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.

Screenshot - 13_02_16 , 10_01_42

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…

Screenshot - 13_02_16 , 10_23_03

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.

Links / References

PA3HHO Multi band end-fed (English)