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RF question...

Discussion in 'Electronic Basics' started by dude, Sep 3, 2004.

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  1. dude

    dude Guest

    Not sure if this is the right group but I have a question about RF strength.

    When using a DOCSIS modem the forward and reverse signal need to be within a
    certain strength. reverse should range from 35dB to 55dB.

    when adding a splitter to the cable line it usually lower the dB. However,
    sometimes there will be a modem that is getting too strong a reverse signal.
    58dB and when we remove the splitter it goes to 50dB or something similar.
    what is happening here? how can the signal strength decrease when REMOVING
    the splitter????
     
  2. Active8

    Active8 Guest

    If the barrel used to replace the slitter is bad, that would do it.

    You need to test this with one output port of the splitter
    terminated. That way you're only measuring the reverse signal on a
    single line. Bad sheilding or connectors on any line can introduce
    interference into the system - ingress.
     
  3. dude

    dude Guest

    Thanks, I never thought about that....

    :)

     
  4. Active8

    Active8 Guest

    If it tests ok that way, you can reconnect the 2nd line and
    terminate the end to see if that line and its connectors are right.
    then when you connect up the other modem and send 2 simultaneous
    returns, you can expect to see both returns combined, less the
    insertion loss. The isolation between splitter output ports is also
    important and splitters *do* go bad.
     
  5. dude

    dude Guest

    Hey, that brings up a 2nd question ;)... I've known that splitters can go
    bad for quite a while, but what actually goes "bad" in them? The few
    splitters I've opened only have a piece of wire coming from the input to
    each output. These were low frequency splitters so maybe that is why they
    were so simple but what can break in any of these splitters?
     
  6. Active8

    Active8 Guest

    coils

    GND IN
    | |
    | ___ |
    +--UUU---+
    ___ ___
    +--UUU--+--UUU---+
    | | |
    | === |
    | GND |
    | |
    |----/\/\/\/-----|
    | 150 |
    OUT OUT
     
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