WEBSDRSWL: Propagation for amateur radio operators or SWL on HF

mercredi 16 avril 2025

Propagation for amateur radio operators or SWL on HF

INTRODUCTION TO HF PROPAGATION 3 to 29 MHz

During a transmission, the transmitter sends HF energy through the antenna. The main energy concentration lobe has an angle, above the horizon, that varies depending on the antenna and its environment. Part of this energy is lost into space, and the other part is guided, reflected, or refracted in the various ionized layers of the ionosphere.

Between the antennas and the first point where the wave returns to the ground, there is a zone in which the signal is not received. The length of this zone depends on the antenna's elevation angle. Depending on the band, it is nevertheless possible to establish short-distance links by ground wave scattering.

The ground wave, which only affects low frequencies, propagates over short distances (+/- 200 km) following the curvature of the Earth; while other waves are refracted by the ionosphere. On amateur bands, we use ground waves very little.

EVOLUTION DURING THE DAY

With sunset, layers D and E disappear, giving way to layers F1 and F2; while during the day, ionization is significant and all layers are present.

The MUF, Maximum Usable Frequency, is the highest frequency that allows a link via ionospheric reflection between two stations (the MUF is higher during the day than at night). The MUF varies depending on the time of day, the season, the position of the stations, the sun's UV radiation, and various ionospheric disturbances. Forecasting software remains significantly less effective than frequency monitoring (Beacons and other stations).

Since the D layer strongly absorbs low frequencies and the noise level increases with decreasing frequency, it seems logical that below a certain frequency, ionospheric propagation no longer allows links.

LUF, Lowest Usable Frequency, is the lowest frequency that can be used to establish a given connection. It is possible to artificially lower LUF by increasing the radiated power in order to increase the signal-to-noise ratio (LUF is lower at night than during the day).

THE SKIP

This is the jump that separates the wave's departure (antenna) and its return to the Earth's surface (after reflection or refraction). In this area, it is not possible to hear the transmitted signal. In this area, the MUF is therefore much lower.

QSB is the fading that causes the signal to rise and fall at varying rates.

To reach the F layers after passing through the ionosphere, the signal can take several paths simultaneously and be refracted by layers with different refractive indices. The signal you receive is therefore composed of several of these refracted signals arriving either in phase (high signal), out of phase (low signal), or out of phase (no signal).

The Long Path, as opposed to the Short Path, is the longest path to contact a distant station.

In some cases, to contact a distant station, it may be advantageous to use a path passing through a non-sunny area and to use the F layer rather than passing through a lit area where there may be very strong absorption from the D layer, low efficiency from the F1 layer, or low reflection from the E layer.

MULTI-HOP

A hop that allows contact between the antipodes is impossible. In the case of a very long link, multiple hops are required. During a transmission, part of the wave passes through the ionosphere and escapes into space (angle too large, critical frequency), another part is absorbed by the layers (collision of atoms and loss of energy), a third part is scattered in several directions by the irregularities of the layers, and finally the last part is refracted by the ionized layer. After returning to Earth, it returns to the ionosphere, and the cycle begins again.

THE GRAY LINE

The Gray Line is the line separating the Earth's surface between the sunlit area and the night zone. In reality, this line isn't a line; it's a fairly wide area in which the transition between day and night occurs. We saw above that the ionosphere evolves between day and night. Some layers merge into one, and others, with strong absorption, disappear at sunset. Conversely, at sunrise, the F layer strengthens before the D and E layers appear. During this period, on the dayside, the D and E layers have not yet appeared, while on the nightside, the F layer is still present. During these brief periods (1 hour at sunrise and sunset), propagation is very good.

EARTH'S MAGNETIC FIELD

The Earth's magnetic field is active (magnetic activity). The direction of the lines of force and their intensity can vary to varying degrees. The solar wind (free electron plasma) determines this geomagnetic activity. The impact of this flow of charged particles on the Earth's field (at a speed of several km/s) compresses the Earth's magnetic field and distorts the field lines, creating a tail (like a comet's). The point of impact is approximately 65,000 km before the Earth's surface (10 radii) and the end of the tail is approximately 650,000 km (100 radii). The solar wind reaches the Earth's magnetic field approximately thirty hours after the start of an eruption. These disturbances in the Earth's magnetic field disrupt the ionosphere, and the HF connections are significantly modified. The closer we get to the maximum of the solar cycle (favorable propagation), the more numerous and significant the eruptions can be (unfavorable propagation).

Aurora Borealis

Following solar flares, when numerous charged particles arrive on Earth, they penetrate the Earth's magnetic field at the poles (the weakest areas) and are guided by the field lines. Ionization then becomes very intense and can even be visible from our latitudes. This phenomenon is called the Aurora Borealis, and its possible effect is a near-total impossibility of establishing RF links below 10 MHz.

Propagation on 40 meter LSB (7 MHz)

The absorption of the D layer is much weaker than that of the lower bands, which results in a near-permanent aperture depending on the propagation mode. During the day, the use of the E layer allows communications with a range of approximately 800 km in very stable conditions. At night, as soon as ionization begins to decrease, the F2 layer allows for very reliable global contacts.

Atmospheric noise is minimal, and static levels, even in summer, are generally lower than signal levels

Propagation on 20 meter (14 MHz): This band is one of the best because propagation is good for DX during the day and sometime at night.

This is the preferred band for global communications for most OMs. Depending on the solar cycle, this band is always open for at least a few hours a day for DX traffic via the F2 layer. Occasionally, it is also possible to establish short-distance contacts via the E layer. During solar cycle maxima, the band can even remain open 24/7. In winter, the band closes relatively early.

Propagation for 17 meter (18 MHz)

This band behaves like the 20-meter band, but is more sensitive to variations in the solar cycle (11 years). During periods of low solar activity, the 17-meter band is only open to DX during the day on a north/south axis and at latitudes below 50 degrees. During periods of maximum solar activity, the band is open to long-distance communications all day, early evening, and even late into the night.

Propagation on 15 meter (21 MHZ)

This band behaves much like the 17 meter band. In 2025 is a very good band for DX.

Propagation on 12 meter (24 MHz)

This band benefits from the advantages of the 15 and 10 meters. It is primarily a daytime band during periods of low or moderate solar activity. During periods of high solar activity, the 12 meters can remain open even at night. During periods of low solar activity, the 12 meters are only open to DX during the day on a north/south axis and at latitudes below 50 degrees; however, during these same periods, the band can remain closed all day.

From 12 meters, ES contacts begin to become possible. ES openings are sometimes observed in winter, but their peak occurs between late spring and summer.

Propagation on 10 meter (28 MHz)

In 2025 its a wonderful band for DX because of big solar activity.

Remember only a 5-meter-long wire antenna is a half-wave ! In fact if you have a small radio try to have a 10-meter-long wire and your wire will listen all bands from 10 to 20 meter !!!

This band benefits from a large number of propagation modes. During periods of high solar activity, the band opens at sunrise and closes a few hours after sunset. During these periods, a power of a few watts allows contacts to be established over several thousand kilometers.

ES( E sporadic propagation) begins to be significant at 10 meters. It allows contacts over a distance of approximately 5,000 kilometers. It reaches its maximum between May and August.

So listen a lot to 10 meter, you will be surprised to listen of very far DXCC .

Try to have the best antenna as possible, even you add only some meters of wire to your telescopique antenna of your small SW radio receiver.

Try to put your antenna outdoor dear SWL

Propagation by Sporadic E As its name suggests, sporadic E activity is an unpredictable event that can occur at almost any time; however, it exhibits significant seasonal and diurnal variations. Sporadic E activity peaks predictably near the solstices in both hemispheres. In the mid-latitudes of the Northern Hemisphere, activity typically begins in mid-May, with the peak occurring most markedly in early June. It begins to taper off after mid-July and becomes much less reliable by early August. A much weaker sporadic E peak occurs at the winter solstice. In the mid-latitudes of the Southern Hemisphere, the periods are reversed; maximum activity occurs at the summer solstice.[2] Communication distances of 800 to 2,200 km (500 to 1,400 miles) can be achieved with a single Es cloud. This variability in distance depends on several factors, including cloud height and density. The maximum usable frequency (MUF) also varies considerably but is most commonly in the 25 to 150 MHz range, which includes FM broadcasting Band II (87.5 to 108 MHz), VHF television Band I (U.S. channels A2 to A6, Russian channels R1 to R5, and European channels E2 to E4, now discontinued in Western Europe), CB radio (27 MHz), and the 2, 4, 6, and 10 m amateur radio bands. On very rare occasions, an MUF of 225 MHz can be achieved.[2] No conclusive theory has yet been formulated regarding the origin of sporadic Es. Attempts to link the incidence of sporadic E to the eleven-year sunspot cycle have provided tentative correlations. There appears to be a positive correlation between sunspot maximum and Es activity over Europe. Conversely, there appears to be a negative correlation between sunspot maximum and Es activity over Australasia. Harrison [3] suggests a correlation between the formation of sporadic E and the ablation of iron and magnesium micrometeoroids in the ablation zone, between 100 and 140 km above the Earth's surface. Maruyama examines this possibility in more detail.[4]

With a directional antenna

What is long-path propagation?

Long-path propagation refers to radio signals traveling a longer arc around the Earth to reach their destination. This path is typically about 40,000 km long, the opposite direction to the shorter, more direct route.

Long-path signals can be stronger than those that follow the short path. This is because they encounter fewer obstacles and experience less signal loss.

For DX enthusiasts, the long path opens up exciting possibilities. It allows you to reach distant stations that might otherwise be impossible to contact via the short path due to adverse conditions.

Short path and long path For a circuit > 10,000km, the major arc (long path) can have fewer losses than the short path. This is especially true for N/S routes that are almost antipodal. Example of a France (Long. 0°) - Adélie Land (Long. 140°) route: • The short path will cross 10 time zones and cross the desert regions of Africa, but will follow the gray line in winter (in France). The connection will therefore be made in the middle of the summer night for Adélie Land, and in the late winter afternoon for France, with short opening times, and for a high Wolf number. • The long path will cross 2 time zones, pass near the North Pole (+180°), then cross 2 time zones. The path is almost entirely oceanic. By having the two gray-lines close to the path, we obtain a better connection budget than for the short path, despite a higher number of reflections. In this case, the connection takes place in the late autumn afternoon (May) for Adélie Land, and in the early spring morning for France

The most simple way to know if there is good propagation

https://icomjapan.blogspot.com/2023/07/the-most-simple-way-to-know-if-there-is.html

Ionospheric storms

High frequency (3–30 MHz) communication systems use the ionosphere to reflect radio signals over long distances. Ionospheric storms can affect radio communication at all latitudes. Some frequencies are absorbed and others are reflected, leading to rapidly fluctuating signals and unexpected propagation paths. TV and commercial radio stations are little affected by solar activity, but ground-to-air, ship-to-shore, shortwave broadcast and amateur radio (mostly the bands below 30 MHz) are frequently disrupted. Radio operators using HF bands rely upon solar and geomagnetic alerts to keep their communication circuits up and running.

Military detection or early warning systems operating in the high frequency range are also affected by solar activity. The over-the-horizon radar bounces signals off the ionosphere to monitor the launch of aircraft and missiles from long distances. During geomagnetic storms, this system can be severely hampered by radio clutter. Also some submarine detection systems use the magnetic signatures of submarines as one input to their locating schemes. Geomagnetic storms can mask and distort these signals.

The Federal Aviation Administration routinely receives alerts of solar radio bursts so that they can recognize communication problems and avoid unnecessary maintenance. When an aircraft and a ground station are aligned with the Sun, high levels of noise can occur on air-control radio frequencies.^{[citation needed]} This can also happen on UHF and SHF satellite communications, when an Earth station, a satellite and the Sun are in alignment. In order to prevent unnecessary maintenance on satellite communications systems aboard aircraft AirSatOne provides a live feed for geophysical events from NOAA's Space Weather Prediction Center.^[38] allows users to view observed and predicted space storms. Geophysical Alerts are important to flight crews and maintenance personnel to determine if any upcoming activity or history has or will have an effect on satellite communications, GPS navigation and HF Communications.

Telegraph lines in the past were affected by geomagnetic storms. Telegraphs used a single long wire for the data line, stretching for many miles, using the ground as the return wire and fed with DC power from a battery; this made them (together with the power lines mentioned below) susceptible to being influenced by the fluctuations caused by the ring current. The voltage/current induced by the geomagnetic storm could have diminished the signal, when subtracted from the battery polarity, or to overly strong and spurious signals when added to it; some operators learned to disconnect the battery and rely on the induced current as their power source. In extreme cases the induced current was so high the coils at the receiving side burst in flames, or the operators received electric shocks. Geomagnetic storms affect also long-haul telephone lines, including undersea cables unless they are fiber optic.^[39]

Damage to communications satellites can disrupt non-terrestrial telephone, television, radio and Internet links.^[40] The National Academy of Sciences reported in 2008 on possible scenarios of widespread disruption in the 2012–2013 solar peak.^[41] A solar superstorm could cause large-scale global months-long Internet outages. A study describes potential mitigation measures and exceptions – such as user-powered mesh networks, related peer-to-peer applications and new protocols – and analyzes the robustness of the current Internet infrastructure.^[42]^[43]^[44]