Basics on I/Q Data Acquisition and Processing
R&S
®
ZNL
18
User Manual 1178.5989.02 ─ 06
reduced. The analog filter stages in the analyzer cause a frequency response which
adds to the modulation errors. An
equalizer filter
before the
resampler
compensates
for this frequency response. The continuously adjustable sample rates are realized
using an optimal decimation filter and subsequent resampling on the set sample rate.
A dedicated memory (
capture buffer
) is available in the R&S
ZNL for a maximum of
25 Msamples (25*1000*1000) of complex samples (pairs of I and Q data). The number
of complex samples to be captured can be defined (for restrictions refer to
ter 4.1.1, "Sample Rate and Maximum Usable I/Q Bandwidth for RF Input"
The block diagram in
shows the analyzer hardware from the IF section to
the processor.
Figure 4-1: Block diagram illustrating the R&S
ZNL signal processing for analog I/Q data (without
bandwidth extension options)
4.1.1
Sample Rate and Maximum Usable I/Q Bandwidth for RF Input
Definitions
●
Input sample rate (ISR)
: the sample rate of the useful data provided by the device
connected to the input of the R&S
ZNL
●
(User, Output)
Sample rate (SR)
: the user-defined sample rate (e.g. in the "Data
Acquisition" dialog box in the "I/Q Analyzer" application) which is used as the basis
for analysis or output
●
Usable I/Q (Analysis) bandwidth
: the bandwidth range in which the signal
remains undistorted in regard to amplitude characteristic and group delay; this
range can be used for accurate analysis by the R&S
ZNL
●
Record length
: Number of I/Q samples to capture during the specified measure-
ment time; calculated as the measurement time multiplied by the sample rate
For the I/Q data acquisition, digital decimation filters are used internally in the
R&S
ZNL. The passband of these digital filters determines the
maximum usable I/Q
bandwidth
. In consequence, signals within the usable I/Q bandwidth (passband)
Processing Analog I/Q Data from RF Input
