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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