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Thread: Multi LNB and dish usage?

  1. #1
    marty's Avatar
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    Multi LNB and dish usage?

    I'll try and keep this as simple as possible
    On a "normal" setup (single LNB) you use the most optimal part of the dish in theory. Manufacturers claim upwards of 70% efficiency.
    Now on a multi LNB setup the LNB's are offset so I assume you use less than the optimal focus? and the more off centre you go the more gain you loose?

    My question is, by how much? e.g. is using a 1m dish with an LNB offset the equivalent of using an 80cm with the LNB central?
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    Rob van der Does's Avatar
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    This will obviously depend on how much the LNB's (i.e. the satellites) are apart: the closer the better.

    But much better would be to use a multi satellite dish: the are oval and don't have one focus-point, but a 'focus-line'.

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    And besides: the bigger the dish, the smaller the opening-angle.
    Meaning that a LNB being out of focus (as will be the case in your suggested line up) has a bigger effect on a large dish then it has on a small dish. In other words: the bigger the dish, the bigger the gain, but the bigger the loss when out of focus.

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    OK, to put it another way

    I want to get 28°/19° and 13° on one dish and stick a motor on the other.
    Would I be better off using an 80cm dish or 1.1m dish? (you know where I live )

    I would like 28° on a fixed dish for instant switching to UK TV. I was thinking of setting 28° central the 19°/13° offset as ASTRA 1 and HOTBIRD don't require a big dish here.

    Open to suggestions (but won't buy yet another dish two is plenty)
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    Rob van der Does's Avatar
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    Quote Originally Posted by marty View Post
    Would I be better off using an 80cm dish or 1.1m dish?
    I prefer to await Huevos to answer that one.


    Quote Originally Posted by marty View Post
    I would like 28° on a fixed dish for instant switching to UK TV.
    Why not combine the fixed dish and the rotor via one 4/1 switch? If you use twin LNB's you can have one tuner getting the combined, and the other tuner the fixed dish only. That's what I use: the best of two worlds (i.e. fast switching for the most used sats on two tuners and still all sats available on one tuner).


    Quote Originally Posted by marty View Post
    I was thinking of setting 28° central the 19°/13° offset as ASTRA 1 and HOTBIRD don't require a big dish here
    That doesn't seem logical, as 13 will then be very much out of focus. I would put 19.2 in the centre, and 13 and 28.2 on both sides of it.

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  6. The Following User Says Thank You to Rob van der Does For This Useful Post:

    marty (24-02-14)

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    Quote Originally Posted by Rob van der Does View Post
    That doesn't seem logical, as 13 will then be very much out of focus. I would put 19.2 in the centre, and 13 and 28.2 on both sides of it.

    Depends on 2E really, try and see I suppose.
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    Yeah, easy enough to change back if SNR is too low.

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  9. #8
    marty's Avatar
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    Busy afternoon
    Fitted the motor to the 1.1m dish (again) after fixing the backlash

    My big surprise was the multi-feed set on an old 80cm dish I had.
    Doesn't look pretty but works (still need to wire it up and fit the 4/1 switch)
    I'm getting 94% SNR on BBC FTA on 28°, 98% SNR on 19.2° and 84° on HOTBIRD.
    Better than expected
    Had to do a bit of bending to get the best results

    d1.jpg

    d2.jpg

    Isn't my boy handsome

    d4.jpg
    VU+ DUO² (Triple S2 tuners) VIX, 750gb
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    1.1m dish, 0.1db Quad LNB, GTSAT DM14MG motor
    80cm dish, 2x 0.1db LNB + 1x Quad 0.2db LNB, Disqec 4/1.

  10. #9
    Rob van der Does's Avatar
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    So your handsome boy did the bending

    Help asked via PM will be ignored.
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