The Growth of Communication Electronics
The puzzling mysteries of the Universe continue to be so, even though humans began their attempt to explore or expose it from time immemorial. As humanity grew into cultures, sects and civilisations, studies and researches also grew into branches and now the most important branch of all Sciences have come to be Electronics. Electronics is defined as the science of controlling electrical energy electrically, in which the electrons have a fundamental role. Lately, the explosion in Communication Electronics has changed the entire globe into one village - causing a great paradigm shift in every area of social life.
Novelist Arthur C Clarke, a popular science fiction writer (author of the much acclaimed novel ‘A Space Odyssey’ - an voyage to Jupiter) hinted in his short story 'The Sentinel’ that future communication would be artificial satellites controlled. The invention of Telegraph by Samuel Morse, was certainly the first step and the invention of Telephone by Alexander Graham Bell turned out to be a Milestone. The Radio, introduced by Guglielmo Marconi, an Italian electrical engineer, made the evolution revolutionary. As the Russian Satellite Sputnik set its' feet in the space in 1958, communication technology and concerned strategies took another giant shift. The US owned Explorer 1 which also appeared in space before long virtually changed the dimension of our expectations too.
Even though SCORE (Signal Communications by Orbiting Relay Equipment) owned by US Air Force was the first satellite to handle a message to a distant place, it is 'Telstar’ designed and launched by Bell Telephone Laboratories (New Jersey), the very laboratory from which transistors came out, that got the credit of being the first communication satellite. SCORE captured world attention by broadcasting a Christmas message from U.S. President Dwight D. Eisenhower to Europe, in 1958, via short wave radio and further through an on-board tape recorder. Today, the entire space around the globe is filled with multitudes of radio signals from satellites, most of them engaged in communication. In another words, we live in an ocean of radio waves.
Always Amateurs had vital roles in inventions - many people experimented with radio frequencies too. Short Wave, SSB.... all are contributions of similar Amateurs. This book, ‘Gateway to Ham Radio' intends to give an opening to all Amateurs who love to enter a world of innovators, known by the title 'Ham Radio Operators'.
Radio Signals
The impact of a sound in the atmosphere is just like a rubble thrown into still water - it causes a chain of waves. If the three dimension waves in the water can be seen, the multi dimensional waves that sound causes in the Air are invisible. It is the number of cycles that a particular wave forms in a second that is counted through the unit, frequency. A cycle, as its' name implies, is a circle. When a number of cycles are to be represented, circle is not a comfortable picture to show continuity. So a cycle is always shown like that seen in the picture C-1/1Here, a circle is shown in a cycle pattern and it begins at 00 and through 900, 1800 and 2700 it reaches 3600 or again back to 00, from where it continues to another cycle of the same configuration. Any cycle has qualities of amplitude and wave length. Suppose we hear a constant whistling sound from an amplifier. As we raise the volume what that changes is the amplitude of the signal. Suppose a man and a woman say good morning in a moderate volume, it is the number of cycles their sounds make in a second that vary. It is measured in frequency - number of cycles per second. Normally male voice is comparatively low in frequency.
C-1/2A | ||
Frequency Range | Name | Short Name |
3KHz – 30 KHz | Very Low Frequency | VLF |
30 KHz - 300 KHz | Low Frequency | LF |
300 KHz - 3000 KHz (3MHz) | Medium Frequency | MF |
3 MHz - 30 MHz | High Frequency | HF |
30 MHz - 300 MHz | Very High Frequency | VHF |
300MHz – 3000MHz (3GHz) | Ultra High Frequency | UHF |
3 GHz – 30 GHz | Super High Frequency | SHF |
30 GHZ – 300 GHz | Extremely High Frequency | EHF |
When it comes to Radio or higher frequencies, the wave length is highly reduced, increasing the frequency proportionally. Velocity is the sum of frequency multiplied with wavelength. You might have noticed that in Radios both wave length and frequency are marked. The velocity of a 500 meters (600 Khz) MW signal is 500 X 600,000 = 300,000,000 (constant). Where ever we have only one of it (frequency or wavelength), divide it with what we have and find the missing factor.
C-1/2B Frequency Range | Band |
0.39 GHz – to 1.55 GHz | L Band |
1.55 GHz to 5.20 GHz | S band |
3.70 GHz to 6.20 GHz | C Band |
5.20 GHz to 10.9 GHz | X Band |
12 GHz to 18 GHz | Ku Band |
18 GHz to 27 GHz | K Band |
27 GHz to 40 GHz | Ka Band |
40 GHz to 300 GHz | m.m Band |
That Radio Frequency classification of Long Wave, Medium Wave and Short Wave has now grown into Bands (see chart C-1/2B). The bandwise categorization begins from Gija Hertz range. A thorough study on radio signals is always necessary to understand properly, why different different frequencies are necessary to serve distinct functions.
The Ionosphere
If all types of radio signals are transmitted rom a particular tower at a time, what that fills most of the global space would be Short Waves. The Ionosphere that surrounds the globe like a shield belt is one among the main factors that decide radio propagation. Ionosphere is the result of millions of radiations in multitudes of frequencies ranging from VHF to Very Ultra High Rays that touch the global space. These radiations from known and unknown stars result in the formation of layers of ionised molecules at a distance of 40-400 kms from earth. For research and observation sake, depending upon its characteristics, ionosphere is divided into four layers - D, F, F1, F2.
Putting the truth in another words, all radio signals move under the mercy of the ionosphere. All signals in VLF (Very Low Frequency), LF (Low Frequency) and MF (Medium Frequency) ranges are fully absorbed by both ionosphere and the earth. Because of this, only signals that move parallel to earth are useful in those ranges. When it come to Short Waves, both the surface of the earth and the ionosphere act like reflecting mirrors. Shortwave signals move reflected between earth and the Ionosphere, until it gets exhausted. At the same time, Ionosphere bypasses all VHF and UHF signals just like light through a plain glass
While Shortwave signals that are reflected from the ionosphere undergo ‘Fading’, 'Frequency Shift’ and ’Noise Interference’, Medium and Long Waves remain practically undisturbed, without any changes in quality. It doesn’t mean that they are not subject to those changes in the earth’s closest atmospheric layers. The nature of Ionosphere is never static - it keeps changing every time. Truly, the quality of Shortwave transmission depends upon the depth and density of Ionospheric layers. Event though the D layer, which is the closest to earth, is seen only now and then, it causes fading of Short Wave signals. Sunspot which appears on the Sun face on a regular pace causes to ionise the D layer heavily and leading to absolute ‘Black Out’s, a rare situation of no radio signal movement on some frequency spectrums on the earth’s surface.
Even though the E layer that is just above the D also influences Short Wave remarkably, it is the F class layers that actually reflects them back to earth. During night time the F1 layer comes down to merge with the F layer and as a result Short Wave signals vary in skip distance between day and night. This means that a signal heard during day time at a certain spot need not necessarily be available during night. A Short Wave signal that reaches a particular point during day time most naturally falls somewhere else during night time. This is the reason why we hear new stations at night time. This is not applicable to signals that reach a radio straight from the tower. Point B which is the nearest point to receive a reflected signal and point A which is the longest point to receive a direct Short Wave signal could be away by many kilometres. This area is called the ‘Skip area’. That particular Short wave signals won’t be available there.
The time bound rhythmic working pattern of the Solar System influences Short Wave transmission greatly. There is an 11 years cycle in the solar System which is based on the Sunspot activity, which changes the propagation condition drastically. Major earthly changes like earthquakes also influence ionosphere because of the property changes in the geomagnetic field that results. In similar cases Radio signals are found to be shifting its frequency even upto 70%, while the frequency shift caused by the ionosphere is upto 20% at normal conditions.
It was told early that at VHF and UHF ranges since ionosphere behaves like a conducting medium, what we can utilise are only Direct Waves. That is one reason why we use VHF and Higher frequencies to communicate with artificial satellites in the space. This is the reason why the covering ranges of VHF equipments (used by Hams) and TV transmissions remain low. These all are basic information which we require to proceed further into Hamology.
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