How do radio amateurs communicate.
There are many modes by which amateurs communicate. Speech, using amplitude modulation, frequency modulation or single sideband, is the most popular mode. Even so, many operators still use morse code or one of the more modern computer generated modes such as PSK31, while some older computer generated modes like RTTY, AMTOR and PACTOR are still widely used. Two types of television are in use. Slow scan television is used on the short wave bands to send single images (similar to a fax) worldwide. Fast scan television, such as you see on your normal TV, is mostly used on the UHF bands
How do radio signals get from A to B
Radio waves, like light waves, travel in straight lines and cannot pass through obstructions. From a practical point of view, the earth's curvature represents a very significant obstruction. Over a distance of 500 miles, a short distance in terms of communication, this curvature is equivalent to an impenetrable obstruction greater in height than Everest. Fortunately there are various ways, depending on frequency, in which signals can avoid this and other obstructions.
We all know that on our domestic stereo system or personal transistor radio that there are different wavelengths shown. There usually is the long and medium wavebands plus the FM waveband. On the long wave we have BBC Radio 4 and a few other French stations. On the medium wave we find many UK stations most of which are local broadcast stations. The FM band is to be found in the Very High frequency (VHF) part of the spectrum. The amateur wavelengths are on
the shortwave bands, the VHF bands, the Ultra High Frequency (UHF) bands and the Super (SHF) and Extra High Frequency (EHF) bands. In round figures, the amateur bands are 160 metres, 80 metres, 40 metres, 30 metres, 20 metres, 17 metres, 15 metres, 12 metres, 10 metres in the short waveband, while 6 metres, 4 metres and 2 metres are in the VHF waveband with 70 centimetres and 23 centimetres are in the UHF waveband. There are other amateur bands in the SHF and EHF wavebands.
Centred at about 250Km above the earth's surface are regions of ionised gas called the ionosphere which encircle the earth. Depending on conditions, the regions can refract short wave signals back to earth where they will be reflected back off the earth's surface to be refracted again and so on. This will enable signals to travel around the curvature of the earth to distant places. In fact at certain times of the day, at certain times of the year and certain times of the solar cycle, signals can completely circumnavigate the earth. Radio waves shorter than 10 metres are not usually refracted back to earth and so you cannot make long distance contacts by means of your signal hopping around the world between the ionosphere and the earth's surface. At these much shorter wavelengths, say of 2 metres and below, amateurs have to look for an alternative to the natural ionosphere in order to transmit their signals over longer distances.
Under certain weather conditions, usually associated with high pressure, layers form in the lower atmosphere at heights up to 5Km, but normally around 1 to 2KM, which are associated with abrupt changes in air temperature. The boundary between warm and cold air can also reflect radio waves. When these unusual conditions occur, interference to your local FM radio stations or TV pictures from afar can often be noticed. Amateurs take advantage of such conditions to make
contacts at long distances. Everyone is familiar with the 'Northern Lights'. Particles radiated from the Sun are trapped in the magnetic field of the
earth becoming densest at the poles. This gives visual effects of shimmering colours in the sky. Ionisation of a lower part of the ionosphere occurs also concentrated at the poles which forms an erratic mirror for VHF signals enabling contacts up to 2000Km. Thousands of meteors burn up in the central region of the ionosphere every day. The high temperature causes ionisation for periods of time from a few hundredths of a second up to 20 seconds depending on size of the meteor. By using high speed morse code or digital transmissions contacts can be made from between 700Km and 2000Km. There are other ways on the VHF bands to achieve longer distances such as Trans-equatorial propagation (TEP), Sporadic E, Auroral E, Field Aligned Irregularity (FAI), Ionoscatter and Troposcatter to name a few. With the exception of TEP, the propagation is enhanced in the middle region of the ionosphere. Many amateurs use the moon as a mirror to reflect VHF and UHF signals to the other side of the world. The path from earth to moon and back is very lossy to radio signals and only the best equipped stations are able to use this method. A much easier possibility of space communication is to contact the International Space Station (ISS). Almost all astronauts on the ISS are licensed amateurs and have equipment installed for their leisure time. Similarly, the Space Shuttle has licensed astronauts making the trip from time to time. This is not a new facility as the Russian MIR cosmonauts were mostly licensed amateurs making many thousands of contacts on many different modes.
There are many modes by which amateurs communicate. Speech, using amplitude modulation, frequency modulation or single sideband, is the most popular mode. Even so, many operators still use morse code or one of the more modern computer generated modes such as PSK31, while some older computer generated modes like RTTY, AMTOR and PACTOR are still widely used. Two types of television are in use. Slow scan television is used on the short wave bands to send single images (similar to a fax) worldwide. Fast scan television, such as you see on your normal TV, is mostly used on the UHF bands
How do radio signals get from A to B
Radio waves, like light waves, travel in straight lines and cannot pass through obstructions. From a practical point of view, the earth's curvature represents a very significant obstruction. Over a distance of 500 miles, a short distance in terms of communication, this curvature is equivalent to an impenetrable obstruction greater in height than Everest. Fortunately there are various ways, depending on frequency, in which signals can avoid this and other obstructions.
We all know that on our domestic stereo system or personal transistor radio that there are different wavelengths shown. There usually is the long and medium wavebands plus the FM waveband. On the long wave we have BBC Radio 4 and a few other French stations. On the medium wave we find many UK stations most of which are local broadcast stations. The FM band is to be found in the Very High frequency (VHF) part of the spectrum. The amateur wavelengths are on
the shortwave bands, the VHF bands, the Ultra High Frequency (UHF) bands and the Super (SHF) and Extra High Frequency (EHF) bands. In round figures, the amateur bands are 160 metres, 80 metres, 40 metres, 30 metres, 20 metres, 17 metres, 15 metres, 12 metres, 10 metres in the short waveband, while 6 metres, 4 metres and 2 metres are in the VHF waveband with 70 centimetres and 23 centimetres are in the UHF waveband. There are other amateur bands in the SHF and EHF wavebands.
Centred at about 250Km above the earth's surface are regions of ionised gas called the ionosphere which encircle the earth. Depending on conditions, the regions can refract short wave signals back to earth where they will be reflected back off the earth's surface to be refracted again and so on. This will enable signals to travel around the curvature of the earth to distant places. In fact at certain times of the day, at certain times of the year and certain times of the solar cycle, signals can completely circumnavigate the earth. Radio waves shorter than 10 metres are not usually refracted back to earth and so you cannot make long distance contacts by means of your signal hopping around the world between the ionosphere and the earth's surface. At these much shorter wavelengths, say of 2 metres and below, amateurs have to look for an alternative to the natural ionosphere in order to transmit their signals over longer distances.
Under certain weather conditions, usually associated with high pressure, layers form in the lower atmosphere at heights up to 5Km, but normally around 1 to 2KM, which are associated with abrupt changes in air temperature. The boundary between warm and cold air can also reflect radio waves. When these unusual conditions occur, interference to your local FM radio stations or TV pictures from afar can often be noticed. Amateurs take advantage of such conditions to make
contacts at long distances. Everyone is familiar with the 'Northern Lights'. Particles radiated from the Sun are trapped in the magnetic field of the
earth becoming densest at the poles. This gives visual effects of shimmering colours in the sky. Ionisation of a lower part of the ionosphere occurs also concentrated at the poles which forms an erratic mirror for VHF signals enabling contacts up to 2000Km. Thousands of meteors burn up in the central region of the ionosphere every day. The high temperature causes ionisation for periods of time from a few hundredths of a second up to 20 seconds depending on size of the meteor. By using high speed morse code or digital transmissions contacts can be made from between 700Km and 2000Km. There are other ways on the VHF bands to achieve longer distances such as Trans-