Cape Electrical and Electronic Technology-Electromagnetic Waves

Cape Electrical and Electronic Technology

Cape Electrical and Electronic TechnologyTopic: Electromagnetic WavesBy: Tahvorn George & Charles,JAmplitude ModulationWhat is Amplitude Modulation?Amplitude Modulation is a technique that is used in electronic Communication, for the transmission of information via a carrier wave.A carrier wave is an electromagnetic wave that can be modulated. For example frequency, amplitude or phrase which is then used to transmit speech, music, images or other signals.In modulation the signal strength of the carrier wave is varied in proportion to the wave that is being transmitted.Forms of Amplitude ModulationDouble Sideband Amplitude Modulation( DSB-AM)Single Sideband Amplitude Modulation( SSB)ModulatorsDemodulatorsNarrowband Broadband Amplitude Modulation

Double Sideband Amplitude Modulation (DSB-AM)Double Sideband Amplitude Modulation also know as simply AM is one of the oldest method of modulation that depends on a carrier-signal( Marcani 1895), which only allows simple implementations by the use of nonlinear components. Also only long, medium and short wave broadcasts use AM or DSB-AM due to the minor need for receivers.Single Sideband Amplitude Modulation( SSB)In radio communications, Single Sideband Amplitude Modulation is an improvement of amplitude modulation by using transmitting power and bandwidth more efficiently. When a carrier wave undergoes amplitude modification it produces an output signal that has twice the bandwidth of the original signal. SSB bypasses all this by simply avoiding bandwidth doubling, hence the name Single Sideband Amplitude Modulation. It also avoids the power that is being wasted on a carrier in exchange for increase device difficulty and more problematic tuning at the receiver.ModulatorsA modulator is a device capable of conducting modulation. Modulation is the process of varying the properties of a periodic waveform( carrier signal), with a modulating signal that would naturally contain information that is to be transmitted.

DemodulatorsA Demodulator is a device capable of conducting demodulation which is simply the opposite of modulation.NarrowbandNarrowband refers to data communication and telecommunication tools, technologies and services that utilize a limited set of frequencies in the communication channel. This channel frequency is mostly considered to be flat.Broadband Amplitude ModulationThe word broadband in telecommunications is the wide bandwidth data transmission with the capability to transmit multiple signals and traffic types at the same time. Basically it is a signaling method that is used to handle a wide band of frequencies.Frequency ModulationIn telecommunications and signal processing, frequency modulation is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave.FM ModulatorFM signals may be generated using either direct or indirect frequency modulation.Direct Frequency Modulation can be attained by directly feeding the message into the input of aVCO( Voltage Controlled Oscillator).For Indirect Frequency Modulation to occur the message signal must be integrated in order to generate a phase-modulated signal( a signal that contains information such as an audio signal). Which is then used to modulate a crystal controlled oscillator, and the end result is then passed through a frequency multiplier to then give an FM signal. This Modulation causes narrowband FM to be generated which will later change to wideband FM later on.

FM DemodulatorAphase-locked loop a Detector/Demodulator is a device that can be used as an FM demodulator.Slope Detection conducts demodulation of an FM signal by the use of a tuned circuit which has its resonant frequency slightly offset from the carrier. As the frequency alternates the tuned circuit provides a changing amplitude of response, converting FM to AM.Super-Heterodyne Radio ReceiverSuper-Heterodyning is mixing two frequencies in order to achieve a lower resultant frequency.A Super-Heterodyne Radio Receiver is a circuit that incorporates a second oscillating frequency that mixes with the tuner frequency to eventually create a lower output frequency.AM & FM Systems in comparisonAM

FM

DefinitionAM - Amplitude ModulationFM - Frequency ModulationModulating differencesIn AM, a radio wave known as the "carrier" or "carrier wave" is modulated in amplitude by the signal that is to be transmitted. The frequency and phase remain the same.In FM, a radio wave known as the "carrier" or "carrier wave" is modulated in frequency by the signal that is to be transmitted. The amplitude and phase remain the same.Pros and consAM has poorer sound quality compared with FM, but is cheaper and can be transmitted over long distances. It has a lower bandwidth so it can have more stations available in any frequency range.FM is less prone to interference than AM. However, FM signals are impacted by physical barriers. FM has better sound quality due to higher bandwidthFrequency RangeAM radio ranges from 535 to 1705 KHz (OR) Up to 1200 bits per second.FM radio ranges in a higher spectrum from 88 to 108 MHz. (OR) 1200 to 2400 bits per second.

Bandwidth RequirementsTwice the highest modulating frequency. In AM radio broadcasting, the modulating signal has bandwidth of 15kHz, and hence the bandwidth of an amplitude-modulated signal is 30kHz.Twice the sum of the modulating signal frequency and the frequency deviation. If the frequency deviation is 75kHz and the modulating signal frequency is 15kHz, the bandwidth required is 180kHz.Zero crossing in modulated signalEquidistantNot equidistantNoiseAM is more susceptible to noise because noise affects amplitude, which is where information is "stored" in an AM signal.FM is less susceptible to noise because information in an FM signal is transmitted through varying the frequency, and not the amplitude.

Bibliographyhttp://www.g4prs.org.uk/http://fas.org/http://www.diffen.com/