Keysight N9030A Measurement Manual

Also see for x series: Manual Installation note Measurement guide Measurement guide Measurement guide

Contents

Keysight N9030A Measurement Manual Manual pdf 26 page image

26ConceptsAM ConceptsAM ConceptsFigure 2-1 AM waveformIn AM (Amplitude Modulation), the instantaneous amplitude of the modulatedcarrier signal changed in proportion to the instantaneous amplitude of theinformation signal.Figure 2-2 Calculation AM index in time and frequency domainThe modulation index "m" represents the amount of the modulation or the degree towhich the information signal modulates the carrier signal. The index for an AMsignal can be calculated from the amplitudes of the carrier and either of thesidebands by the equation:Equation 2-1For 100% modulation, the modulation index is 1.0, and the amplitude of eachsideband will be one-half of the carrier amplitude expressed in voltage. On a decibelpower scale, each sideband will thus be 6 dB less than the carrier, or one-fourth thepower of the carrier. Since the carrier power does not change with amplitudemodulation, the total power in the 100% modulated wave is 50% higher than in theunmodulated carrier. The relationship between m and the logarithmic display can beexpressed as:m = E max E c–E c----------------------- = E max E min–E max E min+---------------------------- = E USB E LSB+E c----------------------------- = 2E SBE c-----------