Several correspondents refer to my article Feasibility study – loop in ground for rx only on low HF – small broadband RF transformer using medium µ ferrite core for receiving use – 50:200Ω and suggest “I got it wrong, #73 is the proven material choice for such a thing, and a 2t primary is optimal”.
In fact, I did explore #73 as an option, this article presents some key comparisons. The two key statistics shown in this article provided the basis for selecting the design.
Note that the scales are different from plot to plot.
Insertion VSWR
Where the magnetising impedance appears in shunt with an ideal transformer with Zin=50+j0Ω, Insertion VSWR can be calculated.
2t on BN73-202
5t on BN43-202
Core loss
Where the magnetising impedance is a shunt component of total Zin=50+j0Ω, Core loss VSWR can be calculated.
2t on BN73-202
5t on BN43-202
Conclusions
Predictions of Insertion VSWR and core loss of the popular BN73-202 transformer with 2t primary for MF and my BN43-202 with 5t primary reveals that the BN43-202+5t is a better transformer for my intended application.
There is no need to follow the traditional design which anecdotally works, but is published without performance predictions or measurements… well that IS traditional.