How far to tighten bolts on serrated tv aerial clamp

Discussion in 'Engineers' Talk' started by bayjohn, Oct 9, 2016.

  1. bayjohn

    bayjohn New Member

    Hi

    Got a new log periodic aerial up and running, but it swings a little horizontally in a side wind, despite seemingly not moving on the mast. The clamp is tightened so that the serrated points are just biting into the 16 gauge 1.25" alloy mast.

    I now wonder should I risk weakening the alloy mast/snapping the clamp bolts by tightening to get all or more of the serrated points into the mast, or should I just accept this type of aerial does swing around a lot.

    I was swayed to buy a log periodic by the low 35N wind loading compared to other aerial types, but maybe the way that is calculated for aerials doesn't fit well with the design of log periodics which seem to me to suffer from a very high side wind loading.

    Anyone with experience with these clamps?

    Thanks in advance
    bayjohn
     
  2. KIAB

    KIAB Super Member

    Last edited: Oct 9, 2016
  3. bayjohn

    bayjohn New Member

    Hi KIAB

    Thanks for the link. It's on a short 3' pole - about 2' 4 inches up from end of mast clamp so the sway is disappointing for an aerial with a supposedly very low wind loading of 35N.

    What concerns me is that the pole is being gripped with only 8 "points" of the serrated clamp/sledges. The clamp is supposedly meant for poles from 1.25 inches to 1.5 inches so it should be suitable, but there again something designed for different size poles may not have the best design for one size. The bolts through the clamp look only about 7 mm, with wing nuts, and I didn't want to overtighten in case the bolts snapped before the points dug more into the pole. I did finger tighten, then use a spanner to tighten one more turn.

    The clamp just doesn't seem as though it has a sturdy grip around the pole even though there was no evidence of the clamp having moved around the post when I took it down to inspect after the wind. Having wing nuts I assumed the thinnish bolts were not meant to be tightened to the point the serrations would puncture the alloy mast - and I suspect it would take an awful lot of pressure to do that, but I would try if that would help.

    To put the sway into context, my aerial was swaying as much as next doors X beam of a similar length (1100mm) in the side wind. So if it's not good practice to get the serrations to really puncture the mast, I may try lowering the aerial a little more if there is nothing else to try.

    Thanks again for the useful link, it look a good site.

    Regards
     
  4. KIAB

    KIAB Super Member

    If I had 1100mm aerial on a 1.25" pole:eek:, I expect it to sway alot on such a small diameter alloy pole, a 1.5" steel would be a lot less movement I would think.
     
  5. bayjohn

    bayjohn New Member

    Hi

    But a 12 inch diameter pole would be even better - lol.
    Yes that might be the problem. I think I will go to drop the aerial a bit first, reception doesn't seem to be an issue where it is. If that doesn't work I'll look into changing the pole, but isn't alloy better than steel?
    Regards
     
  6. KIAB

    KIAB Super Member

    [​IMG]

    I don't know the size of your aerial, what is the pole attached to.

    In my loft there is a 1300mm log periodic , it light weight, & small in shape, so low wind resistance, but If I attached it to a 1.25" pole, the pole would eventally fail, you would need two wall mounts to be assured the pole would survive, but there would still be some flexing further up the pole.
     
    bayjohn likes this.
  7. bayjohn

    bayjohn New Member

    Hi - I would have loved to have gone for a loft install but I'm sure it wouldn't work where I am. The aerial is a Blake DML26 which has the tilting aerial clamp mechanism (I stand corrected it's 1055 mm). I've only got one good bracket on the wall and it certainly seems very sturdily attached to the wall and mast -so that's not the problem at the moment - although I can see how the swinging might warrant an additional bracket. My signal strength and quality (from my Sony TV) show 100% and 78% on the lowest 570 Mhz frequency channel progressively going down to a fluctuating 98-100% and 26-38% on the highest frequency 778 Mhz Sky news channel - that's direct to the TV. Once I put the aerial through my Freeview Play Box the stats improve markedly. So is it worth dropping the aerial a foot or so to see if that alleviates the problem. It's also the easiest option.
    Regards
     
  8. bayjohn

    bayjohn New Member

    I see my problem. This make of log periodic has the aerial bracketed to the bottom beam only, unlike a couple of other makes that have the aerial bracketed to both beams. I had tried to literally followed the makers diagram for sliding the aerial beam so far into the bracket - but I have about another half inch I could push it before the bracket end gets to the start of the upper beam end. When I have time I'll get the aerial down again and see if I can actually push the aerial beam in that half inch and a little bit further than that to try and get the bracket actually overlapping the second beam end a bit. That should give it a little more support if it will work - not sure about that though. And I'll look into getting another type of bracket that can actually capture both the beams. I don't think this aerial is a well thought out design.
     
  9. KIAB

    KIAB Super Member

    Last edited: Oct 10, 2016
    bayjohn likes this.
  10. Mr. Handyandy

    Mr. Handyandy Screwfix Select


    Yeah, and tighten the buggers up with a spanner.

    Mr. HandyAndy - Really
     
    bayjohn likes this.
  11. bayjohn

    bayjohn New Member

    Thanks KIAB and Mr HandyAndy - been away for a few days but now just finished redoing it all. Pushed the aerial boom as far into the tilting bracket as it would go, really tightened those nuts, then replaced the mast fixing wingnuts with nuts, washer and spring washer as suggested and tightened them really hard. Time and the first gale will tell if I should have gone for a different aerial! :)
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice