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Author Topic: Under-eave antenna and lightning  (Read 638 times)
KX4QP
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Posts: 396




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« on: July 10, 2019, 03:40:33 PM »

I live in North Carolina, and we get a lot of thunderstorms from early spring through mid-summer (and by then it's hurricane seasons, though some years we get nothing from that).

I've got an 80m center fed dipole that I originally made to hang from a kite line, and a Heathkit SB-102 80-10 SSB/CW transceiver that appears to work in every way I've tested -- needs the switch contacts cleaned up with some Deoxit, but I want/need to check transmit and antenna matching functions, and I can't do that with the FM broadcast antenna (from the back of an old home stereo) that I've been using to test the receiver function.

Would I be increasing the risk of lightning strikes on the house if I were to temporarily string this antenna under the eaves of the steel roof?  The house is just over half as long as the antenna, so it'd wrap around the ends a bit, but I could follow the roof line there, too, or keep the wire horizontal where it crosses the ends (there'll be fifteen feet or so that wraps around to the back side if I keep the wire level).  Obviously not an optimum 80m antenna, but the idea is that I have this antenna now, and if the radio needs something, I'd rather know it before I spend time and money making/buying a multiband antenna.
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K5LXP
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« Reply #1 on: July 10, 2019, 05:00:28 PM »


Why would a wire under the eaves of your house make you any more susceptible than the wires that are already in your house?  But aside from that, it's a steel roof so I wouldn't expect much in the way of a useful outcome from this plan.

Mark K5LXP
Albuquerque, NM
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KL7CW
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Posts: 576




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« Reply #2 on: July 10, 2019, 07:19:10 PM »

For temporary operation and tests, if you are concerned about lightning why not just disconnect your coax feed outside the house when you are not operating.  Now none of us know how much the metal roof and close proximity to the building will degrade the operation of your antenna, but my guess is that it would significantly degrade the performance, but perhaps not enough to make it completely useless for receiving and some local QSO's if we assume you are running something like 100 watts or so. I have installed a few loops around a house.  If under the eves (not a metal roof) it worked moderately OK for TX but rx was quite noisy (but not completely useless).  I later moved the loop further away from the house, probably an average of 10 feet, and somewhat higher.  Worked better on TX and RX, even some DX, but still not great.  Finally a few years later moved the loop mostly away from the house, some parts perhaps 20 to 40 feet high, lots of zig-zags through trees and shed, etc.  Worked somewhat better on TX and RX, even more DX.
   Now this installation was for a friend and it worked for him, got him on the air for many years.  However I think low loops, and dipoles under the eves are probably quite inferior, perhaps even several S units compared to "good" antennas.  The big unknown is the metal roof.  If possible keep the dipole out away from the house, and hopefully below the roof line as much as possible.  Look at farm supply outfits, they have some electric fence insulators which are over 6 inches long which may or may not work in your situation. (probably less than $ 1 each).             Rick  kL7CW
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K0ZN
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« Reply #3 on: August 03, 2019, 09:14:53 PM »

The metal roof WILL couple to the antenna. Very unlikely that will work very well. May be very difficult to get low SWR on that dipole.

--  K0ZN
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W1BR
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« Reply #4 on: August 09, 2019, 08:42:37 AM »

Is the steel roof grounded?  I believe there are requirements for grounding aluminum siding??

You could always install lighting protection on the roof to bring any strikes right to earth.  Regardless, any antenna near that steel roof is going to be compromised, especially if laid parallel to the eave.
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