[TowerTalk] Antennas on a crank-up

[K7LXC]

In a message dated 98-04-15 08:59:59 EDT, MALEXANDER@HEALTHDYNE.com writes:

> I am getting set to put up a 100' aluminum crank-up tower.  On the top,
>  at 100' I plan to put a Force 12 Magnum 620/340.  Up from that, about 8
>  feet -- will go a Force 12 4BA.  I chose these antennas because of the
>  decreased wind loading, as I am (still) a little nervous about having
>  those up at the tippy top swayin' in the breeze with no guy
>  wires....this is my first attempt with a crank-up tower.

     You should be nervous. What manufacturer and model number is the tower? I
think Heights is the only aluminum crank-up manufacturer but I can't find a
hundred-footer in their catalog. They have a 116 foot version (6 sq.ft.) and a
104 footer (8 sq.ft.) so I'm not sure which one you've got. 

      Nevertheless in case it slipped past you, the 620/340 is a BIG antenna
system (13.4 sq.ft. and over 100 pounds). So the only way you can mount ONE of
your antennas is to crank it down significantly. You might want to read Roger
Cox's and Bruce Horn's articles on crank-up loading and derating. They're a
buck each from TOWER TECH. Mounting both antennas would mean cranking it down
even more.

      BTW, Waukesha County is an 80 MPH wind speed zone. According to the
Heights literature, they "are engineered to withstand an 80 MPH windload
pressure". They also mention guying but I would certainly check with the
factory (talk to Drake Dimitry) with your proposed installation. 

      Aluminum towers are like noodles - they move and sway all over the
place. If you want some real excitement in your life, try climbing a self-
supporting aluminum tower. Yee-ha!

      Bottom line? Talk to the factory to get their recommendations and be
real conservative with your installation. You've got way more antenna than
tower at this point - reality strikes. 

73 and GL,  Steve  K7LXC

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