Basics on I/Q Data Acquisition and Processing
R&S
®
FSV/A3000 I/Q
Analyzer
42
User Manual 1178.8536.02 ─ 01
The window length and the
determine how many FFT calculations
must be performed for each record in averaging mode (see
4.8.4
Frequency Resolution of FFT Results - RBW
The
resolution bandwidth
defines the minimum frequency separation at which the
individual components of a spectrum can be distinguished. Small values result in high
precision, as the distance between two distinguishable frequencies is small. Higher val-
ues decrease the precision, but increase measurement speed.
The RBW is determined by the following equation:
Length
Window
Rate
Sample
Bandwidth
Normalized
RBW
Equation 4-2: Definition of RBW
(Note: The normalized bandwidth is a fixed value that takes the noise bandwidth of the
window function into consideration.)
The maximum RBW is restricted by the
tion, whichever is higher:
3
Rate
Sample
*
Bandwidth
Normalized
RBW
max
If a higher spectral resolution is required, the number of samples must be increased by
using a higher sample rate or longer record length.
The minimum achievable RBW depends on the sample rate and record length, accord-
ing to the following equation:
Length
cord
Re
,
4096
min
Rate
Sample
Bandwidth*
Normalized
RBW
min
To simplify operation, some parameters are coupled and automatically calculated, such
as record length and RBW.
RBW mode
Depending on the selected RBW mode, the resolution bandwidth is either determined
automatically or can be defined manually.
Auto mode
:
This is the default mode in the I/Q Analyzer. The RBW is determined automatically
depending on the
, where the window length corre-
If the record length is larger than the window length, multiple windows are combined;
the FFT length is 4096.
Basics on FFT