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Thread: Coax CATV Splitters

  1. #1
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    Coax CATV Splitters

    My unerstanding is that splitters divide the signal. For instance a two way will send 50% of the signal down each of the two branches, and an 8 way will send 12-1/2% to each leg. And if you divide the signal too many times you will need to install an amplifier to goose up the signal. Do I have this right?

    Somebody told me today that splitters with Poewer Pass do not reduce the signal. Is this true? What is power Pass? Are they configured the same as standard splitters (a two way has one IN and two OUTS).

    Mike

  2. #2
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    Quote Originally Posted by mkgrady
    My unerstanding is that splitters divide the signal. For instance a two way will send 50% of the signal down each of the two branches, and an 8 way will send 12-1/2% to each leg. And if you divide the signal too many times you will need to install an amplifier to goose up the signal. Do I have this right?

    Somebody told me today that splitters with Poewer Pass do not reduce the signal. Is this true? What is power Pass? Are they configured the same as standard splitters (a two way has one IN and two OUTS).

    Mike
    Mike CATV splitters are a little more complicated than that. A two-way splitter is the standard to use where a cable modem is used. One 3.5 leg connects directly to the cable modem and the other output feeds either a TV directly or another splitter when multiple TV's are used.

    The you have what is called unbalanced splitters. One of them is a three-way. One leg is 3.5 db for a cable modem, and the other two are 7 db to feed two TV's. It is all about signal distribution and managing signal losses.

    So for passive splitters you have this

    2-way: -3.5 db per leg. about 60% signal reduction per leg
    3-way: in two flavors one leg -3.5 and two legs at -7.0 (80% signal loss), or three outputs at -7 db
    4-way -7.0 db per leg
    8-way: -12 to 14 db per leg (95% signal loss per leg)

    What you refer to Power Pass I think is what is known ac DC Pass Through. Never heard the term power pass. DC Pass Through allows DC power to pass through to power a line-amp. DC pass has the same attenuation a DC blocked or passive splitter has.

    I think what you might mean is an Active Splitter with a built in amplifier that requires power, they come in 3 flavors

    2-way with 2 db gain
    4-way with 0 db gain
    8-way with -5 db loss

    You are right in you have to use an amplifier is a number of TV's are used. But do not confuse an Active Splitter with an amp as they are not the same thing. As a general rule if you have more than six devices you will need an amp.

    Here is a super secret site that will tell you about every thing you need to know on how to wire up CATV
    Last edited by dereckbc; 09-17-08 at 07:22 PM.

  3. #3
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    Thanks Dereck for response, very informative. You confirmed some things I thought I knew and taught me some things I never knew.

    I'l check the secret site to learn more.

  4. #4
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    You'll find "power pass" stamped on splitters designed for satellite use, but the idea is the same as Dereck describes, to provide power from one of the sat receivers to the LNB at the dish. Some splitters have diode isolation between ports and allow any output port to pass DC to the input without affecting the other ports.
    Gregg

    I'm just here for the pictures!

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    super secret site

    Thanks dereckbc
    rbj, Seattle...Safety is a Professional Courtesy.

  6. #6
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    You dont want to use a multi-switch which is used for sat tv. cable splitters wont allow the voltage to pass which is a good thing being that it can and will damage your tv or vcr.

  7. #7
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    A two-way splitter is technically a power divider. That is, its output will be 3.01 dB less than the input. In practice, there is a slight amount of additional loss in the splitter due to circuit inefficiencies, component losses, basic design, etc., which is why you typically see two-way splitter insertion losses in the 3.3dB or so, depending on frequency.

    An unbalanced 3-way splitter is actually 2 2-way splitters cascaded -- hence, the hot leg with ~7dB loss and the other 2 legs at ~7dB. Balanced 3-way splitters have loss of ~5.5-6.5dB, depending on frequency and manufacturer. As stated previously, 4-ways lose ~7dB, while 8-ways typically lose ~10.5-11.5dB.

    There is no such thing as an active splitter. A splitter is a passive device by design. That's the law of physics. Those devices touted as Active
    Splitters are merely a standard 15dB gain drop amplifier with a splitter on its output, all in the same housing.

    Power passing splitters, while more common in the satellite industry, can be found in the CATV and MATV industries, as well as in some residential antenna applications. Some pass power from the IN to one of the OUT ports, while others pass power on all ports. As grich wrote, some are diode steered so power can go only in one direction.

    The splitters used in the CATV industry have blocking capacitors. The capacitors help prevent voltage buildup and the ensuing magnetism of the ferrites.

    Some cable systems use 2-way splitters for cable modem connections. The majority, though, utilize directional couplers (taps) for that connection.
    CIAO!

    Ed N.

  8. #8
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    Quote Originally Posted by egnlsn
    A two-way splitter is technically a power divider. That is, its output will be 3.01 dB less than the input. In practice, there is a slight amount of additional loss in the splitter due to circuit inefficiencies, component losses, basic design, etc., which is why you typically see two-way splitter insertion losses in the 3.3dB or so, depending on frequency.

    An unbalanced 3-way splitter is actually 2 2-way splitters cascaded -- hence, the hot leg with ~7dB loss and the other 2 legs at ~7dB. Balanced 3-way splitters have loss of ~5.5-6.5dB, depending on frequency and manufacturer. As stated previously, 4-ways lose ~7dB, while 8-ways typically lose ~10.5-11.5dB.

    There is no such thing as an active splitter. A splitter is a passive device by design. That's the law of physics. Those devices touted as Active
    Splitters are merely a standard 15dB gain drop amplifier with a splitter on its output, all in the same housing.

    Power passing splitters, while more common in the satellite industry, can be found in the CATV and MATV industries, as well as in some residential antenna applications. Some pass power from the IN to one of the OUT ports, while others pass power on all ports. As grich wrote, some are diode steered so power can go only in one direction.

    The splitters used in the CATV industry have blocking capacitors. The capacitors help prevent voltage buildup and the ensuing magnetism of the ferrites.

    Some cable systems use 2-way splitters for cable modem connections. The majority, though, utilize directional couplers (taps) for that connection.
    Sorry, the loss through the hot leg of an unbalanced 3-way splitter (paragraph two) was supposed to have been 3.5dB.
    CIAO!

    Ed N.

  9. #9
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    Quote Originally Posted by mkgrady
    I'l check the secret site to learn more.
    Mike,

    FWIW, the premise in the OP is correct. It just that convention uses dBmV to quantify relative signal strength.

    -3 dB = 50% decrease in signal strength

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