----- Original Message -----
From: "G4WGT Gary" <[email protected]>
To: "Rsgb_Lf_Group" <[email protected]>
Sent: Sunday, January 04, 2004 10:55 AM
Subject: LF: Antenna's
Hello again to all at LF,
Happy New Year to you all.
I have had a few days away over NY so I had quite a lot of e-mails to look
thro'.
I see that there has been some debate on antenna's again which suits me
fine
because I am considering trying to improve my LF antenna system. I need to
improve on the support & insulation of the antenna since my recent
experience with corona bringing down part of the antenna, so I going to
try
a different antenna arrangement at the same time.
I have only got a small back garden & at the moment the arrangement is
like
a 80 to 90 mtr loop pulled in to the centre from the middle of the sides &
then pulled upwards to the top of my 14 mtr mast & secured at the lower
corners, this makes it take up a lot less space for the amount of wire
used
(An example of the shape is like a Maltese Cross with the centre up in a
peak & the wide sides of the cross sloping steeply downwards). The "loop"
is
fed with 72 ohm twin feeder at the peak which allowed me to use it on the
80
M (3.5 Mhz) band with a balanced matching unit. Using this gave a great
increase over the umberella top loading with 4 wires following the
criteria
set out on one of the web sites (I think Rik ON7YD).
Hi Gary
My suggestion is to use the mast as a support for a vertical arrangement.
Connect all horizontal wires regardless of configuration together at the top
of your 14 metre mast and use a vertical drop lead to connect to your
loading/matching coil. ie a top loaded vertical. Keep the drop wire about 1
metre out and away from the mast, the wire does not have to be exactly
vertical pull it out at the bottom end about 2 metres. I am assuming your
mast is earthed, if not use the mast as the vertical radiator with the top
wires connected directly to it at the top and feed the bottom end of mast to
the loading coil. Resonate the coil for your preferred frequency on 136 khz
and use a smaller coil at he bottom feed end in series to earth as a 50 ohm
matching device. Earth the coax braid and tap the coax centre conductor up a
few turns from earth to get the perfect match. A small call is preferable to
get an accurate match, tapping up the large coil from the bottom is too
coarse.
Hope this helps you but maybe you know all of this already hi
73 de Mal/G3KEV
| 