The Sun and HF radio propagation

          A summary of the way in which the Sun affects ionospheric propagation (HF wireless propagation) for two way wireless communications, wireless wireless communications, broadcasting, etc.

          As electromagnetic swell, and in this case, wireless signals travel, they interact with things and the newspapers in which they travel. As they do this the wireless pointers can be echoed, refracted or diffracted. These interactions origin the wireless pointers to change main heading, and to reach localities which would not be likely if the wireless signals journeyed in a direct line.

         The Sun has an tremendous impact on HF wireless propagation because it sways the ionosphere which devotes increase to most of the long expanse consequences that enable long expanse radio communications on the HF musicians. As a outcome is substantially affects numerous forms of radio communications from the normally two way wireless communications schemes that are litigated by numerous organisations, and diverse forms of wireless radio communications using the HF musicians to wireless broadcasting, issue to issue wireless communications and wireless amateur transmissions. As a result, a knowledge of how the situation on the Sun affect wireless pointer propagation is essential for wireless designing and prediction HF propagation situation. wireless propagation prediction software furthermore takes the state of the Sun into concern when it calculates its approximates of the propagation situation.

           To look at the way the Sun affects the ionosphere and radio propagation conditions, it is essential to take a quick gaze at the various areas in the air to glimpse which localities influence radio propagation and how the sun affects them. These factors are important in being able to forecast propagation situation and when using radio propagation prediction programmes.

The ionosphere

          For many years it has been known that there are ionised levels in the top reaches of the air that sway diverse types of wireless communications. This region is renowned as the ionosphere, whereas the existence of the an ionised region was first proposed just after the turn of the century, separately by two scientists, namely Kennelly in the USA and Heaviside in the UK. Since then far more has been learned about these layers, especially since the first rockets organised to pass through the ionosphere to assemble facts and figures.

          In most regions of the air it is discovered that the gases are in a steady molecular form. although in certain localities of the atmosphere some of them start to become ionised, splitting into free electrons and positive ions. Of these it is the free electrons that affect the radio pointers, whereas the level where these ions and electrons are discovered is still called the ionosphere. This generally starts to happen at an altitude of round 30 km, although at this size the levels of ionisation are very little and they do not have an effect on radio pointers. although as the altitude rises the number of ions increases.

          The ionosphere is conventionally considered of as having a number of distinct levels. While it is often befitting to think of the ionosphere in this way, it is not strictly factual. The whole of the ionosphere contains ions and free electrons, although there are a number of peaks, and which may be considered as the distinct levels. These levels are given the designations D, E, and F. A design drawing of the about grades of ionisation is shown underneath. This can only be very about because the levels of ionisation vary as a outcome of a number of factors.

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               The approximate levels of ionisation in the ionosphere

          The smallest of the levels is the D layer. This is discovered at altitudes between 60 and 90 km. It only lives during the daytime when it is in outlook of the sun. Above this is the E layer at round 110 km. This lives during the day, and then at evening when it is not in sunlight it becomes very much weaker. eventually there is the F level. This varies considerably, normally living as two levels during the day. These are designated the F1 and F2 levels. They are discovered at altitudes of around 300 and 400 km in summer, and then during the winter they may drop to around 200 and 300 km. At night the two levels generally blend to pattern a lone layer and this is generally round an altitude of 250 to 300 km. It should be remembered that these numbers are only a uneven direct because they change rather substantially according to the time of year and the state of the sun.

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                       Variations of the ionosphere over the day

Formation of ions

          The ionisation in the ionosphere is developed when radiation from the sun strikes the gas substances in the upper air. The radiation is of adequate intensity that it gives the electron in some molecules adequate energy to depart the molecular structure. This departs a free electron and the gas molecule, having one electron too few becomes a affirmative ion.

          At very high altitudes the air is very thin, and as a outcome the grades of ionisation are very reduced. As the air become denser, so the grade of ionisation begins to increase. However the ionisation method utilises up the power of the radiation, and after a certain distance the power of the radiation is such that it does not ionise as numerous gas substances as before and the grade of ionisation begins to drop.

          It is furthermore discovered that for the higher levels including the F and E levels most of the ionisation results from ultra violet light. The D layer being at a smaller altitude outcomes mainly from X-rays that are adept to penetrate farther into the atmosphere.

          It is furthermore discovered that the free electrons and affirmative ions gradually recombine. In other words the emission is causing them to ionise, and then they gradually recombine afterwards. In chemistry this state of activities is called a dynamic equilibrium. It means that if the source of emission is removed, then the grades of ionisation will drop. As a outcome the D layer goes away after nightfall, and the E layer is greatly decreased in power. In outlook of the high grades of ionisation in the F levels and the detail that the air density is so much less, it takes longer for the recombination process to take place and consequently it remains over evening, although its level is reduced. This can be glimpsed in the way that wireless communications vary over the course of a day.

Effect of the ionosphere

           The distinct levels of the ionosphere affect radio ways in somewhat distinct ways. When a signal goes into the D level it sets the free electrons vibrating. As they vibrate they collide with close by substances, and after each collision some power is lost. As a outcome radio signals entering the D layer are attenuated. It is discovered that the level of attenuation is inversely proportional to the rectangle of the frequency. In other phrases increasing two-fold the frequency decreases the attenuation by a component of four. It is discovered that reduced frequency radio pointers are completely soaked up by it. This can be shown by the detail that wireless stations on the intermediate signal announced band can only be perceived over short distances during the day, and then at night when the D level disappears they can be heard over much larger distances.

          The effect is somewhat distinct for the higher layers. Being higher in altitude the gas density is much less. As a result a different effect predominates. Again the electrons are set in shift, but as fewer collisions take place they proceed on the pointer to angle it away from the locality of largest ionisation. In other phrases the signal is refracted back towards the soil. It is furthermore found that the effect declines with frequency and as a result the pointer will finally pass through one level and on to the next.

Variations in the ionosphere

           The effect of the ionosphere is substantially connected to the allowance of radiation it receives. This varies over the time span of a day. At night when the ionosphere obtains no emission from the sun, the level of ionisation falls and connection may not be possible over some paths or distinct frequencies may have to be used.

          Other alterations also sway the ionosphere. In just the same way that winters are chilly because that part of the soil obtains less moderately hot from the sun, so the ionosphere receives less emission, and the grades of ionisation in the ionosphere drop.

Sunspots

          Changes on the sun itself furthermore affect the ionosphere. One of the foremost alterations occurs as the outcome of the sunspots that emerge on the exterior of the sun.

          If the sun is examined by projecting its likeness up on a computer display, then a number of dark localities may be seen from time to time. These spots may last from anywhere between a few hours to days or even weeks. The locations are areas where the surface of the sun is cooler than the surrounding localities. The warmth of the spots is only about 3000 C. This is rather cooling when contrasted to the temperature of the rest of the surface that is around 6000 C! although it is very much hotter under the exterior where temperatures come to in surplus of a million qualifications.

        The sunspots are localities of strong magnetic activity. The magnetic fields in these localities are enormous and as a outcome the exterior of the sun is disturbed. This causes the exterior temperature to drop in these areas causing a darker locality to be seen.

          Round the sunspot itself there is an area that is known as a plage. This is slightly brighter than the surrounding area and is a large radiator of ultra-violet emission and X-rays. The allowance of emission coming from the plage means that there is an general boost in the grade of emission from the sun. In detail it is noticed that the level of radiation from the sun can be approximated from a information of the number of sunspots that emerge on the exterior.

          As sunspots often emerge in assemblies, a procedure of endeavouring to estimate their effect has been developed. A figure renowned as the sunspot number is used. This number does not comprise the number of locations themselves, but the grade of undertaking on the sun and the sunspot number is very nearly related to the amount of emission obtained from the sun.

          The daily readings of the sunspot figures fluctuate substantially. To overcome this, the measurements are flattened mathematically to take out the erratic environment of the measurements and so that the underlying trend can be glimpsed. This number, called the flattened Sunspot Number (SSN) is often quoted in association with propagation accounts.

The sunspot cycle

          The number of sunspots on the Sun's exterior varies. On some days very couple of, or even none may be seen, while at other times there are very numerous. The daily number varies considerably over a short time span of time as the sun rotates, but if the flattened sunspot number is utilised it can be seen that there is a much longer-term tendency. This tendency displays that the number of sunspots increases and falls over a time span of roughly eleven years. This number is only an approximate direct because there is a substantial amount of variety on this.

          Records of the sunspot figures have been kept since the mid-eighteenth years, and by mentioning to these records it has been possible to track the cycles since then. Cycle 22 started in September 1986 with a number of 12. It rose quickly over the next 33 months to come to a top of 158. From then it fell slightly and increased afresh to give a second smaller top before finish in 1996. Now cycle 23 has begun and the figures are increasing.

The effect of the sunspot cycle

          The advanced figures of sunspots mean advanced grades of emission. In turn this means that there are larger levels of ionisation in the ionosphere. Accordingly this sways propagation on the HF bands. It is discovered that the greatest frequencies that can be reflected are increased.

          At the sunspot smallest frequencies of round 15 to 20 MHz are commonly sustained during the day. although at the greatest, frequencies in excess of 60MHz may be influenced. This means that popular ham bands like 24 and 28 MHz may not support communications via usual ionosphere modes in the sunspot minima. Often 28 MHz seems dead with no stations audible. However throughout periods of around the maximum it is an very good band. reduced power positions or those with poorer antennas find it especially good. As the D level attenuation is much less, even low power stations can make very good associates.

          The sunspot number can be utilised to give a very uneven direct to what conditions may be like. The number tends to alter from about 65 at the smallest of the cycle to over 300 at the maximum. For good situation on the higher frequency musicians it is discovered that a figure of in excess of about 100 is required.




By RR Team

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