Introduction
There are several articles on this site describing EFHW transformers using the Jaycar LO1238 toroid, two particularly relevant ones are:
- End Fed Half Wave matching transformer – 80-20m – LO1238 variant; and
- Another small efficient matching transformer for an EFHW – LO1238 – VK3PY, VK3TU build and measurement.
This article presents a design workup of a EFHW transformer using a Jaycar LO1238 core, a pack of 2 for $8 at Jaycar stores (Australia). The LO1238 is a 35x21x13mm Toroid of L15 material (µi=1500). Boxed up, it is probably safely capable of about 5W continuous dissipation.
I will use the meanings explained at On insertion loss.
The design was developed in a SimNEC model which models a EFHW transformer, and can be calibrated against measurements of implementations. This helps evolve the model and develop some experience for likely values for leakage inductance etc. Continue reading 1:49 EFHW transformer using a Jaycar LO1238 core – design workup