Re: LF: Fire in the wire

[Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>]

Hi Warren,

OK, that explains it ;-) I didn't actually do any calculations, just thought about what Bob said

>hi voltage on verticals .low current
>hi current on loops low voltage

But you're running decent power levels and your signal is strong, so the losses must be low, i.e. the currents must be high. Do you really get 50A @ 1kW, i.e. the loop losses (including the capacitor and environmental losses) are in the range of 0.4 Ohm?

When using an isolating transformer, it is possible to ground the loop anyway. But it is not sure that it improves the situation.

Laurence's earth mat is a good idea :-)

73, Stefan/DK7FC

Am 27.04.2013 01:28, schrieb Warren Ziegler:

Hi Bob,

    Yes but Bill always worked at the 1W level. 

I forget the exact numbers but the loop has an inductive reactance of 100-200 ohms, when you multiply that by a loop current of 50A you can get 10kV.

BTW, my RG-11 loop was put up by Bill and I in 2005 - no complaints!

73 Warren

On Fri, Apr 26, 2013 at 7:14 PM, <riese-k3djc@juno.com> wrote:

Thought the loop info Bill Ashloch developed pointed to high currents in
the loop
so a large conductor needed ,, but low voltage and I remember ( ? ) his
idea of pushing
soft plumbing copper through trees and just supporting the CU on the
branches
hi voltage on verticals .low current
hi current on loops low voltage

Bob K3DJC

On Fri, 26 Apr 2013 19:44:01 +0200 =?ISO-8859-1?Q?Stefan_Sch=E4fer?=
<Stefan.Schaefer@iup.uni-heidelberg.de> writes:
> 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
> >
>
>

--
73 Warren K2ORS
                WD2XGJ
                WD2XSH/23
                WE2XEB/2
                WE2XGR/1