How to model a 6:1 ratio balun using NEC2
 

The model has to include a wideband, low-loss step-down transformer.
Which may or may not be a balun. Eg., a 300-ohm down to 50-ohm
transformer.

As Roy implies, such transformers are difficult to construct in
practice because performance depends on source and load impedances.
But very easy to incorporate in a mathematical model. Just divide
line impedance R+jX by 6. Consequently, the model will not accurately
predict what will happen in the real world unless terminating
impedances are fully taken into account.

A Spice simulation program is needed rather than an Eznec type.
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Reg.