Spectrum Monitor Description

Last updated: January 16, 2009

How is the spectrum monitor (SMON) used?

The Spectrum Monitor (SMON) can be used to locate, identify and measure transmitted signals from a device under test. The Spectrum Monitor can be used while a call is in progress.

The Spectrum Monitor is intended to be used for indication only. The Spectrum Monitor does not have the same level accuracy specifications as other measurements provided by the test set, and should therefore not be used when parametric accuracy is required (for example, calibration of a mobile). It is recommended that you use the other wireless format-specific measurements when you require accurate parametric measurements.

From the test set's front panel, the Spectrum Monitor can be accessed by pressing the Instrument Selection key, then selecting Spectrum Monitor . If you require more details on manual operation of the Spectrum Monitor, see How Do I Use the Spectrum Monitor? .

The Spectrum Monitor has the following two modes of operation:

Swept mode, in which the X axis represents frequency , and the Y axis represents absolute amplitude.
Zero span mode, in which the X axis represents time and the Y axis represents absolute amplitude.

You can use the markers on the Spectrum Monitor's graphical display to set the expected frequency and power levels that are used by the test or lab application for parametric measurements.

The center frequency used by the Spectrum Monitor is initially set at the expected frequency maintained by the test set's base station emulator. The expected frequency range is 292.5 MHz to 2700 MHz.

The range of frequencies which the spectrum monitor is calibrated to measure is determined by the range of traffic band frequencies supported by the specific test or lab application that is currently running. For example, if you are using the GSM Test Application, any of the frequencies used by the GSM traffic bands are available for you to monitor accurately. You can view signals which fall outside of any of the frequencies used by GSM, but the Spectrum Monitor will not be calibrated.

Detection Method

Frequency binning is used when the Spectrum Monitor divides the frequency span by the number of display points such that each bin contains a segment of the frequency span. Within each frequency bin, a single value representing each frequency bin is displayed on the test set's screen. The algorithm used to find the value that represents each frequency bin is determined by the detection method. There are three detection methods available in the test set's Spectrum Monitor:

Peak Detection
The largest spectral component in the frequency bin is used to represent each bin.
Sample Detection
The last spectral component in the frequency bin is used to represent each bin.
RMS Detection
The sum of the power across the frequency bin is used to represent each bin.

The command to change the detection method is SETup:SMONitor:DETector[:TYPE] .

Resolution Bandwidth and Frequency Span

The resolution bandwidth can be used to resolve two or more closely spaced signals as long as the resolution bandwidth is less than the difference between the spectral components. A resolution bandwidth greater than or equal to the signal bandwidth can be used to measure the total power of a signal.

Refer to Frequency Span, Resolution Bandwidth and Dynamic Range below. When the Resolution Bandwidth Coupling State is OFF, the Frequency Span and the Resolution Bandwidth can be set to any value in their respective columns, and Resolution Bandwidth setting determines the Displayed Dynamic Range. When the Resolution Bandwidth Coupling State is On, the Resolution Bandwidth and Displayed Dynamic Range settings are coupled with the Frequency Span setting. For example, if the Frequency Span is 100 MHz, the test set automatically sets the Resolution Bandwidth to 5 MHz and the Displayed Dynamic Range to 55 dB.

Frequency Span, Resolution Bandwidth and Dynamic Range
Frequency Span	Resolution Bandwidth	Displayed Dynamic Range
100 MHz	5 MHz	50 dB
80 MHz	1 MHz	55 dB
40 MHz	300 kHz	60 dB
20 MHz	100 kHz	65 dB
12 MHz	100 kHz	65 dB
10 MHz	100 kHz	65 dB
5 MHz	30 kHz	70 dB
4 MHz	30 kHz	70 dB
2.5 MHz	10 kHz	75 dB
1.25 MHz	3 kHz	80 dB
500 kHz	1 kHz	80 dB
125 kHz	300 Hz	80 dB
0 Hz (zero span mode)	100 kHz	65 dB
	300 kHz	60 dB
	1 MHz	55 dB

The command to set the Resolution Bandwidth Coupling State is SETup:SMONitor:BANDwidth|BWIDth:AUTO .

The command to set the Resolution Bandwidth is SETup:SMONitor:BANDwidth|BWIDth:MANual , and the command to set the Frequency Span is SETup:SMONitor:FREQuency:SPAN .

Single or Multi-Measurements

The Spectrum Monitor can return either single or averaged results.

If you set the averaging state OFF then the trace represents a single measurement sweep.
If you set the averaging state ON, and the averaging count number to a value greater than one, then the trace represents the rolling average of the specified number of sweeps.

Input Signal Requirements

The Spectrum Monitor will complete and meet its accuracy specifications under the following input signal conditions.

The signal is within 40 dB of the reference level.
The measurement frequency is within the traffic band frequencies supported by the specific lab or test application that is currently running, and the expected frequency is tuned to the carrier.

Trigger Source

Triggering choices available for the Spectrum Monitor are Immediate, Protocol, RF Rise, and External.

For more information on measurement triggering, refer to Triggering of Measurements .

Calibrating the Spectrum Monitor

See Spectrum Monitor Calibration .