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Video Splitter

Discussion in 'Electronic Design' started by Dodg, Sep 14, 2003.

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  1. Dodg

    Dodg Guest

    I want to feed the video output from my dvd player to my vcr video input as
    well as the video input to my tv. Should I use a video splitter to feed both
    or is paralleling to both devices ok?

    If a splitter is required can I use a 75ohm tv antenna splitter otherwise
    can someone point me to a circuit.... thanks, Don
     
  2. Jim Thompson

    Jim Thompson Guest

    Read your manuals. I have a JVC wide-screen that allows
    "daisy-chaining" by providing a switch that changes the I/O to either
    hi-Z or 75 ohms.

    ...Jim Thompson
     
  3. Andrew Paule

    Andrew Paule Guest

    you can buy splitters from all kinds of sources - try digi
     
  4. Active8

    Active8 Guest

    since you say 75ohm, i guess you *don't* mean baseband so the answer is
    yes, you *could* use a splitter. you could also use an A/B switch. i
    suppose you want to record the DVD on VHS at the same time you are
    watching the movie. you also have the antenna/CATV line to deal with so
    here's what i'd do barring anything useful you find in the manual as per
    Jim's suggestion.

    note: CATV is running up to 1GHz in some systems these days (some of
    it's for inet and some for digital tier) and i'd watch out for cheap
    Radio Shaft splitters if you decide to use a splitter. The frequency
    range should be on the label.



    .--------------
    CATV -- | .---------.
    | -o | .----------. | |
    | __--o- |---| |------ |
    | -o | | VCR | | TV |
    | | '----------' | |
    DVD --- A/B Switch | | |
    '--------------' '---------'
    created by Andy´s ASCII-Circuit v1.22.310103 Beta www.tech-chat.de

    if you want to watch TV while the movie records, there are some other
    creative things you can do with splitters and A/B switches.

    note: CATV splitters have a 3.5 dB insertion loss for a 2-way splitter.
    3-way splits have 2 -7dB ports and 1 -3.5dB port. 4-ways have 4 -7dB
    ports. if you have a splitter installed elsewhere to run multiple
    outlets, these losses add up. the *most* signal you'll see at the
    pole/pedestal is 20dBmV hi channel ( i just found some end of line notes
    from a 750 MHz system (chicago) - EOL readings were from 23dBmV down to
    17dBmV on ch. 78 IIRC - don't count on having that much) with less on
    the low channel. some systems have maybe 15/10 or even 12/10, so after
    adding in cable and passive losses...

    RG-6 cable losses per 100ft. would be approx. 1.53dB on ch 3 (USA),
    4.9dB ch. 78 (about 550 MHz), 5.65dB ch. 117 (~750 MHz), and 6.55dB at
    1GHz (ch. 144 is 912MHz, so i need a new pocket ref :) ) so if you have
    only 12/10 at the tap and a 3-way/4-way splitter on the house, you're
    running out of signal fast. you'll know when your pix goes to hell after
    adding a splitter and a half-assed radio shaft jumper or a fubar'd DIY
    F-connector.

    BTW, all this dB loss stuff just subtracts from the signal and you
    should have 0dBmV min. for a CATV box. older (?) sets were designed to
    run from as low as -15dBmV antenna signal, IIRC. i wouldn't expect newer
    equip to do that, in fact, the CATV company here has a line terminator
    installed on my EOL tap which is a self terminating tap ( the retrofit
    was done in-house and those dweebs never stopped to ask themselves why
    certain taps have an extra housing port cap). of course, the installer
    knows absolutely nothing of line gear, so i have a signal 6dBmV down and
    can't even loop thru my VCR without near total loss of pix. i'd bitch
    but i plan to move and they can have their stinkin' 2 node system. for
    now i'm switching between CATV and VCR with an A/B switch.

    hope this helps,
    mike
     
  5. Andrew Paule

    Andrew Paule Guest

    Yeah - insertion loss!!!!! Why is this never discussed in this
    newsgroup (can you say S12/S21). I think he'll do just find with a good
    splitter - NOT RADIO SHACK - get an amphenol (or rosenberger if you can
    afford it).
     
  6. maxfoo

    maxfoo Guest

    Here's a netlist for a 2way and 3way splitter that will work with
    isolation better than 30dB. note the 75 ohm resistor is the impedence
    of your video device.

    Download Ansoft's student version of Ansoft Designer SV to analyze and
    view the freq response.
    http://www.ansoft.com/ansoftdesignersv/

    **********
    * LC Wilkinson Power Divider Calculation
    ********** 63,000,000 Hz
    BLK
    CAP 1 0 C=47.6E-12F
    IND 1 2 L=268.0E-9H
    CAP 2 0 C=23.8E-12F
    IND 1 3 L=268.0E-9H
    CAP 3 0 C=23.8E-12F
    RES 2 3 R=150
    RES 3 0 R=75
    WPD12: 2POR 1 2
    ISOL23: 2POR 2 3
    END
    FREQ
    STEP 1HZ 252.0E+6HZ 504.0E+3HZ
    END
    **********

    **********
    * LC Wilkinson 3-Way Power Divider Calculation
    ********** 63,000,000 Hz
    BLK
    CAP 1 0 C=71.5E-12F
    IND 1 2 L=268.0E-9H
    CAP 2 0 C=23.8E-12F
    IND 1 3 L=268.0E-9H
    CAP 3 0 C=23.8E-12F
    IND 1 4 L=268.0E-9H
    CAP 4 0 C=23.8E-12F
    RES 2 5 R=75
    RES 3 5 R=75
    RES 4 5 R=75
    RES 3 0 R=75
    RES 4 0 R=75
    CAP 5 0 C=5.00E-13F
    WPD12: 2POR 1 2
    ISOL23: 2POR 2 3
    END
    FREQ
    STEP 1HZ 252.0E+6HZ 504.0E+3HZ
    END
    **********
     
  7. ???

    Baseband, or composite video is 75 ohms, as well. if you want to feed
    multiple monitors, you need a video distribution amplifier to maintain
    the 1V P-P video signal. Look at some of the Maxim video chips
    http://www.maximic.com/
    <http://para.maxim-ic.com/compare.asp?Fam=Vid_Amp&Tree=AudioVideo&HP=AudioVideo.cfm>
    will take you to their video ICs. Select an amp rated to pass the full
    video bandwidth you need, and check the related Maxim application notes.

    A CATV splitter will not go low enough to pass baseband video, unless
    it is just a pair of 75 ohm resistors, which will give a 3 dB loss at
    each output. You need a flat frequency response to well under 100 Hz so
    you don't lose the Vertical sync.
     
  8. Active8

    Active8 Guest

    er, isn't that S21/S12 as in *gain* which will be less than 1?

    i'd name some brands i like, but i'm sure they won't be easy to get in
    single unit qtys. OTOH, TCS (TSC?) on Blankenship (Rd/St/Ave) in HOU, TX
    sold me a single magazine of Raychem F connectors. $0.64 per connector
    back in '90!!! good fittings, too, though.

    but you won't catch me using a split only for this app. i'd be stuck
    watching the movie while it's recording.

    brs,
    mike
     
  9. Active8

    Active8 Guest

    you mean you stuck that 75 ohm resistor in to simulate the load? if so,
    you'd need to do the same thing for node 2 and maybe node 1.

    now i know beyond a shadow of a doubt that 2-way CATV splitters (as well
    as those sold by mini-circuits) only have 1 150 ohm resistor in them and
    the 3-way and higher splits are just cascaded 2-ways. the coils are
    wound on little binocular ferrites.

    just to corroborate my sometimes less that optimal memory, i looked up
    the ol' Wilkinson divider. it *also* has only a single 2*Zo resistor
    between ports 2 & 3.

    as for your 3-way netlist, my refs show a Zo (source if used as a
    splitter) valued R from node 1 to 0 with no cap. i think the caps were
    left out of all the schems, but i know they're there in real life. so
    that's 1 R you *could* be missing. you're (also) missing a 75 ohm R
    between node 2 and ground. my refs show no caps from node 5 to 0, but
    again, they show no caps period. actually, 1 ref does show the caps.

    now i'm probably missing something as far as how Designer implements the
    excitation/stimulus/whatever and it's internal impedance, but those
    missing load Rs in your netlist have me confused.

    also, when i get around to playing with Designer, it might come in handy
    if i know what the lines

    WPD12: 2POR 1 2
    ISOL23: 2POR 2 3

    are for. please elucidate me.

    thanks and brs,
    mike
     
  10. Active8

    Active8 Guest

    i might have surmised as much had i thought about it. never played with
    baseband video save patching stuff together.
    thanks. i'll note that for future ref.
    naturally.

    IIRC, you're the in-house CATV guy i (possibly mistakenly) called cable
    dog, right?

    brs,
    mike
     
  11.  
  12. Active8

    Active8 Guest

    [might as well snip this, too]
    req 1
    req 2
    but you terminated node 3, not node 1. i think i see what's up here.
    no shit, man. you've got one port of a 2 way (node 3) terminated. you
    said 2 ports (node 1&2) are loaded by 'wpd12:2POR 1 2'. so 'wpd12:2POR 1
    2' satisfies req 1 and req 2, leaving node 3 unterminated so you put an
    R there.

    the explanation of the lable cleared that up for me.

    so now i'll probably comprende` what you did with the 3-way. i knew
    there was a good reason to ask about the labels.
    what manual? no... just kidding

    sure, as soon as i need the app. forgive me for 1. pointing out what i
    thought might have been an honest error (people do whip out quick hand
    written netlists) and 2. asking for clarification on a short netlist
    before reading... how many pages am i in for? i'll find out.

    see if you put your snips back in:
    *********
    now i'm probably missing something as far as how Designer implements the
    excitation/stimulus/whatever and it's internal impedance, but those
    missing load Rs in your netlist have me confused.

    also, when i get around to playing with Designer, it might come in handy
    if i know what the lines

    WPD12: 2POR 1 2
    ISOL23: 2POR 2 3

    are for. please elucidate me.
    ***************
    you might surmise why i though it best to ask while you were here before
    i one day read a (big?) manual that may or may not be as lame as the
    PSpice refs. i guess i've been around the block enough times to know to
    ask when i have a chance rather than be stuck later.

    have a nice day,
    mike
     
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