Does anyone have a good link or design for a 6:1 balun ?

I bought some 420 cores and am stacking 2 of them to handle 1.5 kw. I
wound one using # 14 magnet wire and measuring the return loss showed
not too good of a match with a 300 ohm load.

I though the cores may not be what was advertised, so as a check I wound
a 4:1 and the RL was very good with a 200 ohm resistor. The 4:1 was
wound just on a single core. I had ordered 3 cores instead of just 2.

I later tried several other types using some small scrap wire and none
of the 6:1 seemed to work where a 4:1 would.

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