When talking about improving the VK6VZ antenna system in a recent e-mail, I
mentioned the top-loaded delta loop, which drew interested enquiries from a
number of reflectees. As there seems to less knowledge about this antenna
than I thought, the following should help anyone interested in trying one.
The top loaded delta loop (TLDL) was originated by Frank Witt and first
described in Ham Radio magazine in December 1978. You can think of it as a
3/4-sized delta loop with a 1/8 wave-ish top loading wire, fed half way up
one of the vertical sides to achieve vertical polarisation. There is a
great up-date in QST's Hinks and Kinks column in the June 1998 issue,
written by Walter K1YZW, which looks at some different ways of dealing with
the orientation of the loading wire for maximum performance.
Quoting K1YZW: "for low frequency DX work with a simple antenna, the
vertical TLDL is hard to beat. Consider that it is smaller, yet has the
same, or even more, gain than a full-sized delta, depending on local
factors. It may outperform a 1/4 wave vertical due to its elevated feed
point and despite its simplicity, has adequate bandwidth. Best of all, the
TLDL requires no radials."
For 160m, I guess the TLDL would require something like 132' sides, with a
loading wire of around 88 - 96' for resonance. If sloped at around 30
degrees to the vertical, an 80 - 90' tower would probably be adequate to
support it. In the K1YZW installation, Walter slopes his TLDL at 30 degrees
to the vertical - with the top loading wire also sloped at 30 degrees to the
vertical in the opposite direction - giving an 60 degree apex angle between
the TLDL and its top loading wire.
Hope this is of interest.
Vy 73,
Steve, VK6VZ
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|