On 5/25/2014 6:14 PM, Jim W7RY wrote:
The ON4UN low band dxing book has quite a few good low frequency
antennas in it. Any vintage of the book will do.
Yes, good stuff, but I have more to offer. I'm also blessed with tall
trees (redwoods, twice the height of yours). Over the past year or so,
I've been doing an extensive modeling study to help us make the choices
you're faced with. They are at
http://k9yc.com/publish.htm
That work established a "figure of merit" for height -- on 80M, 10 ft is
worth 0.9 dB up to a half wavelength (133 ft); divide by 2 for 40M. On
40M, divide 10 ft by two, and 67 ft to 133 ft is worth 2.5 dB.
My choices were high wires for 80 and 40, lower dipoles for 30M
(budget), and the small 3-el SteppIR for 20-10. Because I'm in the
mountains, I used HFTA extensively; thanks to the high ridge to the east
of me, 120 ft is the best compromise for the SteppIR. If your terrain is
not flat, you MUST use HFTA extensively).
For 80 and 40, higher is better, so I went as high as I could with wire
dipoles at right angles (they are about 120 ft), then added reflectors
for difficult directions (in my case, east coast, AF, and EU). They tell
me I'm loud in W1, and I can call CQ on 80 during the winter and run EU
(I'm near San Francisco). Use these figures of merit to figure the
relative merit of other forms of antennas.
An important factor is the cost of getting wires up there. I hire tree
climbers (about $750/day) to put pulleys up high with rope through them
and clear branches out of thw way of the wires. I budget one day for
both ends of a high dipole at 120 ft.
I'm really excited about this work. I hope you find it useful. There's
other stuff on the website about antenna construction. When you're in
the tops of these trees, you MUST use counterweights so that tree sway
doesn't break the wires. It WILL happen.
73, Jim K9YC
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