25-04-2012, 11:33 AM
Various sources of Information & Signals, their Characteristics and Application
Satellite Communication Analog and Digital Signals.pptx (Size: 1.2 MB / Downloads: 43)
Signals
A signal is a changing value of electric voltage or current through a transmission medium.
Types
Periodic : Periodic signals repeat themselves after a certain period of time -- after they have cycled through one period, following periods don't contain any new information.
Aperiodic : Aperiodic signals don't repeat themselves, and therefore can contain information.
Analog Signals
Analog signals are electrical replicas of the original signals such as audio and video.
Baseband signals are those signals which occupy the lowest, or base, band of frequencies, in the frequency spectrum used by the telecommunications network.
A baseband signal may consist of one or more information signals. For example, a number of analog telephony signals may be combined into one baseband signal by the process known as frequency-division multiplexing (FDM).
Other common types of baseband signals are the multiplexed video and audio signals which originate in the TV studio.
In forming the multiplexed baseband signals, the information signals are modulated onto subcarriers. This modulation step must be distinguished from the modulation process, which places the multiplexed signal onto the microwave carrier for transmission to the satellite.
The Telephone Channel
Natural speech, including that of female and male voices, covers a frequency range of about 80 to 8000 Hz.
The range of 300 to 3400 Hz is accepted internationally as the standard for “telephone quality” speech, and this is termed the speech baseband.
Single-Sideband Telephony
All the information in the original telephone signal is contained in either of the two sidebands, and therefore, it is necessary to transmit only one of these.
For the lower sideband, the frequencies have been inverted, the highest baseband frequency being translated to the lowest transmission frequency and the lowest baseband frequency to the highest transmission frequency.
Conclusion
Overall , digital signals are better than analog signals because of various advantages
Application wise , digital signal processing has a wider gamut of uses compared to analog signal processing