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VOS Diagrams and info about signal attenuation

Discussion in 'DIRECTV Installation/MDU Discussion' started by BennyGregg, May 16, 2013.

  1. BennyGregg

    BennyGregg Legend

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    I know that VOS has posted some diagrams and other nformation about signal attenuation in SWM systems due to cable length and different types of splitters, but I can't find it... could somebody give me a link to it?
     
  2. peds48

    peds48 Genius. DBSTalk Club

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    Dont have the link but I have attached the picture
     

    Attached Files:

  3. BennyGregg

    BennyGregg Legend

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    Thanks, peds48. That diagram helps a lot. VOS's original posting I think had even more information, so I'd still like to be able to find it.
     
  4. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Not sure what you're looking for or whether I could find it.

    That diagram basically shows how you can use the 30 dB loss range of a SWiM.
     
  5. HoTat2

    HoTat2 Hall Of Fame

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    I think these links "were" to the original postings the TS is referring to here.

    http://www.dbstalk.com/topic/176917-how-a-splitter-works/?p=2556998

    But they no longer work unfortunately so I can't check for sure, at least since the changeover to the new forum software.
     
  6. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Not sure why, but those images didn't make the change over.

    What I think they were the board of the splitter circuit

    I think they might be found here: http://www.dbstalk.com/topic/189822-tips-resources-faqs-and-important-links/
     
  7. BennyGregg

    BennyGregg Legend

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    Jul 17, 2009
    Thanks to all who found the information for me.

    Here's what I'm wondering about. I use DirecTV in an RV application with a home assembled dish (a Dish 1000.2 reflector and a four out SL3 LNB and a SWM-8 located at the dish). I usually get 95 or so on 101, and mid 80's on 99 and 103 on the receiver's signal strength screen. Occasionally finding an LOS is a real problem - I was trying to find out what cable length I could use to connect to the dish if the only line of site was far from my trailer. The answer seems to be 250 feet or so with a 1x2 splitter and 300 feet or so without any splitter - just connecting to one receiver. Is that about right?
     
  8. peds48

    peds48 Genius. DBSTalk Club

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    depends what kind of cable you are using and where the power supply is installed. if you use RG6 SCC, you might get 200ft at best, assuming the PI is at the end
     
  9. BennyGregg

    BennyGregg Legend

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    I using solid copper conductor RG6 and quality compression fittings. I'm just looking for enough signal to make a picture, with maybe enough signal extra to allow for a cloud or two passing by; with my setup and a long cable, I know that I won't get signal strength levels that would be required for a permanent install.
     
  10. peds48

    peds48 Genius. DBSTalk Club

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    WIth a SWM8 switch, you have to worry about power loss FIRST rather than signal loss. as you would loose more power with a longer cable. RG11 is recommended for longer cable runs
     
  11. cwtech

    cwtech Mentor

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    am i reading your post right? you are using a modified dish network dish, with your sl3? Myself I would start by getting a proper slimline dish dish, then we get can a little more info from you and give you some options, what receivers are you going to be using, how many? example, if receivers are swm combatible (this isnt recommended but could buy you a extra few feet) assuming you have a swm lnb you could buy a 29v pi instead of a 21v and gain a few valuable feet sometime. but again what type and how many recievers are you going to be using.
     
  12. slice1900

    slice1900 Well-Known Member

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    According to Sonora's measurements, a SWM8 requires a bit over 9 watts of power, exclusive of what the LNB draws. The LNB itself requires another 6 watts or so, for a bit over 15 watts total. Others have measured their SWM8 power draw at 18 watts using a Kill-A-Watt meter. That measurement includes the losses of the power inserter, so it matches Sonora's figures perfectly. Even though 18 watts is overstated, let's use that as our worst case power draw figure for a SWM8.

    RG6 quad SCC cable has ~6.4 ohms of resistance per 1000 feet. Sonora says (and has measured) the SWM8 being powered by voltages ranging from 20 to 29 volts, but let's use 24 volts as our conservative figure here. Thus at our conservative 24 volts our conservative 18 watt draw is a very conservative 750ma. Applying Ohm's Law, 750 ma * 6.4 ohms = 4.8 volts of loss in 1000 feet of coax, or 29 - 4.8 volts = 24.2 volts at the end of 1000 feet! So the PI-29 should be able to power the SWM8 and LNB quite well on a cable run far longer than you could ever manage to push a signal through.

    You lose about 7.5 db per 100 feet on RG6 quad at the (~1200 MHz) frequency range you'd be using when you have only a single receiver on a SWM-8, which would mean 400 feet, maybe 500 if you're really lucky with a receiver pulling in an extra weak signal. If you used all 8 tuners you're using higher frequencies, then your losses are more like 9 or 10 db per 100 feet. In which case 300 feet becomes the likely limit, with 400 only if the wind is at your back. Swapping RG6 for RG11 would give you maybe 40% more length, if you needed more than that you'd need a SWM amplifier somewhere along the line.

    At the length ranges you're talking about, it sounds like RG6 should work and RG11 adds an additional margin of safety. These are my opinions, backed up by the math, others have theirs, likely backed up by actual experience....the gap between theory and reality is where things like damage to cables or connectors, something not working according to spec, and so on will tend to bite you :)

    Of course, all bets are off if your signal is starting out weaker than normal at the LNB due to your frankendish...
     
  13. BennyGregg

    BennyGregg Legend

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    Thanks for the analysis, slice 1900; sounds like I can use a cable long enough to handle most situations. Course, if I don't find a LOS large enough for 99 101 and 103 I can always just look at 101 and settle for SD. Frankenish, indeed; maybe I'll name my dish "Frank".

    RV situations are not like permanent installations. And if some oddball thing I do doesn't work for long, the call back to the installer is usually easy.
     

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