On Thu, 1 Nov 2007 07:30:25 -0700 (PDT), Gary Slagel wrote:
>Looking at YT it looks like that elevation is going to pretty much
>eliminate any low angle radiation below about 2.5degress and I
>figure that's going to be a huge dx disadvantage in that direction
It isn't only line of sight. It is the diffraction of the wavefront
in that range that has a lot to do with your takeoff angle. IMO, you
would be well advised to run the newer HFTA analysis on that QTH,
using the best data you can find out for 2-3 miles.
Also, study the statistical data that goes with that program for
various station locations to various parts of the world. A rather
small percentage of QSO's occur at a few degrees elevation. HFTA
allows you to overlay the diffraction prediction based on terrain
and your antenna height with propagation data.
I'm not suggesting that a QTH on top of that mountain wouldn't work
a lot better, but it may not affect you as much as you think. I've
got a situation a bit worse than you describe, with a more or less
linear rise of about 350 ft in 3/4 mile in the direction of EU.
Further to the north, that rise continues (still more or less
straight line) to about 625 ft at a distance of 1.5 miles. There is
very little difference between the HFTA plots in those two
directions, especially at low angles. That is, it is the linear rise
near the antenna that seems to be dominating my takeoff angle.
My solution is to go as high as possible (which is what HFTA shows
is best) with dipoles in trees at 100-120 ft, rather than much lower
beams. Taking diffraction into account, HFTA predicts that they
start working at about 5 degrees in those directions. Without
diffraction, the cutoff angle is higher. These antennas work VERY
well throughout the US, but EU is a challenge. OTOH, during CQWWSSB
last weekend, the only EU I worked was far northern EU (OH, LA, UA)
which is the direction I have the highest obstruction. And
propagation from W6/W7 (where I am) was nearly non-existent to EU
HFTA comes on the CDROM with recent versions of the ARRL Antenna
Book, and was written by N6BV (who I think also did YT).
Jim Brown K9YC
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