Do big dishes overload sensitive LNBfs?

Discussion in 'Free To Air (FTA) Discussion' started by drg, Sep 15, 2019 at 9:21 PM.

  1. drg

    drg Topic Starter Active SatelliteGuys Member

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    (more newbie Qs)
    Do big dishes overload sensitive LNBfs? If so, do you move them out of the hottest focal point spot?
    The reason I ask is that I may be able to get an old, really big, fiberglass dish. I'd like to do a Titanium LNBF like:
    Titanium Satellite - Store
    for C-band, and then one or more Ku LNBFs on this dish:

    ...or, should one get a combination one like:
    Hot sales High Gain Low noise Universal Dual Band C/Ku Combo LNB LNBF | eBay
    (or, is this too much of a compromise?)

    On a big dish, is signal bleed-over from adjacent satellites an issue for the Ku LNBFs? If so, is there a way to exclude unwanted noise/signal?

    (sorry for all of the Qs. I've installed mini, 18" dishes, but nothing like this)
     
  2. KE4EST

    KE4EST SatelliteGuys Is My Second Home Staff Member HERE TO HELP YOU!

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    I would stick with a 8-12 foot dish for C-Band only. Use a smaller offset dish for Ku at least 90cm, larger is better.
    Those combo C/Ku LNBFs are too much of a compromise.

    What size is the fiberglass dish you have found?
     
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  3. drg

    drg Topic Starter Active SatelliteGuys Member

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    I'm told that it's 12'
     
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  4. Cham

    Cham VE4GLS Pub Member / Supporter

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    A 12 foot C-band dish should not overload an LNBF like the C2PLL you are looking at.
    You always want the LNBF at the focal point.
    The larger the dish the smaller the aperture (angle of reception) so there is less interference from the next satellite or other interfering sources... theoretically, as long as the dish has a good parabola, no dents or bends.
    Congrats on the 12 footer!
    What mounting system does it have? Polar, solid, H-H? Should work fine no matter the mount, just different setup types.
     
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  5. drg

    drg Topic Starter Active SatelliteGuys Member

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    Ha, well, I've not heard back from the owner yet, so...I don't know if I'm getting it...or any answers for the mount question. Judging by the one pic included in the listing, I'd say that it in effect has no mount as it looks unusably rusty.
     
  6. drg

    drg Topic Starter Active SatelliteGuys Member

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    OK, cool, I got the OK from the owner to come get it. :)
    Since you brought up the mount...and its mount is screwed up and will need to be replaced, may I have a recommendation? How have you(+others) mounted yours?(I'm going to run to the search bar to look for posts)
     
  7. Cham

    Cham VE4GLS Pub Member / Supporter

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    If you can take a picture of the back of the dish so we know what's there. It's somewhat easy to fabricate a stationary mount, but if you want a polar mount it is a bit more tricky. I just used the mount that came with the dishes, but one of mine is a bit of an odd put-together of various parts that were kicking around.
    Before worrying about the mount, do a string test on the reflector. If it is bent or warped, there might not be any point in trying to fix it up. Tape two strings over the edge 90deg apart so they cross in the centre of the dish. If they (just) touch or have a very small gap <1/8" then you are likely good to go. If the gap is larger then the focus may not be accurate. I'm afraid if the mount is messed up, damage to the dish may have occurred as well.
     
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  8. drg

    drg Topic Starter Active SatelliteGuys Member

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    I'm not sure that it's bent or anything like that...but, it sure looks to be unusably rusty. The dish may be in ok shape(literally)
     

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  9. Cham

    Cham VE4GLS Pub Member / Supporter

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    Hmmm... that doesn't look too good, sitting on the ground with that heavy pole weighing down on one side. The mount might be ok, is it bent from pulling it up? Otherwise it might just need to be disassembled, cleaned, re-painted, and re-assembled with new hardware (bolts etc). The dish you won't know until it is separated from the mount, or the whole assembly turned over (very carefully). Best to remove the pole first. It's likely rusted into place and bolts seized, some heat and penetrating oil required.
     
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  10. drg

    drg Topic Starter Active SatelliteGuys Member

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    Yeah, it looks ugly. I'm new to this, so I'm doing a lot of guessing. I'm guessing that they left the mounting pole top open, rain entered, the pole subsequently rusted through, and the dish then fell. Plus one(I agree) on that penetrating oil(I will try Liquid Wrench™). I'm bringing an impact wrench too. I like your idea about stripping the rust and repainting...but, if it's a lost cause, I'll be open to buying a new mount(and stainless hardware...I HATE rust)
     

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