Antennas for transmitting skywaves are typically made from horizontal dipoles or bottom-fed loops, both of which emit horizontally polarized waves. The preference for horizontally polarized transmission is because (approximately) only half of the signal power transmitted by an antenna travels directly into the sky; about half travels downward towards the ground and must "bounce" into the sky. For frequencies in the upper HF band, the ground is a better reflector of horizontally polarized waves, and better absorber of power from vertically polarized waves. The effect diminishes for longer wavelengths.