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Author Topic: Coax cable on guy wire?  (Read 6175 times)
5B4AET
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Posts: 41




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« on: June 03, 2011, 06:00:54 AM »

Hi everyone,
Im setting up a new tower. On the very top there will be a VHF-UHF vertical, under it a VHF and UHF yagi on a horizontal mast for elevation movement. Finally at the base a Hygain tribander - TH3-MK4.
So with 4 antennas and 2 rotators (yaesu G5500) I have to run down 6 cables.
My question is: Can I run all the cables attached to one of the guy metal wires instead of running them down on the mast? Or will this affest the HF antenna patern - coax and rotator wires will resonate on HF frequencies?
The dilema here is make the feed line as short as possible or go the traditional away and not risk it ?

Thanks for reading this.

Panicos
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KF7CG
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« Reply #1 on: June 03, 2011, 06:15:39 AM »

The guy wires are metallic anyway, so in most cases the additional wires should have no more effect on the HF antenna pattern the the guys do already.

If there is RF on the sheild of the coax from where it feeds the beam this might change. Of course, since the cables will have a little more exposure to your radiated signal, you might need a little more in the way of filtering to remove RF from the shields before they enter the shack.

Otherwise, this sounds great.

KF7CG
David
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N3OX
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« Reply #2 on: June 03, 2011, 06:22:56 AM »

Panicos, I would be somewhat concerned with the extra weight and windload of the cables.  A small sideways force on a guy wire translates to a great deal of extra tension, and if you're running coax cables down the guy it adds no strength (as opposed to a larger, heavier guy wire, for example).     Maybe this effect is not of much importance, but I would not take that for granted.  It might be useful to estimate the extra tension in the guy in your maximum likely wind.

Your concern about line resonances is also important, especially if you have taken the time to break up the metallic guy wires with insulators so that the guy wires are not resonating by themselves.  You might be able to break up the coax lines somewhat with big ferrite chokes, but that just adds even more weight and windload.

I agree with KF7CG that if you HAVEN'T broken up your guys with insulators, there's probably no electrical harm in running the cables down a guy wire beyond what you'll get from the guys.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
5B4AET
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« Reply #3 on: June 03, 2011, 06:27:04 AM »

Thanks for your reply.

Guy wires are broken down to smaller sizes with egg insulators just to avoid any resonance of the guys.
So the question is only about the coax and rotator cables.

What do you think?
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K1CJS
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« Reply #4 on: June 03, 2011, 06:50:36 AM »

I wouldn't, but that is just me.  The way I look at it, the extra weight and wind load of the coax cables (especially a bundle of six or seven) would mean a constant intermittent pulling effect on that one guy wire leg.  Think of it as a tent pole tied down three ways, with you yanking on one rope repeatedly.  What is going to happen?  That pole is going to move and put strain on the other tie downs.  Sooner or later something is going to give.

What I would do is use a leader wire securely connected to the tower just below the center set of guy wires, with the other end secured to your house/shack to run your coax cables to your shack.  If done that way, the strain would be on the tower just below the guy wire support, one of the solidest areas of the tower there is, and the guy wires would not have any additional strain put on them.  The extra length of coax needed to do it this way would have a negligible effect on your signal losses.
« Last Edit: June 04, 2011, 07:48:03 AM by K1CJS » Logged
N3OX
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« Reply #5 on: June 03, 2011, 07:14:12 AM »

Guy wires are broken down to smaller sizes with egg insulators just to avoid any resonance of the guys.
So the question is only about the coax and rotator cables.

What do you think?

I think that the egg insulators are wasted if you run coax and rotor cables down the guy wires.  The coax and rotor cables will cause the same type of problem as unbroken guy wires, for sure.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WB2WIK
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« Reply #6 on: June 03, 2011, 09:07:17 AM »

I agree.  If you've gone to the trouble of breaking up the guys with insulators to avoid resonances, then you violate all of that by running cables down a guy wire.

I'd just run them down the tower.  Yes, this will take more cable.  On HF, shouldn't matter.  On UHF it will matter, but you can always use better cable.
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5B4AET
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« Reply #7 on: June 03, 2011, 12:37:15 PM »

Ok guys.
Now Im sure that it doesn't worth it.
Will go the "traditional way" and route the coax down the tower.

Very helpfull, many thanks.


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K0ZN
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« Reply #8 on: June 03, 2011, 09:40:54 PM »


There are also some advantages from a lightning protection point for running the coax and cables down the tower CLEAR TO THE GROUND.

Unless you have some really pressing situation, there are many more advantages to running cables in/on the tower.

You have received some good advise in the previous comments.

73,  K0ZN
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K1CJS
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« Reply #9 on: June 04, 2011, 10:31:02 AM »

You can put your arrestor units on the tower in an enclosure and ground them to the tower ground system.  You can have your tower and station set up to use an underground run for your coax and ground cables, or use a just above ground 'trough', or you can use a leader wire to run the cables from the tower to the house, keeping them at or above the ten foot level to prevent damage to them and keep them out of reach of anything done on the ground. 

But to be most effective and to minimize the need of replication of protection, the best idea is to have the grounding and arrestor system point for the incoming cables immediately outside the building that the shack is in, and bond the tower ground, the grounding panel and the house electrical ground together with at least number 6 cables.



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N1UK
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« Reply #10 on: June 04, 2011, 01:01:10 PM »

I ran all my coax and control wires down the inside of the tower. It is a bit more of a hassle but it protects the cables when climbing.


Mark N1UK
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KI4SDY
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« Reply #11 on: June 04, 2011, 01:15:18 PM »

It would not be something I would do either.  Wink
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