connecting a cable box

Discussion in 'Archived Threads 2001-2004' started by Sathyan, Oct 22, 2002.

  1. Sathyan

    Sathyan Second Unit

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    (Moderator: Please move if this is the wrong group.)

    I have the following
    TV with only 1 RF input (no other inputs)
    VCR with RF in/out and AV in/out
    Cable box with RF and AV out (AV out only works for music channels)
    Receiver which can switch AV and Svideo lines (DVD and PC video lines are switched by the receiver then sent into the VCR for RF modulation)


    ---Cable Modem
    CATV -| --Cable Box
    -----VCR ------TV

    The cable box doesnt work with my universal remote so when watching unscrambled channels I'd like to be able to bypass the cable box and tune with the TV or VCR. If the cable box is just in-line [CATV > CBL Box > VCR > TV] it interferes (fills with static) the other channels so it needs to be on a separate line. I've added the splitter seen above (|) but am unsure how to rejoin the cable lines for going into the TV without interfering with each other. What do you suggest?

    At PartsExpress.com I see some CATV switches which might do the job. What is 75 vs 90db isolation?

    thanks,
    sathyan
     
  2. Allan Jayne

    Allan Jayne Cinematographer

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    You need an antenna A/B switch, sometimes called an antenna TV/Game switch. This allows two RF feed lines to be rejoined and connected to the same RF input.
    The dB isolation refers to how well interference from the RF line not chosen gets through anyway, the more dB the better. For consumer grade TV sets I guess 40 dB isolation (I think more correctly it should be minus 40 dB) is sufficient. Simply connecting both two feed lines to one input with no switch in between is zero dB isolation.
    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  3. Sathyan

    Sathyan Second Unit

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    thanks, that was it. i got one of these switches from my cable company
     
  4. Yee-Ming

    Yee-Ming Producer

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    I did something similar, I split the CATV output into two, sending one into the cable box which then goes to the VCR and finally into the TV, the other left loose. on the few occasions when I want to tape something off cable and watch something free-to-air at the same time, I switch the cables at the TV input.

    in the long term this is (a) a nuisance and (b) too much wear and tear on the TV's RF input. so I bought a cheapo antenna switch and tried it last night. unfortunately it doesn't work very well, there seems to be lots of snow and interference. ironically the only "channel" which works fine with the switch in place is the VCR's output, presumably because it is tuned to a channel where there is no other signal at all?

    so: should I invest in a more expensive switch, assuming I can find one in the first place? is there anything I can do to the cheapo one to improve performance? I opened it up and the grounding seems to be combined into one regardless of switch position (if this makes sense), and the switch itself seems rather flimsy.

    any thoughts would be greatly appreciated.
     
  5. Sathyan

    Sathyan Second Unit

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    Yee-Ming,
    The cable box output is interfering with your tuning through the VCR (just like if you use the TV tuner to change to a different channel while the VCR is on). If yours is anything like mine, the cable box will never actually shut off (stop sending signal).

    I've got it cabled this way:

    CATV -- Splitter -- CATV Box
    V V
    VCR ---- SwitchBox ---- TV

    Both the cable box and VCR output on CH3. I only switch on the VCR for RF modulation or to play a tape if the switch is in CATV mode. I have to completely bypass the cable box to tune with the VCR (switch to VCR mode).

    Ask your cable provider for a switch. They gave me a Pico PAB-2 (TWC, no charge).

    Try to diagram where you put the switch
     
  6. Yee-Ming

    Yee-Ming Producer

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    Thanks for the input Sathayan!

    although my setup is different, the cable box feeds into the VCR and then to the TV; whether the VCR is on or not I am able to tune the TV to the cable box -- I guess the VCR can pass the RF signal right through without interfering, but evidently the cable box interferes with free-to-air (or should I say unscrambled?) channels, hence my alternative route is CATV direct to TV.

    the cable company here does charge extra for providing a cable box with what they call "connection B" which allows you to do what I'm trying to set up by myself.

    worse-case scenario, I'm going to just buy a short RF cable extension, leave that plugged into the TV permanently, and manually switch cables with the extension's plug, to reduce wear and tear on the TV's input.
     

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