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" <[email protected]>
To: <[email protected]>
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: [email protected]
> [mailto:[email protected]]On Behalf Of James Moritz
> Sent: Sunday, March 28, 2010 4:09 PM
> To: [email protected]
> 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" <[email protected]>
> To: <[email protected]>
> 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
> >
> >
> >
> >
>
>
>
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