same service ground as the electrical system. You DON'T want a big potential difference between the house ground wires and the antenna ground - that's what causes the lightning to jump to the house wires.
This is my opinion, not Aeroflex's.
I WILL NOT give you proprietary information. I make too much money to jeopardize my job.
I AM NOT the Service department: You want official info, manuals, service info, parts, calibration, etc., contact Aeroflex directly, please.
I WILL NOT give you proprietary information. I make too much money to jeopardize my job.
I AM NOT the Service department: You want official info, manuals, service info, parts, calibration, etc., contact Aeroflex directly, please.
Re: Antenna and Lightning
You're better off installing lightning rods on top of your house than grounding an antenna that's inside the attic. If the house gets struck and jumps to the antenna that is well grounded, that wire is going to get HOT, and can still jump to the house wiring on the way out. Think of all the insulation and combustibles in your attic that you'd have to run that wire through or past. You're practically inviting 100,000 amps into your attic, and praying that it makes it out without starting a fire.
Properly installed lightning rod(s) - on the roof - will safely direct a lightning strike to the ground without the risk of it entering the house.
Properly installed lightning rod(s) - on the roof - will safely direct a lightning strike to the ground without the risk of it entering the house.