It is more a question of practicality.
It is being done by those with crankup towers, if they want to optimize, say
between DXing at low angles and domestic QSOs at higher angles. If you want
to be flexible, get crankup tower and StepIR antenna.

What you suggesting is asking for mechanical complexity, guy wires, multiple
antennas on the same tower in the way, etc.

Propagation is not clear cut X angle. It is more like drunken, wobbly
signals varying in angles, polarization and direction. Antennas have quite a
wide lobes to accommodate most of that. Serious DXers and contesters use
stacks that give them instantaneous selection of major angles.

Tilting up antenna about 5 deg. helps somewhat, beyond that it doesn't.
Vertical angle of beam is given by the height of the antenna.

So it the question of practicality vs. "precision" and complexity. Moving it
10 ft up or down doesn't really buy you anything.

73 Yuri, K3BU

"CW" wrote in message
oups.com...
Dave,

Thanks for the reply. Multiple switched Yagi's at various heights is a
practical approach, and I'm delighted to hear that "sometimes there is
a lot of difference". What you are describing is a coarse grained
approach to the problem, which is also commonly done in the horizontal
plane by switching vertical antenna arrays, etc.
A fellow ham in the area has a Yagi mounted about half way up his guyed
tower, on a swing arm. It can rotate, but is limited to about 300
degrees of rotation. A similar setup could be used on a side mounted
tower trolly, where the height could be continuously varied by 30 feet
or more, AND rotated through about 300 degrees.
73,
CW-AI4MI



its really only practical on crank up type towers, for those with guyed
towers its usually not possible.

10' change on 20m would likely not be very useful though. my hf stacks
for
10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with
those
height changes (which i can select instantly so i can make direct
comparisons without worrying about fading) there is often little
difference
between antennas... though sometims there is a lot of difference. This
highlights the fact that often the signals arrive with a wide range of
angles, though at some times they must be in a relatively narrow range.
so
having multiple antennas at different heights that can be selected in
various combinations is a handy thing to do.