Spectrum Analyzer Measurements : Setting Sweep Parameters
Setting Sweep Parameters
Sweep parameters are set using the SWEEP Menu.
When the Continuous toggle is pressed, the instrument toggles between single sweep and continuous sweep. In single sweep setting, the instrument waits until SWEEP ONCE is pressed or another setting is selected.
Trace Points
The number of trace points is the number of display points in the trace generated from the measurement data. The default number of points is 501; the range is settable from 10 to 10,001 points.
Sweep Limitations
With some spectrum analyzers, the user has control over sweep time (the elapsed time of each sweep, also referred to as scan time). An analyzer cannot be swept arbitrarily fast while maintaining its specified accuracy, therefore, it will have a sweep rate limitation depending upon the resolution bandwidth, video bandwidth, and frequency range selected. The sweep rate is not usually chosen by the user, but is determined by the frequency range swept divided by the sweep time. The limitation on sweep rate comes from the settling or response time of the resolution and video bandwidth filters. If an analyzer is swept too quickly, the filters do not have time to respond, and the measurement is inaccurate. Under such conditions, the analyzer display tends to have a “smeared” look to it, with the spectral lines being wider than normal and shifted to the right and at a lower amplitude than is correct.
Anritsu Spectrum Master is designed to relieve the user from having to calculate the sweep speed or experiment to discover a sweep speed that yields accurate results. When changing the RBW and VBW, the sweep speed automatically changes to the fastest sweep speed that will yield accurate results. The sweep speed will be faster for a wide RBW or VBW and slower for a narrow RBW or VBW. Regardless of the minimum sweep time, the instrument will never sweep faster than the RBW and VBW settings will allow. The instrument is designed to ensure that no uncalibrated measurement conditions will occur.
Toggles between continuous sweep and single sweep. When the toggle is off, the instrument is in single sweep. In single sweep, the results of a sweep are displayed on the screen while the instrument awaits a trigger event to start a new sweep. The current state of the instrument is displayed in the status panel. With average/hold number (in TRACE menu) set to 1, or averaging is off, or no trace in trace average or hold, a single sweep is equivalent to a single measurement. A single sweep is taken after the trigger condition is met and the analyzer stops sweeping after that sweep has completed. To take one more sweep without resetting the average count, press the SWEEP ONCE button. This sweep control is also available in the status panel.
The restart function restarts the current sweep or measurement from the start frequency.
When sweep is set to single sweep, SWEEP ONCE triggers a single measurement sweep.
When sweep is set to single sweep and trace type is set to average, rolling average, rolling max hold, or rolling min hold, SWEEP TO N triggers N consecutive measurement sweeps, where N is the number of averages set in the TRACE menu. Each time the button is pressed, it will restart the average count, then sweep N times. This button has no function when the instrument is in continuous sweep.
Sets the number of data points per sweep and displayed in each trace. The current value of points is displayed parenthetically, next to the sweep time in the lower-right corner of the display. Using more points provides greater resolution. Using fewer points compacts the data and decreases the time required to access a trace. The minimum setting is 10 and the maximum setting is 10001.
The minimum capture time feature allows you to control the capture time by forcing the analyzer to take more data at each sampling point. Increasing the minimum capture time might increase the overall sweep time. Note that the actual capture time of the instrument is dependent on several variables and will not exactly match the MIN CAPTURE TIME user entry. The actual capture time is displayed in the status panel on the left side of the user interface. The capture time will always snap to the next highest possible value greater than the user entered minimum capture time. Therefore, setting the minimum capture time to 0 (zero) is the easiest way to set the actual capture time to the minimum allowable by the instrument. The maximum allowed capture time is based on the selected span and RBW. Generally, narrower RBW and span settings will increase the maximum possible capture time.
This feature is useful for measuring fast signals such as periodic pulsed or other modulated signals. In many cases, the capture time can be set long enough for the analyzer to capture the characteristics of the input signal that change over time without missing these events.