[Amps] 2:1 Transformer

[Yury VE3XB]

I want to build a 2:1 transformer for HF frequencies to match 25 ohm
impedance. I am wondering if anyone can point me to some info on how to wind
such transformer - number of turns, where to tap the coil and what type/size
of core should I use, say for 100 watts?

Thanks in advance,

Yuri VE3XB