Loss in multi input antenna combiner?

Discussion in 'General Electronics Chat' started by spinnaker, Apr 30, 2013.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    I want to gang a some television antennas. Right now it is just 2 but in the future, I might add one or two others.

    I understand that the combiner will give me some loss of signal. Is the loss simply per input or across the whole combiner. In other words, is the loss multiplied by the number of inputs even if unused?

    I would think that the loss would be from each input and it really doesn't matter how many inputs I have even if unused. Is this right?

    http://www.ebay.com/itm/Channel-Vis...627?pt=LH_DefaultDomain_0&hash=item41703c5613
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    The loss will depend on the path. If the combiner uses a mechanical rotary switch the other inputs are isolated from the selected path. If you want to do this in a non-mechanical way start by googling the Wilkinson Power Divider.

    http://en.wikipedia.org/wiki/Wilkinson_power_divider

    This is a jumping off point for all kinds of cool stuf you can do with printed circuit boards. It is symmetrical and also works as a combiner.
     
  3. Sue_AF6LJ

    Member

    Mar 16, 2013
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    The divider / splitter will have some loss.
    As a general rule about 3 DB for a two way splinter.
    About 6 DB for four way splitter, and about 7.5 DB (give or take) for six way splitter.
    Those types of splitters use resistive networks to split the signal and maintain a reasonably constant 75 Ohm impedance at all the ports.
    I should point out any unused ports must be terminated in a 75 ohm non inductive resistor. You can buy termination resistors made for the application for next to nothing......

    Oh and yes...
    That loss is per port...
     
  4. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    Thanks


    But will unused ports affect used ports? In other words, should I just get a 2 way combiner since that is all I need now?
     
  5. #12

    Expert

    Nov 30, 2010
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    If you need to lose 6db instead of 3db, use a 4 port combiner with 2 terminating resistors attached.

    ps, I'm not kidding. Sometimes you need to lose 6 db to balance the signal levels before going into an amplifier.
     
    Last edited: May 1, 2013
  6. Sue_AF6LJ

    Member

    Mar 16, 2013
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    That's what I would do.
     
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