[UK-CONTEST] ANTENNA SUPPORT

[G3RAU at aol.com]

In a message dated 24/06/2009 11:01:05 GMT Daylight Time,  
g3ozf at btinternet.com writes:

What's  the best way of attaching the dipole to the top of the stub mast, 
so that the  beam can still be turned without it winding-in the halyard ? Do 
I need to find  a proper slip bearing, or is there a sneaky and cheaper way 
? Or do I just  leave 30 cm of slack halyard between the pulley and the 
dipole centre  insulator, and let the thing wind/unwind as the beam turns  ?

Thanks

73

Don, G3BJ


 
Don, 
Almost no matter what you do, the dipole will somehow end up touching the  
stub mast.  Any insulation will eventually be worn thru by wind action. The  
answer is to use a non metallic section at the top of the stub mast, then 
it  doesn't matter.  Secondly, at that height there will be a winter icing  
problem, so any clever device may will seize up with ice, so just do as you  
suggest and have the dipole centre dangle 12 inches below the top of the 
stub on  a rope.  That way there is nothing to ice up and it can rotate  
freely.  Practical problems which arise are a) when I say a rope I  mean a really 
tough rope with a paralleled backup because of the rubbing action  on the 
stub mast in the wind  b) do be aware of the tremendous amount of  sag that 
ice loading can produce on the dipole/supports.  It will try its  best to 
tangle with the beam believe me...HI!  and c) depending on the  exact alignment 
of the dipole you may end up with the dipole centre knocking or  vibrating 
against the stub mast,which can produce an annoying  noise which  carries a 
long way from 90ft high.   Lastly something which you can  not readily 
predict is the "Wothering Heights" sound effect of the wind  whistling through the 
dipole at certain wind speeds, which can be very  irritating to the ear. I 
don't have a neat solution to that one, sorry!
Have fun
Derek G3RAU