Rohde&Schwarz R&S®ZNL I/Q Analyzer User Manual
R&S®ZNL
I/Q Analyzer
(Option R&S®ZNLxx‑B1)
User Manual
(;ÜÉç2)
1178598902
Version 14
This manual applies to the following R&S®ZNL models with firmware version 1.61 and higher:
●
R&S®ZNL3, 5 kHz to 3 GHz, 2 ports, N(f) connectors, order no. 1323.0012K03
●
R&S®ZNL4, 5 kHz to 4.5 GHz, 2 ports, N(f) connectors, order no. 1323.0012K04
●
R&S®ZNL6, 5 kHz to 6 GHz, 2 ports, N(f) connectors, order no. 1323.0012K06
●
R&S®ZNL14, 5 kHz to 14 GHz, 2 ports, N(f) connectors, order no. 1323.0012K14
Serial numbers 101200 and higher
●
R&S®ZNL20, 5 kHz to 20 GHz, 2 ports, 3.5 mm (m) connectors, order no. 1323.0012K20
Serial numbers 101200 and higher
The following firmware options are described:
●
R&S®ZNL3-B1 Spectrum Analysis (1323.1802.02)
●
R&S®ZNL4-B1 Spectrum Analysis (1303.8099.02)
●
R&S®ZNL6-B1 Spectrum Analysis (1323.2067.02)
●
R&S®ZNL14-B1 Spectrum Analysis (1303.8082.02)
●
R&S®ZNL20-B1 Spectrum Analysis (1303.8101.02)
In addition to the I/Q Analyzer application, the following options are described:
●
R&S®FPL1-B5, Additional Interfaces (1323.1883.02)
●
R&S®FPL1-K9 Power Sensor Support (1323.1754.02)
●
R&S®FPL1-B40, Bandwidth extension 40 MHz (1323.1931.02)
© 2022 Rohde & Schwarz GmbH & Co. KG
Muehldorfstr. 15, 81671 Muenchen, Germany
Phone: +49 89 41 29 - 0
Email: info@rohde-schwarz.com
Internet: www.rohde-schwarz.com
Subject to change – data without tolerance limits is not binding.
R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG.
All other trademarks are the properties of their respective owners.
1178.5989.02 | Version 14 | R&S®ZNL
Throughout this manual, products from Rohde & Schwarz are indicated without the ® symbol, e.g. R&S®ZNL is indicated as
R&S ZNL.
R&S®ZNL
Contents
Contents
1 Preface.................................................................................................... 5
1.1 Documentation overview..............................................................................................5
1.2 Conventions used in the documentation....................................................................7
2 Welcome to the I/Q Analyzer application.............................................9
2.1 Starting the I/Q Analyzer application.......................................................................... 9
2.2 Understanding the display information.................................................................... 10
3 Measurement and result displays...................................................... 13
4 Basics on I/Q data acquisition and processing................................ 17
4.1 Processing analog I/Q data from RF input............................................................... 17
4.2 Basics on FFT..............................................................................................................20
4.3 Basics on input from I/Q data files............................................................................ 26
4.4 I/Q data import and export......................................................................................... 26
5 Configuration........................................................................................28
5.1 Configuration overview.............................................................................................. 28
5.2 Import/export functions..............................................................................................30
5.3 Receiving data input and providing data output......................................................33
5.4 Amplitude.....................................................................................................................42
5.5 Frequency settings..................................................................................................... 47
5.6 Trigger settings........................................................................................................... 48
5.7 Data acquisition and bandwidth settings................................................................. 52
5.8 Display configuration................................................................................................. 58
5.9 Adjusting settings automatically...............................................................................58
6 Analysis................................................................................................ 62
6.1 Trace settings..............................................................................................................62
6.2 Spectrogram settings................................................................................................. 66
6.3 Trace / data export configuration.............................................................................. 71
6.4 Marker usage............................................................................................................... 74
7 How to perform measurements in the I/Q Analyzer application......98
7.1 How to capture baseband (I/Q) data as RF input..................................................... 98
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Contents
7.2 How to analyze data in the I/Q Analyzer................................................................... 99
8 How to export and import I/Q data................................................... 100
9 Remote commands to perform measurements with I/Q data........ 102
9.1 Introduction............................................................................................................... 102
9.2 Common suffixes...................................................................................................... 107
9.3 Activating I/Q Analyzer measurements...................................................................107
9.4 Configuring I/Q Analyzer measurements................................................................112
9.5 Configuring the result display................................................................................. 147
9.6 Capturing data and performing sweeps................................................................. 155
9.7 I/Q Analysis................................................................................................................161
9.8 Retrieving results...................................................................................................... 211
9.9 Importing and exporting I/Q data and results........................................................ 221
9.10 Programming examples........................................................................................... 222
Annex.................................................................................................. 226
A Formats for returned values: ASCII format and binary format...... 226
B Reference: format description for I/Q data files..............................227
C I/Q data file format (iq-tar)................................................................. 229
C.1 I/Q parameter XML file specification....................................................................... 230
C.2 I/Q data binary file..................................................................................................... 234
List of commands (I/Q analyzer mode)............................................ 237
Index....................................................................................................243
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Preface
Documentation overview
1 Preface
This chapter provides safety-related information, an overview of the user documentation and the conventions used in the documentation.
1.1 Documentation overview
This section provides an overview of the R&S ZNL user documentation. Unless specified otherwise, you find the documents at:
www.rohde-schwarz.com/manual/ZNL or www.rohde-schwarz.com/manual/ZNLE.
1.1.1 Getting started manual
Introduces the R&S ZNL and describes how to set up and start working with the product. Includes basic operations, typical measurement examples, and general information, e.g. safety instructions, etc.
A printed version is delivered with the instrument. A PDF version is available for download on the Internet.
1.1.2 User manuals and help
Separate user manuals are provided for the base unit and the firmware applications:
●
Base unit manual
Contains the description of all instrument modes and functions. It also provides an
introduction to remote control, a complete description of the remote control commands with programming examples, and information on maintenance, instrument
interfaces and error messages. Includes the contents of the getting started manual.
●
Firmware application manual
Contains the description of the specific functions of a firmware application, including remote control commands. Basic information on operating the R&S ZNL is not
included.
The contents of the user manuals are available as help in the R&S ZNL. The help
offers quick, context-sensitive access to the complete information for the base unit and
the firmware applications.
All user manuals are also available for download or for immediate display on the Internet.
1.1.3 Service manual
Describes the performance test for checking compliance with rated specifications, firmware update, troubleshooting, adjustments, installing options and maintenance.
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Preface
Documentation overview
The service manual is available for registered users on the global Rohde & Schwarz
information system (GLORIS):
https://gloris.rohde-schwarz.com
1.1.4 Instrument security procedures
Deals with security issues when working with the R&S ZNL in secure areas. It is available for download on the Internet.
1.1.5 Printed safety instructions
Provides safety information in many languages. The printed document is delivered with
the product.
1.1.6 Data sheets and brochures
The data sheet contains the technical specifications of the R&S ZNL. It also lists the
firmware applications and their order numbers, and optional accessories.
The brochure provides an overview of the instrument and deals with the specific characteristics.
See www.rohde-schwarz.com/brochure-datasheet/ZNL or www.rohde-schwarz.com/
brochure-datasheet/ZNLE.
1.1.7 Release notes and open source acknowledgment (OSA)
The release notes list new features, improvements and known issues of the current
firmware version, and describe the firmware installation.
The software makes use of several valuable open source software packages. An opensource acknowledgment document provides verbatim license texts of the used open
source software.
See www.rohde-schwarz.com/firmware/ZNL or www.rohde-schwarz.com/firmware/
ZNLE.
1.1.8 Application notes, application cards, white papers, etc.
These documents deal with special applications or background information on particular topics.
See www.rohde-schwarz.com/application/ZNL or www.rohde-schwarz.com/application/
ZNLE.
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Preface
Conventions used in the documentation
1.1.9 Calibration certificate
The document is available on https://gloris.rohde-schwarz.com/calcert. You need the
device ID of your instrument, which you can find on a label on the rear panel.
1.2 Conventions used in the documentation
1.2.1 Typographical conventions
The following text markers are used throughout this documentation:
Convention Description
"Graphical user interface elements"
[Keys] Key and knob names are enclosed by square brackets.
Filenames, commands,
program code
Input Input to be entered by the user is displayed in italics.
Links Links that you can click are displayed in blue font.
"References" References to other parts of the documentation are enclosed by quota-
All names of graphical user interface elements on the screen, such as
dialog boxes, menus, options, buttons, and softkeys are enclosed by
quotation marks.
Filenames, commands, coding samples and screen output are distinguished by their font.
tion marks.
1.2.2 Conventions for procedure descriptions
When operating the instrument, several alternative methods may be available to perform the same task. In this case, the procedure using the touchscreen is described.
Any elements that can be activated by touching can also be clicked using an additionally connected mouse. The alternative procedure using the keys on the instrument or
the on-screen keyboard is only described if it deviates from the standard operating procedures.
The term "select" may refer to any of the described methods, i.e. using a finger on the
touchscreen, a mouse pointer in the display, or a key on the instrument or on a keyboard.
1.2.3 Notes on screenshots
When describing the functions of the product, we use sample screenshots. These
screenshots are meant to illustrate as many as possible of the provided functions and
possible interdependencies between parameters. The shown values may not represent
realistic usage scenarios.
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Preface
Conventions used in the documentation
The screenshots usually show a fully equipped product, that is: with all options installed. Thus, some functions shown in the screenshots may not be available in your particular product configuration.
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Welcome to the I/Q Analyzer application
Starting the I/Q Analyzer application
2 Welcome to the I/Q Analyzer application
The R&S FPL1 I/Q Analyzer is a firmware application that adds functionality to perform
I/Q data acquisition and analysis to the R&S ZNL.
The R&S FPL1 I/Q Analyzer features:
●
Acquisition of analog I/Q data
●
Import of stored I/Q data from other applications
●
Spectrum, magnitude, I/Q vector and separate I and Q component analysis of any
I/Q data on the instrument
●
Export of I/Q data to other applications
Availability of the I/Q Analyzer
The I/Q Analyzer becomes available when you equip the R&S ZNLxx with the optional
spectrum analyzer hardware option R&S ZNLxx-B1.
For the R&S ZNLE and for R&S ZNL14 and R&S ZNL20 with serial numbers below
101200, a spectrum analyzer hardware option is not available.
This user manual contains a description of the functionality that the application provides, including remote control operation.
All functions not discussed in this manual are the same as in the base unit and are
described in the R&S ZNL User Manual. The latest version is available for download at
the product homepage http://www.rohde-schwarz.com/product/ZNL.
Additional information
Several application notes discussing I/Q analysis are available from the Rohde &
Schwarz website:
1EF85: Converting R&S I/Q data files
1EF92: Wideband Signal Analysis
1MA257: Wideband mm-Wave Signal Generation and Analysis
1EF84: Differential measurements with Spectrum Analyzers and Probes
Installation
The R&S FPL1 I/Q Analyzer application is part of the optional "Spectrum" application
and requires no further installation.
2.1 Starting the I/Q Analyzer application
The I/Q Analyzer is an application on the R&S ZNL.
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Welcome to the I/Q Analyzer application
Understanding the display information
To activate the I/Q Analyzer application
1. Select the [MODE] key.
A dialog box opens that contains all applications currently available on your
R&S ZNL.
2. Select the "I/Q Analyzer" item.
The R&S ZNL opens a new channel setup for the I/Q Analyzer application.
The measurement is started immediately with the default settings.
It can be configured in the I/Q Analyzer "Overview" dialog box, which is displayed
when you select the "Overview" softkey from any menu (see Chapter 5.1, "Configura-
tion overview", on page 28).
Multiple Channel Setups and Sequencer Function
When you activate an application, a new channel setup is created which determines
the measurement settings for that application (channel setup). The same application
can be activated with different measurement settings by creating several channel setups for the same application.
The number of channel setups that can be configured at the same time depends on the
available memory on the instrument.
Only one measurement can be performed at any time, namely the one in the currently
active channel setup. However, in order to perform the configured measurements consecutively, a Sequencer function is provided.
If activated, the measurements configured in the currently defined channel setups are
performed one after the other in the order of the tabs. The currently active measurement is indicated by a
The result displays of the individual channel setups are updated in the tabs (as well as
the "MultiView" ) as the measurements are performed. Sequential operation itself is
independent of the currently displayed tab.
For details on the Sequencer function see the R&S ZNL User Manual.
symbol in the tab label.
2.2 Understanding the display information
The following figure shows a measurement diagram during I/Q Analyzer operation. All
different information areas are labeled. They are explained in more detail in the following sections.
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Welcome to the I/Q Analyzer application
Understanding the display information
1 2 3 4
56
Figure 2-1: Screen elements in the I/Q Analyzer application
1+4 = Window title bar with diagram-specific (trace) information
2 = Channel Setup bar for firmware and measurement settings
3 = Diagram area
5 = Diagram footer with diagram-specific information, depending on result display
6 = Instrument status bar with error messages and date/time display
Channel Setup bar information
In the I/Q Analyzer application, the R&S ZNL shows the following settings:
Table 2-1: Information displayed in the channel setup bar for the I/Q Analyzer application
Ref Level Reference level
(m.+el.)Att (Mechanical and electronic) RF attenuation
Ref Offset Reference level offset
Freq Center frequency
Meas Time Measurement time
Rec Length Defined record length (number of samples to capture)
SRate Defined sample rate for data acquisition
RBW (Spectrum evaluation only) Resolution bandwidth calculated from the
sample rate and record length
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Welcome to the I/Q Analyzer application
Understanding the display information
In addition, the channel setup bar also displays information on instrument settings that
affect the measurement results even though this is not immediately apparent from the
display of the measured values (e.g. transducer or trigger settings). This information is
displayed only when applicable for the current measurement.
Window title bar information
For each diagram, the header provides the following information:
4
1 2 3
Figure 2-2: Window title bar information in the I/Q Analyzer application
1 = Window number
2 = Window type
3 = Trace color
4 = Trace number
5 = Detector
6 = Trace mode
5 6
Diagram footer information
The information in the diagram footer (beneath the diagram) depends on the evaluation:
●
Center frequency
●
Number of sweep points
●
Range per division (x-axis)
●
Span (Spectrum)
Status bar information
Global instrument settings, the instrument status and any irregularities are indicated in
the status bar beneath the diagram.
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Measurement and result displays
3 Measurement and result displays
Access: "Overview" > "Display Config"
Or: [MEAS] > "Display Config"
The I/Q Analyzer can capture I/Q data. The I/Q data that was captured by or imported
to the R&S ZNL can then be evaluated in various different result displays. Select the
result displays using the SmartGrid functions.
Result displays for I/Q data:
Magnitude .................................................................................................................... 13
Spectrum ......................................................................................................................13
I/Q-Vector .....................................................................................................................14
Real/Imag (I/Q) .............................................................................................................15
Marker Table ................................................................................................................ 15
Marker Peak List .......................................................................................................... 16
Magnitude
Shows the level values in time domain.
Remote command:
LAY:ADD:WIND? '1',RIGH,MAGN, see LAYout:ADD[:WINDow]? on page 148
Results:
TRACe<n>[:DATA]? on page 215
Spectrum
Displays the frequency spectrum of the captured I/Q samples.
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Measurement and result displays
The specified Analysis Bandwidth is indicated by vertical blue lines.
Note that a peak search is performed only within the indicated Analysis Bandwidth ,
unless you specify Search Limits ( Left / Right ) in the marker settings.
Remote command:
LAY:ADD:WIND? '1',RIGH,FREQ, see LAYout:ADD[:WINDow]? on page 148
Results:
TRACe<n>[:DATA]? on page 215
I/Q-Vector
Displays the captured samples in an I/Q-plot. The samples are connected by a line.
Note: For the I/Q vector result display, the number of I/Q samples to record ( "Record
Length" ) must be identical to the number of trace points to be displayed ("Sweep
Points"; for I/Q Analyzer: 10001). For record lengths outside the valid range of sweep
points the diagram does not show valid results.
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Measurement and result displays
Remote command:
LAY:ADD:WIND? '1',RIGH,VECT, see LAYout:ADD[:WINDow]? on page 148
Results:
TRACe<n>[:DATA]? on page 215
Real/Imag (I/Q)
Displays the I and Q values in separate diagrams.
Remote command:
LAY:ADD:WIND? '1',RIGH,RIM, see LAYout:ADD[:WINDow]? on page 148
Results:
TRACe<n>[:DATA]? on page 215
Marker Table
Displays a table with the current marker values for the active markers.
This table is displayed automatically if configured accordingly.
(See " Marker Table Display " on page 78).
Tip: To navigate within long marker tables, simply scroll through the entries with your
finger on the touchscreen.
Remote command:
LAY:ADD? '1',RIGH, MTAB, see LAYout:ADD[:WINDow]? on page 148
Results:
CALCulate<n>:MARKer<m>:X on page 181
CALCulate<n>:MARKer<m>:Y? on page 220
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Measurement and result displays
Marker Peak List
The marker peak list determines the frequencies and levels of peaks in the spectrum or
time domain. How many peaks are displayed can be defined, as well as the sort order.
In addition, the detected peaks can be indicated in the diagram. The peak list can also
be exported to a file for analysis in an external application.
Remote command:
LAY:ADD? '1',RIGH, PEAK, see LAYout:ADD[:WINDow]? on page 148
Results:
CALCulate<n>:MARKer<m>:X on page 181
CALCulate<n>:MARKer<m>:Y? on page 220
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Basics on I/Q data acquisition and processing
Processing analog I/Q data from RF input
4 Basics on I/Q data acquisition and process-
ing
Some background knowledge on basic terms and principles used when describing I/Q
data acquisition on the R&S ZNL in general, and in the I/Q Analyzer application in particular, is provided here for a better understanding of the required configuration settings.
The I/Q Analyzer provides various possibilities to acquire the I/Q data to be analyzed:
●
Capturing analog I/Q data from the [RF Input] connector
●
Importing I/Q data from a file
Background information for all these scenarios and more is provided in the following
sections.
● Processing analog I/Q data from RF input..............................................................17
● Basics on FFT.........................................................................................................20
● Basics on input from I/Q data files.......................................................................... 26
● I/Q data import and export...................................................................................... 26
4.1 Processing analog I/Q data from RF input
Complex baseband data
In the telephone systems of the past, baseband data was transmitted unchanged as an
analog signal. In modern phone systems and in radio communication, however, the
baseband data is modulated on a carrier frequency, which is then transmitted. The
receiver must demodulate the data based on the carrier frequency. When using modern modulation methods (e.g. QPSK, QAM etc.), the baseband signal becomes complex. Complex data (or: I/Q data) consists of an imaginary (I) and a real (Q) component.
Sweep vs sampling
The standard Spectrum application on the R&S ZNL performs frequency sweeps on
the input signal and measurements in the frequency and time domain. Other applications on the R&S ZNL, such as the I/Q Analyzer, sample and process the individual I
and Q components of the complex signal.
I/Q Analyzer - processing complex data from RF input
The I/Q Analyzer is a standard application used to capture and analyze I/Q data on the
R&S ZNL. By default, it assumes the I/Q data is modulated on a carrier frequency and
input via the "RF Input" connector on the R&S ZNL.
The A/D converter samples the IF signal at a rate of 100 MHz. The digital signal is
down-converted to the complex baseband, lowpass-filtered, and the sample rate is
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Basics on I/Q data acquisition and processing
Processing analog I/Q data from RF input
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 Chap-
ter 4.1.1, "Sample rate and maximum usable I/Q bandwidth for RF input",
on page 18).
The block diagram in Figure 4-1 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 measurement 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)
remain unchanged, while signals outside the usable I/Q bandwidth (passband) are
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4.1.1.1 Relationship between sample rate, record length and usable I/Q bandwidth
Basics on I/Q data acquisition and processing
Processing analog I/Q data from RF input
suppressed. Usually, the suppressed signals are noise, artifacts, and the second IF
side band. If frequencies of interest to you are also suppressed, try to increase the output sample rate, which increases the maximum usable I/Q bandwidth.
Bandwidth extension options
You can extend the maximum usable I/Q bandwidth provided by the R&S ZNL in the
basic installation by adding options. These options can either be included in the initial
installation (B-options) or updated later (U-options). The maximum bandwidth provided
by the individual option is indicated by its number, for example, B40 extends the bandwidth to 40 MHz.
As a rule, the usable I/Q bandwidth is proportional to the output sample rate. Yet, when
the I/Q bandwidth reaches the bandwidth of the analog IF filter (at very high output
sample rates), the curve breaks.
● Relationship between sample rate, record length and usable I/Q bandwidth......... 19
Up to the maximum bandwidth, the following rule applies:
Usable I/Q bandwidth = 0.8 * Output sample rate
Regarding the record length, the following rule applies:
Record length = Measurement time * sample rate
Maximum record length for RF input
The maximum record length is the maximum number of samples that can be captured.
Table 4-1: Maximum record length
Sample rate Maximum record length
100 Hz to 100 MHz 25 Msamples
The Figure 4-2 shows the maximum usable I/Q bandwidths depending on the output
sample rates.
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Usable I/Q
bandwidth
[MHz]
40
35
30
25
20
15
12.8
10
5
Figure 4-2: Relationship between maximum usable I/Q bandwidth and output sample rate
RF-Input:
BW = 0.80 *
f
out
16
2010
4.2 Basics on FFT
Basics on I/Q data acquisition and processing
30 40 50 60 70 80 90 100
Basics on FFT
With 40 MHz
bandwidth
ext. option
Without
bandwidth
extension
Output sample
out
[MHz]
rate f
The I/Q Analyzer measures the power of the signal input over time. To convert the time
domain signal to a frequency spectrum, an FFT (Fast Fourier Transformation) is performed which converts a vector of input values into a discrete spectrum of frequencies.
4.2.1 Window functions
The Fourier transformation is not performed on the entire captured data in one step.
Only a limited number of samples is used to calculate an individual result. This process
is called windowing.
t[s]
FFT
f[Hz]
After sampling in the time domain, each window is multiplied with a specific window
function. Windowing helps minimize the discontinuities at the end of the measured signal interval and thus reduces the effect of spectral leakage, increasing the frequency
resolution.
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Basics on I/Q data acquisition and processing
Basics on FFT
Various different window functions are provided in the R&S ZNL to suit different input
signals. Each of the window functions has specific characteristics, including some
advantages and some trade-offs. Consider these characteristics to find the optimum
solution for the measurement task.
Ignoring the window function - rectangular window
The rectangular window function is in effect not a function at all, it maintains the original sampled data. This may be useful to minimize the required bandwidth. However, be
aware that if the window does not contain exactly one period of your signal, heavy
sidelobes may occur, which do not exist in the original signal.
Table 4-2: Characteristics of typical FFT window functions
Window type Frequency
Rectangular Best Worst Worst No function applied.
Blackman-Harris
(default)
Gauss (Alpha
= 0.4)
Flattop Worst Best Good Accurate single tone measurements
5-Term Good Good Best Measurements with very high
4.2.2 Overlapping
The I/Q Analyzer calculates multiple FFTs per measurement by dividing one captured
record into several windows. Furthermore, the I/Q Analyzer allows consecutive windows to overlap. Overlapping "reuses" samples that were already used to calculate the
preceding FFT result.
Magnitude
resolution
Good Good Good Harmonic detection and spurious
Good Good Good Weak signals and short duration
resolution
Sidelobe suppression
Measurement recommendation
Separation of two tones with almost
equal amplitudes and a small frequency distance
emission detection
dynamic range
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Basics on I/Q data acquisition and processing
Basics on FFT
In advanced FFT mode with averaging, the overlapping factor can be set freely. The
higher the overlap factor, the more windows are used. This leads to more individual
results and improves detection of transient signal effects. However, it also extends the
duration of the calculation. The size of the window can be defined manually according
to the record length, the overlap factor, and the FFT length.
An FFT overlap of 67%, for example, means the second FFT calculation uses the last
67% of the data of the first FFT. It uses only 33% new data. The third FFT still covers
33% of the first FFT and 67% of the second FFT, and so on.
Figure 4-3: Overlapping FFTs
In "Manual" or "Auto" FFT mode, an FFT length of 4096 and a window length of 4096
(or the record length, if shorter) is used to calculate the spectrum.
Combining results - trace detector
If the record length permits, multiple overlapping windows are calculated and combined
to create the final spectrum using the selected trace detector. If necessary, the trace
detector is also used to reduce the number of calculated frequency points (defined by
the FFT length) to the defined number of sweep points. By default, the Autopeak trace
detector is used.
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Basics on I/Q data acquisition and processing
Basics on FFT
Since the frequency points are reduced to the number of sweep points, using a detector other than "Auto Peak" and fewer than 4096 sweep points can lead to false level
results.
4.2.3 Dependencies between FFT parameters
FFT analysis in the R&S ZNL is highly configurable. Several parameters, including the
resolution bandwidth, record length, and FFT length, are user-definable. Note, however, that several parameters are correlated and not all can be configured independently of the others.
Record Length
Defines the number of I/Q samples to capture. By default, the number of sweep points
is used. The record length is calculated as the measurement time multiplied by the
sample rate.
If you change the record length, the Meas Time is automatically changed, as well.
For FFTs using only a single window ("Single" mode), the record length (which is then
identical to the FFT length) must not exceed 512k.
FFT Length
Defines the number of frequency points determined by each FFT calculation. The more
points are used, the higher the resolution in the spectrum becomes, but the longer the
calculation takes.
In "Auto" or "Manual" mode, an FFT length of 4096 is used.
If the FFT length is longer than the Window Length the sample data is filled up with
zeros up to the FFT length. The FFT is then performed using interpolated frequency
points.
For an FFT length that is not a power of 2, a DFT (discrete Fourier transform) is performed, which requires more time for calculation, but avoids the effects of interpolation.
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LengthWindow
RateSample
BandwidthNormalizedRBW
3
RateSample*BandwidthNormalized
RBW
max
LengthcordRe,4096min
RateSampleBandwidth*Normalized
RBW
min
Basics on I/Q data acquisition and processing
Basics on FFT
To display all calculated frequency points (defined by the FFT length), the number of
sweep points is set to the FFT length automatically in advanced FFT mode.
Window Length
Defines the number of samples to be included in a single window in averaging mode.
(In single mode, the window length corresponds to the " Record Length " on page 54.)
Values from 3 to 4096 are available in "Manual" mode; in "Advanced" FFT mode, values from 3 to 524288 are available. However, the window length must not be longer
than the FFT Length .
If the window length is shorter than the FFT Length , the sample data is filled up with
zeros up to the FFT length.
If the window length is longer than the Record Length (that is, not enough samples are
available), a window length the size of the Record Length is used for calculation.
The window length and the Window Overlap determine how many FFT calculations
must be performed for each record in averaging mode (see " TransformationAlgorithm
" on page 55).
4.2.4 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 values decrease the precision, but increase measurement speed.
The RBW is determined by the following equation:
Equation 4-1: 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 Analysis Bandwidth , or by the following equation, whichever is higher:
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, according to the following equation:
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Basics on I/Q data acquisition and processing
Basics on FFT
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 Sample Rate and Window Length , where the window length corresponds to the Record Length , or a maximum of 4096.
If the record length is larger than the window length, multiple windows are combined;
the FFT length is 4096.
A Flatop window function is used.
Manual mode:
The RBW is user-definable.
The Window Length is adapted to comply with Equation 4-1. Since only window
lengths with integer values can be employed, the Sample Rate is adapted, if necessary, to obtain an integer window length value.
If the record length is larger than the window length, multiple windows are combined;
the FFT length is 4096.
A Flatop window function is used.
Advanced FFT mode
The RBW is determined by the advanced FFT parameters, depending on the selected
FFT calculation methods method.
4.2.5 FFT calculation methods
FFT calculation can be performed using different methods.
Single
In single mode, one FFT is calculated for the entire record length, that means the window length is identical to the record length.
If the defined FFT Length is larger than the record length, zeros are appended to the
captured data to reach the FFT length.
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Basics on I/Q data acquisition and processing
I/Q data import and export
Figure 4-4: FFT parameters for single FFT calculation
Averaging
In averaging mode, several overlapping FFTs are calculated for each record; the
results are combined to determine the final FFT result for the record.
The number of FFTs to be combined is determined by the Window Overlap and the
Window Length .
Figure 4-5: FFT parameters for averaged FFT calculation
4.3 Basics on input from I/Q data files
The I/Q data to be evaluated in a particular R&S ZNL application cannot only be captured by the application itself, it can also be loaded from a file, provided it has the correct format. The file is then used as the input source for the application.
The I/Q data must be stored in a format with the file extension .iq.tar. For a detailed
description, see Chapter C, "I/Q data file format (iq-tar)", on page 229.
An application note on converting Rohde & Schwarz I/Q data files is available from the
Rohde & Schwarz website:
1EF85: Converting R&S I/Q data files
When using input from an I/Q data file, the [RUN SINGLE] function starts a single measurement (i.e. analysis) of the stored I/Q data, while the [RUN CONT] function repeatedly analyzes the same data from the file.
4.4 I/Q data import and export
Baseband signals mostly occur as so-called complex baseband signals, i.e. a signal
representation that consists of two channels; the inphase (I) and the quadrature (Q)
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Basics on I/Q data acquisition and processing
I/Q data import and export
channel. Such signals are referred to as I/Q signals. The complete modulation information and even distortion that originates from the RF, IF or baseband domains can be
analyzed in the I/Q baseband.
Importing and exporting I/Q signals is useful for various applications:
●
Generating and saving I/Q signals in an RF or baseband signal generator or in
external software tools to analyze them with the R&S ZNL later.
●
Capturing and saving I/Q signals with the R&S ZNL to analyze them with the
R&S ZNL or an external software tool later
As opposed to storing trace data, which can be averaged or restricted to peak values, I/Q data is stored as it was captured, without further processing. Multi-channel
data is not supported.
The data is stored as complex values in 32-bit floating-point format. The I/Q data is
stored in a format with the file extension .iq.tar.
An application note on converting Rohde & Schwarz I/Q data files is available from the
Rohde & Schwarz website:
1EF85: Converting R&S I/Q data files
The import and export functions are available in the "Save/Recall" menu which is displayed when you select the
"Import/export functions", on page 30).
"Save" or "Open" icon in the toolbar (see Chapter 5.2,
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Configuration
Configuration overview
5 Configuration
Access: [MODE] > "I/Q Analyzer"
The I/Q Analyzer is a special application on the R&S ZNL.
For details see the "Operating modes, applications, channel setups, and result displays" chapter in the R&S ZNL User Manual.
When you switch to an I/Q Analyzer channel setup the first time, a set of parameters is
passed on from the currently active application. After initial setup, the parameters for
the channel setup are stored upon exiting and restored upon re-entering the channel
setup. Thus, you can switch between applications quickly and easily.
When you activate a channel setup for the I/Q Analyzer application, data acquisition
from the input signal is started automatically with the default configuration. The "I/Q
Analyzer" menu is displayed and provides access to the most important configuration
functions.
The remote commands required to perform these tasks are described in Chapter 9,
"Remote commands to perform measurements with I/Q data", on page 102.
Importing and Exporting I/Q Data
The I/Q data to be evaluated in the I/Q Analyzer application can not only be captured
by the I/Q Analyzer itself, it can also be imported to the R&S ZNL, provided it has the
correct format. Furthermore, the captured I/Q data from the I/Q Analyzer can be exported for further analysis in external applications.
For details see Chapter 4.4, "I/Q data import and export", on page 26.
● Configuration overview............................................................................................28
● Import/export functions............................................................................................30
● Receiving data input and providing data output......................................................33
● Amplitude................................................................................................................ 42
● Frequency settings..................................................................................................47
● Trigger settings....................................................................................................... 48
● Data acquisition and bandwidth settings.................................................................52
● Display configuration...............................................................................................58
● Adjusting settings automatically..............................................................................58
5.1 Configuration overview
Access: all menus
Throughout the channel setup configuration, an overview of the most important currently defined settings is provided in the "Overview".
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Configuration
Configuration overview
Multiple access paths to functionality
The easiest way to configure a channel setup is via the "Overview" dialog box, which is
available from all menus.
Alternatively, you can access the individual dialog boxes from the corresponding menu
items, or via tools in the toolbars, if available.
In this documentation, only the most convenient method of accessing the dialog boxes
is indicated - usually via the "Overview".
Figure 5-1: Configuration Overview for I/Q Analyzer primary
In addition to the main measurement settings, the "Overview" provides quick access to
the main settings dialog boxes. The individual configuration steps are displayed in the
order of the data flow. Thus, you can easily configure an entire channel setup from
input over processing to output and analysis by stepping through the dialog boxes as
indicated in the "Overview".
The "Overview" for the I/Q Analyzer provides quick access to the following configuration dialog boxes (listed in the recommended order of processing):
1. Input settings
See Chapter 5.3.1, "Radio frequency input", on page 33
2. Amplitude settings
See Chapter 5.4, "Amplitude", on page 42
3. Frequency settings
See Chapter 5.5, "Frequency settings", on page 47
4. Optionally, Trigger/Gate settings
See Chapter 5.6, "Trigger settings", on page 48
5. Bandwidth settings
See Chapter 5.7, "Data acquisition and bandwidth settings", on page 52
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Configuration
Import/export functions
6. Analysis settings and functions
See Chapter 6, "Analysis", on page 62
7. Display configuration
See Chapter 5.8, "Display configuration", on page 58
To configure settings
► Select any button in the "Overview" to open the corresponding dialog box.
Select a setting in the channel bar (at the top of the channel setup tab) to change a
specific setting.
For step-by-step instructions on configuring I/Q Analyzer measurements, see Chap-
ter 7, "How to perform measurements in the I/Q Analyzer application", on page 98.
Preset Channel Setup
Select the "Preset Channel" button in the lower left-hand corner of the "Overview" to
restore all measurement settings in the current channel setup to their default values.
Note: Do not confuse the "Preset Channel" button with the [Preset] key, which restores
the entire instrument to its default values and thus closes all channel setups on the
R&S ZNL (except for the default channel setup)!
Remote command:
SYSTem:PRESet:CHANnel[:EXEC] on page 111
Specifics for
The channel setup can contain several windows for different results. Thus, the settings
indicated in the "Overview" and configured in the dialog boxes vary depending on the
selected window.
Select an active window from the "Specifics for" selection list that is displayed in the
"Overview" and in all window-specific configuration dialog boxes.
The "Overview" and dialog boxes are updated to indicate the settings for the selected
window.
5.2 Import/export functions
Access: "Save"/ "Open" icon in the toolbar > "Import" / "Export"
The R&S ZNL provides various evaluation methods for the results of the performed
measurements. However, you may want to evaluate the data with further, external
applications. In this case, you can export the measurement data to a standard format
file (ASCII or XML). Some of the data stored in these formats can also be re-imported
to the R&S ZNL for further evaluation later, for example in other applications.
The following data types can be exported (depending on the application):
●
Trace data
●
Table results, such as result summaries, marker peak lists etc.
●
I/Q data
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