GM Wes and happy thanksgiving !
Surprisingly when the rope (knot portion with antenna) is hoisted up and
the antenna pulled tight that still tightens up those vertical ropes. Do
you remember that problem we were all given in college to calculate the
tension in a rope if you pulled on it in the middle perpendicular to
that rope? Even though that perpendicular pull is WAY WAY off on one end
it still seems to pull it out and away from the tower almost a foot
stretching the entire vertical ropes.
Probably did a poor job explaining that but in the end the tension in
those vertical ropes does increase when the "dipole" is made nice and
tight and 30 or so pounds of tension is applied. Add to that some wind
or 1/2" of ice and that 30 pounds seems to turn into several hundred
pounds of tangential pull.
Gedas, W8BYA
Gallery at http://w8bya.com
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 11/28/2019 8:06 AM, Wes wrote:
Hi Gedas,
Originally you used the flag on a flagpole as an analogy. Absent the
flag, I see little need for a lot of tension in the loop. Then if the
flag is hoisted by that portion of the loop located above the joining
knot then the knot still sees very little stress; it's just along for
the ride. Remove the flag and attach the antenna. Nothing changes.
Wes N7WS
On 11/27/2019 2:50 PM, Gedas wrote:
Hi Wes and TU. I am not sure I am positive what you mean by only a
load on the upper side of the knot.
I am going to have two pulleys, one at the top of the tower and one
at the bottom. I am going to have a single long rope threaded around
both pulleys and I am going to use a fisherman's knot or similar to
tie the two together nice and tight. Not going to be much tension in
the rope at this point, maybe 10 pounds just to keep both sides of
the line nice and tight with no slop.
Now, I was hoping for a single knot that not only joined the two ends
of the rope together but that also left me with an open loop so I
could easily slip in something like a temporary chain link etc and
then attach one end of a dipole etc to that link.
This way from the ground I would be able to hoist up or down that end
of the dipole as I pleased. Now, when the end of the dipole gets
attached to the other end of that temporary chain link etc and the
dipole is up in the air stretched tight there may be 30-40 pounds of
tension pulling on that line. Since the two pulleys are fixed that
tension from the dipole will get translated to my ropes going up and
down the tower between the pulleys.
I have been doing this type of arrangement for 20 years but only with
a pulley at the top of the tower. Up until now I just had the long
single rope looped around a round aluminum cross member of my free
standing tower.
There was some friction with the rope looping around the 3/8" dia
round & smooth diagonal but I never had a failure. This season I
installed a meaty pipe across the tower at about the 5' level and
attached a pulley at each end (I am going to have several ropes going
up and down so I can support and mess with more then 1 antenna).
I hope that paints a more clear picture. So far I have had a lot of
great ideas and the only issue is me understanding their words and
making my fingers tie the knots the way I'm supposed to hi-hi.
Gedas, W8BYA
Gallery at http://w8bya.com
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 11/27/2019 4:25 PM, Wes wrote:
I'm with the other Wes on this one. If I understand correctly you
only have a load on the upper side of the knot. I would join the
ends with any old knot and tie a alpine butterfly loop on the upper
side of the knot:
https://www.animatedknots.com/alpine-butterfly-loop-knot or one I
find easier to tie, a bowline on a bight:
https://www.animatedknots.com/bowline-on-a-bight-knot
Wes N7WS
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