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AM - FM lecture

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   f  fmfm  f   actual  max  max f  max AMPLITUDE MODULATION  - is a system of modulation in which theamplitude of the carrier is made proportional to the instantaneousamplitude of the modulating signal. - types of modulation wherein the amplitude of the carrier is being variedin accordance with the modulating signal. carrier   - radio frequency signal, intelligence signal modulating signal  – information signal, audio signal, modulating wave modulation index – the extent to which amplitude of the carrier wave isvaried by modulating wave  - modulation factor, coefficient of modulation % modulation  – it is a measure of the extent to which a carrier voltage isvaried by the intelligence.Forms of Amplitude Modulation1.Double Sideband, Full carrier (A3E) – this is the Am used for broadcasting.2.Double sideband, Suppressed carrier 3.Single sideband, Full carrier (H3E) – this could be used as acompatible AM broadcasting system with A3E receivers. Distortion isnot exceeding 5% is claimed for H3E transmission received by an A3E receiver.4.Single sideband, Suppressed carrier- (J3E) – this is the system sofar referred to as “SSB” in which the carrier is suppressed by at least45 dB in the transmitter.5.Independent sideband (B8E) – two independent sidebands, with acarrier that is most commonly attenuated or suppressed. It is usedfor HF point-to-point radio telephony, in which more than one channelis required. It can simultaneously convey a totally differenttransmission, to the extent that the upper sideband could be used for telephony while the lower sideband carrier telegraphy.6.Vestigial sideband – a system in which a vestige, i. e., a trace of theunwanted sideband, usually with a full carrier. It is used for videotransmission in all the world’s various TV systems to conservebandwidth.Frequency Modulation – a type of modulation wherein the frequency of the carrier is changed in accordance with the modulating signal.Frequency deviation – is the change in frequency that occurs in the carrier when it is acted on by a modulating signal.Modulation index – used to describe the depth of modulation achieved for a given amplitude and frequency modulating signal.Carrier swing – peak-to-peak frequency deviationm f   = _____ = ______where   or   deviation or frequency deviationfm is frequency of the modulating signal%m f   = _____x 100 maximum deviation = 75 KHzmaximum fm = 15 Khzdeviation ratio – the shift in the carrier frequency from the resting point compared to the amplitude of the modulating signaldeviation ratio = _____ for FM broadcast, deviation ratio = 5 for TV, deviation ratio = 1.67 carrier swing, cs = 2  unmodulated carrier : x = A sin (  t +  )where x – instantaneous value    - angular velocity A maximum deviation    - phasef  H  = fc +  f  f  L  = fc -  f  cs = fmax - fmin   f = fc ( 1 + KVmcos  mt) instantaneous frequency of FMfc – carrier frequency K – proportionality constantVmcos  mt – instantaneous modulating voltage at maximum valuee FM  = Ec sin (  c t + mf sin  m t) ----- FM equation  OSCBuffer Amp ModulatedAmpIntelligenceAmp ModulatorMixer AudioAmplifier  BalancedModulator  Sideband Filter RF Oscillator AM TRANSMITTER BLOCK DIAGRAMFILTER METHODAudio Amplifier BalancedModulator RFOscillator 90  Phase ShiftBalancedModulator 90  Phase Shift
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