To set the sweep parameters, press the Shift key followed by the Sweep (3) key.

When this submenu key is pressed, the instrument toggles between single sweep and continuous sweep. In single sweep mode, the instrument waits until the Sweep Once submenu key is pressed or another triggering mode is selected.

Several sweep modes are available on the instrument. Press the Sweep Mode submenu keys to select between Fast (default), Performance, No FFT, or Burst Detect. Note that Burst Detect is supported on MS2720T and MT8220T instrument models only.

Improperly installed cellular boosters can sometimes produce burst interference. By using Burst Detect mode when available, a narrow-pulsed or burst signal is easily seen in spectrum analyzer mode, capturing emitters as narrow as 200 μs. Burst Detect works in a maximum span of 15 MHz.

Figure: Example of Burst Detect Sweep Mode shows two traces. The yellow trace is the live trace with Burst Detect sweep mode, while the green trace is a max hold trace. There is not much difference between the two traces, thus, max hold is no longer needed in order to see narrow pulsed signals.

The Show Help submenu key displays a table detailing the trade‑off between sweep speed and performance of the sweep mode options.

To select a specific type of triggering in zero span, press the Triggering submenu key followed by the Source submenu key. Selections are:

Zero Span IF Output (Standard or Option 89): Zero Span IF Output provides an IF signal that is nominally at 140 MHz out of a BNC female connector labeled IF Out 140 MHz or IF Out (option) 140 MHz.

You can select Normal or any one of four fixed IF bandwidths of 7 MHz, 10 MHz, 16 MHz, or 32 MHz. In Normal, the bandwidth is set by the spectrum analyzer RBW selection (BW > Zero Span RBW). When Normal is selected, the IF bandwidth is influenced by the selection of RBW filters, although the digital RBW filters themselves are not employed.

Zero Span IF output effectively uses the spectrum analyzer as a receiver front‑end, converting the input signal at the spectrum analyzer RF In connector to a signal centered at 140 MHz out of the IF Out 140 MHz connector. You can then process the IF signal in a way that meets your needs. That may mean using an A‑to‑D converter or some other signal processing method. An anti‑aliasing filter can be employed in the signal processing to reduce the effect of noise and spurious signals. A filter centered on 140 MHz with a bandwidth slightly wider than 32 MHz is also advised to eliminate any undesired out‑of‑band signals on the IF output. In particular, signals at 100 MHz and its harmonics (that would be eliminated by the filter) are on the IF output.

When IF output is turned on by setting the instrument to zero span, then pressing the Zero Span submenu key a second time displays the Zero Span IF Bandwidth menu (Figure: Zero Span IF Bandwidth Selection Menu). The selectable bandwidth values may differ among instrument types. This figure is typical.

The Normal IF BW choice selects a bandwidth that uses analog bandpass filters in the normal RBW chain. By changing the RBW, different filter bandwidths are selected.

The spectrum analyzer has several mixer bands. Depending on the operating frequency, the local oscillator may be above or below the input frequency. When the local oscillator frequency is below the input frequency, an increase in the input frequency results in an increase in the IF output frequency. When the local oscillator is above the input frequency, an increase in the input frequency moves it closer to the local oscillator frequency and the IF output frequency consequently decreases. The following tables show the bands and indicates where the LO frequency is, in relation to the RF frequency.

You need to take frequency inversion into account when processing the IF signal. Assuming that the IF has been processed to yield I and Q data, inversion is easily done by swapping I and Q.

A residual frequency offset of the IF may exist compared to the RF due to the resolution of the first and second local oscillators, as well as the calibration of the IF filters. This offset is usually on the order of several kHz, but may be up to 10 kHz or so if the narrowest IF filters are selected. To determine the residual offset, you need a second spectrum analyzer or a frequency counter.

To set up the instrument for gated sweep measurements, press the Gated Sweep Setup key under the Sweep menu. The instrument screen changes to a dual graph view that makes it easier to set up the Gate Length and Gate Delay using the time domain/zero span view in the bottom graph while simultaneously viewing the signal spectrum in the top graph. The Gate Length is represented by the width of the displayed blue dashed rectangle. See Figure: Gated Sweep Example - External Gate Source. This is useful for measuring signals in the time domain such as pulsed RF, time multiplexed, or burst modulated signals.

The Gate Source selected determines the trigger source from which the gate is controlled. Not all instrument models and options support all triggering selections. (Refer to Gate Setup Menu.) Gate Polarity controls the triggering edge of the selected triggering source.

The Gate View Settings key brings up a submenu where you can independently set the Zero Span RBW, Zero Span VBW, and Zero Span Time. Zero Span Time controls the time scale of the Gate View graph.

After the gate has been set up, you can apply gating to the spectrum by setting Gated Sweep to On. Gating continues to be applied when you press Back and access other measurements and functions of the spectrum analyzer until either: (1) Gated Sweep is explicitly set to Off or (2) the Span setting is changed to Zero Span. Gated Sweep is not allowed in Zero Span mode.