Diplexers and video quality

Discussion in 'Archived Threads 2001-2004' started by Al_Swanson, Aug 18, 2001.

  1. Al_Swanson

    Al_Swanson Agent

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    Greetings all. I have cable, DSS and now OTA feeds to my house. Rather than pull cable all over the place, I was thinking of using diplexers. Do any of you have experience with them? Since I want to use them for both DSS and OTA HDTV, I want to make sure video quality is the highest priority. If you have used them, is there a brand you recommend?
    Here's my planned uses:
    DSS/OTA in one pull. DSS/DSS in one pull (is that even possible?) and cable/DSS for the other pulls.
    Thanks in advance for any help.
     
  2. Todd Hochard

    Todd Hochard Cinematographer

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    Al,
    Welcome to the forum!
    The diplexer should work for the DSS/OTA HDTV combo. Since both carry digital signals, provided the signal strength is adequate for the box to pick up, then the video quality will be unaffected, and "perfect," so to speak.
    I don't know if the DSS/DSS thing will work.
    If your cable is analog, then this MAY affect the quality slightly. However, since analog cable stinks anyway, you should have no problem, either. [​IMG] For the digital cable signal, that should work the same way as DSS.
    Todd
     
  3. James Reyes

    James Reyes Stunt Coordinator

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    DSS/DSS on one diplexor will not work. The reason for this is volage switching. With satellite there exists polarity in the channel spectrum. Some channels travel through the air in a clockwise or right-hand spiral (right hand circular polarity or RHCP) and others travel in a counterclockwise or left-hand spiral (left hand circular polarity LHCP). As a result the LNB must constantly switch between RHCP and LHCP. The LNB knows which polarity to switch to by the voltage it receives from the receiver. If the receiver sends back about 13 volts, the LNB switches to RHCP and about 18 volts for LHCP. If I understand you correctly, using a diplexor to combine two LNBS into a diplexor and then back out to two receivers wont work due to resulting voltage conflict. If the two receivers are trying to get opposite polarities, only one will win out and the other box will get a loss of signal. This is also the reason you must use a home run toplogy when wiring a DBS setup and why splitting the signal along a tap cable will not work.
    Hope that helps [​IMG]
     

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