I can see this is the beginning of a long thread since everyone has their own ideas. In commercial work a sharpened spike above the thing to be protected is to DRAW the lightning to a well insulated and very well grounded ground system. This is to protect the equipment below it. To dissipate, the ball should be rounded like a car radio antenna to gently discharge the corona. We put up a series of 150 foot towers at work with a 21 foot stainless sharpened lightning spike above the tower top to draw the lightning. All of our ( 92 each) microwave towers had a 3 or four inch diameter sharpened brass rod 2 feet above the tip top of the tower. It's ground cable was insulated from the tower all the way down. Of course the tower and all the guys were also grounded to the common ground. A dipole can easily discharge static build up with a 100 k ohm resistor of at least 1 fourth watt. This keeps the system equalized. Lightning usually hit the HIGHEST ( though noy always) spot, so if there are taller trees they would get it first. I like insulated wire instead of bare since the damp wind will not build up thousands of volts when it blows over..just before a storm. For fun take the antenna connector and put in a mason jar and place near ground and watch the 4 inch long blue firs just before a storm on a hilltop. A Johnson Matchbox sounds like a fourth of July celebration if left connected. I guess, in the end a direct strike is bad news in every case. Most of us are really talking about big static discharges I think. A real strike will blow every receptacle in the house out and the wire on on side of every power cord will vaporize and the fuse box will be blown off the wall. Let the tall trees take that!.. 73 Mike ----- Original Message ----- From: "Jim candela" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" <[email protected]> Sent: Saturday, August 05, 2006 2:36 PM Subject: [AMRadio] Antenna Idea and lightning precautions
> > > Hi All, > > I am contemplating putting up an inverted Vee antenna where the center > point is above my house suspended with a 30' Lowes push up mast attached to > my roof with a tripod mast base made for roof mounting. This would make the > apex at almost 50', and with the trees around my home, the ends at about > 30'. Other locations that I might have the antenna apex at will be densely > surrounded by trees, and I am trying to avoid that. > > My question is about lighting concerns with this approach. I would have > multiple 12 awg ground straps from the mast base to earth ground via copper > ground stakes at least 5' long. This would act as a counterpoise for the > antenna, and provide a DC ground reference for the 30' mast. My fear is that > the antenna would attract a lightning hit (direct) and that would cause my > home to burn up in a flaming fireball. > > Then I was thinking about how lightning rods work, and when done > properly, don't lightning rods work by having a sharp point at the tip, > where they bleed the static (a corona discharge) to prevent a lightning > strike? If so, why can't I take a 1/8" stainless 8' whip with a point on > top, mounted above the inverted Vee apex, and use that as a lightning rod? I > guess I'd need to beef up my ground wiring scheme just in case of a direct > hit. Any suggestions? > > I am hoping for having more lightning protection with my antenna in place > over that of no antenna at all? Is this possible? > > Regards, > Jim Candela > WD5JKO > -- > No virus found in this outgoing message. > Checked by AVG Free Edition. > Version: 7.1.394 / Virus Database: 268.10.7/409 - Release Date: 8/4/2006 > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb >
