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I'm designing an antenna system for my home that will consist of a 2"x2"x1/4" aluminum square tubing mast with a trolley system that will raise and lower the antenna(s). I'm going to be testing a new repeater also, before it is deployed to a permanent installation. The square mast will be 20' tall and will be secured at the 19' level with a bracket attached to the eve of the 2nd floor. The base will be bolted to a traditional concrete footer. The trolley will be raised and lowered with a 12 volt winch, stainless steel cable, and a pulley at the top of the square mast. The antenna(s) will be mounted to a round aluminum mast that will slip into a receptacle on the trolley and held in place with two bolts.

I want the round mast that fits into the trolley receptacle to be about 10' to 15' long. One of the antennas that will be used in the testing is 8' tall. Once the trolley reaches the top of the square mast, there will be 18' to 23' of unsupported round mast and antenna. That's too much, so I want to use guy wires, but this is problematic. I promised my wife this installation will be hidden from view behind trees and this works only if I don't have traditional guy wires at 45 degree angles.

I've seen light poles that have a guy cable near the top that comes down at a 45 degree angle, but not all the way to the ground at that angle. The guy cable passes through the end of a steel arm/pole that extends out from the light pole at 90 degrees about 4 feet, then the guy cable goes to the ground at a slight angle. This allows the light pole to be guyed, but the guy cable is only about 2 feet from the utility pole.

Here's my engineering question. I'd like to use this concept but somewhat differently. Rather than have the guy wires go straight down from the support arms to the ground, I'd like to them angle toward and secure to the trolley. There would be a ring just below the antenna to which the guy wires would attached. They would come out at some angle (perhaps 45 degrees, perhaps less), pass through an arm (about 2' feet long), then secure to the trolley. I could have 3 guy wires 120 degrees apart and not interfere with the raising and lowering of the trolley. Will this give support, or does the tension on the arm in the direction of the mast offset the tension in the opposite direction? I'm guessing that the only way it would work is if the guy wires came straight down from the 45 degree arm on the round mast.

I've attached a crude drawing.

Thanks,
Chas.

Chuck.

I would recommend making your trolley with a second connection point maybe 5 feet below where it attaches to the mast. This gives you a five foot moment arm on the trolley. Rather than use guy wires in the method you describe, make the antenna connection on top of the trolley five feet high (again, a five foot moment arm).

I haven't done the math on what I describe, but intuitively it seems substantial enough.

If you'd like to discuss, please send me a PM and I'd be happy to talk through what I think about this method.

As far as your guy wires go, there's no advantage to putting them on "outriggers" as you have drawn. If you want to guy to the trolley, simply run your guy wires from the antenna down to the connection points on the trolley. For that scenario, the bigger the foot print of the trolley the better. I'd still try and put a second connection point under the trolley to help sustain the moment caused by wind loads on the antenna.

My two cents.

RJGold wrote:Chuck.

I would recommend making your trolley with a second connection point maybe 5 feet below where it attaches to the mast. This gives you a five foot moment arm on the trolley. Rather than use guy wires in the method you describe, make the antenna connection on top of the trolley five feet high (again, a five foot moment arm).

I haven't done the math on what I describe, but intuitively it seems substantial enough.

If you'd like to discuss, please send me a PM and I'd be happy to talk through what I think about this method.

As far as your guy wires go, there's no advantage to putting them on "outriggers" as you have drawn. If you want to guy to the trolley, simply run your guy wires from the antenna down to the connection points on the trolley. For that scenario, the bigger the foot print of the trolley the better. I'd still try and put a second connection point under the trolley to help sustain the moment caused by wind loads on the antenna.

My two cents.

I see what you mean and I like that idea much better. There's nothing magic about bringing the trolley down to ground level, so I can simply add a connection point below the trolley and extend the top connection/pipe. Then I could make the antenna mast that goes into it from two different sizes aluminum pipe so that one telescopes into the other adding more strength. Not having the outriggers makes it a much easier installation and easier to keep concealed.

Thanks!
Chas.

Let me know if I can help get this done. I'm a mechanical engineer by degree but have worked Construction for 25+ years and put myself through school as a welder.

Good luck with your project.

Also, at the connection points between the lower trolley mast connection and the trolley, and the antenna support and the trolley, there should be gussets (some may call these stiffeners).

My two more cents.

I agree with RJ Gold. This would be a better solution than the cables as described.

Thanks guys, this is a much better solution.

Chas.

Charles.

I was just looking for something in the "my posts" section and noticed I called you Chuck in this thread. While I was typing it, my wife and I were having a conversation about a friend of ours named Chuck. Proves that I can't multi-task.

My apologies for the typo. Didn't want you to think I was being flip.

I agree with eliminating the spreaders ("outriggers") as it would also complicate tension adjustments, assuming you're planning on using steel cable versus wire rope of some kind. I didn't see turnbuckles in your drawing but I'm assuming you will want to include a similar method to keep tension fairly even on each support. Question. What kind of 12v power source are you using?

If you do use the synthetic wire rope guys, I found a cheap and easy DIY method of adjusting their tension without causing too much abrasion to the guy rope. You can see my "linegrip" page here. http://analogthinker.com/hamradio/bhlinegrip.aspx
The illustrations show hard plastic material, but the one's made from rubber tie downs worked better for my application because I wanted a little bit of "give" when the winds were strong. The hard plastic grips were too rigid and caused too much stress on the vertical in gusty, strong winds.

RJGold wrote:Charles.

I was just looking for something in the "my posts" section and noticed I called you Chuck in this thread. While I was typing it, my wife and I were having a conversation about a friend of ours named Chuck. Proves that I can't multi-task.

My apologies for the typo. Didn't want you to think I was being flip.

Thanks, but no apology necessary. I've been called Chuck by a lot of folks over the years and I didn't think twice.

Chas.

K5GU wrote:I agree with eliminating the spreaders ("outriggers") as it would also complicate tension adjustments, assuming you're planning on using steel cable versus wire rope of some kind. I didn't see turnbuckles in your drawing but I'm assuming you will want to include a similar method to keep tension fairly even on each support. Question. What kind of 12v power source are you using?

I'll be running Andrews hardline and a control cable through the attic to the "shack," so I'll run a DC line as well. I'll see what the current draw is for the winch and either buy or build a power supply with a sufficient rating. I've considered a battery at the base of the permanent mast with a solar charger, but that's too much trouble and expense for something that will be activated infrequently.

I may not use the guy cables, if I make the trolley mast telescoping. There won't be much load (weight or wind load) with the antennas. It would also add more flexibility when testing new antennas I'll be teaching kids how to build.

Chas.

SRO1911 wrote:Just out of curiosity, since I am building a vaguely similar set up for a mobile repeater using telescoping tubing, how are you handling grounding/lightning protection?
The wheels/slides on the trolley are not the most ideal conductors.

I'm going to drive a copper ground rod next to the base of 2"x2"x1/4" aluminum, then attach an Alpha Delta surge protector with a mount from DXengineering.com. There will be sufficient coax to reach this point, then back up through conduit to enter the attic through the second floor soffet.

Chas.