tower5.art

一个很小和天线计算程序

SUBJECT: Towers, part 5

    SMALL STEEL CRANK-UPS:  I own one of these babys.  The tower has
two sections, each nineteen feet six inches. The base section is  
nine inch triangular, while the upper section is seven inch triangular.
The upper section is rasied and lowered with a small boat winch.

    The tower is a lay-over design, hinged at the bottom.  Since I have 
another 18 foot, 15 inch triangular tower beside it that is used as a 
work stand, I have a second boat winch and pulley system to lay the 
crank-up over on it's side.

    These towers are stronger than they appear and can raise a large
beam to a height of 35 feet safely.  To add to that strength, a
push-up mast drive-shaft configuration was added to the tower, 
transforming the weight of the antenna to the base.  The rotor is located
beneath the tower, as well as a set of vertical bearings (1000-lb
lazy susan bearings), in a two foot high steel stand.  There is no
weight on the rotor. 

    There are other configurations to consider.  Small Steel crank-ups
would be excellent for VHF/UHF antennas with the rotor mount on top
of the tower.  They are excellent supports for wire antennas and 
verticals. 

    Some of the draw-backs are:

    o They are made from steel and are heavy.
    o They rust.
    o They require yearly refurbs.

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    ROHNS:  These are probably the most common type of antenna tower
used by hams today for QTH set-ups.  The ROHN name is actually a company
which to my surprize, many hams didn't know.  I got a good laugh when a
third ham told me it was a type of antenna and not a company.  Oh well.

    The Rohn tower sections are easy to install but have some draw-backs.
They should be greased where they meet.  Stainless bolts and nuts are a 
must.  And the tower needs guying past two sections with anything larger
than a VHF beam. 

    A good base is needed for proper support as in any tower and a lay-over
hinge is recommended.  Two adults can set-up a four section hinged tower 
in minutes (KB4DCZ & KB4YLY) with guy wires.

    The Rohn tower is excellent for shaft-drives as the push-up mast can be 
replaced with 2-in standard pipe.  The Rohn sections come various flavors
and can meet most hams needs.  Many of these sections can be purchased
at local hamfests or you can buy new.

    Rohn is the way to go for a first tower.

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-WS