Roy Lewallen wrote:

Close. Sometimes two or more propagation modes are possible, such as
single and double hop. From here to say, New York, I might have single
hop at 3 degrees and double hop at 12. (Please forgive me if those
particular propagation angles can't really occur at the same time, but
they're in the ballpark.) It doesn't matter one iota what the angle of
maximum radiation from my antenna is. All that matters is the gain or
field strength at elevation angles of 3 and 12 degrees. All the rest of
the radiation will go some place besides New York. As a general rule, I
can get a stronger signal to New York with X dBi at 3 degrees than the
same gain at 12, because the single hop path loss is usually less. So it
might pay me to maximize my gain at that angle at the expense of 12
degrees. On the other hand, the other station's antenna pattern is just
as important -- if it has a lot more gain at 12 degrees than 3, he might
not hear me if I put out most of my energy at 3 rather than 12. But in
any case, it doesn't matter how much I'm radiating at 1, 5, 7, or 15
degrees, or what my antenna's maximum angle is. All that counts is how
much I'm radiating at 3 or 12 degrees. Other than manipulating your
antenna to radiate more or less at those two angles, you don't get to
"manipulate propagation" to support other angles at a given time,
frequency, and path. You're stuck with those until the ionosphere
changes. Knowledgeable DXers (which I'm not) spend a lot of time working
out what the angles will be for propagation to various target locations,
and how to design, build, and switch antennas to maximize the amount of
radiation at those angles.
snip
Roy Lewallen, W7EL

Roy

The Canadian with 2 calls, VE3GK/VE2GK, Gerry King, made a very nice 20
meter antenna system, which he gave a great talk about at our local
hamfest in northern NY back around 1978 +-. This system was unique, at
least then, in that he had 2 20 meter beams that could be used singly,
upper or lower, or as a stack, and could independently vary their
heights. He reported very good success, since he could vary the angle
of greatest radiation at will.

He is now a silent key, unfortunately, but his site is still up. I will
leave it to those interested to find it, it's not hard, but his heirs
don't need useless traffic. I am not sure if his old system is pictured
on the page.

tom
K0TAR