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Re: LF: Re Antenna experiments

To: [email protected]
Subject: Re: LF: Re Antenna experiments
From: "James Moritz" <[email protected]>
Date: Wed, 13 Mar 2002 12:07:33 +0000
In-reply-to: <[email protected] 5>
Reply-to: [email protected]
Sender: <[email protected]>
At 03:13 13/03/2002 -0800, you wrote:
BTW I have had some problems with burning at the top of the fibre glass mast and am wondering whether the filler might be carbon black??
73, John, G4CNN
Dear John, LF Group,

I think the carbon is just what is left after the resin bonding the fibreglass has been decomposed by the discharge. I'm sure a chemist could tell you more, but I think it is true that virtually all resins are organic compounds that leave a carbon residue when burned. I have had similar sooty residues after arcing on various types of plastic, as well as fibreglass and wood - usually the discharge leaves an interesting branched pattern of the black residue. The process seems to be a vicious circle - once the residue is formed, it provides a conductive path for the discharge to spread along - much the same as the "tracking" you sometimes get on car engine ignition components. I have actually seen it happening - little white arcs move across the surface of the plastic, leaving a smouldering trail behind them.
On my antenna I have largely stopped this happening by fitting "corona
rings" - these are just hoops of wire about 100mm in diameter attached, and
electrically connected to, wherever the highest field gradients are - the
ends, corners, and junctions in the wire normally. They reduce the
potential gradient and suppress the discharge.
Cheers, Jim Moritz
73 de M0BMU

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