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Two new SL5 LNBs With Different ma readings

Discussion in 'DIRECTV Installation/MDU Discussion' started by gabolh, Sep 9, 2013.

  1. Sep 9, 2013 #1 of 12
    gabolh

    gabolh New Member

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    I have two new LNBs with different ma readings
    a. SL5K4NR0-02 = 219 ma (made in china no brand name)
    b. SL5PIG-Z = 165 ma ( Zinwell brand )
    What does this difference in ma readings mean?
     
  2. Sep 9, 2013 #2 of 12
    peds48

    peds48 Genius.

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    Were both measured with the same load? or for that matter no load?
     
  3. Sep 9, 2013 #3 of 12
    HoTat2

    HoTat2 Hall Of Fame

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    AIUI, for a four output legacy LNB as those models are, its supposed to be the maximum current flow at the minimum control voltage allowed for the 18v (or 18v + 22 KHz) control signal on any line to the LNB, which is considered to be 16v.

    Therefore the lower the current figure the greater the maximum distance allowed between the LNB and the receiver or multiswitch for a given type of coax.

    For example the 165 ma LNB with SCC coax which has a resistance of about 4 ohms/100 ft. can have a max. coax distance of 18v-16v/.165 amps/4 ohms per 100 ft. = approx. 300 ft.

    For the 219 ma LNB with SCC coax cable its 18-16/.219/4 = approx. 228 ft.

    NOTE: The figures above assume Zinwell is being truthful of course about the 165 ma level as this number is typically around 200 ma as the Chinese manufactured one is,
     
  4. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Seems like the resistance values got mixed up between CCS & SCC.
    SCC is about 1.6 Ohms/100'
    CCS is about 4 Ohms/100'
     
  5. HoTat2

    HoTat2 Hall Of Fame

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    I got the figures from Sonora Ass.

    4 ohms/100 ft. for SCC

    8 ohms/100 ft. for CCS

    But I'll sure be happy to change them. :)
     
  6. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Between you and me, I'd check a second source before accepting Sonora.
    Perfect Vision makes RG6:

    CCS https://www.perfect-vision.com/WebStore/ProductList.aspx?pcID=117
    center conductor 29.9 Ohms/1000' & Shield 10.3 Ohms/1000'

    SCC https://www.perfect-vision.com/WebStore/ProductList.aspx?pcID=111
    center conductor 6.4 Ohms/1000' & Shield 2.8 Ohms/1000'
     
  7. P Smith

    P Smith Mr. FixAnything

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    I would measure my cable's DC parameters first or assume worst case [4 or 8 Ohm/100'] for estimate max length, but it would be just 1/2 of full requirement.
    Because there is second and not less important parameter: RF attenuation and it's dependence by frequency.
     
  8. slice1900

    slice1900 Well-Known Member

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    It appears Sonora is overstating the resistance of SCC by a significant factor. I assume this was in a document trying to sell you a polarity locker? ;)

    According to Sonora a SL5 LNB is supposed to be fed 200ma on the 18v lines and 50ma on the 13v lines. This adds up to about 8.5 watts. If you substitute 16v and 11v for the minimum it would be fed, it adds up to 7.5 watts. I measured the power draw of my SWM16s once and found they draw 17 watts when not powering the LNB, 24 watts otherwise, which is essentially identical to figures Sonora provided. I measured this at the plug of the regulated 24v 2 amp power supply using a Kill-A-Watt.

    If you substitute Sonora's 200ma for Zinwell's 165ma figure and the Perfect Vision resistance numbers you get (18v-16v)/0.2A/3 ohms = 333 feet for CCS or (18v-16v)/0.2A/0.64 ohms = 1562.5 feet for SCC. Somehow that doesn't seem quite right - there would be no need for SCC cable, at least if you knew your voltage started out at 18v. If anything I'd guess the voltage starts out higher, anyone ever measure the voltage on the 18v ports of a SWM16?

    For a SWM LNB it would matter more, since all the power is traveling down one coax the amperage is higher. I'm not sure exactly what they draw, but as it is essentially an SL3/SL5 combined with a SWM8, it can't draw much more than half what a SWM16 does plus the LNB, so maybe 10 watts worst case, plus 8 for the LNB or 18 watts total. At 21v that's 0.86A, so (21v-16v)/0.86A/3 ohms = 193 feet of CCS, or just over 900 feet of SCC.

    Am I missing a decimal place or something with these length calculations? These figures make it look like SCC is pretty much unnecessary for either a SL3/SL5 + SWM8/SWM16/WB16 or SL3S/SL5S install. I think it would still be valuable in a legacy install with no multiswitch or only a WB68, where the receivers are powering the dish. When the power supplies start to die on the receivers they may start out with less than 18v and leave less margin for error.

    Getting back to the point of the thread, I don't see why 165ma can't be the correct figure for the Zinwell. Maybe it is a newer design and/or uses some slightly more efficient components and requires less power than others. I doubt it matters, but just because it uses less power doesn't mean it is better. Maybe there is less signal power coming from it, or more noise or something else that would make the other LNB a better choice.
     
  9. samrs

    samrs MANC

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    It doesn't mean nothing, unless your a dumb ass engineer of some flavor. Leave your hair alone, DAE don't have none, watch TV, relax. Peace:)
     
  10. P Smith

    P Smith Mr. FixAnything

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    :ewww:
    :scratch:
    :mad2:
     
  11. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    There are good and bad engineers, just like installers.
    I'd say a good installer would know the difference.
     
  12. samrs

    samrs MANC

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    I guess I'm bad then. So long as it can pass IV, year after year without needing a re-peak, is all that matters to me.
     

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