The article Small efficient matching transformer for an EFHW laid out a design for a small EFHW transformer.
This article builds an NEC model for an EFHW antenna at 3.6MHz incorporating a realistic model of the above transformer.
NEC provides for a NT card characterising a two port network using Y parameters.
Y parameter model for the transformer
The Y parameter model is based on measured input impedance with port 2 open circuit, and short circuit, and the observed turns ratio.
Impedance was measured with the uncompensated transformer at 3.6MHz using an AA-600, the compensation in the reference article has little effect at 3.6MHz.
Above, the calculated Y parameter model including a prototype NT card. This model captures the various loss components of the transformer, mainly magnetising loss, at 3.6MHz. Continue reading Small efficient matching transformer for an EFHW – NEC model at 3.6MHz