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20 m (14.0-14.35 MHz) Propagation..
The 20m band is the best DX band because it is open for long-skip for more hours than any other band and it doesn’t suffer from QRN as the lower bands. In years of high sunspot numbers, short-skip and long-distance DX can be worked at the same time during daylight hours. Although DX is there most of the time, most of the DX worked is at sunrise, sunset, and all night during peak sunspot years. During the years of low sunspots, it is common to work into Europe and Africa during the day and into Asia and the South Pacific during the evening hours and early at night. Low sunspot numbers cause 20m to go dead for east to west contacts at night an hour or so after sunset, but there is some TE propagation. During periods of moderate sunspot numbers, the propagation on this band is a blend of propagation of low and high sunspot years.

17 m (18.067-18.167 MHz) Propagation..

The 17m band propagation acts much like 20m except it is affected more by low sunspot numbers than 20m. In periods of low sunspot numbers, this band doesn’t stay open as late as 20m, fading out as the sun begins to set. Yet, the 17m band does stay open all night when the sunspot numbers are high. The propagation on this band is like a blend of 20m and 15m, but it is closer to 20m. Most users of this band use dipoles and other simple antennas since triband beam antennas wont work here.

15 m (21.0-21.45 MHz) Propagation..

15m-band is a fantastic DX band during the high sunspot years. This band may be open for 24 hours, and it is common to work more than 100 countries during a contest weekend on this band. Many have worked more than 300 different countries on 15m. In years of low sunspot numbers, 15m may be completely dead for several days in a row. When it opens during those years, you may hear only the Caribbean, South America, and on rare occasions the extreme southern part of Africa via TE-propagation.
Afternoon TE-propagation (TransEquatorial-propagation)
Afternoon TE-propagation peaks during the mid-afternoon and early evening hours and is generally limited to distances of 6.000 - 8.000 km (4,000 – 5,000 miles). Signals propagated by this mode are limited to approximately 60 MHz. Afternoon TE-propagation signals tend to have high signal strength and suffer moderate distortion due to multipath reflections.
Evening TE-propagation

The second type of TE-propagation peaks in the evening around 1900 to 2300 hours local time. Signals are possible up to 220 MHz, and even very rarely on 432 MHz. Evening TE-propagation is quenched by moderate to severe geomagnetic disturbances. The occurrence of evening TE-propagation is more heavily dependent on high solar activity than is the afternoon type.

12 m (24.89-24.99 MHz) Propagation..
The 12m band is much like 15m, but it is affected more by sunspot numbers. Because this band is little used, many hours can pass without hearing any amateur signals. Occasionally you will hear "CB-pirates" on lower sideband. It is mostly a daytime band but openings to Asia and the South Pacific are common early at night during peak sunspot years. The reason this band is little used is that beam antennas don’t cover this band.

10 m (28.0-29.7 MHz) Propagation..

The band that is most affected by the sunspot numbers is 10m. You may have noticed in this discussion, the higher the frequency, the more it is affected by sunspots. During peak sunspot years, 10m can be open some days for 24 hours. Mostly it is a daytime band. When they are at the peak, the sunspots enable you to work worldwide with power as low as 5 Watts. In the low sunspot years, the band can be closed for days. 10m band can open for very short skip by sporadic E-propagation during the summer months. Very short skip means contacts as close as 350km (200miles) out to 1500km (1000 miles). Sporadic E-propagation can suddenly occur without regard to the sunspot numbers.

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160-m (1.8-2.0 MHz) Propagation..

Each amateur band propagates signals differently. The 160m band is our only MW band and it acts similar to the broadcast band. It is primarily a nighttime and wintertime band as it suffers from high summertime static (QRN). Most hams that use this band for nearby contacts use horizontal dipoles or inverted-V antennas. Some hams use vertical antennas on this band to work DX. These DX contacts are made in the fall and wintertime at night via F-layer or greyline propagation when the static levels are low. Dipoles and inverted-V antennas do not work well for DX on this band.9. 80-m (3.5 4.0 MHz) PropagationThe CW part of this band is called the 80m band and the voice part of the band is known as 75m. Like 160m, eighty meters suffers from the same QRN in the summertime. Working DX on this band is a popular avocation during the fall and winter. However, 80m is used primarily for working nets and ragchewing. 80m is primarily a nighttime band. This band can vary from being open most of the day in years with low sunspot numbers to being closed during the middle of the day in years with many sunspots. Many DX contacts have been made using dipoles and inverted-V antennas, but a vertical with many ground radials will be better.

40-m (7.0-7.2 MHz) Propagation..

The 40m band has propagation that can act like either 80m or 20m. It just depends on the stage of the sunspot cycle. During the years with high sunspot numbers, nearby contacts are possible all day. At night, the skip lengthens making contacts possible to those parts of the world where it is still dark. Working DX on 40m is a nighttime or greyline event. When the sunspots are low, 40m may have long skip during the day, and nearby contacts may be impossible or they may be very weak. During the time when we suffer from low sunspot numbers, many DX contacts are made during early morning, late afternoon, and at night.If your primary interest on 40m is SSB, our 40m voice band is a broadcast band in Regions 1 and 3. Region 1 is Europe, North Asia, and Africa and Region 3 is the Pacific, Southern Asia, and Australia. The top part of 40m is a voice band in Region 2, which is North and South America. To work SSB on 40m at night, you will have to find a frequency between broadcast stations. Strong broadcast stations heard at night begin to fade out slowly as the morning sun rises and moves higher in the sky. As the suns angle declines in the afternoon, the broadcast stations begin to break through the noise becoming stronger as the sun begins to set. It is only in the middle of the day when no broadcast stations are heard on 40m. Since DX stations in region 1 and most of region 3 can only transmit below 7100 kHz, working DX on 40m SSB is still possible. Stations in those regions will have to transmit below 7100 kHz. (Australian and New Zealand amateurs can operate up to 7200 kHz.) They call CQ and announce where they are listening in our voice band above 7150 kHz. This is what is called "working split".

30 m (10.1-10.15) Propagation..

This band has such a narrow frequency that the only modes allowed here are CW and digital modes. That means no SSB. Propagation here is much like 40m and 20m. Unlike 20m, this band stays open longer at night during years with low sunspot numbers. During the daylight hours, it has much shorter skip than 20m.

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Greyline Propagation..
Greyline propagation occurs when the sun is low in the sky near dawn or dusk, although we have seen greyline propagation occur as early as two hours before sunset or as late as two hours after sunrise. It is often used to work stations on the other side of the world on 160m and 80m. For example, at certain times of the year when it is approaching sunset here in Europe, the sun will have just risen in Asia or Australia and vice-versa. At that time, radio waves propagate along the semidarkness path that encircles the Earth called the greyline. Both locations must be in the greyline in order to make 2-way contacts. The tilt of the Earth makes the position of the greyline change as the seasons change. Greyline propagation occurs between any two locations for a brief period of a few weeks. Afterwards, different places fall into the greyline. For several weeks in the fall of the year, an interesting example of greyline propagation occurs in Europe can be heard for about an hour before sunset coming in by greyline propagation. Stations to the east hear it before we do. Stations farther to the west can hear the fading signals after it fades out here because the greyline moves as the earth rotates. For those hearing it, the signal fades in, it peaks, and it slowly fades out.

Long Path Propagation..
Long path propagation occurs when signals propagate the long way around the world. It can occur on any band. It usually occurs from stations on the opposite side of the world from you. We have worked South Africa via long path by beaming northwest early in the morning on 20m. When this happens, we are working him long path through the nighttime side of the earth. Since at all times half the Earth has daytime and half the Earth has night, long path propagation is determined by whether the signal is propagated through the nighttime path or daylight path. Sometimes the daylight path will bring in stations by long path propagation and at other times the darkness path provides long path propagation. One night on 20m, we heard a station in India coming in short path and long path simultaneously, but the short path was stronger. At the same time, other countrys working India by long path and they could not hear him short path. They were working him through the daylight path, and he was stronger here via the nighttime path.

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Skywave Propagation..
Skywave propagation occurs when radio waves are reflected from the ionosphere. Practically all HF communication is done by skywave. In the ionosphere, the waves are really refracted twice, and they just appear to be reflected. The reflections are frequency sensitive, meaning each ham band reflects differently from the others. Low frequencies, such as 80m, reflect mainly from the lower levels of the ionosphere and the reflected signal comes nearly straight back down. This causes 80m to propagate to points from local out to more than a few hundred km in the daytime. At night, when the D-layer and E-layer are absent, signals striking the ionosphere at lower angles may propagate many thousands km on 80m. On the bands from 10m to 20m, high angle signals pass straight through the ionosphere and do not reflect back down to the nearby stations. The low angle signals on these higher bands reflect from the ionosphere near the horizon and return to the Earth some km away. The in-between region can’t hear the TX signals nor can you hear signals coming from this region. The in-between region is called the "skip zone". Only when the ionosphere is weakly ionized do you have a skip zone on 80m. Another interesting type of skywave propagation seen on the higher HF bands is called chordal hop propagation seen frequently in trans-equatorial propagation, which is propagation crossing the equator. When this occurs, signals entering the ionosphere are trapped inside the F2-layer then they are finally refracted back to earth across the equator thousands km away. There is no propagation between the signal entry point and the exit point. This is skip in the extreme. One time when we working Europe and North America at the same time, we could not hear the European stations because our path to him was via chordal hop propagation. Another way of describing chordal hop propagation is to call it ionospheric ducting. Skywave propagation sometimes produces an effect called "backscatter." What happens is the radio waves that strike the ionosphere, instead of only reflecting father away from the transmitting station, part of the signal reflects backwards toward the TX station. Stations that are too close to hear each other by direct wave can communicate by the backward reflecting waves. Both stations that communicate by backscatter must point their directional beam antennas in the same direction although their direction toward each other may be at some other azimuth. Backscatter will confuse front-to-back measurements of directional beam antennas. This is because, when you turn the back of the antenna toward the station you are hearing, you may be able to hear him on backscatter from a direction opposite from him. You will be hearing him from the ionized atmospheric cloud in the opposite direction. During intense solar magnetic storms, when aurora occurs at high latitudes, stations are able to communicate by backscatter on VHF and UHF by both stations pointing their directional beams toward the aurora. This will be due north for stations in the Northern Hemisphere and due south for stations in the Southern Hemisphere. Audio from aurora backscatter will have a "wispy" sound.

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Ground-Wave Propagation..
Ground wave works only with vertical polarization. One side of the antenna is the vertical radiator and the other side of the antenna is the earth ground. The surface wave in the air travels faster than the part of the wave flowing through the ground. The surface of the earth is curved like the curved part of a racetrack. On the curved track, a car on the outside of the track has to travel faster than the car on the inside lane to stay even, and the two cars travel in a curved path. Although the wave in the air travels faster than the wave on the ground, the two parts of the wave cannot be separated. Because of this, the radio wave also travels in a curved path that follows the curvature of the earth. The AM broadcast stations use ground wave propagation during the day and skywave propagation at night. Since radio waves at lower frequencies conduct better through the ground, an AM broadcast station on 540 kHz will be many dB stronger than a station on 1600 kHz, if both run the same power. This fact is important in understanding why ground mounted verticals do not work as well at high frequencies as they do on the broadcast band.
Direct Wave Propagation..
Antennas located on high structures can "look" over the horizon and "see" the receiving antennas. Because refraction is involved, direct waves travel 20% farther than light waves due to scattering of radio waves by the environment. Trees and other foliage are invisible to HF radio waves. Direct wave propagation is possible at all frequencies, but this mode of propagation is seldom used on our HF bands, but it is the usual propagation mode used by repeaters and others on VHF and UHF. If you watch TV on an outside antenna , you are receiving the signal by direct wave propagation.
Propagation by Refraction..
Refraction occurs when the lower part of a wave travels slower than the top part of the wave because the wave is passing through two media. These media can be two layers of air at different temperatures or they can be air and a solid. One form of refraction is caused by a radio wave passing over a hill or ridge being bent as it passes over the obstruction. This is known as "knife edge refraction”. Another form of refraction occurs when layers of air of different temperatures bend the radio waves around the horizon. This is called tropospheric ducting. This mode of propagation makes long distance contacts possible at VHF frequencies. Tropospheric ducting does occur on 10m and lower frequencies and is noticeable when other forms of propagation are absent. On HF bands, many hams mistakenly call tropospheric ducting and direct wave "ground wave".

HF propagation...

The Ionosphere.
In the upper air around 80km (50miles) and higher, radiation from the sun strips electrons from oxygen molecules causing the mole-cules to become ionized forming the ionosphere. The ionized oxygen molecules and its free electrons float in space forming radio-reflec-ting layers. Ionization of the ionosphere varies by the time of day, seasons of the year, and the sunspot cycle. The strength of ionization also varies from day to day and hour to hour. Since the height of the ionosphere varies, the higher the ionized layer becomes, the farther the skip will be. The part of the earths atmosphere called the iono-sphere is divided into three layers. The three layers are, from lowest to highest, the D-layer, the E-layer, and the F-layer. Each layer has a different effect on HF radio propagation.
Being at a lower altitude, the D-layer molecules are squeezed closer together by gravity than those in higher layers, and the free electrons reattach to the molecules easily. The D-layer requires constant radiation from the sun to maintain its ionization. Radio waves at lower frequencies such as the frequencies of the AM broadcast band cannot penetrate this layer and are absorbed. The higher frequency signals are able to pass through the D-layer. The D-layer disappears at night causing AM broadcast stations to reflect from the higher layers. This is why AM broadcast signals only propagate by ground wave in the daytime and they can be received from great distances at night. Like the broadcast band, the D-layer absorbs signals on 160m and to a lesser extent 80m during the day making those bands go dead. During solar flares, the D-layer becomes ionized so strongly that all high frequency radio waves are absorbed, causing a radio blackout.
E-layer propagation is not well understood. Being at a lower altitude than F-layer, the E-layer is responsible for summertime short skip propagation on the higher HF bands. The skip zone is around 1500km (1000 miles), but at times when the E-cloud covers a wide area in the summer, double hops can be seen. A double hop occurs when the signal reflects from the ionosphere, then returns to the ground, reflects from the ground back to the ionosphere where it is reflected back to the ground. A double hop can propagate the signal 3000km (2000 miles) or more. The E-layer forms mostly during the day, and it has the highest degree of ionization at noon. The E-layer like the D-layer disappears at night. Even so, sporadic-E propagation can and does form at night. There is a minor occurrence of sporadic-E propagation during the wintertime. On rare occasions, sporadic-E propagation can surprise you by occurring anytime regardless of the sunspot cycle or the season of the year.
The F-layer is the highest layer and it is divided into two levels: F1 and F2. At night the F1 and F2 merge into one layer. During the day, the F1-layer doesn't play a part in radio propagation, but F2 does. It is responsible for most high-frequency long distance propagation on 20m and above. However, the F-layer makes it possible for you to work DX on the lower bands at night. Sunspots are responsible for the ionization layers and in years with high sunspot numbers, worldwide contacts can be made easily on 10-20m by F2-layer propagation. In years of low sunspot numbers, working distant stations is difficult on those bands. Consequently, 10m and 15m will be completely dead most days and 20m will go dead at night. In years of low sunspot numbers DX contacts are easily made at night on 160m, 80m, and 40m. The sunspot numbers increase and decrease in 11-year average cycles.
Since the curvature of the earth averages about 5m (16ft) every 8km (5 miles), an object 8km (5 miles) from you on perfectly flat earth will be 5m (16ft) below the horizon. Because light travels in straight lines, you cannot see objects beyond the horizon. Radio waves travel in straight lines, but there are ways to get them beyond the horizon. This is referred to as propagation.