[TowerTalk] Counter-balanced "Tower" Design

[K7LXC at aol.com]

In a message dated 2/25/2008 12:42:59 P.M. Pacific Standard Time,  
towertalk-request at contesting.com writes:

>  I have been looking at a number of options for a fairly  light-weight, 
free-standing (unguyed) tower (mast) with a counter-balanced  tilt-over.

> The antenna(s) I am considering are simple and  light-weight, either

>  1)  a 20 meter wire Moxon,  or
2)  a 20 meter - (or 5 band) Hex-beam.

>  The mast  height would be between 25 and 30 feet.

>  My QTH is on a high  bluff about salt-water.  The mast base would be at 
about 100 ft  elev.  The ground then slopes very gently to the edge of 
the bluff,  which then drops almost vertically about 80 ft to the beach. 
The  distance from mast base to bluff is about 60-70 ft.  

>   For various reasons - esthetic and neighbors, and installation and  
maintenance, I am looking at a low elevation, low visual impact antenna  
with a tilt-over capability.  Not a crank up.  Not a  "traditional" 
looking lattice tower.  I don't want to climb.  I  want to lay the tower 
over for maintenance and wind (it can blow a lot  here!)  I have 
considered the MA-40.  I think it is over-kill  for my situation.  I also 
don't like the tilt-over scheme - cable and  winch.

>  So, I considered a simple tilt-over.  I have a  DX Engineering vertical 
tilt-over.  It tilts from the base.  The  combined antenna/mast/modest 
rotator would weigh about 25-30 lbs.   Plus the weight of the mast.  I 
could "walk" it up or down without  too much trouble.  But, it seems to 
me a counter-balanced scheme  would be superior.

>  I made up a simple drawing - you can find  it here:

>  _http://www.rbogash.com/Tower%20design.jpg_ (http://www
.rbogash.com/Tower%20design.jpg) 

>   The mast would normally be locked in the vertical position and lowered 
for  maintenance and wind events.  However, I have also contemplated the  
option of leaving it unlocked and "floating."  In the event of a wind  
storm, with say sustained winds of 50 and gusts to 75, the antenna/mast  
might float to an angle - say 20 degrees off vertical in the  sustained 
wind, and, in effect, become "unloaded."  When a 75 mph  gust struck, the 
mast would then really be seeing only a 25 mph delta  increment.
 
    First of all, the windspeed rating for Kitsap  County is 85MPH. And wind 
forces go up as the sum of the squares so your  windloading on anything will 
be reasonably significant. The MA-series UST is  rated for about a 25# antenna 
@ 85MPH.
 
    Your design might work for you but I'd run it by  an engineer just to be 
on the safe side. 
 
Cheers,
Steve    K7LXC
TOWER TECH 



 



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