890
BW
More Information
When the Res BW is manually selected, it may be returned to the coupled state by pressing the Res BW
key until Auto is underlined. This may also be done by pressing Auto Couple or by performing a Preset.
When Res BW is set to Auto, the bandwidth selected depends on the Filter Type (see “Filter Type”
below).
Only certain discrete resolution bandwidths are available. The available bandwidths are dependent on the
Filter Type or the EMC Standard. If an unavailable bandwidth is entered with the numeric keypad, the
closest available bandwidth is selected.
The zero-span case deserves some mention, because RBW is coupled to Span when in a swept
(non-zero) span and in zero span there is normally no meaningful RBW coupling in Zero Span.
However, when a MIL or CISPR EMC Standard is selected, there IS a meaningful coupling for RBW in
Zero Span – in fact, it is coupled to Center Frequency, in order to make measurements according to the
EMI specifications.
The annotation under RBW in the bottom left of the screen shows the type of filter or bandwidth that is
being used. The following examples illustrate this:
–3 dB (Normal) filter BW:Res BW 300 Hz
Dependencies When in Zero Span with no EMI Standard selected, there is no Auto setting
for Res BW. The Auto/Man line on the Res BW key disappears in this case,
and if the SCPI command [:SENSe]:BWID[:RESolution]:AUTO ON is
sent, it generates an error.
Couplings Res BW is normally coupled to Span; if Res BW is set to Auto, as the Span
decreases, so will the Res BW. Normally, in Zero Span, this coupling is
turned off and Res BW has no Auto setting.
When a CISPR or MIL EMI Standard is in use, the Res BW is coupled to
Center Frequency and not to Span, and this is true even in Zero Span.
Sweep time is coupled to RBW when in a non-zero span. If Sweep Time is set
to Auto, then the sweep time is changed as the RBW changes, to maintain
amplitude calibration.
Video bandwidth (VBW) is normally coupled to RBW. If VBW is set to Auto,
then the VBW is changed as the RBW changes, to maintain the ratio set by
VBW:3dB RBW. See the ““VBW:3dB RBW” on page 892” key description.
Preset 3 MHz
ON
State Saved Saved in Instrument State
Min 1 Hz
Max 8 MHz is the max equivalent –3 dB RBW, which means that the named RBW
(the one shown on the key) can actually exceed 8 MHz if using a filter other
than –3 dB Gaussian
Default Unit Hz
Initial S/W Revision Prior to A.02.00