Parameters for helix HF antenna at 12 Mhz

Anybody design helix HF antenna? i want to design a helix antenna which work for 12Mhz?how to define its parameter?thanks.

I am not shure the frequency is correct, but for 12MHz, 10dB gain you will have dimensions length=57 feet and diameter 26 feet for 3 turns. I think such antenna would be impractical.