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Re: [TowerTalk] High VSWR

To: "'Jim Thomson'" <jim.thom@telus.net>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] High VSWR
From: "Doug Ronald" <doug@dougronald.com>
Date: Sun, 1 Sep 2019 11:41:19 -0700
List-post: <mailto:towertalk@contesting.com>
I would like to talk to you about that vane idea when I get further along on
the repair of this LP. Those back 4 elements are really heavy, so placing
the boom-to-mast mounting plate in the physical center of the boom would
have required massive counter weights on the high-frequency end of the boom.
There are already two counter weights there now with about 240 pounds weight
total.
The wind torque on this antenna is so much that I have to remove the drive
chain from the rotor in a storm to prevent breaking the shear pin in the
rotor.
If the vane idea will neutralize the boom's torque, what about the 104 foot
long back elements? In a steady wind, how will the antenna orient itself if
free to rotate 360 degrees? Of course now in a steady wind, the butt end
always faces the wind direction.
Doug, W6DSR

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Thomson
Sent: Sunday, September 1, 2019 09:22
To: towertalk@contesting.com
Subject: [TowerTalk] High VSWR

From: "dj7ww@t-online.de" <dj7ww@t-online.de>
To: Jim Thomson <jim.thom@telus.net>
Cc: "towertalk@contesting.com" <towertalk@contesting.com>
Subject: Re: [TowerTalk] High VSWR

<That is a bad idea, the torque force on the rotor under high winds will
become much larger.

<73
<Peter

## Nope.  It  will  reduce  torque  down  to  virtually  zero.  In  his
case, it  gets  even  better,  the  LPDA
is  mounted  ABOVE  the  mast, instead of  the  SIDE  of  the  mast.  Tq
will  be  zero. 

##  Two  ways  to  tq  balance a  yagi.    1- mount  at  center  of  boom,
and  use a counterweight  at far  end of  boom,  the  light  end. 
2-   mount  boom  at    CG, then  use a sail /  vane  at  far end .....short
end  of  boom.  

## I  have  used  both methods  with  great  success.  Both  designed  with
software  from  DXE  +  also K7NV.  

##  Fellow  across town has a  20m  yagi,  with CG  way  away  from center
of  boom.    It  would   rip  up  a  T2X in  mere
months.  After  3  destroyed, I  designed a flat  plate  sail  as a TQ
compensator.    It  was  tested on  the  low  30  ft  high  test  tower.
No  rotor  installed,  just a mast  and a pair  of  bearings.  Owner
climbed the  30  ft  tall  bracketed  tower  during  a windstorm, and  could
point  the  boom  in  any compass  direction....  by hand...and  it  always
stayed  put.   Good  enough,  so  yagi moved  to  top  of  higher  tower.

##  zero  problems  with  rotor ever  since,  that  was  13  yrs  ago.
Zero  issues  since  u  can turn it  by  hand.   Its  tq  balanced.
However, 
since  the  yagi is  mounted to the  side of a 2 inch mast,  and  with  boom
directly  into  wind,   there is a slight  offset  between center  of  2
inch boom,
and  center  of  2 inch  mast,   which  is a 2 inch  offset.....  so  not
quite tq balanced for  that  case.    With  boom  broadside  to  wind,  it
is 100%  tq  balanced. 

##  yagis  and  LPDAs that  are  not tq  balanced is a pet peeve  of  mine.
Simple fix.    Alternative is stupid  amounts of  tq  required....esp on
long booms. 

Jim  VE7RF   

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