[CQ-Contest] Question regarding crank-up tower feedlines

[VE2TZT]

Jim,I have a US Tower HDX572 72ft telescopic tower with a DB42 at the 
top and a 3el steppIR on a side.

When came the time to install the cables I passed through the same 
questions as you are asking.

I am living in Montreal and it was very interesting if not funny to see

how people in the South were just considering leaving the cables on the

ground when the tower is in the low position. Here, during the winter if

you leave the cable lying on the ground within a few days if not hours

the cables will get stuck into the ice and you just have to wait the

spring before being able to extend the tower again.

So, after several tries I finally found the solution. It will be faster

to explain it with pictures so have a look at the following link :

https://drive.google.com/file/d/0ByGzx2yN6nC3QzY0clpyUmtoV1E/view?usp=sharin

where you can upload a PowerPoint in pdf format.
Please visualize the pdf in full screen not just on the web site in 
small format. I have extracted for you and other interested hams a part 
of a presentation that I did to some local clubs about the installation 
of the tower.

First I did a scale 1:1 simulation of the top of my tower to determine

the length and path of the cables when the rotor is moving on 450 deg.

That reproduction had also helped me to write a procedure to install the

DB42 on the tower. You can "run the movie" in both directions my pushing

the arrow keys.

A Second part shows how I have attached the cable on the standoffs. The

very important thing is that with the numerous moves up and down that

you will do, if the cables are bonded directly to the standoffs the

cables will be bent with a too small bending radius and are going to

break by metal fatigue. So to keep the cable out of the minimum bending

radius I invented a simple system consisting in attaching the cables on

small metal plates which are rotating around the standoffs. That way the

cable and plates are articulated and are rotating while the tower is

retracting respecting a loop shape.

Third, you must arrange the cable loops in a way they cannot pass into

each other neither pass around any standoff. Otherwise you will live

catastrophic experience of teared out cables and standoff. On the last

pictures of the pdf, as for the rotor simulation you can "run the movie"

of the tower retracting and observe how the cables are turning from a

straight line to loops while retracting.


Then in any position of the tower you have a clear tower and never the 
cable will lay on the ground.

Enjoy

Gilles VA2EW / VE2TZT


On 25/12/2016 14:04, Jim George wrote:
> I've had a three-section crank-up tower (it used to be called the 
> LM-354) that's 54 feet tall when fully extended. For a long time, I 
> used it in a permanent fully-extended manner, with phased ten meter 
> yagis at the top and half-way up. Now, it will have a triband yagi and 
> a two-element 40 yagi on it, above the thrust bearing, and I wish to 
> keep it at least semi-nested between contests to avoid storm damage. 
> What is the recommended way of bringing down two the coax feedlines 
> and the rotator cable for a tower that will go up and down fairly 
> regularly? I'm going to use the three original "stand-offs" to keep 
> the coax and the rotator cable hanging vertically as these three 
> standoffs are positioned such that they nest properly when the tower 
> is down. Is it okay simply to hang the feedlines and the rotator cable 
> down through the top standoff, which seems to rotate around as the 
> rotator moves the mast, and  simply let the coax and cable drop down 
> vertically? In this case, there would be no traditional rotator loop. 
> That configuration has worked okayrecently with only the small 40 
> meter yagi on the top.
>
> Another possibility would be to form a five or ten foot "rotator loop" 
> with the feedlines and rotator cable and then route them back up onto 
> the top standoff and down vertically through the other two. In this 
> way, the system would not require that top standoff to move around on 
> its tower leg as the mast and antennas rotate. Not sure if I described 
> this in a clear way. If I were sure that the top standoff would move 
> around on its tower leg, that would work, but if the top standoff got 
> stuck and didn't move, then the feedlines and rotator cable could get 
> stretched and damaged. For some reason, I haven't seen anything on 
> this, or have forgotten. Any recommendations?
>
> Thanks in advance, and all the best at the Christmas and other holiday 
> breaks and new year.
>
> 73, Jim George N3BB
>
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