Occupied Frequency Bandwidth & XdB Down method of Spectrum Analyzer

Chapter Occupied Frequency Bandwidth

Guide to Spectrum and Signal Analysis
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Guide to Spectrum and Signal Analysis

  • www.anritsu.com | 371) Averaging noise powerSince a spectrum analyzer has a peak hold circuit in front of the A/D converter, when noise is measured, the maximum power of the noise over the sampling period is displayed. Generally, noise is evaluated as the average value of the power against time. Consequently, it is necessary to use a sampling detector and to narrow the video bandwidth in order to average the noise power.2) Conversion for noise bandwidthSince the value of the measured noise power depends on the noise bandwidth used, correction for a 1 Hz noise bandwidth is required.3) Correction of average noise valueWith a spectrum analyzer, since the signal is logarithmically converted and envelope detected, the average value of the noise appears to be lower than the actual RMS noise value, so this value must also be corrected.Occupied Frequency BandwidthA common measurement carried out on radio transmitters is that of occupied frequency bandwidth (OBW). This measurement calculates the bandwidth containing the specified amount of the total integrated power of the displayed spectrum. However there are two different methods of calculation depending on the technique used to modulate the carrier.a) XdB Down methodThe occupied frequency bandwidth is defined as the bandwidth between the upper and lower frequency points at which the signal level is XdB below the peak carrier value (Figure 43).Figure 43