I just build a 2.25:1 balun using 14 gauge STANDED run of the mill insulated wire.
Trifilary wound, close spaced winding to match around 100 Ohms to 50.
Donít have it handy, but something THW or similar type of wire.
In his book Transmission line transformers, Mr Sevick uses solid wire and never really elaborates why.
He does mention that the characteristic impedance of bifilary wound transformer is important and describes various insulation / spacing schemes for the wiring.
Unfortunately he does not elaborate much on trifilary would toroid.
Any thoughts on using stranded wire in these transmission line transformers??