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50-Ω antenna

  1. Sep 27, 2011 #1
    hello, good afternoon. i'm a little bit confused about the use of matching transformer. I made a 50 ohm tv antenna, and i connected it to a 50 ohm coaxial line. However, i've found out that for tv applications, 75 ohm coax should be used. my question is, if i will replace my 50 ohm coax, can i use a matching transformer, that is, from 50 ohm antenna to my new 75 ohm coax? thanks
     
  2. jcsd
  3. Sep 27, 2011 #2

    rbj

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    i wouldn't worry about it too much. the mismatch (if there is any) is not great.
     
  4. Sep 27, 2011 #3
    To answer your question, yes. But wouldn't it be easier to put your matching transformer between your television and the 50 ohm cable? That way you wouldn't have to change your cable.
     
  5. Sep 27, 2011 #4

    berkeman

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    Staff: Mentor

    How did you make a 50 Ohm antenna?
     
  6. Sep 27, 2011 #5

    Averagesupernova

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    Only a ham would post such a thing. I was thinking the exact same question. Haha
     
  7. Sep 27, 2011 #6
    i was thinking of that too, but i couldn't find a 50 to 75 ohm matching transformer in our place hehe :D i designed it using the moxon calculator :D it is okay to use a 50 ohm coaxial cable for tv?
     
  8. Sep 27, 2011 #7

    berkeman

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    Staff: Mentor

    Ah, a Moxon design. Yeah, that can get you to 50 Ohms, from what I've read. I haven't worked with Moxon type antennas in the past. Do they still need a Balun to go from unbalanced coax? Is the Moxon inherently unbalanced or balanced?
     
  9. Sep 28, 2011 #8
    i've read that it's already balanced, but in some cases, a balun is needed. how do you exactly make a balun?
     
    Last edited: Sep 28, 2011
  10. Sep 28, 2011 #9

    berkeman

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    To feed a balanced antenna like a dipole with an unbalanced feed line like coax, you need to use a balun ("balanced to unbalanced converter"). It is basically a transformer, and can have a turns ratio to match different feed line impedances to the antenna impedance.

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

    .
     
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