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video over cat5 without baluns

Discussion in 'General Electronics Discussion' started by Magoogle, Oct 8, 2012.

  1. Magoogle

    Magoogle

    62
    1
    Jul 31, 2012
    Hey guys, I have some CCTV cameras I got but all the orginal wire is short and extensions are expensive.. I have alot of cat5 though and i made a 75ft lead for testing purposes. The goal here is to only use 2 twisted pairs if possible.

    So i soldered it up to the camera and supplyed power locally on the camera. Didnt work.

    I assumed baluns were just pass through devices that just make it easy for people to go from one connector to another. Now from what im reading it "balances" the connection.

    Cat5 is 100ohm, and coax is 75 ohm. The camera and dvr are expecting 75 ohm. Can i add a 25ohm resistor at the DVR end of the cable to achieve the 75 ohms its looking for? if so what wattage does the resistor need to be?

    Thanks for the help!
     
  2. davenn

    davenn Moderator

    13,242
    1,742
    Sep 5, 2009
    hi there Magoogle
    Welcome to the forums :)

    you really need to use the proper BALUNS, they serve 2 purposes
    1) impedance matching - coax to twisted pair
    2) Balanced twisted pair line to Unbalanced coax

    any results you get without them are likely to be poor, especially over any reasonable line length

    cheers
    Dave
     
  3. Magoogle

    Magoogle

    62
    1
    Jul 31, 2012
    Yes I agree baluns would be the best option but im intersted in DIY kinda stuff. How would i go about doing this? I have experence with electronics but just need a schematic and list of parts to put it all together.
     
  4. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    Baluns can be made cheaply but need to be made for the frequency to be transmitted, they have limited bandwidth and introduce loss. you need the right core.

    What is the attenuation of cat5 cable at the frequency you are using?

    As an alternative you could use a common mode choke and accept the impedance mismatch.

    Any resistor in a signal line would not need to be more then a quarter watt.
     
  5. Magoogle

    Magoogle

    62
    1
    Jul 31, 2012
    how do get this information? the camera models are KG-CW20R1B1 and the cat5e cable says 350mhz on the cable 24 gauge
     
  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
  7. Magoogle

    Magoogle

    62
    1
    Jul 31, 2012
    i have seen those on amazon also.. but i thought they were just bnc to screw terminal adapters? do they have anything inside them besides just 2 wires?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,689
    Jan 21, 2010
    I dunno, I think the part in the description that says "Single channel passive video balun" is the dead giveaway.
     
  9. Magoogle

    Magoogle

    62
    1
    Jul 31, 2012
    now if i wanted to use power via the cat5 cable also, i assume there would be a voltage drop of some kinda? the factory power block is 12v 1.2a but is designed to power 4 cameras at a time. say the average run is 75 ft, i would assume i would need about 14v at that point to compensate. I should beable to just use another pair of wires on the cat5 correct?
     
  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    That's the max rating on the PSU, your draw per camera will be much less. At 75' I wouldn't loose any sleep over the voltage drop on CAT5.

    Chris
     
  11. duke37

    duke37

    5,211
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    Jan 9, 2011
    Looking up some data, translating from AWG to SWG and viewing my old book, you could have 0.07 ohm/yard. You can calculate the voltage drop if you know the current, remember that the length of the wire is twice that of the cable.
     
  12. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    At 75 feet, ..150 feet round trip, I really don't see an issue with CAT5. Even if it is a problem you have two more free pairs you can parallel up.

    Chris
     
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