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Help with the output transformer

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  • William
    I m attempting to change the power output on my Sierra by replacing the L10 choke with an impedance transformer. I need some help getting my head around how
    Message 1 of 1 , Mar 18, 2010
      I'm attempting to change the power output on my Sierra by replacing the L10 choke with an impedance transformer. I need some help getting my head around how this intuitively works.

      First let me tell you what I did. I removed the choke and placed a second winding (10 turns) parallel to the first. The first wire was red and the second green. The proximal red went to the V+. The distal red connected to the proximal green and then went to the final collector. The distal green went to the filter on the module via a capacitor. I also changed the output transister from a 2n3553 to a 2sc1969.

      The current is flowing in both windings in the same direction. The RF in the first winding induces an opposing current in the same winding which gives it its inductive reactance. It also induces the same current in the second winding which multiplies the reactance. Thus it seems to me that the output impedance of the amplifier is increased and the input impedance of the filter is unchanged.

      The various postings I read seem to indicate that the object was to lower the filter impedance. Taking a turn off of L5 would do this but at the expense of the filter parameters.

      My knowledge is a little shaky on this whole transformer impedance thing. Can someone give an intuitive explanation of how this all works?

      Various posts indicate 10 windings like on the original choke and others indicated 12. Does it matter?

      Thanks in advance for the help.

      Bill, WV1N
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