Editing High frequency (section)

==Antennas==
The most common antennas in this band are wire antennas such as wire dipoles or [[rhombic antenna]]s; in the upper frequencies, multielement [[dipole antenna]]s such as the [[Yagi-Uda antenna|Yagi]], [[quad antenna|quad]], and [[log-periodic antenna]]s. Powerful shortwave broadcasting stations often use large wire [[curtain array]]s.

Antennas for transmitting skywaves are typically made from horizontal [[dipole antenna|dipoles]] or bottom-fed loops, both of which emit [[Horizontal polarization|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 [[Horizontal polarization|horizontally polarized]] waves, and better absorber of power from [[vertical polarization|vertically polarized]] waves. The effect diminishes for longer wavelengths.

For receiving, [[random wire antenna]]s are often used.  Alternatively, the same directional antennas used for transmitting are helpful for receiving, since most noise comes from all directions, but the desired signal comes from only one direction. Long-distance (skywave) receiving antennas can generally be oriented either vertically or horizontally since refraction through the ionosphere usually scrambles signal polarization, and signals are received directly from the sky to the antenna.

The antenna should have a wide enough [[ Bandwidth (signal processing)|bandwidth]] to cover the desired frequency range. [[Broadband]] antennas can operate over a wider range of frequencies, while [[narrowband]] antennas are more efficient at specific frequencies.

To improve the transmit and receive sensitivity of an HF antenna, the more metal parts are exposed to the air, this helps to increase the receive sensitivity. However, in places with a lot of radio signal noise, such as urban areas, the surrounding noise signals are also heard, so the design method is applied by using a directional high frequency (HF) radio antenna, or using an HF antenna in a remote area with a low HF Noise Floor level and connecting the HF transceiver.