The dimensions of the helix are determined by the wavelength λ of the radio waves used, which depends on the frequency. In order to operate in axial-mode, the circumference should be equal to the wavelength. The pitch angle should be 13 degrees, which is a pitch distance (distance between each turn) of 0.23 times the circumference, which means the spacing between the coils should be approximately one-quarter of the wavelength (λ/4). The number of turns in the helix determines how directional the antenna is: more turns improves the gain in the direction of its axis at both ends (or at 1 end when a ground plate is used), at a cost of gain in the other directions. When C<λ it operates more in normal mode where the gain direction is a donut shape to the sides instead of out the ends.