Where to point antennas in storm?
Fri, 6 Sep 1996 08:13:09 -0600
Since some of this discussion was cross-posted, I will do the
same thing this one time and then move all of my comments
over to towertalk.
There is no general answer to this question of where to point the
beam in a storm! It all depends on what you are trying to
accomplish and specific details of the particular installation.
1) If the tower is the weak link in the system (usually not the case
for guyed towers, but it might be the case for a self-supporting one)
then the antenna should be pointed to minimize the load on the
tower by orienting it to put the minimum area towards the prevailing
2) If the rotator needs the protection then the antenna should
be oriented to minimize the torque on the rotator. If the mast is
not mounted at the center of the boom, then the beam should
be pointed in line with the wind direction, rather than having an
asymetrical boom at right angles to the wind which will try to
windmill and torque the rotator.
3) If the elements are the weak link in the system then they should be
aligned parallel to the wind flow.
4) If the boom is the weak link then it should be aligned parallel to
the wind flow.
As you can see it is not as simple as "always do this, or always do
that". It all depends on what is trying to be protected and the
specific details of the individual installation.
For my own installations, I plan to make sure that 1) my towers
are very rugged 2) that my rotators are strong and the beams are
mounted with their booms centered about the mast to reduce the
torque (won't eliminate it since there is always turbulence to deal with)
3) side guy my booms to really beef them up 4) turn the booms
at right angles to the wind to reduce the wind load on the elements.
This is the right decision for me because I use beams with lots of
elements and it is easier to side guy the boom than to side guy
each individual element. Plus it is a cleaner installation to not have
side guys on every element.
Sorry, just no easy answer. There has been an evolution in thinking
on this subject due to the publishing of the cross-flow method of
analysis of the wind loading and much of the earlier information
on how to design Yagis and how to calculate their windloads needs
to be updated because the early work is overly simplistic.
Hope this helps.
John Brosnahan W0UN
24115 WCR 40
La Salle, CO 80645
"Radio Contesting IS a Contact Sport"