R&S®FSMR3-B1
I/Q Analyzer
User Manual
(;Ý1W2)
1179013902
Version 02
This document describes the following R&S®FSMR3000 models:
●
R&S®FSMR3008 (1345.4004K08)
●
R&S®FSMR3026 (1345.4004K26)
●
R&S®FSMR3050 (1345.4004K50)
The contents of this manual correspond to firmware version 1.10 and higher.
The following firmware options are described:
●
R&S®FSMR3-B1 (1345.3050.08)
●
R&S®FSMR3-B1 (1345.3050.26)
●
R&S®FSMR3-B1 (1345.3050.50)
© 2022 Rohde & Schwarz GmbH & Co. KG
Mühldorfstr. 15, 81671 München, Germany
Phone: +49 89 41 29 - 0
Fax: +49 89 41 29 12 164
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.
Trade names are trademarks of their owners.
1179.0139.02 | Version 02 | R&S®FSMR3-B1
Throughout this manual, products from Rohde & Schwarz are indicated without the ® symbol , e.g. R&S®FSMR3000 is indicated as
R&S FSMR3000.
R&S®FSMR3-B1
1 Preface.................................................................................................... 7
1.1 About this manual.........................................................................................................7
1.2 Documentation overview..............................................................................................8
1.2.1 Getting started manual....................................................................................................8
1.2.2 User manuals and help................................................................................................... 8
1.2.3 Service manual............................................................................................................... 8
1.2.4 Instrument security procedures.......................................................................................9
1.2.5 Printed safety instructions............................................................................................... 9
1.2.6 Data sheets and brochures............................................................................................. 9
1.2.7 Release notes and open-source acknowledgment (OSA).............................................. 9
1.2.8 Application notes, application cards, white papers, etc...................................................9
Contents
Contents
1.3 Conventions used in the documentation....................................................................9
1.3.1 Typographical conventions..............................................................................................9
1.3.2 Conventions for procedure descriptions........................................................................10
1.3.3 Notes on screenshots................................................................................................... 10
2 Welcome to the I/Q analyzer application............................................11
2.1 Starting the I/Q analyzer application......................................................................... 11
2.2 Understanding the display information.................................................................... 12
3 Measurement and result displays...................................................... 15
4 Basics on I/Q data acquisition and processing................................ 20
4.1 Processing analog I/Q data from RF input............................................................... 20
4.1.1 Sample rate and maximum usable I/Q bandwidth for RF input.....................................21
4.1.1.1 Relationship between sample rate, record length and usable I/Q bandwidth............... 22
4.2 Basics on input from I/Q data files............................................................................ 23
4.3 Receiving and providing trigger signals...................................................................24
4.4 I/Q data import and export......................................................................................... 25
4.5 Basics on FFT..............................................................................................................25
4.5.1 Window functions.......................................................................................................... 26
4.5.2 Overlapping...................................................................................................................27
4.5.3 Dependencies between FFT parameters......................................................................28
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4.5.4 Frequency resolution of FFT results - RBW..................................................................30
4.5.5 FFT calculation methods...............................................................................................31
5 Configuration........................................................................................32
5.1 Configuration overview.............................................................................................. 32
5.2 Import/export functions..............................................................................................34
5.3 Configuring data inputs and outputs........................................................................ 38
5.3.1 Inputs............................................................................................................................ 38
5.3.1.1 RF input.........................................................................................................................38
5.3.1.2 Power sensors.............................................................................................................. 40
5.3.1.3 External generators.......................................................................................................40
5.3.1.4 Probes...........................................................................................................................40
5.3.1.5 Settings for input from I/Q data files..............................................................................40
Contents
5.3.2 Outputs..........................................................................................................................41
5.4 Configuring the amplitude..........................................................................................44
5.4.1 Configuring level characteristics................................................................................... 44
5.4.2 Scaling the level axis.....................................................................................................48
5.5 Configuring frequency characteristics..................................................................... 49
5.6 Configuring triggered measurements.......................................................................51
5.7 Data acquisition and bandwidth settings................................................................. 55
5.7.1 Data acquisition.............................................................................................................55
5.7.2 Sweep settings..............................................................................................................60
5.8 Display configuration................................................................................................. 62
5.9 Adjusting settings automatically...............................................................................62
6 Analysis................................................................................................ 66
6.1 Trace configuration.....................................................................................................66
6.2 Marker settings............................................................................................................67
6.3 Display lines and limit lines....................................................................................... 67
7 How to work with I/Q data................................................................... 69
7.1 How to perform measurements in the I/Q Analyzer application.............................69
7.1.1 How to capture baseband (I/Q) data as RF input..........................................................69
7.1.2 How to analyze data in the I/Q Analyzer....................................................................... 70
7.2 How to export and import I/Q data............................................................................ 70
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8 Remote commands for the I/Q analyzer.............................................73
8.1 Introduction................................................................................................................. 73
8.1.1 Conventions used in descriptions................................................................................. 73
8.1.2 Long and short form...................................................................................................... 74
8.1.3 Numeric suffixes............................................................................................................74
8.1.4 Optional keywords.........................................................................................................75
8.1.5 Alternative keywords..................................................................................................... 75
8.1.6 SCPI parameters...........................................................................................................75
8.1.6.1 Numeric values............................................................................................................. 76
8.1.6.2 Boolean......................................................................................................................... 77
8.1.6.3 Character data.............................................................................................................. 77
8.1.6.4 Character strings...........................................................................................................77
8.1.6.5 Block data..................................................................................................................... 77
Contents
8.2 Common suffixes........................................................................................................ 78
8.3 Activating I/Q analyzer measurements..................................................................... 78
8.4 Performing measurements.........................................................................................83
8.5 Retrieving results........................................................................................................90
8.5.1 Retrieving captured I/Q data......................................................................................... 90
8.5.2 Retrieving I/Q trace data............................................................................................... 94
8.5.3 Retrieving marker and peak search results...................................................................98
8.6 Configuring I/Q analyzer measurements................................................................ 101
8.6.1 Configuring input sources........................................................................................... 102
8.6.2 Configuring outputs..................................................................................................... 106
8.6.3 Configuring level characteristics................................................................................. 107
8.6.4 Configuring the attenuator...........................................................................................109
8.6.5 Configuring the preamplifier........................................................................................ 110
8.6.6 Scaling the Y-Axis........................................................................................................112
8.6.7 Configuring the frequency........................................................................................... 114
8.6.8 Configuring trigger.......................................................................................................116
8.6.9 Configuring trigger output............................................................................................121
8.6.10 Configuring gated measurements............................................................................... 123
8.6.11 Configuring data acquisition........................................................................................125
8.6.12 Automatic configuration...............................................................................................132
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8.6.13 Configuring the result display......................................................................................135
8.7 Analyzing results...................................................................................................... 142
8.8 Importing and exporting I/Q data.............................................................................143
8.9 Querying the status registers.................................................................................. 145
8.10 Programming examples........................................................................................... 145
8.10.1 I/Q analysis with graphical evaluation......................................................................... 145
8.10.2 Basic I/Q analysis with improved performance........................................................... 146
A Annex: reference................................................................................148
A.1 Formats for returned values: ASCII format and binary format............................. 148
A.2 Reference: format description for I/Q data files.....................................................149
A.3 I/Q data file format (iq-tar)........................................................................................ 150
Contents
Annex.................................................................................................. 148
A.3.1 I/Q parameter XML file specification........................................................................... 151
A.3.1.1 Minimum data elements.............................................................................................. 152
A.3.1.2 Example...................................................................................................................... 153
A.3.2 I/Q data binary file....................................................................................................... 155
List of Remote Commands (I/Q Analyzer)....................................... 159
Index....................................................................................................162
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1 Preface
1.1 About this manual
Preface
About this manual
This R&S FSMR3 I/Q Analyzer User Manual provides all the information specific to
the application and processing I/Q data. All general instrument functions and settings common to all applications are described in the main R&S FSMR3 User Manual.
The main focus in this manual is on the measurement results and the tasks required to
obtain them. The following topics are included:
●
Welcome to the I/Q Analyzer application
Introduction to and getting familiar with the application
●
Typical Applications for the I/Q Analyzer and optional input interfaces
Example measurement scenarios for I/Q data import and analysis
●
Measurements and Result Displays
Details on supported measurements and their result types
●
Basics on I/Q Data Acquisition
Background information on basic terms and principles in the context of the I/Q Analyzer application as well as processing I/Q data in general
●
Configuration and Analysis
A concise description of all functions and settings available to import, capture and
analyze I/Q data in the I/Q Analyzer, with or without optional interfaces, with their
corresponding remote control command
●
How to Work with I/Q Data
The basic procedure to perform an I/Q Analyzer measurement with step-by-step
instructions
●
Optimizing and Troubleshooting the Measurement
Hints and tips on how to handle errors and optimize the test setup
●
Remote Commands to perform Measurements with I/Q Data
Remote commands required to configure and perform I/Q Analyzer measurements
or process digital I/Q data in a remote environment, sorted by tasks;
(Commands required to set up the environment or to perform common tasks on the
instrument are provided in the main R&S FSMR3 User Manual.)
Programming examples demonstrate the use of many commands and can usually
be executed directly for test purposes.
●
Annex
Reference material, e.g. I/Q file formats and a detailed description of the LVDS
connector
●
List of remote commands
Alphabetical list of all remote commands described in the manual
●
Index
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1.2 Documentation overview
1.2.1 Getting started manual
1.2.2 User manuals and help
Preface
Documentation overview
This section provides an overview of the R&S FSMR3 user documentation. Unless
specified otherwise, you find the documents on the R&S FSMR3 product page at:
www.rohde-schwarz.com/product/FSMR3000.html/
Introduces the R&S FSMR3 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.
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.
●
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 FSMR3 is
not included.
The contents of the user manuals are available as help in the R&S FSMR3. 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.
1.2.3 Service manual
Describes the performance test for checking the rated specifications, module replacement and repair, firmware update, troubleshooting and fault elimination, and contains
mechanical drawings and spare part lists.
The service manual is available for registered users on the global Rohde & Schwarz
information system (GLORIS):
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1.2.4 Instrument security procedures
1.2.5 Printed safety instructions
1.2.6 Data sheets and brochures
Preface
Conventions used in the documentation
Deals with security issues when working with the R&S FSMR3 in secure areas. It is
available for download on the Internet.
Provides safety information in many languages. The printed document is delivered with
the product.
The data sheet contains the technical specifications of the R&S FSMR3. 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/FSMR3000/
1.2.7 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 open-source acknowledgment document provides verbatim license texts of the
used open source software.
See www.rohde-schwarz.com/firmware/FSMR3000/
1.2.8 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/FSMR3000/
1.3 Conventions used in the documentation
1.3.1 Typographical conventions
The following text markers are used throughout this documentation:
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Preface
Conventions used in the 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.
1.3.2 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.
1.3.3 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.
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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2 Welcome to the I/Q analyzer application
Welcome to the I/Q analyzer application
Starting the I/Q analyzer application
The R&S FSMR3 I/Q Analyzer is a firmware application that adds functionality to perform I/Q data acquisition and analysis to the R&S FSMR3.
The R&S FSMR3 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
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 FSMR3 User Manual.
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 FSMR3 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 FSMR3.
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 FSMR3.
2. Select the "I/Q Analyzer" item.
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Welcome to the I/Q analyzer application
Understanding the display information
The R&S FSMR3 opens a new channel 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, "Configura-
tion", on page 32).
Multiple Channels and Sequencer Function
When you activate an application, a new channel is created which determines the
measurement settings for that application (channel). The same application can be activated with different measurement settings by creating several channels for the same
application.
The number of channels 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. However, in order to perform the configured measurements consecutively, a Sequencer function is provided.
If activated, the measurements configured in the currently defined channels 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 channels 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 FSMR3 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 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 bar information
In the I/Q Analyzer application, the R&S FSMR3 shows the following settings:
Table 2-1: Information displayed in the channel bar for the I/Q Analyzer application
Ref Level Reference level
Att 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 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.
For details see the R&S FSMR3 Getting Started manual.
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.
Furthermore, the progress of the current operation is displayed in the status bar.
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3 Measurement and result displays
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 FSMR3 can then be evaluated in various different result displays. Select
the result displays using the SmartGrid functions.
Up to 6 evaluations can be displayed in the I/Q Analyzer at any time, including several
graphical diagrams, marker tables or peak lists.
For details on working with the SmartGrid see the R&S FSMR3 Getting Started manual.
Measurements in the time and frequency domain
The time and frequency domain measurements and the available results are described
in detail in the R&S FSMR3 User Manual.
Result displays for I/Q data:
Magnitude..................................................................................................................... 15
Spectrum.......................................................................................................................16
I/Q-Vector......................................................................................................................16
Real/Imag (I/Q)..............................................................................................................17
Phase vs. Time..............................................................................................................17
Marker Table................................................................................................................. 18
Marker Peak List........................................................................................................... 18
Magnitude
Shows the level values in time domain.
Remote command:
LAY:ADD:WIND? '1',RIGH,MAGN, see LAYout:ADD[:WINDow]? on page 136
Results:
TRACe<n>[:DATA]? on page 96
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Measurement and result displays
Spectrum
Displays the frequency spectrum of the captured I/Q samples.
Remote command:
LAY:ADD:WIND? '1',RIGH,FREQ, see LAYout:ADD[:WINDow]? on page 136
Results:
TRACe<n>[:DATA]? on page 96
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 136
Results:
TRACe<n>[:DATA]? on page 96
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 136
Results:
TRACe<n>[:DATA]? on page 96
Phase vs. Time
Shows the phase values in the time domain.
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Measurement and result displays
Remote command:
LAY:ADD? '1',RIGH, POLar, see LAYout:ADD[:WINDow]? on page 136
Marker Table
Displays a table with the current marker values for the active markers.
This table is displayed automatically if configured accordingly.
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 136
Results:
CALCulate<n>:MARKer<m>:X on page 100
CALCulate<n>:MARKer<m>:Y? on page 100
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.
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Measurement and result displays
Remote command:
LAY:ADD? '1',RIGH, PEAK, see LAYout:ADD[:WINDow]? on page 136
Results:
CALCulate<n>:MARKer<m>:X on page 100
CALCulate<n>:MARKer<m>:Y? on page 100
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4 Basics on I/Q data acquisition and process-
Basics on I/Q data acquisition and processing
Processing analog I/Q data from RF input
ing
Some background knowledge on basic terms and principles used when describing I/Q
data acquisition on the R&S FSMR3 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..............................................................20
● Basics on input from I/Q data files.......................................................................... 23
● Receiving and providing trigger signals.................................................................. 24
● I/Q data import and export...................................................................................... 25
● Basics on FFT.........................................................................................................25
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 FSMR3 performs frequency sweeps on
the input signal and measurements in the frequency and time domain. Other applications on the R&S FSMR3, 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 FSMR3. 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 FSMR3.
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Basics on I/Q data acquisition and processing
Processing analog I/Q data from RF input
The A/D converter samples the IF signal at a rate of 200 MHz. The digital signal is
down-converted to the complex baseband, lowpass-filtered, and the sample rate is
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 FSMR3 for a maximum
of 400 Msamples (400*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
Chapter 4.1.1, "Sample rate and maximum usable I/Q bandwidth for RF input",
on page 21).
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 FSMR3 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 FSMR3000
●
(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 FSMR3
●
Record length: the 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 FSMR3000. The passband of these digital filters determines the maximum usable
I/Q bandwidth. In consequence, signals within the usable I/Q bandwidth (passband)
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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
remain unchanged, while signals outside the usable I/Q bandwidth (passband) are
suppressed. Usually, the suppressed signals are noise, artifacts, and the second IF
sideband. If frequencies of interest to you are also suppressed, try to increase the output sample rate, which increases the maximum usable I/Q bandwidth.
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......... 22
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, that is, the maximum number of samples that can be captured, depends on the sample rate.
Table 4-1: Maximum record length
Sample rate Maximum record length
100 Hz to 200 MHz 440 Msamples
200 MHz to 20 GHz
(upsampling)
Usable I/Q
bandwidth [MHz]
90
80
70
60
50
40
30
20
10
220 Msamples
RF input:
BW = 0.80*f
80 MHz bandwidth
out
20 40 60 80 100 120 140
Figure 4-2: Relationship between maximum usable I/Q bandwidth and output sample rate
[…] 10000
Output sample
rate f
[MHz]
out
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4.2 Basics on input from I/Q data files
Basics on I/Q data acquisition and processing
Basics on input from I/Q data files
The I/Q data to be evaluated in a particular R&S FSMR3 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.
For example, you can capture I/Q data using the I/Q Analyzer application, store it to a
file, and then analyze the signal parameters for that data later using the Pulse application (if available).
The I/Q data must be stored in a format with the file extension .iq.tar. For a detailed
description, see Chapter A.3, "I/Q data file format (iq-tar)", on page 150.
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 importing data from an I/Q data file using the import functions provided by some
R&S FSMR3 applications, the data is only stored temporarily in the capture buffer. It
overwrites the current measurement data and is in turn overwritten by a new measurement. If you use an I/Q data file as input, the stored I/Q data remains available for any
number of subsequent measurements. Furthermore, the (temporary) data import
requires the current measurement settings in the current application to match the settings that were applied when the measurement results were stored (possibly in a different application). When the data is used as an input source, however, the data acquisition settings in the current application (attenuation, center frequency, measurement
bandwidth, sample rate) can be ignored. As a result, these settings cannot be changed
in the current application. Only the measurement time can be decreased, to perform
measurements on an extract of the available data (from the beginning of the file) only.
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.
Sample iq.tar files
If you have the optional R&S FSMR3 VSA application (R&S FSMR3-K70), some sample iq.tar files are provided in the C:/R_S/Instr/user/vsa/DemoSignals
directory on the R&S FSMR3.
Furthermore, you can create your own iq.tar files in the I/Q Analyzer, see Chap-
ter 7.2, "How to export and import I/Q data", on page 70.
Pre-trigger and post-trigger samples
In applications that use pre-triggers or post-triggers, if no pre-trigger or post-trigger
samples are specified in the I/Q data file, or too few trigger samples are provided to
satisfy the requirements of the application, the missing pre- or post-trigger values are
filled up with zeros. Superfluous samples in the file are dropped, if necessary. For pretrigger samples, values are filled up or omitted at the beginning of the capture buffer.
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4.3 Receiving and providing trigger signals
Basics on I/Q data acquisition and processing
Receiving and providing trigger signals
For post-trigger samples, values are filled up or omitted at the end of the capture buffer.
Using one of the "TRIGGER INPUT / OUTPUT" connectors of the R&S FSMR3000,
the R&S FSMR3 can use a signal from an external device as a trigger to capture data.
Alternatively, the internal trigger signal used by the R&S FSMR3000 can be output for
use by other connected devices. Using the same trigger on several devices is useful to
synchronize the transmitted and received signals within a measurement.
For details on the connectors see the R&S FSMR3 "Getting Started" manual.
External trigger as input
If the trigger signal for the R&S FSMR3 is provided by an external device, the trigger
signal source must be connected to the R&S FSMR3000 and the trigger source must
be defined as "External" in the R&S FSMR3.
Trigger output
The R&S FSMR3000 can provide output to another device either to pass on the internal trigger signal, or to indicate that the R&S FSMR3000 itself is ready to trigger.
The trigger signal can be output by the R&S FSMR3000 automatically, or manually by
the user. If it is provided automatically, a high signal is output when the
R&S FSMR3000 has triggered due to a sweep start ("Device Triggered"), or when the
R&S FSMR3000 is ready to receive a trigger signal after a sweep start ("Trigger
Armed").
Manual triggering
If the trigger output signal is initiated manually, the length and level (high/low) of the
trigger pulse is also user-definable. Note, however, that the trigger pulse level is always
opposite to the constant signal level defined by the output "Level" setting, e.g. for
"Level" = "High", a constant high signal is output to the connector until the "Send Trigger" button is selected. Then, a low pulse is provided.
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4.4 I/Q data import and export
Basics on I/Q data acquisition and processing
Basics on FFT
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)
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 FSMR3 later.
●
Capturing and saving I/Q signals with the R&S FSMR3 to analyze them with the
R&S FSMR3 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.
For example, you can capture I/Q data using the I/Q Analyzer application and then perform analog demodulation on that data using the R&S FSMR3 Analog Demodulation
application, if available.
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 "Save" or "Open" icon in the toolbar (see Chapter 5.2,
"Import/export functions", on page 34).
4.5 Basics on FFT
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.
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4.5.1 Window functions
Basics on I/Q data acquisition and processing
Basics on FFT
t[s]
FFT
f[Hz]
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.
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.
Various different window functions are provided in the R&S FSMR3 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
resolution
Magnitude
resolution
Sidelobe suppression
Measurement recommendation
Rectangular Best Worst Worst No function applied.
Separation of two tones with almost
equal amplitudes and a small frequency distance
Blackman-Harris
(default)
Good Good Good Harmonic detection and spurious
emission detection
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Basics on I/Q data acquisition and processing
Basics on FFT
Window type Frequency
Gauss (Alpha
= 0.4)
Flattop Worst Best Good Accurate single tone measurements
5-Term Good Good Best Measurements with very high
4.5.2 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 Weak signals and short duration
resolution
Sidelobe suppression
Measurement recommendation
dynamic range
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.
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Basics on I/Q data acquisition and processing
Basics on FFT
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.
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.
4.5.3 Dependencies between FFT parameters
FFT analysis in the R&S FSMR3 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.
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Basics on I/Q data acquisition and processing
Basics on FFT
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.
In advanced FFT mode, the FFT length is user-definable. If you use the arrow keys or
the rotary knob to change the FFT length, the value is incremented or decremented by
powers of 2. If you enter the value manually, any integer value from 3 to 524288 is
available.
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.
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 57.)
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 "Transformation Algorithm"
on page 59).
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LengthWindow
RateSample
BandwidthNormalizedRBW
3
RateSample*BandwidthNormalized
RBW
max
LengthcordRe,4096min
RateSampleBandwidth*Normalized
RBW
min
4.5.4 Frequency resolution of FFT results - RBW
Basics on I/Q data acquisition and processing
Basics on FFT
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:
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.
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