Message-ID: <003801c9cfed$3754c170$0301a8c0@mal769a60aa920>
From: "mal hamilton" <g3kevmal@talktalk.net>
To: <rsgb_lf_group@blacksheep.org>
References: <4A01AEA0.1030308@btconnect.com> <4A01B25C.2040404@btconnect.com> <00a201c9ce65$850fe540$0301a8c0@mal769a60aa920> <6BA400053F4E4A45935BEA7FF2FC10EC@JimPC>
Date: Fri, 8 May 2009 15:56:49 +0100
MIME-Version: 1.0
Subject: LF: Re: Re: 500kHz Portable
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Jim
You do not need 2 masts for an inv L or T antenna.
The so called horizontal wire(s) can slope down and the far end tied to a 
bush or tree, or a stake in the ground via an insulator, as far away as 
possible from the vert section, the longer the better.
Keep it simple.
mal/g3kev

----- Original Message ----- 
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, May 06, 2009 7:26 PM
Subject: LF: Re: 500kHz Portable


> Dear Richard, LF Group,
>
> I would suggest using an "umbrella" top-loaded vertical using a telescopic
> fibreglass mast. From experience, antennas with horizontal sections like
> inverted Ls or Ts have the disadvantage of requiring at least two masts
> (unless there is a suitable support already on your hilltop), and are a 
> real
> handful when the wind starts blowing due to the masts flexing, requiring
> several guys to keep the antenna in shape. The umbrella is somewhat less
> efficient for the same overall height, but only needs a single mast, and 
> the
> sloping top loading wires double as guys to keep the mast straight. The
> height is the most important dimension. A 10m mast would make a reasonable
> 500kHz antenna.
>
> For a reasonable estimate of antenna capacitance, assume 6pF per meter of
> wire. For antennas with a number of wires running close together, such as 
> an
> umbrella, the actual capacitance will be a bit lower due to proximity
> effects, but this is a good first estimate. You can use NEC antenna
> simulators to calculate the capacitance quite accurately, although the
> resistance will probably be way off. Small antennas will have very sharp
> resonance, so you will want to add a variometer to your loading coil, or
> some other means of fine tuning. G4FGQ's DOS software runs fine in a DOS 
> box
> under Windows 98 and Vista here.
>
> For insulated ground radials to work well, their capacitance to ground 
> needs
> to be much larger than that of the antenna, so you probably want a few
> hundred metres of wire in total. If the ground is soft, a few 1m ground 
> rods
> connected together works well as a ground.
>
> There is a lot of handy info on LF antennas at
> http://www.wireless.org.uk/on7yd/index.htm
>
>
> Hope to work you /P soon...
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>
>>
>>> Dear all
>>>
>>> I am hoping to be granted an NoV for portable operating on 500kHz. I
>>> have parts on order for the GW3UEP Economy transmitter which will be run
>>> on 12 Volts. Suggestions for portable aerials that can be set-up by one
>>> person on remote and windy hilltops will be most welcome.
>>>
>>> 73
>>>
>>> Richard
>>> G3CWI
>>>
>
>


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