If you use 73 material cores about 1 or two inches of stack height,
a two turn primary is enough for 75 ohms. It is the area inside the
core exposed to the wire and the number of turns that mainly
controls impedance in a given core material.
I use a two turn primary and five turn secondary of 75 ohm
primaries, and the transformers are good from below the BC band
to over 30 MHz with very low loss and a flat SWR.
A two turn primary and six turn secondary works for 50 ohm
feedlines.
I keep the secondary isolated from the primary, to prevent the
feedline from being part of the antenna system.
73, Tom W8JI
w8ji@contesting.com
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