I made one out of a FT240 core because it was the only thing I had in stock.
At 2 MHz you really don't care so much about the high frequency properties.
I have 13 trifilar turns. Since you don't care so much about capacitive
coupling between the windings I would put on as many turns as will
comfortably fit. What I did find to be important is to make sure that the
windings don't move. The first one I tried worked fine at low power but
when I turned on my amp I think the forces between the wires caused some
motion of the wires and generated enough reflected power to trip the
detector in my amplifier. After I put on enough electrical tape to keep
everything in place it seems to work quite well.
Good Luck,
Tom, KH7CC
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