Message-ID: <517ABCE1.8060802@iup.uni-heidelberg.de>
Date: Fri, 26 Apr 2013 19:44:01 +0200
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <CAMFjj72gqagv0cw7__THvXCXgAbAC=xb82SD4Sp-sGngx2V7qw@mail.gmail.com>
In-Reply-To: <CAMFjj72gqagv0cw7__THvXCXgAbAC=xb82SD4Sp-sGngx2V7qw@mail.gmail.com>
Subject: Re: LF: Fire in the wire
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


Warren,

What is the voltage between the tree (GND) and loop? I thought that the 
voltages are rather small, i.e. below 100V, especially when a large loop 
is used. Isn't it possible to ground the loop?

73, Stefan

Am 26.04.2013 19:21, schrieb Warren Ziegler:
>
> Just a quick report on a failure mode for LF TX antennas.
> Last Fall my original TX loop made up of approximately 500 feet of 
> RG-11 coax suspended from trees went open circuit (both center 
> conductor and shield), some time later part of the wire actually came 
> down. I had thought that abrasion from contact with the trees had 
> eventually worn through it.
>
> What I found was a little more interesting. Looking at the downed end, 
> it appeared that the insulation had melted for a considerable distance 
> and there were burn marks further up the cable. My hypothesis is that 
> the outer insulation was abraded away and the coax shield came into 
> contact with the tree limb causing the burning/melting.
> Will try to get some pictures this weekend and put them up on my website.
>
> Long term if one wants to operate at the kW level either better 
> insulation or a better way of supporting the antenna than trees would 
> be required!
>
> -- 
> 73 Warren K2ORS
>                 WD2XGJ
>                 WD2XSH/23
>                 WE2XEB/2
>                 WE2XGR/1
>