Re http://www.qsl.net/nidxa/kb9cry/kb9cry_40meterAnt.htm :
Lovely pictures Phil! Thank you.
> Problem: How does one hoist up a large antenna without it getting it
> caught in tower guy wires, especially those top most guys?
> Answer: Helicopter (Expensive), Crane (No Access), Tram (Never tried it
> but always a first time)
There is a fourth way, which we used to put up a stack of full-size 3-ele 40m
yagis (these things are heavy - 12m(40 foot) boom, 22m(~72 foot) reflector)
at ES5TV's this spring:
( mast and tower pictures at http://www.lhv.ee/images/files/es5tv.htm )
0) Think it over **0)
1) Put a pulley to the top mast above the beam's attachment point, and
another to the tower near ground level. Route a hoist rope (we used a cheap
polypropylene less than 1/2") up along the tower, through the top pulley back
down to a winch in safe distance from the tower **1).
2) Attach the reflector and director temporarily to the boom (don't use
locking nuts!). Find the centre of gravity of this system and mark it on
the boom. Unbutton the elements.
3) Hoist the boom up the tower vertically, secure (SECURE!) it to the
tower so its upper end is above the upper guys. I prefer the director end up.
4) Raise the "upper" element (director) and attach it to the top of the
boom. Well, if the boom's low end is above the second set of guys, start with
the "lower" element (reflector).
5) Raise the "T" so the boom's tail is above the lower set of guys. Have
the boom through rope loops so it can't go sideways. Secure the "T" to the
tower.
6) Turn the "T" --> "Lazy H" by attaching the lower element.
7) Tie the hoist rope to the CG point (see 2)). I used a modified double
constrictor hitch secured by two hose clamps on both sides just in case it
wants to slip along the boom (It doesn't if you have worked the knot up well
enough. Heave the lazy H up so the knot is just above the tower top.
8) Awaken the lazy H by rotating it in vertical plane. If the reflector
tip does not clear the lower guys, tilt the boom away from the tower and dance
the boom around the mast. Now, here's a CATCH! The elements of a full size 40
are so heavy that they will turn themselves to UNDER the boom and you can not
hold them by grabbing the boom, if at all. We could not do it, and we could not
turn the antenna around using two BIG plumber's wrenches. So let the elements
go where they want to go! The elements must have been attached between the
tower and the boom to achieve this or else they hit the upper guys from below.
9) Attach the boom truss. Lower the by now flat H to the mast plate, adjust the
boom truss as needed. Attach the boom to the mast plate.
10) Add the missing element.
**0) In fact I built a wooden scale model of the tower complete with the
guy rings, and wire models of two JP2000 tribanders and a 3el40.
And good I did, discovered a lot :-)
**1) The ground crew MUST NOT be located near the tower. A wrench handle
accidentally fell out of my pocket while at tower top, and landed upright
four inches deep in hard ice. The ground crew was instructed but this unwanted
illustration sure helped to drive the warnings home!
**2) We used only the top pulley, but two pulleys are probably safer.
**3) Be slow. Big antennas are hard to stop once they go fast.
**4) The tribanders were raised in one piece propelling them around the
guys.
Christmas quiz: how do you get the upper three antennas in place?
Seasons greetings!
--
Juhan ES5QX
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|