How many brackets to hold 80-97cm sat dish on 10FT (3M) Mast?

Discussion in 'Satellite TV, Sky TV & FreeSat' started by meansizzler, Mar 1, 2014.

  1. meansizzler

    meansizzler
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    I am thinking of mounting an 80 or 97cm sat dish on a 10ft pole. 8ft (2.4M) long, 2inch (50mm) wide, 2mm thick.

    The dish would be on the top of the pole to get enough roof clearance, Probably 1.2M of pole stick up from top of roof.

    The pole is quite thick aluminium at 2" it's one of the strongest I can find, I will have 4x LNB and 14x coax cable coming from dish. The brackets are 12" t & K and will be below the dish. Will be using M8 x 10 Rawbolts.

    How many brackets would I need to hold the pole securely and take the weight of the dish?

    Would 1 t and 1 k be enough or should I add another T?. .

    Any ideas on brackets spacing distance from each other?

    Would it be able to take the load if 2 or 3 brackets fitted, without pole bending in heavy wind or coming out from wall?
     
    Last edited: Mar 1, 2014
  2. pedro2000uk

    pedro2000uk
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    ali 2" dia x 1.6mm wall isn't usually up to it although there are some impressive hard ali alloys but you should be looking at double that wall thickness or better- lots have been done that way though, it can be done to a 'sort of seems to work' level

    what distance will it be from the top bracket to the dish's az/el.
     
  3. meansizzler

    meansizzler
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    rough guess is 1.5m?

    I realised the pole I have is 8ft x 2" x 2MM thick

    Looking at this aricle here, seems a 10ftx 2" x 16G pole is fine the so 14G one I have should be ok.

    Aerial Arrays

    do you reckon 1 K and 2 x t or 1 x k and 1 x t, what do you think of bracket space distance?
     
    Last edited: Mar 1, 2014
  4. meansizzler

    meansizzler
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    I have got the k bracket installed, and the bolts for the t, just need to try and find a 12" K bracket in London today and some 2" v bolts, anyone got any ideas?
     
  5. MartinPickering

    MartinPickering
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    See the info. on my web site about installing Bracket T+K.
    Calculating the wind load on a 1m dish and the bending moment on a 1.5m pole is beyond my capabilities but you really ought to get it worked out before you begin. My own 1.2m dish is on a 3' x 3" patio mount and shielded from the prevailing wind by a 1000 litre water tank.
    See youtube.com/watch?v=SIG3kDGFSu8
     
  6. meansizzler

    meansizzler
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    94N is the wind load on the dish, as for the pole its 2.4M, 2mm thick and 2" wide and it is only 70CM sticking out from top of first bracket, the pole was tested by aerials and tv and does fair quite well on stress tests, I will have two K brackets and a T in the middle of them to hold it down, using m8 x 10 rawbolts.. I will cut 30cm off from the pole at the bottom bracket..

    What is your patio mount resting on?, can you not use steel rod and adhesive and bolt to secure it to ground if concrete, or decking screws if wood or just some slabs if its grass..
     
    Last edited: Mar 1, 2014
  7. pedro2000uk

    pedro2000uk
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    That's for AERIALS which ...

    a) have much lower wind loading than dishes

    b) don't see an appreciable amount of signal to noise ratio loss if they sway a little

    c) because a pole for an aerial can sway a % without serious adverse effect on reception, then the pole itself has less stress & can effectively be of a cheaper construction as can the brackets on the principle that the branch that bends in the wind survives where the branch that doesn't ... breaks.

    Those are mostly the wrong engineering properties you want for satellite installations, the aim is to achieve good (eg solid) functionality up to c. 60mph wind speeds & survival between 60mph to 100mph+ (the same ratings as most decent non broadcast satellite dishes) so you can use the system most of the time in most winds & on very high wind speeds the antenna can & will go off sat briefly & return.

    What you are designing will go off sat well under 60mph - probably 20-30mph which is far more common and at 1.5m it's not impossible to do this.....
    [​IMG]
    I've just redone one today that was installed by a er satellite company - typical aerial fitter's mistakes & a big dish on a pole like that one above -
     
  8. meansizzler

    meansizzler
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    Hi pedro, I have rechecked and the pole will be 70cm above the top bracket, not 1.5M, the dish will be mounted 5cm from top of mast. I will be using 2 x k brackets and 1 t bracket in the middle, so 3 brackets in total to hold the pole, so 70cm pole above top bracket and 1.3m pole between the 3 brackets and 5cm below bottom bracket, rest blow shave off... so 2.05m of pole. Using rawbolts to secure brackets to wall.

    2inch wide pole, 2mm thick
     
  9. pedro2000uk

    pedro2000uk
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    Still not ideal - 70cm x 2mm wall 2" ali - generally I'd not go below 3mm - 3.5mm wall on 2" but as I've said there are some very clever alloys - steel & ali so it's not a given until you have a material in your hands & do the tests.

    I've seen plenty of jobs where someone has used several brackets on a long pole down a wall to try to make a solid job for a sat dish over a roof & known instantly it was just a lot of pole & brackets down a wall but at the actual dish it would be unacceptably unstable
    [​IMG]

    & 70cm x 2mm 2" would be just that unless it was exceptionally ht alloy & even then there's 'twist' on a too thin pole- as I said it can be done 'sort of'.
     
  10. meansizzler

    meansizzler
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    The pole was not cheap cost me 20 bucks, also with 2mm wall thickness it is tested to be twice as strong as 1.6mm thick pole. Do you know where I can get a 2" wide alloy pole with 3-4mm wall thickness you suggested., good poles are not easy to aquire.., especially when you need them delivered
     
  11. pedro2000uk

    pedro2000uk
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    it's not perfect but scaffold is used a lot = 49mm OD x 3.5mm wall & to the latest BS & it's galvanized - ideally new & not used scaff that's been damaged around building sites or is pre the latest regs - it comes in either standard galvanized steel or higher tensile thinner wall that's called high yield or there's ali - high yield or ali isn't as strong as standard but are lighter
     

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