2-3 Making Spectrum Analyzer Measurements Spectrum Analyzer
2-2 PN: 10580-00349 Rev. M Spectrum Analyzer MG
Both positive and negative offset values are allowed. Negative offsets can be useful for seeing
differences from expected values. Enter a negative offset of the expected value, and the
received antenna frequency should display in the 0 Hz range.
When enabled, Offset is displayed at the bottom of the screen (Figure 2-40), and the
Center Freq, Start Freq, and Stop Freq submenu keys indicate that a frequency offset has been
turned on by adding the word Offset before Center, Start, and Stop. For menu examples, see
Figure 2-36 on page 2-50 and Figure 2-38 on page 2-53.
To remove a frequency offset, set the Freq Offset to 0Hz.
Setting Bandwidth Parameters
Both resolution bandwidth (RBW) and video bandwidth (VBW) can be coupled to the
frequency span automatically or manually set. When set to Auto RBW, RBW adjusts
automatically in proportion to the frequency span. The default ratio of the span width to the
resolution bandwidth is 100:1, and can be changed as follows:
1. Press the BW main menu key.
2. Press the Span/RBW submenu key. The current Span/RBW ratio is shown as part of the
submenu key label. Change the value using the keypad, the directional arrows, or the
rotary knob and then press Enter.
When auto-coupling between the span and RBW is selected (the Auto RBW submenu key is
toggled to “On”), this is indicated on the left side of the display with the RBW label and
underneath it one to three digits followed by the frequency units; this represents the
resolution bandwidth value. If manual RBW is selected (the Auto RBW submenu key is
toggled “Off”), the label and value turn red and a ‘#’ symbol is shown in front of the RBW
label. Adjust resolution bandwidth independently of the span. If an unavailable resolution
bandwidth is entered, then the instrument selects the next higher resolution bandwidth. If a
value greater than the widest RBW is entered, then the widest RBW will be selected.
VBW can be set two ways – manually or by auto coupling. Auto coupling of the VBW links the
video bandwidth to the resolution bandwidth, so that VBW varies in proportion to RBW. Auto
coupling is indicated on the left side of the display with the VBW label and underneath it one
to three digits and the frequency units; this represents the video bandwidth value. If manual
VBW coupling is selected, the label and value turn red and the “#” symbol is shown in front of
VBW on the left side of the display. Adjust video bandwidth independently of the RBW. If a
non-existent video bandwidth is entered, then the instrument will select the next higher
video bandwidth. If a value greater than the widest VBW is entered, then the widest VBW
will be selected.
The ratio of the resolution bandwidth to the video bandwidth can be changed by pressing the
BW main menu key, the RBW/VBW submenu key, and then using the keypad, the directional
arrows, or the rotary knob to set the ratio. By default, the RBW/VBW ratio is set to 3.
The current value of the ratio is shown as part of the submenu key label.
1. Press the BW main menu key.
2. Press the RBW/VBW submenu key. The current RBW/VBW ratio is shown as part of the
submenu key label. Enter the desired value.
The RBW range varies with instrument features. Refer to the RBW submenu key description
in “BW (Bandwidth) Menu” on page 2-60, and check your Technical Data Sheet for the RBW
range of your instrument.