Telecommunication II
What is Telecommunication?
It is a method or principles of radio transmission.
Transfer of information (speech, music, image, computer data etc.) by radio can be
presented in its simplest form with block - diagram as on Pic.2.1. That is a transmission
realized by amplitude - modulated signal. Since, in our example, the information being transferred is the sound, the first step of such transmission is converting the sound into electrical signal, this being accomplished by a microphone. The low - frequency (LF) voltage at microphone output (Pic.2.1-a), that represents the electrical "image" of the sound being transferred, is being taken into the transmitter. There, under the effect of LF signal, the procedure called amplitude modulation is being carried out, and on its output high - frequency (HF) voltage is generated, its amplitude changing according to the current LF signal value. HF voltage creates HF current in the antenna, thus generating electromagnetic field around it. This field spreads through the ambient space, being symbolically shown on Pic.2.1 with dashed circles. Traveling at the speed of light (c=300,000 km/s), the electromagnetic field gets to the reception place, inducing the voltage in the reception antenna, as shown on Pic.2.1-c. This voltage has the same profile as the one on Pic.2.1-b, except it has much smaller amplitude. In the receiver, the amplification and detection are carried out first, resulting with the LF voltage on its output, that has the same profile as the one on Pic.2.1-a. This voltage is then transformed into sound by loudspeaker, that sound being exactly the same as the sound that acted upon the microphone. This, naturally, is the way it would be in ideal case. Back to reality, due to device imperfection as well as the influence of various disturbances, the sound being generated by the loudspeaker differs from the one that acts upon the microphone membrane. The block - diagram on Pic.2.1 (excluding the HF signal shape) is also applicable in case of radio transmission being carried out by frequency modulation. In that case frequency modulation is being carried out in the transmitter, under the effect of LF signal coming from the microphone, therefore HF signals on Pics.2.1-b and 2.1-c having constant amplitude, and their frequency being changed in accordance with the actual value of LF signal from the microphone. In fact, all types of radio transmission can be presented with Pic.2.1. First, the information being sent is always transformed into electrical signal through the appropriate converter. In telegraphy this converter is the pushbutton, in radiophony it's a microphone, in television engineering an image analysis
cathode ray tube (CRT) etc. Then, with this "electrical image" of information, the modulation is being done. The modulated HF signal is being transferred into antenna and
transmitted. On the reception place, the modulated signal from the reception antenna is
It treated the following topics;
Week 1
AM Transmitter
Lecture Note
Week 2
FM Transmitter
Week 3
TV Transmitter
Week 4
Electromagnetic Spectrum
Week 5
Electromagnetic radiation
Week 6
Radio frequency
Week 7
Microwave
Week 8
Antenna characteristics
Week 9
Very Low Frequency (VLF) / Low Frequency (LF) Antennas
Week 10
High Frequency (HF) Antennas
Week 11
Very High Frequency (VHF) / Ultra High Frequency (UHF) Antennas
Week 12
Introduction to Wave Propagation
Week 13
Wave Propagation Characteristics
Week 14
Atmospheric Effects on Wave Propagation
Week 15
Modes of Wave Propagation
It was designed for all Polytechnics that offer engineering course can also be used by other institutions such as University and college of education base on topic treated.
Practical Manual
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