short-wave helix antenna

i want to design a helix antenna which work at 6MHZ. I want to know what decide the frequency in all parameter of the helix.turn spacing?length?

how to get the size?please help me!

This may be very large if you want the axial mode. The length of one turn is one wavelength. If you want the radial mode you can experimentally try one quarter wavelength of wire wrapped around your form support.