Message-ID: <00cb01bfc1e4$d4aee840$c4804dd1@tractorb>
From: "Dave Brown" <tractorb@ihug.co.nz>
To: rsgb_lf_group@blacksheep.org
References: <16548447.958758107528.JavaMail.imail@bubbles.excite.com>
Subject: Re: LF: Re: Puckeridge Decca station - Big & small antennas
Date: Sat, 20 May 2000 10:51:53 +1200
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> Perhaps I missed it, but I would be very interested to know why the
umbrella
> ribs are extended so far-----

 Hi John
 I have been in the habit of keeping some of the more interesting posts on
this reflector as there is no message archive but I don't seem to have kept
the one in question.( And it is possible I followed a link elsewhere to get
the information) As I recall it was a modification of the original structure
as a result of storm damage, the structure 'as is' being a more maintainable
compromise. I think the down wires were originally supported around mid?
mast height on horizontal struts that projected radially outwards quite some
distance from the mast axis. Whoever posted the original info may be able to
provide more information.

As a top loading exercise  the setup 'as is' looks to be far from optimum
but the efficiency is obviously still fairly good. Again, some figures were
quoted a while back for the setup 'as is', but I can't recall them.
My suggestion of 8 down wires was based on Derek's comments but there may
be 10. It's obviously in that order and  I would be very interested to see
what happens if the bottom ends were all temporarily strapped back onto the
insulated tower legs.
 Don't have my 'extract' from Watt handy but seem to recall that optimum top
loading  for a short vertical was where the 'droop' was no lower at the
outer ends than around 70% of the mast height.  A few other constraints as
well, but you get the general idea.   The 'as is' structure at Puckeridge is
not a conventional top loaded structure though, and thats why it is of
interest as there may be some useful lessons there for us all. Be interested
in the derivation of your formula John.
73
Dave, ZL3FJ