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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|