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Message-ID: <000001cacff8$8520f890$0901a8c0@lark>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <MFEJIKCLCMPDFHOKMANAKEAKOFAA.paulc@snet.net>
Date: Tue, 30 Mar 2010 11:53:41 +0100
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Subject: LF: Re: RE: Re: RE: Re: PF per Meter  dependant on wire size?
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Hi Paul the significance of the tress could be a function of the spacing of
your mast from them. I have always used, as a guide, the height of the
mast...thus any trees more than 30m away from your mast are not going to
make too much difference.....they will absorb some I guess, but hopefully a
small portion. Unfortunately the only real test is to try it.
Good Luck
Alan G3NYK

----- Original Message ----- 
From: "Paul A. Cianciolo" <paulc@snet.net>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, March 30, 2010 2:43 AM
Subject: LF: RE: Re: RE: Re: PF per Meter dependant on wire size?


> Alan,
>
> There is no free lunch.
> It sounded too simple to be true..
>
> But installation of the system you describe would not be very difficult.
> Keeping it stable and in one place as you say would be problematic.
>
> Then there is matter of trees.
> Just finished reading about Jim Moritz experiment measuring tree current.
> My tower has many behind it 2 acres of trees that are 60' high
> I am afraid now that any current I do manage to get into the air will all
be
> shunted to ground!!!!
>
> His experiments were done at 137 so perhaps this loss might be less at
> 9KHz??
> I doubt it though
>
> Is there nothing about working this band that is an advantage? :>)
>
> Thank you again Alan
>
> PauLC
> W1VLF
>
>
>
>
>
>
>
>
>
>
>
> -----Original Message-----
> From: owner-rsgb_lf_group@blacksheep.org
> [mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of Alan Melia
> Sent: Monday, March 29, 2010 7:16 PM
> To: rsgb_lf_group@blacksheep.org
> Subject: LF: Re: RE: Re: PF per Meter dependant on wire size?
>
>
> Hi Paul, there could be a slight problem I suspect. As I understand your
> set-up, you have a wire (soon to be wires) from the shack to the top of
the
> mast. The bottom of the wires is about 6feet above ground level.
>
> The problem that I can see is as follows.......ideally you want the extra
> capacitance beyond the "radiating part" of the antenna. The radiatingpart
> being the vertical section in most cases. I think of extra capacitance low
> in the vertical section as shunting antenna current to ground "before it
has
> passed through all the radiation resistance"....so it is lost power. I
> believe when I was searching for ideas fro 136kHz the suggestion was to
> spread the wires at the top of the vertical but cone them in to a single
> point from 20 or 25 feet above ground level. I finished with a flat-top  6
> feet wide but with the vertical
> wired brought in to a single point. This idea is not quite so easy to
> install in your system. You may need to dummy or strainer cords to stop
the
> upper section thashing around.
>
> There is not a lot of advantage to spreading 4 wires over 9m to speading
> them over 3m. my "guess" is you will get about 800 to 850pF with 4 wires
on
> a 3m spreader and about 1000pF if you go to a 9m spreader. (dont ask me to
> explain I knock things over when I wave my arms around :-))  )
>
> Alan G3NYK
> ----- Original Message -----
> From: "Paul A. Cianciolo" <paulc@snet.net>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Monday, March 29, 2010 11:36 PM
> Subject: LF: RE: Re: PF per Meter dependant on wire size?
>
>
> > Hi Jim
> >
> > Thank you for the formula for calculating "C" of a wire.
> > Also the information about adding additional wires is valuable.
> >
> > There are 2 methods I could try with my 55 meters of wire.
> > With the use of fiberglass spreaders, multiple wires could be spread
apart
> > at the top of the tower forming a fan of the wires.
> > With a single point on the shack end where the wires would all would
> > combine.
> >
> > Probably better would be to support 4 wires equally spaced on a fiber
> glass
> > poles 9 meters long on both the tower end and the shack end.
> >
> > This seems too easy Jim, there must be a point of diminishing returns.
> >
> > Knowing that the wire is 55 meters long, and 1 wire measures at 340 pf
> would
> > you hazard a guess as to 4 wires 1 meter apart each the value of "C"
> >
> > Do you think 700 pf is achievable?
> >
> > Thank you for reading
> >
> > PaulC
> > W1VLF
> >
> >
> >
> >
> > -----Original Message-----
> > From: owner-rsgb_lf_group@blacksheep.org
> > [mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of James Moritz
> > Sent: Sunday, March 28, 2010 4:09 PM
> > To: rsgb_lf_group@blacksheep.org
> > Subject: LF: Re: PF per Meter dependant on wire size?
> >
> >
> > Dear Paul, LF Group,
> >
> > One formula for C per unit length:
> >
> > C = 24/Log(4H/d) picofarads/m , H= height, m, d = diameter, m
> >
> > So the capacitance depends on the logarithm of the ratio of height over
> wire
> > diameter, which only varies a little for a large change in diameter, e.g
> for
> > 1mm wire at 10m high = 5.2pF/m, 10mm diameter wire at 10m high 6.7pF/m.
> > Actually this formula only applies to an infinitely long, uniform,
> > horizontal, straight wire. In practice, the presence of ends, downleads,
> > things on the ground, insulation on the wire, etc. etc. will all have an
> > effect, and are difficult to calculate, so 6pF/m is usually as good an
> > estimate as you are likely to get.
> >
> > Adding multiple wires will increase capacitance. If the wires are many
> > metres apart (spacing large compared to height), you can multiply the
> > capacitance by the number of wires. But usually, the wires are more
> closely
> > spaced, and there is less increase in capacitance. The figures I have to
> > hand are for two 1mm wires 100mm apart, C is higher by 39% compared to a
> > single wire, 1m apart and C is 68% higher.
> >
> > Cheers, Jim Moritz
> > 73 de M0BMU
> >
> > ----- Original Message -----
> > From: "Paul A. Cianciolo" <paulc@snet.net>
> > To: <rsgb_lf_group@blacksheep.org>
> > Sent: Sunday, March 28, 2010 8:24 PM
> > Subject: LF: PF per Meter dependant on wire size?
> >
> >
> > > Hello,
> > >
> > > I see from previous posts that a number of  aprox 6 PF what size wire
is
> > > this for?
> > >
> > > Increasing wire size should in "C"  as should several conductors in
> > > parallel
> > > spaced a few feet apart.
> > >
> > > PauLC
> > >
> > > W1VLF
> > >
> > >
> > >
> > >
> >
> >
> >
>
>
>