Embedded Files
Students Learn About:
telecommunications including:
– analogue and digital systems
– modulation, demodulation
– radio transmission (AM, FM, digital)
– digital television transmission and display media such as plasma, LED, LCD, 3D
– telephony: fixed and mobile
– transmission media
– cable
– wireless
– infrared
– microwave
– fibre-optic
satellite communication systems, geostationary, low orbit satellite and GPS
digital technology (AND, NAND, NOR, OR GATES)
Students Learn To:
describe the basic concepts and application of modulation/ demodulation in telecommunications
describe the types and methods of radio and digital television transmission and reception systems in telecommunications
contrast the differences in fixed and mobile telephony systems in telecommunications
distinguish the communication bands in the electromagnetic spectrum
contrast the differences in transmission media
describe the basic principles of satellite
communication systemsexplain elementary digital logic
- telecommunications including:
analogue and digital systems
analogue and digital systems
Analogue signals:
Analogue signals are naturally occurring forms of information transfer such as speech and music and are continuously variable in time and amplitude.
Analogue transmission uses electrical impulses to emulate the audio waveform of sound.- Advantages of analogue signals:
uses less bandwidth than digital transmission
more accurate transmission of signals.
- Disadvantages of analogue signals:
signals are affected by electrical noise and interference from trees, hills etc.
more difficult to multiplex (which is the simultaneous transmission of several messages along a single channel of communication)
less secure than digital transmission
analogue signals cannot be compressed as much as digital signals.
Digital signals:
Digital signals use discrete (or discontinuous) values to represent information to be transferred whereas analogue systems use a continuous range of values to represent information.
- Advantages of digital signals:
digital signals are less affected by 'electrical noise' and interference
error detection and correction is possible
more reliable, more secure and less expensive
easier to multiplex
easily interfaced with other digital systems
can be compressed so more information can fit in the signal (clearer image)
can transmit multiple messages within a single frequency (multicasting).
- Disadvantages of digital signals:
the transmitter and receiver must synchronise accurately for the information to make sense
digital signals are subject to sampling errors
digital signals require more bandwidth to transmit the same information.
modulation, demodulation
modulation, demodulation
Modulation of signals
In telecommunications, modulation is the process of varying a waveform to more efficiently convey a message. Generally a high frequency carrier wave is modulated in such a way that it mirrors the information wave. Three parts of the carrier wave: the amplitude, frequency and phase, can be modified by the low frequency information signal to produce the modulated wave. Both analogue and digital signals can be modulated.
Reasons for modulating signals include:
Multiplexing which is the simultaneous transmission of several signals along a single path without any loss of identity of the original signal
higher carrier frequencies allow for smaller, more directional antennas
less loss and dispersion occurs in higher frequency carrier waves.
Amplitude modulation (AM) changes the amplitude of the high frequency carrier wave carrier wave by an amount proportional to the amplitude of the information wave.
Frequency modulation (FM) changes the frequency of the high frequency carrier wave carrier wave by an amount proportional to the amplitude of the information wave.
Frequency-shift keying (FSK), amplitude-shift keying (ASK) and phase-shift keying (PSK) are modulation methods for digital signals by discrete changes in the frequency, amplitude and phase respectively of the carrier waves.
AM and ASK are more susceptible than FM and FSK to interference because electrical interference affects the amplitude of a wave more than the frequency.
FM can generally carry more information because of its higher frequency.
digital television transmission and display media such as plasma, LED, LCD, 3D
digital television transmission and display media such as plasma, LED, LCD, 3D
telephony: fixed and mobile
telephony: fixed and mobile
transmission media
transmission media
Concept Check
Concept Check
Complete the table below, to a level that is usebale as quick notes
cable
cable
Define
Define
Positive
Positive
Negative
Negative
wireless
wireless
Define
Define
Positive
Positive
Negative
Negative
infrared
infrared
Define
Define
Positive
Positive
Negative
Negative
microwave
microwave
Define
Define
Positive
Positive
Negative
Negative
fibre-optic
fibre-optic
Define
Define
Positive
Positive
Negative
Negative
- satellite communication systems, geostationary, low orbit satellite and GPS
Satellite communications provide long distance transmission of voice, data, television as well as weather, navigation and scientific research data about the Earth. Communications satellites are microwave links which simply use an orbiting tower. Satellites are either geostationery (or geosynchronous or synchronous) or asynchronous:
Satellite communications provide long distance transmission of voice, data, television as well as weather, navigation and scientific research data about the Earth. Communications satellites are microwave links which simply use an orbiting tower. Satellites are either geostationery (or geosynchronous or synchronous) or asynchronous:
Geostationary satellites
Geostationary satellites
Geostationary satellites are fixed in a set orbit above the equator at an altitude of about 36,000 km and are used for communications, television and weather data because they can provide a wide view of the Earth.
MEO and GPS
MEO and GPS
Medium earth orbit satellites (MEO) orbit between 2000 km and the geostationery orbit of about 36,000 km and are commonly used for navigation such as Global Positioning System (GPS) which uses a constellation of between 24 and 34 MEO satellites orbiting at about
20.000 km.GPS receivers require 4 satellites to accurately locate a position - 3 satellites give 3 intersection points because of the inaccuracy of the GPS clock (an error of 0.001 seconds produces a positional error of about 300 km!).
The 4th satellite uses it's atomic clock to correct and record the inaccuracy of the GPS clock and accurately locates the position which is the centre of the 3 intersection points.
LEO and ISS
LEO and ISS
Asynchronous satellites include the following:
Low earth orbit satellites (LEO) orbit from 160 to 2000 km and the International Space Station is in a LEO of about 340 km. A majority of satellites are LEO because they require less energy to place them in orbit and less powerful amplifiers for successful communication. However a network of satellites is required for continuous coverage. Polar LEO satellites orbit at 90° to the equator and are used for worldwide voice and data communications using handheld satellite phones.
- digital technology (AND, NAND, NOR, OR GATES)
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