Balun to match your multiband antenna to 50 ohm
There is many baluns on the market for sale or many home made stuff
9:1 balun on a Amidon T200-2 is 11 Trifilar woundings for longwire,beverage etc.
1:1 to balun on a Amidon T200-2 is 11 Trifilar woundings straigth
4:1 balun on a Amidon T200-2 17 woundings Bifilar
6:1 balun on a Amidon T200-2 with 10 Bifilar woundsings, but tapped on the 8 turn
MHz chart for different Powder Cores
Windom balun articles