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BASIC TELECOMMUNICATIONS

BASIC TELECOMMUNICATIONS . RF (Radio Frequency) technology Part ll. BASIC TELECOMMUNICATIONS . The three key parameters of a periodic waveform are its amplitude , its phase and its frequency .

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BASIC TELECOMMUNICATIONS

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  1. BASIC TELECOMMUNICATIONS RF (Radio Frequency) technology Part ll

  2. BASIC TELECOMMUNICATIONS • The three key parameters of a periodic waveform are its amplitude, its phaseand its frequency. • Any of these properties can be modified in accordance with a low frequency signal to obtain the modulated signal. • Typically a high-frequency sinusoid (sine wave) waveform is used as carrier signal, but a square wave pulse train may also be used.

  3. BASIC TELECOMMUNICATIONS Amplitude is the peak-to-peak change between peak (highest amplitude value) and trough (lowest amplitude value, which can be negative)

  4. BASIC TELECOMMUNICATIONS Phaseis the initial angle of a sinusoidal (sine wave) function at its origin and is sometimes called phase offset. Another usage is the fraction of the wave cycle which has elapsed relative to the origin

  5. BASIC TELECOMMUNICATIONS Frequencyis the number of occurrences of a repeating event per unit time or the rate at which electrical current alternates, usually measured to one second, in the U.S. an electrical outlet is rated at 60Hz (60 alterations in 1 second

  6. BASIC TELECOMMUNICATIONS • In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted • Modulation of a sine waveform is used to transform a baseband message signal into a passband signal, for example low-frequency audio signal into a radio-frequency signal (RF signal), at the destination point the signal has to be demodulated

  7. BASIC TELECOMMUNICATIONS • A device that can both modulate and demodulate a signal is called a modem Digital modulationis to transfer a digital bit stream over an analog bandpass channel, for example over the public switched telephone network (where a bandpassfilter limits the frequency range to between 300 and 3400 Hz), or over a limited radio frequency band • Remember that the voice frequency range for a POTS line is approximately 3000Hz (300 to 3400Hz)

  8. BASIC TELECOMMUNICATIONS Analog modulationis to transfer an analog baseband (or lowpass) signal, for example an audio signal or TV signal, over an analog bandpass channel at a different frequency, for example over a limited radio frequency band or a cable TV network channel

  9. BASIC TELECOMMUNICATIONS • Analog and digital modulation facilitate frequency division multiplexing (FDM), where several low pass information signals are transferred simultaneously over the same shared physical medium, using separate passband channels (several different carrier frequencies)

  10. BASIC TELECOMMUNICATIONS Bandpassis an adjective that describes a type of filter or filtering process; it is frequently confused with passband, which refers to the actual portion of affected spectrum • A dual bandpass filter has two passbands. • A bandpass signal is a signal containing a band of frequencies away from zero frequency, such as a signal that comes out of a bandpass filter

  11. BASIC TELECOMMUNICATIONS Here is a side by side comparison of an analog waveform and digital waveform, as you can see analog waves are measured in Hertz and digital wave forms are measured in Bits per Second or baud rate How many bits equals a byte?

  12. BASIC TELECOMMUNICATIONS A digital signalis a physical signal that is a representation of a sequence of discrete values (a quantified discrete-time signal), for example of an arbitrary bit stream, or of a digitized (sampled and analog-to-digital converted) analog signal • In digital systems, a waveform that switches between two voltage levels representing the two states of a Boolean value (0 and 1) is referred to as a digital signal, even though it is an analog voltage waveform, since it is interpreted in terms of only two levels

  13. BASIC TELECOMMUNICATIONS An analog signalis any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity • Electrically, the property most commonly used is voltage followed closely by frequency, current, and charge, Any information may be conveyed by an analog signal

  14. BASIC TELECOMMUNICATIONS • The primary disadvantage of analog signaling is that any system has noise – i.e., random unwanted variation, as the signal is copied and re-copied, or transmitted over long distances, these apparently random variations become dominant • Electrically, these losses can be diminished by shielding, good connections, and several cable types such as coaxial or twisted pair, UTP, ScTP or STP

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