The Basics
Radio Propagation
There are three main types of propagation
Radio Wave Propagation is the process in which your radio signal gets from your antenna to the antenna of the amateur station that you're talking to.
Line-of-Sight
Line-of-sight propagation requires a path where both antennas are visible to one another and with no obstructions. A path normally used by VHF and UHF communication.
Ground-Wave
Ground-waves follow the surface of the earth, rapidly attenuating at higher frequencies. Normally used by lower frequency transmissions such as Medium wave to Long wave
SkyWave
As the name indicates sky-waves go skywards and are reflected by the Ionosphere, providing long-distance communication. Normally used by High Frequency transmissions.
Radio Waves
When you transmit through your antenna, it is energised and radiates electromagnetic waves. The waves spread outwards and travel in free space at 300,000Km per sec or 186,000 miles per sec, or the speed of light. When the waves enter an ionized area the speed is modified. The further the wave moves away from the antenna the less strength it will have. (Field strength).
Polarization
A Radio Wave is Polarized in the direction of the electromagnetic wave of the field of the wave. A Horizontal antenna would normally radiate Horizontally Polarized waves and a Vertical antenna Vertically Polarized waves. If you transmit waves from your HF antenna, part of the energy follows the surface of the ground (Ground Wave) and is rapidly absorbed by the earth, therefore the range is very short, but most of the energy leaves at an angle as a Sky Wave and would be lost in space if it were not for the presence of the Ionosphere, which with the right conditions will bend or reflect the wave back to earth often at great distances from the transmitting station. This can be repeated a number of times where it can cover even greater distances known as Hops.
The Ionosphere
The Ionosphere consists of a number of ionized regions called layers. All of these layers except the lowest can reflect the waves back to earth if the layers are sufficiently ionized.A layer is said to be ionized when ultra-violet rays from the sun have caused gas atoms to lose free electrons and the stronger the ultra-violet rays, the more dense the layer becomes (the dielectric constant). If the ionization of the layer is too low, or the frequency too high, the wave will continue through the layer on to the next layer or space. If ionization is just right, the wave will bend back to earth in one or more hops.
Ionosphere Layers or regions
D layer is the lowest of the layers at a height of 50-90km above the earth. It forms rapidly at sunrise and disperses rapidly at sunset particularly where HF and medium wave signals are concerned. The D layer attenuates these frequencies until sunset and is therefore has its greatest attenuation during midsummer.
E layer >is at a height of about 120km above earth and is the lowest reflecting layer.
F1 layer is about 200km above earth and is a weak layer present only during the day for part of the year. It is capable of reflecting signals further than the E-layer, because of its greater height.
F2 layer exists during the day at a height of 350km during the spring, summer and autumn days. This is the main layer for daytime DX'ing during these times.
F layer is a result of the F1 and F2 layers combining at a height of about 200km at night and during winter days. The layers expand due to exposure to the sun for long periods of time(F2) and contract at night or in winter when there is little sun.
So you can see that propagation is dependant upon a number of factors: The time of day, the time of year, your antenna system, your power output, (to a degree) and also the amount of ultra-violet rays that the ionosphere is exposed to. The latter is determined by the solar cycle which we will deal with on the Solar Page.
These are only the very basics of propagation that you will require to get a good understanding, but it is an immense subject and there are many websites which deal with the different aspects and levels, which I have listed on the Links Page.
Radio Wave Propagation(Requires Power Point Program.)
Ethics and Operating Procedures for all Radio Amateurs.
Download a PDF file for info on Operating Ethics.
Frequencies and Transmitting Modes
Radio Amateurs or "Hams" use a number of different frequencies for communications, these frequencies are allocated by the FCC for amateur use.
Hams may operate from just above the AM broadcast band to the microwave region, in the gigahertz range.
Many Ham Bands are found in the frequency range that goes from above the AM radio band (1.6 MHz) to just above the citizens band (27 MHz).
During daylight, 15 to 27 MHz is a good band for long-distance communications. At night, the band from 1.6 to 15 MHz is good for long-distance communications. These bands are often referred to historically as short-wave bands.
Unlike frequencies used by FM radio stations and TV stations, which are line-of-sight and therefore limited to 40 or 50 miles, short-waves "bounce" off the ionosphere from the transmitter to the receiver's antenna. The higher the frequency, the "shorter" the wavelength.
The Sun
All the stars, including our Sun, are gigantic balls of superheated gas, kept hot by atomic reactions in their centers.
In our Sun, this atomic reaction is hydrogen fusion: four hydrogen atoms are combined to form one helium atom. The temperature at the core of our Sun must be 20 million degrees centigrade, and the surface temperature averages 6,000 Deg C, or about 11,000 Deg F.
The diameter of the Sun is 865,400 miles, and its surface area is approximately 12,000 times that of Earth. Compared with other stars, our Sun is just a bit below average in size and temperature, and is a yellow dwarf star. Its fuel supply (hydrogen) is estimated to be sufficient for another 5 billion years.
Rotation
Our Sun is not motionless in space; in fact it has two proper motions. One is a seemingly straight-line motion in the direction of the constellation Hercules at the rate of about 12 miles per second.
But since the Sun is a part of the Milky Way system and since the whole system rotates slowly around its own center, the Sun also moves at the rate of 175 miles per second as part of the rotating Milky Way system.
In addition to this motion, the Sun rotates on its axis. Observing the motion of sunspots (darkish areas that look like enormous whirling storms) and solar flares, which are usually associated with sunspots, has shown that the rotational period of the Sun is just short of 25 days.
But this figure is valid for the Sun's equator only; the sections near the Sun's poles seem to have a rotational period of 34 days. Naturally, since the Sun generates its own heat and light, there is no temperature difference between poles and equator.
In 1998, scientists saw for the first time that solar flares produce seismic waves in the Sun's interior that resemble those created by earthquakes.
They observed a flare-generated solar quake equivalent to a 11.3 magnitude earthquake. It contained about 40,000 times the energy released in the great 1906 San Francisco earthquake.
Solar Cycle
The Sun is like a giant nuclear reactor, made up mostly of electrically charged Hydrogen and Helium gas and the temperature at the core is around 15,000,000 Deg C.
The Sun is not a solid body, but a jelly like mass, and the surface, or Photosphere rotates once every 25 days at the equator, once in 28 days at latitude 45 Deg and once in 34 days near the poles, so you can see that the poles are continually being lapped by the equator, causing the magnetic field, carried by the Plasma (electrically charged gas), to wind itself up as the Sun rotates.
After an approximate 11 year cycle, the magnetic field lines short circuit and the field strength falls; in turn the whole field reverses polarity and a new cycle begins.
An 11 year cycle is the average, but a cycle can be as short as 5 years, or as long as 16 years.
Solar Flares
As the Sun's magnetic field is being wound up, an immense amount of energy is stored and local field strengths are increased as they are attempting to repel each other.
Eventually, the repulsion between the lines become strong enough to overcome gravity and mixed with the Plasma, in their fury, they will burst through the Photosphere (surface). Sometime later the Sunspots will be visible and because they are much cooler than the Photosphere, they show up as much darker areas.
At the Solar maximum when these events occur, Sunspots are at their peak and most aggressive and the ultra violet rays from the Flares are most intense, causing excessive ionization of the ionosphere. Solar Flares often reach earth, carried by the Solar wind (energy escaping from the Sun towards earth) and by increased ionization of the ionospheres layers, can affect propagation in many different ways and can cause problems here on earth when it reaches earth's magnetic field.
Photosphere
What we call the Sun's surface is technically known as the photosphere. Since the whole Sun is a ball of very hot gas, there is really no such thing as a surface; it is a question of visual impression.
The next layer outside the photosphere is known as the Chromosphere, which extends several thousand miles beyond the photosphere.
It is in steady motion, and often enormous prominences can be seen to burst from it, extending as much as 100,000 miles into space. Outside the Chromosphere is the corona.
The corona consists of very tenuous gases (essentially hydrogen) and makes a magnificent sight when the Sun is eclipsed.
The End
As the Sun ages, it gradually expands and heats. In 1994, American astrophysicists studying the eventual fate of the Sun estimated that its brilliancy will increase by 10% over the next 1.1 billion years or more and, in about 6.5 billion years hence, our aging star will have doubled its present luminosity.
The extreme heat generated will cause a catastrophic greenhouse effect on Earth and our oceans will boil away, and life on Earth as we know it will end. The Sun will eventually expand enormously to 166 times its present size and become over 2,000 times as bright.
Eight billion years from now, the Sun's radius will engulf the planet Mercury and extend beyond the present orbit of Venus, causing the total destruction of the Earth. The Sun is the closest star to the earth, approximately 93,000,000 miles away and the end of its influence extends well beyond the orbit of Pluto 3,765,000,000 miles away. It has been shining for 4.6 billion years and will shine for another 4.4 billion years before starting its death. It uses up its nuclear fuel at a rate of 7 million tons per second.
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