A correspondent asked about the use of a Jaycar LO1238 ferrite core in VK3IL’s EFHW matching unit for 40m and up. The LO1238 implementation would use 3t primary and 24t secondary on the core.
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 VSWR50 to the radio, a simple approximation involves calculating the magnetising admittance of the 3t 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 3t winding is 0.00177-j0.00204S. (The impedance of a sample wind could be measured with a suitable analyser and converted to admittance.) Continue reading End fed matching – VK3IL design on LO1238