grrr_arrghh

Hi.

I don’t think I would ever want to do this; its too risky, but simply because it interests me, I’m going to ask anyway.

Say I am in a valley, and the signal to my car radio is not very good, because of the sides of the valley blocking the signal (I don’t know if this actually happens, but never mind). So, I get my kite, and attach a really long piece of wire to it. Then, I send the kite up into the air, and it takes the piece of wire above the level of the hills, so that it can receive the radio signal (the wire is connected to where the aerial usually is). I don’t know if this would actually work, but again we’ll gloss over that for the moment.

However, stupidly, I don’t keep an eye on the weather, and a thunderstorm brews up, and my ‘aerial’ gets hit by lightning. The lightning streaks down my really long wire, and blows my radio to pieces, and quite possibly the current would jump to me (who is sitting near by), killing the radio and me. This would be slightly inconvenient.

How, then, do I protect it from this kind of high voltage. Could I put a high value resistor in the line, so that when a reasonable amount of current is drawn, a high voltage fuse would blow when the current reaches above a certain point?

Also, when the fuse blew, how would I prevent the current from trying to find another path to earth (probably me)?

Am I just talking complete and utter rubbish? Or is there a good way to do this?

Thanks

Tim

Nigel Goodwin

Basically you can't protect against a direct lightning strike on an aerial, even a close strike is likely to destroy any electrical items in your house.

If you think about it, a standard fuse is 20mm long, so when the fuse blows you have a 20mm air gap between the ends. The lightning has already jumped across an air gap probably measured in the hundreds of feet - I don't think a further 20mm is going to stop it :lol:

I see a LOT! of lightning damaged equipment at work, I've even seen one house which was struck twice, roughly a year apart. Mostly it's from near strikes, on the odd occasion of a direct strike the damage is unbelieveable.

This is disregarding the kite idea, interesting as it would be to have a kite that flys itself - personally I can never get the things off the ground!.

If you need a high aerial you need to use a tower or mast, fitting this with an effective lightning conductor should help to protect things.

Also, a lot depends on what radio signals you are trying to receive, if it's FM you don't have a long aerial - and if it's AM (where you do) the quality is so poor it's not worth bothering :lol:

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grrr_arrghh

a self flying kite, now theres an idea... :lol:

i was slightly concerned about the air gap in the fuse, for that very reason.

A couple of years ago lighting hit the phone line on a house just down the road (the bloke whos house it was got thrown accross the room) and the surge came down the phone line and blew my modem to kingdom come. Luckely the 'blow out' resistors on the modem blew (leaving some lovely black scorch marks) and protected the rest of the computer.

Point taken about FM and AM, as I said, I would never bother, I was just interested in the pricipal.

Thanks a lot,

Tim

andrew2022

av herd before if u have knots in the cables and itz hit by lightning, the power works against itself burning out the cable nd nothin (or very little) past it. any1 kno if this is tru?

grrr_arrghh

the same applies as with nigels point about the fuse, the lighting has already jumped several hundered feet or more, a break in the cable isn't going to stop it now... At least I wouldn't have though so, or are you trying to say that all the energy is taken up by burning te cable?

andrew2022

from what i read, the energy is used to burn the cable out so hopefully itll spend more time damaging the cables rather than computers etc

ChrisP

This is probably what you are talking about. The cited author (Mark Minasi) does in fact make the claim that knots in power cords will protect equipment from line surges -- I have two different editions of the referenced book on hand here. If anyone wants the page numbers, let me know and I'll post them.

He's not alone in recommending this, either.

Modern version of an "old wives' tale"? Who knows??

Nigel Goodwin

I've seen the plaster blown off the wall for a metre to both sides of every wire in the house - I doubt a knot is going to stop anything.

I suspect this has come about from the practice of looping mains leads through ferrite rings, but it's to help reduce interference - not stop 5,000,000 volts!.

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Oznog

33' fiberglass mast, $99, more practical than a kite:

http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW

RGBrainbow

Hi,
just to continue the kite thing:
How about rising a second kite higher than the 'antenna-kite' but with the wire grounded?
This should prevent the 'antenna-kite' from being toasted.
regards
joachim

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laroche73

An old amateurs' (wives?) saying was that a vertical antenna grounded through a heavy-duty lightning arrestor (spark gap ><) provided a "cone of protection" around one's property. Sounds good at first glance, but then so did Get Smarts' "cone of silence". The opposing viewpoint held the ariel attracted undue attention to itself.

grrr_arrghh

hmm, good point, although if you are stupid enough to fly a kite in a thunder storm, you'll get what you deserve...

I just posted the question because I wondered if there was an electronic way to do this, not because I actually thought it was a good idea!!

although to have a lightning conductor is probably the only way to do it (it would be easier with the fibreglass pole than the kite, but still).

Thanks for the ideas guys.

If there's one thing I've learnt, its not to fly kites in storms!!

Tim

andrew2022

[quote="grrr_arrghh"]is that from experience?! :lol:

In Lupus Corpore

The 2nd kite approach, although probable, isn't reliable. There are reams and volumes on the subject of lightning protection on the internet. Lot's of good data collected. Still, the bottom line is, the exact nature of lightning is not understood. The experts agree, though, on one characteristic; lightning is unpredictable. It has been known to ignore a radio tower with arresting devices to destroy a wooden mine shack. A number of people have been killed by lightning strikes under clear, sunny skies. It often, apparently, follows the path of the MOST resistance. It's true lightning tends to favor elevated objects (towers/trees.) But don't plan your life on what people THINK they know about it. Lupus

quote: "I yam what I yam." Popeye

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grrr_arrghh

lol, no, i just meant what i had learnt from this thread...