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=== angle of incidence ====== D layer absorption ===In the low altitude D layer, the density of atmospheric particles is much greater than the density in the higher E and F layers.The D layer absorbs HF frequencies below the 20-meter band. When the D layer dissipates after dark the lower frequencies are free to propagate by skywave or skip from the E and combined F layers. Because of this, ham radio operators use the higher HF bands of 20-meters and above during the daytime, and use the lower bands at night.While the 20-meter band and higher frequencies are not significantly attenuated by D layer energy absorption due to their smaller wavelengths, absorption at lower frequencies is usually too severe for DX. You can expect the 20-meter band to work to some extent both day and night.* Frequencies above 20-meter up to MUF propagate better at day.* Frequencies below 20-meter propagate better at night.=== angle of incidence ===Concerning the D layer and NVIS: Near Vertical Incidence Skywave (NVIS) technique causes lower HF signals to travel through the D layer in the shortest dimension, nearly at a right angle to the layer's spherical shell overhead. As a result, absorption of low frequency signals is minimized and NVIS regional communications is viable during daylight hours, particularly on the 40-meter band.The MF and HF regions of the radio spectrum are most impacted by ionosphere charge and the solar sunspot cycle. The MF and HF regions of the radio spectrum are most impacted by ionosphere charge and the solar sunspot cycle. During periods of high sunspot cycles there is an increase in the skip distance of the skywave at night. Solar flares: increased ultraviolet and X-ray radiation from solar flares will affect radio communication in only 8 minutes of the solar event occurring. Frequencies below 10 MHz travel most efficiently by skywave at night. Frequencies above 10 MHz travel better during the day. [[Citizens Band radio]] skywave [[Citizens Band radio]] skywave propagation characteristics are going to behave like and available when 10-meter ham band skip occurs. CB radio operators tend to use different language or lingo than licensed ham radio operators. CB operators like to call the practice of DX'ing on 11-meter by the term "skip shooting." Some CB operators use special directional antennas such as a horizontal beam antenna sending the signal to the ionosphere at an angle which helps them to make distant contacts or DX. Technically this activity is forbidden by the FCC on CB. However, operators using legal power limits are not actively sought out with any punitive action. Part 95, Subpart D of the FCC rules. It is illegal to engage in, or attempt to engage in communications with any station more than 155.3 miles from your location There is no law against listening. Any CB radio owner may listen for DX (DX hunting) with their CB radio during periods of skip activity without breaking any regulation. CB operators attempting to communicate via skip shooting tend to use SSB (single side band) capable transceivers. If you are interest in listening you will need a receiver that is capable of tuning SSB. Most shortwave radios do only AM. Think of SSB as one side of AM less the carrier. Standard 40 channel CB radios are AM only at 4 watts legal transmit power. SSB capable CB radios can transmit up to 12 watts on SSB while still being capable of 4 watts on AM, using the upper or lower side band USB or LSB, legally.