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Optimum Dish Size

  • 04-04-2006 7:30am
    #1
    Hagar
    Closed Accounts Posts: 16,793 ✭✭✭✭


    Is there an optimum dish size to use based on location? I'm asking this because minimum size always seems to be specified but I'm wondering will too big a dish cause problems by picking up "overspill" from nearby sats. Most people around here, Southern France, use 60cm for Hotbird etc but I have to use 1m minimum to pick up Astra 28.2E. Even then I get breakup in very bad weather. I may have problems putting up a second dish so a motorized system may be my only option. If I motorize my dish will it give me grief? Will I have trouble with Sky if I keep moving off it?


Comments

  • #2
    Zaphod
    Registered Users, Registered Users 2 Posts: 1,733 ✭✭✭Zaphod


    The bigger the dish, the narrower the beamwidth so overspill is less than with a small dish. This might seem counterintuitive, but it is harder to align a big dish than a smaller one, as they are more tighly focussed on a smaller area.

    For the really big dishes, they must be continually adjusted as satellites which appear to be stationary (e.g. Astra 2D) to a small dish, are actually moving within 10 mile box.

    http://news.bbc.co.uk/2/hi/programmes/click_online/3744964.stm


  • #3
    watty
    Registered Users, Registered Users 2 Posts: 32,417 ✭✭✭✭watty


    1m is hard to adjust. 3.4m is a total pig to find ANYTHING. Easy to find a sat with a 40cm, and it may even pickup two satellites! but lose everything in rain.

    Almost all satellites are slightly inclinded so people using REALLY big dishes out east or south in Europe for Astra 2D tend to lose the signal twice a day. The installer must do alignment for peak viewing time! This is why my friends 3.4m dish has an elevation jack. Of course this means his system can track old badly inclined satellites that would only work for two short periods a day on a small dish.

    A motorised system is harder to aling really accurate above 80/90cm. Also most Diseqc motors will only cope with wind load of up to 1.1m (110cm) dish. For larger (1.4m, 1.8m) you need a 36V system and a lot of concrete.

    Above a certain size of dish you can only pickup Astra 2D (28.2E BBC & ITV) OR Eurobird (28.5E some Sky FTA channels) with a fixed dish as the 0.3 degree becomes significant. Even with my 80cm dish I can see signal quality change on weaker signals with 0.2 degree motorised movement.

    Interesting BBC article, Zaphod, Thanks.


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