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AM Spectrum XT: Spectrogram

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Spectrogram –
Historical Performance of the Spectrum

The Spectrogram graph provides another way to present the data as shown on the Real-Time FFT chart.  It displays the changes in the spectrum over a period of time and identifies any shift in frequency use along with the duration of such shifts.  The X-axis shows the frequency range covered by the selected radio band and the Y-axis shows, in real time, the number of sweeps the spectrum adapter scans the RF spectrum.   It displays the historical performance of the spectrum over the last few minutes and can maintain, for a short while a record of events, that a user could potentially miss in other graphs. It is also useful for picking out patterns in the detected data transmissions and determining if a signal is background noise or an interference source

Each time the AirMagnet spectrum adapter scans the RF spectrum, it is called a sweep cycle.  This graph adds one color-coded line to the base of the graph with each sweep cycle.  This begins to build up data as new data appears.  By default, the new line appears at the bottom and pushes up the old data.  This graph will display up to 250 sweep cycles.  After this, the oldest sweep cycle is discarded as a new cycle appears.  The color legend in the upper right corner of the graph indicates the minimum power values which are shown in blue and the maximum power values which are shown in red.

Chart Configuration

Display Settings

  • View Type: allows the configuration of the type of data to be displayed on the Spectrogram
    • Current: Plots current power readings on the Spectrogram.
    • Average:  Plots the Average power on the Spectrogram for the last five sweeps..
    • Maximum (default):  Plots maximum power readings on the Spectrogram.
    • Duty Cycle: Plots duty cycle readings (from the Duty Cycle graph) on the Spectrogram.
  • Scroll Type:  Allows the configuration of direction the graph scrolls.
  • Y-Axis Label Type:
    • System Time (default): Displays system time.
    • Sweep Cycle: Displays the number of scans of the Spectrogram.
    • Relative Time:  Displays the time relative to the start of either the Spectrum XT or a live capture session (which is 00:00:00 by default). 

Color Scale

  • Maximum: specifies the maximum value for the coloring scale
  • Minimum:  specifies the minimum value for the coloring scale

Span Settings:

  • Start Frequency: Specifies the start frequency (GHz) for the graph.
  • Stop Frequency:  Specifies the end frequency (GHz) for the graph.