COMMUNICATION SYSTEMSBarriers to Human Communication,XLanguage,XDistanceElectronic CommunicationsThe transmission, reception, and processing of information using electronic circuits.Historymid-19th century V James Clark Maxwell studied electromagnetic wave and predicted that it can be propagated through free space.
1837 V Samuel Morse invented the telegraph.1876 V Alexander Graham Bell and Thomas A. Watson transmitted human conversation over a functional telephone system.
1888 V Heinrich Hertz radiated electromagnetic energy from a machine he called oscillator.1894 V Guglielmo Marconi was the first to accomplish wireless transmission.1908 V Lee DeForest invented the triode vacuum tube.1933 V Major Howard Armstrong invented frequency modulation.1948 V William Shockley, Walter Brattain and John Bardeen invented the transistor.Electromagnetic SpectrumElectromagnetic SpectrumThe entire range of frequency.FrequencyThe number of times an alternating current goes through its complete cycle per second is known as its frequency.
The international unit of measurement of frequency is hertz, abbreviated Hz. The English unit is cycles per second, abbreviated cps (1 Hz = 1 cps). It is rarely used.To simplify terminology, 1000 Hz is called kilohertz, abbreviated kHz, and 1000000 Hz is called a megahertz, abbreviated MHz.The vibration rate of sound waves in air may also use the term frequency. When middle C is played on a musical instrument, for example, an air disturbance with a frequency of 262 Hz is set up.
The lowest tone that can be heard by human beings is about 15 Hz. The highest audible, audio, or sonic tones are usually 12 to 22 kHz (22 kHz for youngsters, 12 kHz for seniors). A microphone is a device or transducer that can change sound waves in air to an equivalent-frequency ac in wires.Frequencies that produce sound waves audible to humans are said to be audio frequencies (AF). Frequencies that can be fed to antennas and will radiate electromagnetic and electrostatic waves in space are considered to be radio frequencies (RF). FCC Band Designations Frequency RangeDesignations30 V 300 HzELF (Extremely Low Frequencies)0.3 V 3 kHzVF (Voice Frequencies)3 V 30 kHzVLF (Very Low Frequencies)30 V 300 kHzLF (Low Frequencies)0.3 V 3 MHzMF (Medium Frequencies)3 V 30 MHzHF (High Frequencies)30 V 300 MHzVHF (Very High Frequencies)0.
3 V 3 GHzUHF (Ultra High Frequencies)3 V 30 GHzSHF (Super High Frequencies)30 V 300 GHzEHF (Extremely High Frequencies)0.3 V 3 THzInfrared 3 V 30 THzInfrared 30 V 300 THzInfrared 0.3 V 3 PHzVisible Light3 V 30 PHzUltraviolet 30 V 300 PHzX-rays0.3 V 3 EHzGamma rays3 V 30 EHzCosmic rays,’ FCC stands for Federal Communications Commission Wavelength, U The length that one cycle of an electromagnetic wave occupies in space, also, the distance between similar points in a repetitive wave.
wherek= velocity factor (equal to 1 in free space)c= velocity of light in free space= 299793000 m/s ,l 3 ,e 108 m/sf= [email protected] high frequencies, wavelength is too short and is usually expressed as Angstrom.Bandwidth and Information CapacityLimitations of Communication Systems,Xnoise,XbandwidthBandwidth, BWunit:Hz (Hertz)A portion of electromagnetic spectrum occupied by a system.Minimum range of frequencies required propagating the source information through the system.must be sufficiently large (wide) to pass all significant information frequencies.difference between the upper and lower limit frequencies.Information CapacityA measure of how much source information can be carried through the system in a given period of time.
Hartleys LawInformation Capacity N Bandwidth ,e timeSignal AnalysisFactors Affecting the Signal,XDistortion V signal alteration due to imperfect response of the system to the desired signal.,XInterference V contamination of extraneous signal usually man-made to a form similar to the desired signal.,XNoise V random, undesirable high frequency spikes.,XAttenuation V decrease in signal level.Types of Signals,XBaseband Signal,XModulated SignalTypes of Intelligence Transmitted,XAnalog ,XDigitalAdvantages of Digital Over Analog,Xeasier to multiplex,Ximproved noise immunity,Xbetter performance,Xeasier to interfaceDisadvantages of Digital Over Analog,Xneed for large (wide) bandwidth,Xneed for synchronization,Xneed for additional equipment,Xrestriction to wired topologyKinds of Signal Representations,XTime-Domain V amplitude vs. time,XFrequency-Domain V amplitude vs. frequencyClassifications of Signals:According to Period,XPeriodic V signals that keep on repeating at a regular interval.
,XNon-periodic V signals that keep on changing continuously and has no definite period.According to Form of Electrical Signal,XSinusoidal V has the form,XNon-sinusoidal V sum of series of sinusoidalAccording to Symmetry,XEven Symmetry V a periodic waveform that is symmetrical about the vertical (amplitude) axis ,XOdd Symmetry V a periodic waveform that is symmetrical about a line midway between the vertical and the negative horizontal axes.,XHalf-wave Symmetry V a periodic waveform is such that for the first half cycle (t=0 to t=T/2) repeats itself except with the opposite sign for the second half cycle (t=T/2 to t=T).Communication SystemThe totality of the mechanism that provides transfer of information from one point to another. Includes the components, equipment that is being utilized to execute the communication process.Basic Block Diagram of a Communication SystemTransmission ModesSimplex (SX),Xone-way-only, receive-only, transmit-onlyHalf-duplex (HDX),Xtwo-way-alternate, either-way, over-and-out systemFull-duplex (FDX),Xtwo-way simultaneous, both-way linesFull/full Duplex (F/FDX),Xtransmit and receive simultaneously but not necessarily between the same two locations.Echoplex,Xthe transmitted information will be sent back in a different form.
TransmittersA transmitter is a collection of electronic components and circuits designed to convert the information into a form suitable for transmission.Basic Block Diagram of a TransmitterComponents of a TransmitterModulator V accomplishes modulationOscillator V produces high frequency carrierAntenna V radiates the signal to the mediumTransmitter RequirementsFrequency Accuracy and StabilityThe accuracy and stability of the transmitter frequency are essentially fixed by the carrier oscillator. The exact requirements vary with the use to which the transmitter is put and are set by government regulatory bodies. Depending on the application, frequency accuracy and stability are specified in Hz or as a percentage of the operating frequency. Frequency AgilityFrequency agility refers to the ability to change operating frequency rapidly without extensive retuning.Spectral PurityAll transmitters produce spurious signals, they emit signals at frequencies other than those of the carrier and the sidebands required for the modulation.
Power OutputThere are a number of ways to measure power, depending on the modulation scheme.EfficiencyTransmitter efficiency is important for two reasons. One is energy conservation and heat dissipation.
Modulation FidelityA transmitter should be capable of modulating baseband frequency onto a carrier at any modulation level, to preserve the information signal as much as possibleFCC Emission DesignationsFirst SymbolSecond SymbolThird SymbolA – Amplitude Modulation, Double Sideband Full CarrierB – Independent SidebandC – Vestigial SidebandF – Frequency ModulationG – Phase ModulationH – Single Sideband Full CarrierJ – Single Sideband Suppressed CarrierK – Pulse Amplitude ModulationL – Pulse Width (Duration) ModulationM – Pulse Position ModulationN – Unmodulated CarrierP – Unmodulated Pulses R – Single Sideband Reduced Carrier0 – Absence of Any Modulation1 – Digitally Keyed Carrier2 – Digitally Keyed Tone3 – Analog (voice, music)7 – Multiple Digital Channel8 – Multiple Analog Channel9 – Channels with analog and digitalA – Telegraphy (manual)B – Telegraphy (automatic)C – FacsimileD – Telemetry (Data)E – Telephony (Sound Broadcasting)F – Television (video signal)N – No InformationW – Combination of aboveFirst Symbol (letter) V type of modulation of the main carrierSecond Symbol (number) V nature of modulationThird Symbol (letter) V type of information being transmittedChannelIt is the medium by which the electronic signal is sent from one point to another.Unguided Media,Xor wireless communication, transport electromagnetic waves without using a physical conductor.Kinds of Wave PropagationGround WaveSky WaveSpace WaveGuided Media,Xthose that provide a conduit from one device to another.
Copper (Twisted-pair Cable, Coaxial Cable, Parallel Line)Fiber Optic CableWaveguideReceiversReceivers are collection of electronic components and circuits that accepts the transmitted message back into a form understandable by human.Basic Block Diagram of a ReceiverComponents of a Receiver Antenna V picks up the signal from free spaceOscillator V produces high frequency carrierDemodulator V extracts the information from the modulated signalNoiseAny unwanted form of energy tending to interfere with the proper and easy reception and reproduction of wanted signals.Any undesired voltage or current that ultimately ends up appearing in the receiver output.Results of Noise,Xhiss/static,Xsnow/confetti,Xbit errors,Xsignal lossKinds of NoiseCorrelated Noise V mutually related to the signal and cannot be present in a circuit unless there is an input signal and is produced by nonlinear amplification. No signal, no noise!Harmonic Distortion V unwanted harmonics of a signal are produced.Intermodulation Distortion V the generation of unwanted sum and difference frequencies (cross products) when two or more signals are amplified in a nonlinear device.Uncorrelated Noise V present regardless of whether there is a signal present or not.
Kind of Uncorrelated NoiseExternal Noise V generated outside the device or circuit.Atmospheric Noise V naturally occurring electrical disturbances that originate within the earths atmosphere.Extraterrestrial Noise V consists of electrical signals that originate from outside Earths atmosphere.
Solar Noise V directly from the suns heat.Cosmic Noise V from the stars.Man-made Noise V produced by manufactured equipment, such as automotive ignition systems, electric motors and generators.
Internal Noise V generated within a device or circuit. Shot Noise V caused by the random arrival of carriers (holes and electrons) at the output element of an electronic device.Transit-Time Noise V shows up as a kind of random noise within the device and is directly proportional to the frequency of operation.Thermal Noise V associated with the rapid and random movement of electrons within a conductor due to thermal agitation.Noise ComputationsNoise Powerthe average noise power is proportional to the absolute temperature of the conductor and to the bandwidth or spectrum of the thermal noise.wherePN= noise power (W)T= Temperature of the conductor (K)B= bandwidth of the noise spectrum (Hz)k= Boltzmanns Constant = Noise VoltagewhereVN= rms noise voltageT= Temperature of the conductor (K)B= bandwidth of the noise spectrum (Hz)k= Boltzmanns Constant = R= equivalent resistance generating the noisefor combinations of resistancesSeries Parallel Power Spectrum Density or Noise Density,Xaverage noise power per Hertz of bandwidth,Xa figure that determines the amount of noise contained in a specified bandwidth.Signal-to-Noise Ratio,Xa relative measure of the desired signal power to the noise power.
In decibel form:wherePS= signal powerPN= noise powerVS= signal voltage VN= noise voltage Noise FactorwhereSi= input signal powerNi= input noise powerSo= output signal powerNo= output noise powerNoise Figurefor ideal noiseless networkfor a network that contributes noiseReactance Noise Effects,Xthe significant effect of reactive circuits on noise is their limitation on frequency response.,Xthe equivalent bandwidth to be used in noise calculations with reactive circuits iswhereB3dB= half power bandwidth Equivalent Noise TemperaturewhereTeq= equivalent noise temperature To= reference absolute temperature = 290 KF= noise factorNoise Due to Amplifiers in CascadeFriiss FormulaOver-all noise factor of n stagesOver-all noise temperature of n stagesOver-all noise resistancewhereA= voltage gain (ratio)G= power gain (ratio)Shot Noise,Xa form of internal noise, which is due to the random variations in current flow in active devices such as tubes, transistors and diodes.WhereiN= rms noise currentq= charge of an electron = B= bandwidth over which the noise is observed I= dc bias current in the deviceProblems:1.What is the shot noise current for a diode with a forward bias of 1.15 mA over a 50-kHz bandwidth?2.An amplifier operating over the frequency range of 455 kHz to 460 kHz has a 200 kC input resistance.
What is the rms noise voltage at the input to the amplifier if the ambient temperature is 17XC?3.Two resistors, 5 kC and 20 kC are at 27XC. Calculate the thermal noise power and voltage for a 10 kHz bandwidth. a) for each resistor, b) for their series combination, and c) for their parallel combination.4.Three matched amplifiers are available to amplify a low level signal, they have the following characteristics.
AmplifierPower GainNoise FactorA6 dB1.5B12 dB2C20 dB4The amplifiers are to be connected in cascade. Calculate the lowest overall noise factor obtainable noting the order in which the amplifiers must be connected.