2.4 meter Prime Focus high quality dish performs worse than a 90 cm Chinese offset dish on Ku

Discussion in 'Free To Air (FTA) Discussion' started by enb141, Sep 3, 2018.

  1. enb141

    enb141 Topic Starter SatelliteGuys Pro
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    Hi, I bought a prodelin prime focus 2.4 meter dish satellite with an invacom LNB + Feedhorn for prime focus dish which claims to be designed for prime focus dishes. According to the manufacturer it supports 0.32 to 0.43 on f/d (Prodelin has 0.37 f/d), so I know that offset LNBs have about 0.60 f/d and that's why those ones cannot be used with this dish but this LNB + feedhorn is supposed to give good results on a prime focus dish but after doing some tests with my 90 cm chinese prime focus dish on the same satellite / frequency and the 2.4 meter dish performed worse than the 90 cm prime focus.

    I would like to know if there's something I'm doing wrong or if not, what other LNB do you suggest me to use instead for Ku on this dish.

    Currently I'm also waiting to receive a primesat prime focus feedhorn, an inverto single C120 flange 0.2dB Black Pro and a Primesat PR-PFLNBF LNB with integrated feedhorn to see if any of this LNBs are "really" designed for prime focus dishes (0.32-0.43 f/d) in mind.
     
  2. Brct203

    Brct203 SatelliteGuys Pro

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    Maybe try the LNBF from your 90cm dish on the Prodelin and see how that performs. It should theoretically "see" only about about 1.5 meter of the dish because of its higher F/D. But it should still outperform the 90cm.
    If that works well, then the invacom might have a problem. If it's worse than on the 90cm, maybe the Prodelin has some problems... I'm not familiar with that dish, is it fiberglass or metal?
     
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  3. enb141

    enb141 Topic Starter SatelliteGuys Pro
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    The Prodelin dish is made of 3 pieces of fiberglass, looks pretty solid to me in comparison with the 90 cm chinese that is made of metal.

    It's raining season here, so it rains every day, I don't like to climb into my roof in those conditions but as soon as I find a sunny day I'll test one of of those offset LNB to see how they perform on that dish.
     
  4. enb141

    enb141 Topic Starter SatelliteGuys Pro
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    Hi, finally I was able to change the LNB, this time I tried a normal Ku Band LNB for offset dish and pretty much it has about the same results as with the Invacom + C120 flange.
     
  5. RimaNTSS

    RimaNTSS SatelliteGuys Pro

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    enb141 Are you sure you have placed LNB in proper position? Did you measure your dish and calculated it's focal point? It is not right to use LNBs designed for offset antennas on prime-focus antennas, as they have quite different F/D. Look for LNBF like GI-209P, it does not cost a lot but works well on PF dishes.
    And, yes, post some pictures of your installation, please.
     
  6. enb141

    enb141 Topic Starter SatelliteGuys Pro
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    Hi, thanks for the response, yes, I'm aware that prime focus dishes need prime focus LNBs that's why I was previously using an invacom prime focus LNB + C120 feedhorn shown in the pictures. Then the other guy, Brct203, suggested to try another LNB, right now I only have offset LNBs to test so I did the test but the results were pretty much the same in comparison with the invacom + feedhorn lnb.

    for the offset LNB I'm using this LNB holder:

    [​IMG]

    this is the dish I'm using and according to the manual the f/d is 0.37

    https://www.sateng.com/downloads/1252-53.pdf
     

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  7. RimaNTSS

    RimaNTSS SatelliteGuys Pro

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    It does not really matter what LNB-holder you use, more important is that holder holds LNB in proper position. Did you measure your dish and calculated position of it's focal point? The focal distance for PFA I marked in red line. LNB should be pointed directly to the center of the dish. And also make sure that LNB is located exactly in the middle of the dish (green lines are equal).
    Do you have possibility to exactly measure the leaning of the dish?
    20181004_123017.jpg
     
  8. enb141

    enb141 Topic Starter SatelliteGuys Pro
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    Green line is 129 cm, I was able to test from 4 different sides, red line is 91 cm
     
  9. RimaNTSS

    RimaNTSS SatelliteGuys Pro

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    And what about blue line and yellow line?
     

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  10. enb141

    enb141 Topic Starter SatelliteGuys Pro
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    Blue line: diameter 240cm (2.4 meters), don't know about the yellow line because I would need another person to help me to read that value.
     
  11. RimaNTSS

    RimaNTSS SatelliteGuys Pro

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    Blue and yellow lines are main measurements should be done for PFA. If the dish is 2.4m it does not necessary mean that it's working area is exactly 2400mm. When you have your friend over to help you to measure yellow line, just in case you also take precise measurement of the blue line. When you know exactly blue and yellow you can calculate red and green lines. And then make sure that calculated red line equals to measured red line.
    BTW, I have measured my 4.6m PFA without any external help.... I mean it is possible. :)
     
  12. Magic Static

    Magic Static FTA Geek
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    Since it's the mesh embedded in the fiberglass resin that does the work, does anyone know for sure it is a Ku frequency sized mesh? Is there a known working example of this dish on Ku?
     
  13. enb141

    enb141 Topic Starter SatelliteGuys Pro
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    How you did to measure blue and yellow by yourself?
     
  14. enb141

    enb141 Topic Starter SatelliteGuys Pro
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  15. RimaNTSS

    RimaNTSS SatelliteGuys Pro

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    Fix string across the "face" of the dish, mark points where string touches edges of the working area. When string is still across the dish use measuring tape to measure the depth of the dish.
     
  16. a33

    a33 SatelliteGuys Pro

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    You can also measure:
    1. blue line (working area!), and then:
    2. Middle of dish to End of blue line. (Or to beginning of blue line, that should be the same)

    With a bit of trigonometry you can calculate the yellow line.
    (Or you post your values, and I let my calculator calculate all),

    Greetz,
    A33
     
  17. RimaNTSS

    RimaNTSS SatelliteGuys Pro

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    And, BTW, you better check geometry of the dish by string test. After reading the manual I see that is very important to follow assembly procedures. It is also written in the manual that focal distance of the dish is 35.8 inches which is 909mm (exactly as you have said before) . Anyway, I think it is nice dish, designed for Ku/C reception, so it should work as 2.4m. Double check all the distances (colored lines), use LNBF for PFA and results should come. If you wish I can look for GI-209P in our shops and sen it over to you. I had good reception results using such LNBF.
     
  18. enb141

    enb141 Topic Starter SatelliteGuys Pro
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    I was lucky, my brother came today and he helped me to measure yellow and blue.

    Blue 243 cm

    Yellow 40.5cm

    Yeah look up for the GI-209P, if it is universal, yes because I really need an universal LNB
     
  19. RimaNTSS

    RimaNTSS SatelliteGuys Pro

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    Is that the working area or distance from edge to edge?
     
  20. enb141

    enb141 Topic Starter SatelliteGuys Pro
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    Edge to Edge
     

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