Attenuators vs Splitters

Discussion in 'TiVo Roamio DVRs' started by Humble, May 22, 2015.

  1. Humble

    Humble Member

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    If I take a 4 way splitter and cap three of the outlets and use the fourth as a pass through to my Tivo Roamio Plus, what is the reduction in DB's compared to an attenuator?
     
  2. hefe

    hefe Rebus Philbin

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    An attenuator will attenuate by its rating. They can be built for different values. Could be a 3 dB attenuator...6 dB, 10 dB...whatever the rating is.

    A 4 way splitter will attenuate the signal because of 2 things. The splitting loss, actually dividing the power between the ports, and the insertion loss...the loss caused by the signal just passing through the device itself. A 4 way splitter will cause 6 dB of loss due to the splitting, and the insertion loss depends on the quality of the splitter. You can probably assume about 1 dB or so, although it may be less. So, around 7 dB is a good estimate.
     
  3. Humble

    Humble Member

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    hefe: Thank you for the very clear explanation. It has been driving me nuts.
     
  4. Marc

    Marc Well-Known Member TCF Club

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    If the splitter doesn't have anything else plugged into it, though, will it still provide the 6 dB attenuation?
     
  5. JoeKustra

    JoeKustra in the other Alabama TCF Club

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    I like the brand "Extreme". They have the signal loss written on their splitters. 1 to 2 is 3.5dB, 1 to 4 is 7.5dB.
     
  6. JoeKustra

    JoeKustra in the other Alabama TCF Club

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    Yes, and you should terminate unused ports.
     
  7. hefe

    hefe Rebus Philbin

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    It will, although in a perfect world and a perfect installation, any unused ports should be terminated. Not just "capped." A terminator matches the impedance that the port is expecting. Without a terminator, you can get signal reflecting back from the unterminated ports into the source and affect the isolation between the splitter ports. Possibly even cause interference on the original signal.

    So if the intent is just to reduce the signal on a single cable, an attenuator is the device to use if possible. But I've used unterminated splitters myself in the house to split to a couple TVs. I wouldn't do it in a communication system where we need to recover every last bit of signal possible.
     
  8. waynomo

    waynomo My One Time

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    Do you want attenuation?

    If not, sounds like trying to use the splitter to to connect 2 shorter coax cables together. They make a simple female female coax connector. They are really inexpensive. Would that be a better solution?
     
  9. hefe

    hefe Rebus Philbin

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    Yup...so that's 3 dB every time you halve the signal + 1.5 dB insertion loss.
     
  10. Humble

    Humble Member

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    hefe: When I said the unused outlets were capped, I mean the cap is a silver cover with a pointy end. Does that "terminate" the outlet? To one of the other commentators, I was looking to attenuate, not split my signal.
     
  11. hefe

    hefe Rebus Philbin

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    Does it have a center conductor? A terminator has a center conductor, like this.

    [​IMG]
     
  12. Humble

    Humble Member

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    They do have the center conductor and look exactly like the ones on the right. Thanks again.
     
  13. Humble

    Humble Member

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    Last question, hopefully. I ended up buying a 16db attenuator and putting it on the back of the Tivo Roamio Plus and hooking it up to the Frontier Fios cable (used to be Verizon Fios). When I started, my signal strength was 99-100% and my SNR was 38-41. After putting the 16db attenuator on, my signal strength is 93-98 and my SNR is 37-39. My picture is now fantastic and I get zero corrected and uncorrected errors.

    Question? Why doesn't the signal strength fall 16db's and the SNR ratio fall slightly further? Thanks in advance and I will try not to become a pest.
     
  14. unitron

    unitron Well-Known Member

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    If you check them with an ohmmeter and get a reading in the neighborhood of 75 Ohms, then you've got the right thing, because they're supposed to put a 75 Ohm load from the center wire to ground.
     
  15. JoeKustra

    JoeKustra in the other Alabama TCF Club

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    Perhaps you shouldn't trust everything shown by the diagnostics? It has been demonstrated by many that the signal level never goes above 100. That's why a number in the low 90s is better than 100. The SNR seems pretty good though. My TiVo Roamio, Premiere, TV and cable modem all have a SNR of 35-36dB from one cable feed. Given that the premiere has a signal level of 75 and the Premiere is 90, I'm not sure if I trust the Roamio. Also, the error counters of the Premiere increment when I have noise, as does the cable modem. The Roamio displays the noise on the screen but the counters on all four tuners are stuck at zero.

    You're not a pest. :)
     
  16. hefe

    hefe Rebus Philbin

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    That's because the number you are seeing on the screen is not an RF strength measurement. It is a quality number that the TiVo calculates internally, probably a combination of factors including strength and bit error rate on a scale that ends at 100.
     
  17. Humble

    Humble Member

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    Thanks to the last two posters. I get it.
     
  18. Humble

    Humble Member

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    unitron: If you saw my question re the "pointy end" on the terminator you can assume I probably don't own or know what an ohmmeter is. It did give me a great laugh and thank you for your guidance.
     
  19. JoeKustra

    JoeKustra in the other Alabama TCF Club

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    I guess if you were asked about the difference between resistance and impedance you would have busted a gut laughing too. :D
     
  20. Humble

    Humble Member

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    I was a CPA for 35 years. I didn't say I was bright! If someone asked me the difference between resistance and impedance, they might have enjoyed the blank stare they would receive.
     

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