I'm starting to plan for the 160 meter contests. I've used an inverted L in
the past with satisfactory results. This is a LOW inverted L, the vertical
part being only 43 ft tall. This year I'll be using a Marconi at least some
of the time - again with a 43 ft vertical segment and two top wires about 70
ft long each. These two choices are all I can fit on my small lot, hence
the sub-optimal dimensions. Both would be fed against a radial field of 32
radials from 30 to 80 ft long (again space constrained). Due to antenna
restrictions, I need to take them down during the day and put them up at
dusk - actually a fairly fast operation!
Have spent a fair amount of time modeling these antennas. As expected, the
Marconi shows up as better at low angles - about 3 db better in the
direction that is down on the inverted L due to its asymmetry and about
equal to the inverted L in the opposite direction. Max radiation angle is
26 degrees for the Marconi vs. 30 degrees for the inverted L. So I will
definitely use the Marconi when trying to maximize DX performance.
OK, now for the question for you folks. As expected, the Marconi has a
vertical null whereas the inverted L has lots of high angle radiation. The
two are equal at a vertical angle of 55 degrees, and above that the inverted
L is stronger. The Marconi is down about 2 db at 60 degrees, 4 db at 70
degrees and 7 db at 75 degrees. Above 75 degrees, the inverted L is 10 to
15 db better. These numbers are for the direction not favored by the
inverted L. My question is: is the better performance of the inverted L
above 60 degrees of any practical advantage for working close-in states?
Phrasing it another way, what are the optimal take-off angles on 160 for
working stations within a radius from 100 to 1000 miles? I'm located in
Colorado, if that is any consideration.
Thanks and 73
... Craig AC0DS
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