T and K brackets-which at the top?

[hexah]

I remembered Triax had a note on calculating wind loading on masts. Here it is.



The diagram shows a 'through the roof' mount which is bolted onto the rafters. These are common on the continent. Note that the dish is a TD110 here described as a 1 meter. Maybe the graphic designer had the Gibertini 1m in mind!



There is a gaiter around the mast where it goes throught the tiles.

http://www.triax.com/en/FindProduct/ProductDetails.aspx?product={05EF900E-CC13-46E1-A568-86CFF846287A}


The mast is likely a 50mm (2 inch) diameter mast 2mm thick 1.4 gauge. They give a maximum bending moment in their mast catalogue.

http://www.triax.com/en/FindProduct.aspx?category={31904A4E-7ED5-4F06-9015-27CE35548B39}


The mast clamps are not very impressive. They are bolted into the rafters around the pole.

http://www.triax.com/en/FindProduct/ProductDetails.aspx?product={B00760B0-2D6D-4E7A-8D36-2FEADEA5436E}


They are not in the same league as T and K brackets.

So this suggests to me that there is no point in worrying too much about the T and K brackets in solid walls if small steel brackets work well on wooden rafters with 1 meter dishes partly above the ridge line plus other antenna above the ridge on the same mast.

So no problem putting the K on top to spread the weight. Or the T on top if you like!

What is important is that the clamped length of the mast should be at least one sixth of the total mast length. I have always used one fifth as my rule of thumb.

As it is I have one set with a K on top for a dish and another with a T on top for an 18 element yagi.

Went out to check and they are both K on top.

 

[Piltdownpaul]

So tempted to see whats going on with this motor. I really dont want to send it back, its all time and messing about which i havent got at the moment, although i had a partial success with my gum abcess today.

 

[rolfw]

There are threads elsewhere on the forum on this, but in all of them the 'K at the bottom because of the weight' argument is a non-starter as gravity works vertically down (round here anyway), and so the two brakets share this equally.

Sorry, but that's fundamentally incorrect CH, if installed properly, the weight is only on the K bracket at the bottom (unless two Ks fitted), the T bracket will have vertical movement of several millimetres and is not designed to support any vertical weight, whereas the K is rigid.

 

[Piltdownpaul]

Clamps well spread probably 1 fifth of the total length.

 

[hexah]

Sorry, but that's fundamentally incorrect CH, if installed properly, the weight is only on the K bracket at the bottom (unless two Ks fitted), the T bracket will have vertical movement of several millimetres, whereas the K is rigid.

Do you know what the CAI say? I had one of their old booklets, like decades old, but I can't find it.

I got the one fifth rule of thumb from one of the old 'best practice' sheets from the BBC or IBA.

 

[rolfw]

No idea I'm afraid, not a big fan of the CAI, a couple of their biggest members have had numerous mentions on rogue traders.

It depends entirely on what I'm putting up and the quality of the wall as to how much I have above the brackets compared to the spacing of the brackets.

 

[hexah]

I remembered just after I typed it that many people would think of CAI not as windloading experts but wind breaking experts.


The rule of thumb can be a bit unrealistic with short chimneys though!

 

[Piltdownpaul]

I'm a windbreaking expert, much to the disgust of wife pingu.

 

[satelliteman]

No longer with CAI but was for 10 yr when quality mattered.

Their CoP literature quotes T at top. Have good communication with several installers, as does Rolf and the census is as above. Today on bigger rigs, depending on spacing, wind loading etc, K&K is preferred.


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[Piltdownpaul]

Anyhow theres 2 foot of pole above the garage,i'm 18 stone ish and i've had a pull on it. It aint going anywhere- bit like me really. I cant see it going anywhere soon.

 

[hexah]

Thanks for that satelliteman. My booklet would have been from the mid 1980s I think. Good times in the satellite world!

As I said in an earlier post it is a pity no one is selling K and K sets, a bit belt and braces but with the winds here it is not a bad idea. I wouldn't pay for two sets of T and K brackets though. You installers would use the spare bits sooner or later, in my case it would lurk in the shed forever. Still prefer the K on the top though!

 

[Channel Hopper]

Sorry, but that's fundamentally incorrect CH, if installed properly, the weight is only on the K bracket at the bottom (unless two Ks fitted), the T bracket will have vertical movement of several millimetres and is not designed to support any vertical weight, whereas the K is rigid.

Whilst the 'T' is not designed to carry weight, if the clamps are tight on both the T and the K, then the downward force of the dish and motor through the pole shared equally by them.
Both brackets attempt to convert their share of downward force into a turning force, pulling the upper end of the bracket outwards, and the lowest point of the bracket inwards toward the wall, however the 'K' bracket by virtue of its longer distance from top to bottom is better at reducing a concentrated damaging force, moving it away from the points that attach it to the wall. The actual turning is prevented in the main by the opposing force exerted by the wall on the lower point.

 

[Robbo]

Thanks for that satelliteman. My booklet would have been from the mid 1980s I think. Good times in the satellite world!

As I said in an earlier post it is a pity no one is selling K and K sets, a bit belt and braces but with the winds here it is not a bad idea. I wouldn't pay for two sets of T and K brackets though. You installers would use the spare bits sooner or later, in my case it would lurk in the shed forever. Still prefer the K on the top though!

K and K sets are sold actually, but I suspect not available from any retail outlets. I have purchased them a number of times.

 

[wod]

Yeah, I had to buy two sets of brackets to get them.

 

[satelliteman]

Blakes UK sell a high quality Galv K&K set with added support arms, but not cheap.

 

[hexah]

Have you (or anyone else) tried the Blake chimney strap system? I thought of using it when the rusty old wire failed in heavy wind bringing down the old aerial rig.

Blake are good quality. I have one of their x beams they are like the old jaybeams in x style. I generally use Antiference though. I have decades old TC10 and TC18 that still are like new.

I ended up using some old T and K brackets on the wall for the TC18 instead of a chimney lashing as I used to put up Band I antenna etc over 'summer' but there was no way I would leave my pride and joy up over winter!

Dodgy chimney installs worry me more than T and K installs. Some of the satellite chimney installs I have seen have been frightening. They are much more likely to come down in a storm onto your car or break your tiles.

There are a number of grid aerials installed round here for their beamwidth due to trees being in the way of the transmitter. One was installed over the summer on a 20 foot pole and a single mitre bracket and a few months later into autumn looked like the tower of pizza. Predictably the pole acted as a big lever. Two brackets and re-tighening the J bolts after a few weeks may have avoided that. But the really amusing thing is that if it was mounted a few feet above ground level at the end of the garden it would see under most of the trees, enough to get a decent signal and because the grid is so thin it would not really be visible.

 

[rolfw]

Yes, use the ratchet strap brackets for light rigs when accessing the other side of the chimney is impossible. Work well.

 

[satelliteman]

Yep, they say it's okay even if twisted. Personally wouldn't be happy.
13 inch mitre brackets are good but the 7.5 inch is pants having only one ratchet.



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[rolfw]

That's the old one Paul, the 8" cradle has two ratchets.

 

[Piltdownpaul]

Mast so far with new invisidish fitted picking up very little.....
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