tv balun used backwards?

Discussion in 'General Electronics Chat' started by lokeycmos, Jun 24, 2014.

  1. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
    432
    7
    im putting together a quick Make project DTV antenna that needs a 300ohm to 75ohm balun. im wondering if I can use a 75 to 300 ohm in reverse with same results? I would use a coax coupler to make it work with the coax to the tv. if I cant use that, can I make an acceptable one with limited parts and time? thanks!
     
  2. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
    315
    Yes you can.

    There are differences in the internals but either are bi-directional.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    A balun is a transformer. Transformers are bidirectional. The work equally well in both directions.
     
  4. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
    432
    7

    thanks for verifying. I knew that about transformers, but wasn't sure if on the one I have the two ceramic caps on the 300ohm side would be on the 75 ohm side on the the one the project recommends
     
  5. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
    315
    No they are not the same. That's one of the differences mentioned in 2nd post.

    Normal balun is isolated dc-wise. No dc connection between any lead. (capacitors) Reverse balun has low resistance between all leads. (auto transformer)

    There may be variations.

    It makes a difference with "power thru coax" system.
     
  6. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    Actually,if you use the one in your LH picture instead of that in the RH pix,it is not reversed.

    They are both designed to convert 300 Ω to 75 Ω,only in one case,it is from the antenna to a 75 Ω cable,& in the other from a 300 Ω ribbon cable to a 75 Ω TV set input impedance.

    Maybe there is some other problem,but it is not anything to do with their impedance matching function.
     
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