# End fed matching – PA3HHO design review #2

A correspondent having read End fed matching – design review raised a similar design by PA3HHO which uses a#43 ferrite toroid as part of an end-fed matcher, see Multi band end-fed (English).

Further to End fed matching – PA3HHO design review , this article has a solution to PA3HHO’s “original 40/20/10 version” using FT140-43 with a 2t primary.

If the transformer is simply used without an ATU between it and the radio, and we assume that the antenna system is adjusted to present low VSWR(50) to the radio, a simple approximation involves calculating the magnetising admittance of the 2t 50Ω winding, and calculating the portion of total input power that is dissipated in that admittance. Using the calculator at Calculate ferrite cored inductor, the admittance (G+jB) of the 2t winding is 0.00715-j0.0104S. (The impedance of a sample wind could be measured with a suitable analyser and converted to admittance.)

For a 50Ω match, the total conductance G is 1/50=0.02, and the percentage power lost in the magnetising admittance is Gcore/Gtotal*100=0.0071/0.02*100=36%.

That gives a core efficiency of 64% or core loss of 2dB.

The 2t primary on FT240-43 is better… Using the calculator at Calculate ferrite cored inductor, the admittance (G+jB) of the 2t winding is 0.00573-j0.00834S. (The impedance of a sample wind could be measured with a suitable analyser and converted to admittance.)

For a 50Ω match, the total conductance G is 1/50=0.02, and the percentage power lost in the magnetising admittance is Gcore/Gtotal*100=0.00573/0.02*100=29%.

That gives a core efficiency of 71% or core loss of 1.5dB.