: OTA Mounts, Towers, Rigging Hardware
2009-10-11, 09:49 PM
I have a 30' tower concreted 4' into the ground and lag bolted to the wall of the house (lags would not coming out in a tornado :)) The top 20' seems pretty solid with a bit of wobble. I always tie off with a full body harness. My question is if I do fall (knock on wood) will the tower buckle from the sideways force? Are there instructions on how to put a tower safely, in the forums or online.
2009-10-11, 10:18 PM
You've over-engineered your mount. It probably wasn't necessary to bolt the structure to the house, given that you're at an acceptable depth with concrete.
Most towers (including tubular types) are designed to accomodate the weight of a worker; including the amount of potential energy realized in a fall situation. The exception would be towers that are compromised due to rust, metal fatigue, and/or improper fasteners connecting the sections together.
You can mitigate the risk of structural failure/damage due to a fall by using a proper tether that is designed to deaccelerate you. It is preferable to connect such a tether to a rear D-ring on a harness--this will protect you from doing a "face plant" against the tower should you fall. Never use such a tether to actively support you while on the tower. They are specifically for fall protection only.
Such tethers, with a large rebar hook, typically retail for about $80 for a 6' length.
I also recommend a web rebar assembly for positioning. This assembly uses two locking hooks that connect to either side of the harness at your hips, which are connected via a short web (9") to a middle rebar hook. It allows you to work hands-free by actively supporting you (unlike the tether).
You can make your own "web rebar assembly" by visiting stores that sell climbing equipment (MEC, for example). I was able to create one by buying two small locking carabiners, a large auto-locking carabiner (3.5" gate), and a 18" sling; all for under $100. The small carabiners are rated at 24kN (kilo-newtons of force), the sling 27kN, and the large carabiner 41kN. More than enough strength to hold you and several people during a fall.
Remember that you must maintain at least one tether connected to the tower at all times. Never trust yourself to hold on while climbing/positioning without a tether.
2009-10-13, 03:02 PM
My understanding is a fall from 30' and above is generally considered fatal. There are, of course, a lot of variables to consider (landing surface type, hitting objects on the way down, how you land, etc.)
2009-10-13, 07:35 PM
Even less than that can be fatal. Right now I'm working on a project for one of the new cell companies, setting up the back haul microwave links. The installations are on top of buildings and if we work near the edge, we wear a harness & lanyard etc., even when standing on a flat roof.
2009-10-14, 10:31 AM
That's why I said there are lots of variables to consider.
20' into a swimming pool and you'll probably walk away.
20' head-first onto a concrete patio and the outcome will be extremely bad.
I'm not at all surprised you have to wear harnesses and lanyards while you're at work. That's very much an occupational health and safety requirement.
2009-10-14, 12:53 PM
I have a basic question: How do you mount a satellite dish on a antenna tower?
What kind of brackets do you need and where can I get them?
I looked at the Sat thread and I saw nothing.
2009-10-15, 02:05 AM
Fall Fatality Assessment stats that a fall from just 10 feet will prove fatal in 40% of cases studied....
30 feet you’re walking up the stairway to Heaven.
2009-10-15, 10:15 AM
A number of recent posts have explored the forces involved when a mast is supported by two mounting brackets. Can someone offer an opinion on what forces are involved when that same mast is supported by three brackets.
In my case, I had a 10' mast with two mounting brackets 3' apart - 7' of mast above the top bracket. The mast would sway in the wind and there was a corresponding movement of the section of mast between the two mounting brackets. It occured to me that this dynamic and constantly changing load may stress the brackets and the points where they are lag bolted into the brick. In order to eliminate this loading I added a third bracket between the original pair and it has eliminated the movement between the brackets.
My concern is that I may have inadvertently caused the forces to be concentrated at or above the upper bracket. I am not concerned with the possibility of the mast bending - it can be replaced if that happens. I do want to ensure that I don't over stress the brickwork.
Any and all opinions are greatfully received. Maybe the engineers out there could come up with some numbers to support their position.
2009-10-15, 12:38 PM
I do want to ensure that I don't over stress the brickwork.
I think the biggest issue you would have is if the 3 brackets did not line up correctly, then the mast could be causing a pre-load on the bracket that would stress the bricks. As long as when you installed the new bracket you didn't have to distort the mast to get it into the fitting you are ok. You have added more anchorage points, so it will be stronger overall, but it might only be marginal gains.
Is the swaying a continual swaying like the mast is vibrating, or does it just deflect when there is a gust of wind?
Maybe the engineers out there could come up with some numbers to support their position.
Sorry, not enough data available :)
2009-10-19, 04:21 PM
Hello there, similar question as above...
I currently have a CM4221HD wall-mounted on a 15' (10' + 5') mast. The brackets are 4' aparts and I have ~2 feet of the mast below the lowest bracket (i.e.: I could go up ~2 more feet).
Would I cause a problem by adding a 2nd set of brackets to the mast? I would like to add two brackets in the middle in order to stabilize the mast in the wind.
I'll try to post a picture of my setup a bit later.
2009-10-19, 04:51 PM
Sorry for the delayed response.
A third or forth bracket (between the other brackets) will not make a significant difference. The top bracket acts as the fulcrum and thus takes most of the load. A third or forth bracket will reduce the load on the bottom bracket by a bit, but will have no effect on the top bracket.
2009-10-19, 06:30 PM
Interesting... I see that many people use the 3-point bracket on the bottom of the mast.
I didn't know where to you use it so I chose the top bracket (in an upside-down "V"). Is the the correct way to install the bracket, considering that the top bracket will have the most force applied to it?
2009-10-20, 07:48 AM
pshelston, I am not sure what type of bracket you are talking about. Could you post a picture?
2009-10-20, 10:30 AM
It's the 12" Channel Master wall mount stand-off bracket.
I've seen some people (http://www.digitalhome.ca/forum/showpost.php?p=964114&postcount=408) in the pimp my gear thread use the 3 point bracket at the bottom... but since the bracket doesn't come with any guidelines/instructions, I just used it on the top. I'm not sure which one is correct or better.
2009-10-20, 03:40 PM
I'm putting up my DB8 antenna on the side of my dwelling using mounting brackets. I'd like to put it up as high as possible. My question is, does anyone know if my reception will be hampered when its up close to the overhang of my roof? Would signals be disturbed because of this? Obviously, I'd like it as high as possible but not at the expense of any signal loss.
2009-10-20, 03:48 PM
My question is, does anyone know if my reception will be hampered when its up close to the overhang of my roof? Would signals be disturbed because of this?
Unless its a metal soffit, it wont be hampered by that hardly at all. But at that height, youre probably not getting the antenna up over the neighbors roofs, which will hamper the reception.
2009-10-20, 04:08 PM
yes, I'm aware of that. This is temporary until I can buy and install a tripod mount likely next spring now. The overhang is aluminum soffat and faccia. Is that OK? Thanks for responding.
2009-10-20, 04:23 PM
The overhang is aluminum soffat and faccia. Is that OK?
Well, it will affect reception. But with careful placement by experimentation, its possible to make it work in your favor.
2009-10-20, 07:35 PM
but since the bracket doesn't come with any guidelines/instructions, I just used it on the top. I'm not sure which one is correct or better.
The third leg is going to take the vertical weight component of the entire system. With the 3rd leg down, the fastener in the wall is in compression. With the leg facing up, the bolt is going to be in tension. If you use a good tapcon or lag, it probably doesn't matter which way you do it. However, if over the years the fastener gets a bit of corrosion, or you are bolted into wood that starts to get a bit soft, the tension could eventually become a problem. I don't think I would bother changing it around, but if you move the antenna or have to do other major work on it, I would probably switch it so the leg is down.
2009-10-20, 11:03 PM
Sage advice is definitely welcome!
Right now my major concern, is that my mast is way too TOP HEAVY. The 4228HD is quite big!!!!
I have it on an 8ft, 1" conduit with a rotor and preamp, and then the antenna is on a 5ft, 1" conduit.
13ft total of 1" pipe. All of this is mounted to the chimney with 3 RCA chimney brackets.
When I give the pole a good shake, it moves about quite a bit. I'm not liking this!! Gut feeling is that this will not survive a heavy storm. The rotor bracket will snap. Thoughts??