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Thread: Antenna Impedance Matching/Balun

  1. #1

    Default Antenna Impedance Matching/Balun

    I ran across a talk Ward Silver gave on impedance matching posted on YouTube. He made the statement that an impedance matching transformer isn't the same as a balun and that if a balun is needed it's added to the transformer.

    I'm trying to understand why the output from the transformer would not be balanced. In some references the claim is made that the output of an impedance matching transformer is balanced. I'm thinking I'm missing some key point.

    This would be for the purpose of making a dipole, so the outputs of the secondary coil would each be attached to one of the two elements of the dipole.

  2. #2

    Join Date
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    He probably meant that an impedance matching transformer is not a transmission line transformer. Either one can be used for a BALUN function. Some designs exhibit a low impedance to differential mode transmission line currents while exhibiting a high choking impedance to common-mode currents.

  3. #3

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    Makes perfect sense. Impedance matching does NOT require an output that is balanced. Quite a few designs use a common shared ground - input to one winding, output from the other winding with the other ends of the windings linked. After all, if you are tuning a long wire, you will have a shared ground, while tuning a dipole, you won't and will have somewhere a component providing the balanced output from the radio's balanced one. One commercial AT I had years ago had dual outputs, one, on a SO239 that had the screen bonded to the case, and on two sockets, a balanced out - with a switch to select 75 or 300 Ohms - and two terminal posts plus a 239 on an insulated plate. It worked brilliantly, but annoyed me by having the switches on the rear panel, and tuners on the front - which wasn't very convenient.

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