Message-ID: <000901becd8c$0f99b640$e8daac3e@default>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: "rsgb_lf_group" <rsgb_lf_group@blacksheep.org>
Subject: LF: re problems G3XDV and whippy mast extensions?
Date: Wed, 14 Jul 1999 00:43:57 +0100
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

Hi again Mike, Ahh that explains it...it did have that kind of 'arcing' feel
to it. Difficult keeping a decent spacing for 20kV or so of RF when the wind
blows. I must admit I saw some 3in pyrex insulators at a rally recently,
snapped them up and squirrelled them away.

On the 'whippy mast front'....I have often wondered, living near the sea but
not being a Yachtty, whether it would be possible to brace a light mast in
the same way that racing yacht masts are braced. They have a stand-off in
the middle with wire stays from top to
bottom. I guess this puts the mast in compression, and 'stiffens it up'. I
gather that top notch racers even 'tune' the mast tension, but I dont reckon
that will effect the ERP! I think to keep the capacity of the vertical
section to ground down, the braces would have to be non-conducting, in our
case. I'm not an mechanical engineer so I'm not sure how it would work. I
suspect,like some of the racing disasters, if the wind did exceed the design
value your mast would probably 'go off' like a bolt from a cross-bow. It
wouldn't be any good for HF beams etc. but it might be a useful technique to
get an LF wire a little higher using very light materials..

My other loony idea was to use a balloon, not like Steve does to hold up the
weight of the whole of his 20m vertical (I think), but just to extend the
height of a 15 metre lightweight mast. If the bottom 15m of wire were thick,
supported by the mast, the upper 15m could be quite thin, light wire.( OK
higher losses but its not top loaded so the current tapers to zero at the
balloon) One would not get the top loadin effect of course, but a thumb-nail
calculation suggests that the increase in radiation resistance might be
worth it. A light mast might support a small loading coil at its top, which
might be worthwhile at this sort of height.  I think most of us would like a
30m vertical (wind allowing, of course) The other effect would be to keep
the aerial clear of local obstacles,( which must be quite a problem if there
is even a breath of wind) because to 'blown around bit' of wire would be
clear of houses and many trees.  If it did come down it would just dangle
alongside the mast not drape over the neighbours garden arcing menacingly.
(Full of stupid ideas at this site!)
73 de Alan G3NYK
Alan.Melia@btinternet.com