dansawyeror wrote:
I am trying to measure impedance through a balun, or more accurately a
1:1 in line "transformer". For test purposes the transformer is two
windings of 10 turns each on a toroid. The winding are tightly wound on
opposite sides. The material is #43, the toroid is 3/4 inch OD.

For 4 MHz, I would use #61 material and
bifilar windings.
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73, Cecil http://www.qsl.net/w5dxp