Lesson 4 – Amplitude Modulation Terms 1.Modulation -is the process of altering a characteristic of the carrier in accordance with the instantaneous value of the intelligence signal. -amplitude, frequency, and phase 5.Modulation index -the term that describes the amount of amplitude change in an AM waveform -it is also called Coefficient of Modulation, Modulation Factor, or Modulation depth π= π¬π π½πππ − π½πππ = π¬π π½πππ + π½πππ 2.Demodulation Perfect Modulation: -is the process of recovering the intelligence signal from a modulated carrier signal π=π -is the act of extracting the original informationbearing signal from a modulated carrier wave Reasons for modulation π¬π = π¬π Undermodulation: π<π -minimizing interference -frequency assignment -making antenna sizes practical -multiplexing π¬π < π¬π Overmodulation: π>π π¬π > π¬π 3. Emission Designator code Bandwidth for AM -is associated with a frequency channel that gives information about the channel’s frequency bandwidth and the nature of the signal on that frequency π©πΎ = πππ Power Calculations π½ππͺ πΉπ΄πΊ π¬ππ π·π = = πΉ ππΉ 4. Amplitude Modulation (AM) -is the simplest way of superimposing the characteristic of the intelligence signal onto a carrier. -The AM signal is produced by varying the amplitude of the carrier signal in proportion to the instantaneous amplitude of the intelligence signal. -is a technique used in electronics communication, most commonly for the strength of the transmitted signal in relation to the information being sent ππ = π¬π πππππ π ππ =instantaneous value of the intelligence signal π·π³πΊπ© = π·πΌπΊπ© π½ππ³πΊπ© πΉπ΄πΊ π·π ππ = = πΉ π Total Transmitted Power π·π» = π·π + π·π³πΊπ© + π·πΌπΊπ© ππ π·π» = π·π [π + ] π Percent Power %π·π = π·π π·π» %π·πΊπ© = π·πΊπ© π·π» Peak Voltage of the Modulated Carrier π¬π» = π¬π √π + ππ π Peak Current of the Modulated Carrier π°π» = π°π √π + ππ π Effective Modulation index ππ = √πππ + πππ + πππ + β― + πππ Important Facts regarding AM -Among the three signals comprising AM, only the sidebands contain the information -The information found in the upper sideband is identical with the lower one. -At 100% modulation, 66.67% of the total power is contained in the carrier and only 33.33% is in the sidebands. -Thus, it is wasteful to transmit the carrier and is redundant to transmit both sidebands.
