Rohde & Schwarz FSWP-K7 User Manual
R&S®FSWP-K7
Analog Modulation Analysis
User Manual
(;ÛÆé2)
1177569102
User Manual
Version 08
This manual describes the following R&S®FSWP models with firmware version 1.90 or higher:
●
R&S®FSWP8 (1322.8003K08)
●
R&S®FSWP26 (1322.8003K26)
●
R&S®FSWP50 (1322.8003K50)
The following firmware options are described:
●
R&S FSWP-K7 (1325.4238.02) (requires R&S FSWP-B1)
© 2019 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 the owners.
1177.5691.02 | Version 08 | R&S®FSWP-K7
Throughout this manual, products from Rohde & Schwarz are indicated without the ® symbol , e.g. R&S®FSWP is indicated as
R&S FSWP.
R&S®FSWP-K7
1 Preface.................................................................................................... 5
1.1 About this Manual......................................................................................................... 5
1.2 Documentation Overview............................................................................................. 6
1.3 Conventions Used in the Documentation...................................................................7
2 Welcome to the Analog Modulation Analysis Application.................9
2.1 Starting Analog Modulation Analysis......................................................................... 9
2.2 Understanding the Display Information....................................................................10
3 Measurements and Result Displays...................................................14
4 Measurement Basics........................................................................... 25
4.1 Demodulation Process............................................................................................... 25
Contents
Contents
4.2 Demodulation Bandwidth...........................................................................................27
4.3 Sample Rate and Demodulation Bandwidth.............................................................28
4.4 AF Triggers.................................................................................................................. 29
4.5 AF Filters......................................................................................................................29
4.6 Time Domain Zoom.....................................................................................................29
4.7 Analog Modulation Analysis in MSRA Operating Mode..........................................31
5 Configuration........................................................................................33
5.1 Configuration According to Digital Standards.........................................................33
5.2 Configuration Overview..............................................................................................35
5.3 Data Input and Output.................................................................................................36
5.4 Amplitude.....................................................................................................................43
5.5 Frequency.................................................................................................................... 46
5.6 Trigger Configuration................................................................................................. 47
5.7 Data Acquisition..........................................................................................................53
5.8 Demodulation.............................................................................................................. 57
5.9 Demodulation Display................................................................................................ 72
5.10 Automatic Settings..................................................................................................... 72
6 Analysis................................................................................................ 76
6.1 Trace Configuration.................................................................................................... 76
6.2 Marker Settings........................................................................................................... 77
3User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
6.3 Display Lines and Limit Lines....................................................................................77
7 I/Q Data Import and Export..................................................................78
7.1 Import/Export Functions............................................................................................ 78
7.2 How to Export and Import I/Q Data............................................................................81
8 How to Perform Measurements in the Analog Modulation Analysis
8.1 How to Export Trace Data and Numerical Results...................................................84
9 Measurement Example: Demodulating an FM Signal.......................85
10 Optimizing and Troubleshooting the Measurement......................... 91
11 Remote Commands for Analog Modulation Analysis...................... 92
11.1 Introduction................................................................................................................. 92
Contents
Application............................................................................................83
11.2 Common Suffixes........................................................................................................97
11.3 Remote Commands to Select the Application......................................................... 97
11.4 Remote Commands to Configure Analog Modulation Analysis...........................101
11.5 Configuring the Result Display................................................................................151
11.6 Working with Measurement Results........................................................................159
11.7 Analyzing Results..................................................................................................... 170
11.8 Importing and Exporting Data..................................................................................172
11.9 Programming Example.............................................................................................173
Annex.................................................................................................. 175
A Reference............................................................................................175
A.1 Predefined Standards and Settings........................................................................ 175
A.2 Formats for Returned Values: ASCII Format and Binary Format......................... 177
A.3 Reference: ASCII File Export Format...................................................................... 177
A.4 I/Q Data File Format (iq-tar)......................................................................................178
List of Commands..............................................................................184
Index....................................................................................................188
4User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
1 Preface
1.1 About this Manual
Preface
About this Manual
This Analog Modulation Analysis User Manual provides all the information specific to
the application. All general instrument functions and settings common to all applications and operating modes are described in the main R&S FSWP 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 Analog Modulation Analysis Application
Introduction to and getting familiar with the application
●
Measurements and Result Displays
Details on supported measurements and their result types
●
Measurement Basics
Background information on basic terms and principles in the context of the measurement
●
Configuration + Analysis
A concise description of all functions and settings available to configure measurements and analyze results with their corresponding remote control command
●
I/Q Data Import and Export
Description of general functions to import and export raw I/Q (measurement) data
●
How to Perform Measurements in the Analog Modulation Analysis Application
The basic procedure to perform each measurement and step-by-step instructions
for more complex tasks or alternative methods
●
Measurement Examples
Detailed measurement examples to guide you through typical measurement scenarios and allow you to try out the application immediately
●
Optimizing and Troubleshooting the Measurement
Hints and tips on how to handle errors and optimize the measurement configuration
●
Remote Commands for Analog Modulation Analysis Measurements
Remote commands required to configure and perform Analog Modulation Analysis
measurements 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 FSWP User Manual)
Programming examples demonstrate the use of many commands and can usually
be executed directly for test purposes
●
List of remote commands
Alphabetical list of all remote commands described in the manual
●
Index
5User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
1.2 Documentation Overview
1.2.1 Getting Started Manual
Preface
Documentation Overview
This section provides an overview of the R&S FSWP user documentation. Unless
specified otherwise, you find most of the documents on the R&S FSWP product page
at:
www.rohde-schwarz.com/manual/fswp
Introduces the R&S FSWP 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.
1.2.2 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.
●
Manuals for (optional) firmware applications
Contains the description of the specific functions of a firmware application, including remote control commands. Basic information on operating the R&S FSWP is
not included.
The contents of the user manuals are available as help in the R&S FSWP. 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 download for registered users on the global
Rohde & Schwarz information system (GLORIS):
https://gloris.rohde-schwarz.com
6User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
1.2.4 Instrument Security Procedures
1.2.5 Basic 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 FSWP in secure areas. It is
available for download on the Internet.
Contains safety instructions, operating conditions and further important information.
The printed document is delivered with the instrument.
The data sheet contains the technical specifications of the R&S FSWP. It also lists the
options 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/fswp
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/fswp
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/fswp
1.3 Conventions Used in the Documentation
1.3.1 Typographical Conventions
The following text markers are used throughout this documentation:
7User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
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.
8User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
2 Welcome to the Analog Modulation Analysis
Welcome to the Analog Modulation Analysis Application
Starting Analog Modulation Analysis
Application
The R&S FSWP-K7 AM/FM/PM measurement demodulator option converts the
R&S FSWP into an analog modulation analyzer for amplitude-, frequency- or phasemodulated signals. It measures not only characteristics of the useful modulation, but
also factors such as residual FM or synchronous modulation.
The R&S FSWP Analog Modulation Analysis application features:
●
AM, FM, and PM demodulation, with various result displays:
– Modulation signal versus time
– Spectrum of the modulation signal (FFT)
– RF signal power versus time
– Spectrum of the RF signal
●
Determining maximum, minimum and average or current values in parallel over a
selected number of measurements
●
Maximum accuracy and temperature stability due to sampling (digitization) already
at the IF and digital down-conversion to the baseband (I/Q)
●
Error-free AM to FM conversion and vice versa, without deviation errors, frequency
response or frequency drift at DC coupling
●
Relative demodulation, in relation to a user-defined or measured reference value
Availability of the analog modulation analysis application
Analog modulation analysis requires the optional spectrum analyzer hardware
(R&S FSWP-B1).
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 FSWP User Manual. The latest version is available for download
at the product homepage http://www.rohde-schwarz.com/product/fswp.
Installation
You can find detailed installation instructions in the R&S FSWP Getting Started manual
or in the Release Notes.
2.1 Starting Analog Modulation Analysis
Analog modulation analysis is a separate application on the R&S FSWP.
9User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Welcome to the Analog Modulation Analysis Application
Understanding the Display Information
To activate analog modulation analysis
1. Select the [MODE] key.
A dialog box opens that contains all operating modes and applications currently
available on your R&S FSWP.
2. Select the "Analog Demod" item.
The R&S FSWP opens a new channel for the application for analog modulation
analysis.
The measurement is started immediately with the default settings. It can be configured
in the analog modulation analysis Configuration Overview dialog box, which is displayed when you select the "Overview" softkey from any menu.
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 "Channel"s 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 "Channel"s 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 FSWP User Manual.
symbol in the tab label.
2.2 Understanding the Display Information
The following figure shows a measurement diagram during analog modulation analysis. All different information areas are labeled. They are explained in more detail in the
following sections.
10User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Welcome to the Analog Modulation Analysis Application
Understanding the Display Information
1 = Channel bar for firmware and measurement settings
2+3 = Window title bar with diagram-specific (trace) information
4 = Diagram area
5 = Diagram footer with diagram-specific information, depending on result display
6 = Instrument status bar with error messages and date/time display
MSRA operating mode
In MSRA operating mode, additional tabs and elements are available. A colored background of the screen behind the channel tabs indicates that you are in MSRA operating
mode.
For details on the MSRA operating mode see the R&S FSWP MSRA User Manual.
Channel bar information
In the Analog Modulation Analysis application, the R&S FSWP shows the following settings:
Table 2-1: Information displayed in the channel bar in the application for analog modulation analysis
Ref Level Reference level
m.+el.Att Mechanical and electronic RF attenuation
Offset Reference level offset
AQT Measurement time for data acquisition.
RBW Resolution bandwidth
DBW Demodulation bandwidth
Freq Center frequency for the RF signal
11User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Welcome to the Analog Modulation Analysis Application
Understanding the Display Information
Window title bar information
For each diagram, the header provides the following information:
Figure 2-1: Window title bar information in the application for analog modulation analysis
1 = Window number
2 = Modulation type
3 = Trace color
4 = Trace number
5 = Detector
6 = Trace mode
7 = Reference value (at the defined reference position)
8 = AF coupling (AC/DC), only in AF time domains, if applicable
9 = Results are selected for demodulation output
Diagram footer information
The diagram footer (beneath the diagram) contains the following information, depending on the evaluation:
RF Spectrum
CF: Center frequency
of input signal
RF Time domain
CF: Center frequency
of input signal
AF Spectrum
AF CF: center frequency of demodulated signal
AF Time domain
CF: Center frequency
of input signal
Sweep points Span: measured span
Sweep points Time per division
Sweep points AF Span: evaluated span
Sweep points Time per division
For most modes, the number of sweep points shown in the display are indicated in the
diagram footer. In zoom mode, the (rounded) number of currently displayed points are
indicated.
Status bar information
Global instrument settings, the instrument status and any irregularities are indicated in
the status bar beneath the diagram.
12User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Welcome to the Analog Modulation Analysis Application
Understanding the Display Information
Furthermore, the progress of the current operation is displayed in the status bar.
13User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
3 Measurements and Result Displays
Measurements and Result Displays
Access: "Overview" > "Display Config"
Or: [MEAS] > "Display Config"
The data that was measured by the R&S FSWP can be evaluated using various different methods. In the Analog Modulation Analysis application, up to six evaluation methods can be displayed simultaneously in separate windows. The results can be displayed as absolute deviations or relative to a reference value or level.
The abbreviation "AF" (for Audio Frequency) refers to the demodulated AM, FM or PM
signal.
Basis for evaluation
All evaluations are based on the I/Q data set acquired during the measurement. The
spectrum of the modulated signal to be evaluated is determined by the demodulation
bandwidth. However, it can be restricted to a limited span ("AF Span") if only part of the
signal is of interest. Furthermore, the time base for evaluations in the time domain can
be restricted to analyze a smaller extract in more detail, see Chapter 4.6, "Time
Domain Zoom", on page 29.
AM Time Domain...........................................................................................................14
FM Time Domain...........................................................................................................15
PM Time Domain...........................................................................................................16
AM Spectrum................................................................................................................ 17
FM Spectrum.................................................................................................................18
PM Spectrum................................................................................................................ 19
RF Time Domain...........................................................................................................20
RF Spectrum.................................................................................................................21
Result Summary............................................................................................................22
Marker Table................................................................................................................. 23
Marker Peak List........................................................................................................... 24
AM Time Domain
Displays the modulation depth of the demodulated AM signal (in %) versus time.
14User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurements and Result Displays
Remote command:
LAY:ADD? '1',RIGH,'XTIM:AM:REL'
(See LAYout:ADD[:WINDow]? on page 153)
FM Time Domain
Displays the frequency spectrum of the demodulated FM signal versus time.
15User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurements and Result Displays
Remote command:
LAY:ADD? '1',RIGH,'XTIM:FM'
(See LAYout:ADD[:WINDow]? on page 153)
PM Time Domain
Displays the phase deviations of the demodulated PM signal (in rad or °) versus time.
16User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurements and Result Displays
Remote command:
LAY:ADD? '1',RIGH,'XTIM:PM'
(See LAYout:ADD[:WINDow]? on page 153)
AM Spectrum
Displays the modulation depth of the demodulated AM signal (in % or dB) versus AF
span. The spectrum is calculated from the demodulated AM signal in the time domain
via FFT.
17User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurements and Result Displays
Note: If a high pass or low pass AF filter is defined, the filter is indicated by a vertical
red line in the spectrum display.
Remote command:
LAY:ADD? '1',RIGH,'XTIMe:AM:REL:AFSPectrum1'
(see LAYout:ADD[:WINDow]? on page 153)
FM Spectrum
Displays the frequency deviations of the demodulated FM signal (in Hz or dB) versus
AF span. The spectrum is calculated from the demodulated AM signal in the time
domain via FFT.
18User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurements and Result Displays
Note: If a high pass or low pass AF filter is defined, the filter is indicated by a vertical
red line in the spectrum display.
Remote command:
LAY:ADD? '1',RIGH,'XTIMe:FM:AFSPectrum1'
(see LAYout:ADD[:WINDow]? on page 153)
PM Spectrum
Displays the phase deviations of the demodulated PM signal (in rad, ° or dB) versus
AF span. The spectrum is calculated from the demodulated AM signal in the time
domain via FFT.
19User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurements and Result Displays
Note: If a high pass or low pass AF filter is defined, the filter is indicated by a vertical
red line in the spectrum display.
Remote command:
LAY:ADD? '1',RIGH,'XTIMe:PM:AFSPectrum1'
(see LAYout:ADD[:WINDow]? on page 153)
RF Time Domain
Displays the RF power of the input signal versus time. The level values represent the
magnitude of the I/Q data set.
20User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurements and Result Displays
Remote command:
LAY:ADD? '1',RIGH,'XTIM:AM'
(see LAYout:ADD[:WINDow]? on page 153)
RF Spectrum
Displays the spectrum of the input signal. In contrast to the Spectrum application, the
frequency values are determined using FFT from the recorded I/Q data set.
21User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurements and Result Displays
Remote command:
LAY:ADD? '1',RIGH,'XTIM:SPECTRUM'
(see LAYout:ADD[:WINDow]? on page 153)
Result Summary
The result summary displays the results of the demodulation functions for all windows
in a table.
For each demodulation, the following information is provided:
Table 3-1: Result summary description
Label Description
+Peak Positive peak (maximum)
-Peak Negative peak (minimum)
+/-Peak/2 Average of positive and negative peaks
RMS Root Mean Square value
Mod Freq Modulation frequency
22User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
power distortion noise
power total
log20dBSINAD
1
2
2
2
log20
i
i
i
i
U
U
dBTHD
Measurements and Result Displays
Label Description
SINAD Signal-to-noise-and-distortion
(Calculated only if AF Spectrum is displayed)
Measures the ratio of the total power to the power of noise and harmonic distortions.
The noise and harmonic power is calculated inside the AF spectrum span. The DC
offset is removed before the calculation.
THD Total harmonic distortion
The ratio of the harmonics to the fundamental and harmonics. All harmonics inside
the AF spectrum span are considered up to the tenth harmonic.
(Calculated only if AF Spectrum is displayed)
Note: Relative demodulation results. Optionally, the demodulation results in relation to
user-defined or measured reference values are determined. See Chapter 5.8.6, "Result
Table Settings", on page 70.
In addition, the following general information for the input signal is provided:
●
Carrier Power: the power of the carrier without modulation
●
Carrier Offset: the deviation of the calculated carrier frequency to the ideal carrier
frequency
●
Modulation Depth (AM or RF Time Domain only): the difference in amplitude the
carrier signal is modulated with
Remote command:
LAY:ADD? '1',RIGH,RSUM, see LAYout:ADD[:WINDow]? on page 153
Results:
CALCulate<n>:MARKer<m>:FUNCtion:ADEMod:PM[:RESult<t>]? on page 164
CALCulate<n>:MARKer<m>:FUNCtion:ADEMod:PM[:RESult<t>]:RELative?
on page 164
Marker Table
Displays a table with the current marker values for the active markers.
This table is displayed automatically if configured accordingly.
Type Shows the marker type and number ("M" for a nor-
mal marker, "D" for a delta marker).
Ref Shows the reference marker that a delta marker
refers to.
Trace Shows the trace that the marker is positioned on.
X- / Y-Value Shows the marker coordinates (usually frequency
and level).
23User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurements and Result Displays
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 153
Results:
CALCulate<n>:MARKer<m>:X on page 167
CALCulate<n>:MARKer<m>:Y on page 168
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.
Tip: To navigate within long marker peak lists, simply scroll through the entries with
your finger on the touchscreen.
Remote command:
LAY:ADD? '1',RIGH, PEAK, see LAYout:ADD[:WINDow]? on page 153
Results:
CALCulate<n>:MARKer<m>:X on page 167
CALCulate<n>:MARKer<m>:Y on page 168
24User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
4 Measurement Basics
4.1 Demodulation Process
Measurement Basics
Demodulation Process
Some background knowledge on basic terms and principles used in Analog Modulation
Analysis measurements is provided here for a better understanding of the required
configuration settings.
● Demodulation Process............................................................................................25
● Demodulation Bandwidth........................................................................................ 27
● Sample Rate and Demodulation Bandwidth........................................................... 28
● AF Triggers............................................................................................................. 29
● AF Filters.................................................................................................................29
● Time Domain Zoom.................................................................................................29
● Analog Modulation Analysis in MSRA Operating Mode..........................................31
The demodulation process is shown in Figure 4-1. All calculations are performed simultaneously with the same I/Q data set. Magnitude (= amplitude) and phase of the complex I/Q pairs are determined. The frequency result is obtained from the differential
phase.
For details on general I/Q data processing in the R&S FSWP, refer to the reference
part of the I/Q Analysis remote control description in the R&S FSWP User Manual.
25User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurement Basics
Demodulation Process
Figure 4-1: Block diagram of software demodulator
26User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurement Basics
Demodulation Bandwidth
The AM DC, FM DC and PM DC raw data of the demodulators is fed into the "Trace
Arithmetic" block that combines consecutive data sets. Possible trace modes are:
Clear Write, Max Hold, Min Hold and Average. The output data of the "Trace Arithmetic" block can be read via remote control ([SENS:]ADEM:<evaluation>:RES?,
see [SENSe:]ADEMod:AM[:ABSolute][:TDOMain]:RESult? on page 161.
The collected measured values are evaluated by the selected detector. The result is
displayed on the screen and can be read out via remote control.
In addition, important parameters are calculated:
●
A counter determines the modulation frequency for AM, FM, and PM.
●
average power = carrier power (RF power)
●
average frequency = carrier frequency offset (FM)
●
The modulation depth or the frequency or phase deviation; the deviations are
determined from the trace data
AC coupling is possible with FM and PM display.
4.2 Demodulation Bandwidth
The demodulation bandwidth determines the span of the signal that is demodulated. It
is not the 3 dB bandwidth of the filter but the useful bandwidth which is distortion-free
with regard to phase and amplitude.
Therefore the following formulas apply:
●
AM: demodulation bandwidth ≥ 2 x modulation frequency
●
FM: demodulation bandwidth ≥ 2 x (frequency deviation + modulation frequency)
●
PM: demodulation bandwidth ≥ 2 x modulation frequency x (1 + phase deviation)
If the center frequency of the analyzer is not set exactly to the signal frequency, the
demodulation bandwidth must be increased by the carrier offset, in addition to the
requirement described above. This also applies if FM or PM AC coupling has been
selected.
In general, the demodulation bandwidth should be as narrow as possible to improve
the S/N ratio. The residual FM caused by noise floor and phase noise increases dramatically with the bandwidth, especially with FM.
For help on determining the adequate demodulation bandwidth see "Determining the
demodulation bandwidth" on page 91.
A practical example is described in Chapter 9, "Measurement Example: Demodulating
an FM Signal", on page 85.
27User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
4.3 Sample Rate and Demodulation Bandwidth
Measurement Basics
Sample Rate and Demodulation Bandwidth
The maximum demodulation bandwidths that can be obtained during the measurement, depending on the sample rate, are listed in the tables below for different demodulation filter types. The allowed value range of the measurement time and trigger offset
depends on the selected demodulation bandwidth and demodulation filter. If the AF filter or the AF trigger are not active, the measurement time increases by 20 %.
A maximum of 24 million samples can be captured, assuming sufficient memory is
available; thus the maximum measurement time can be determined according to the
following formula:
Meas.time
The minimum trigger offset is (-Meas.time
Table 4-1: Available demodulation bandwidths and corresponding sample rates
Demodulation BW Sample Rate (Flat Top) Sample Rate (Gaussian Top)
= Sample count
max
/ sample rate
max
max
)
100 Hz 122.0703125 Hz 400 Hz
200 Hz 244.140625 Hz 800 Hz
400 Hz 488.28125 Hz 1.6 kHz
800 Hz 976.5625 Hz 3.2 kHz
1.6 kHz 1.953125 kHz 6.4 kHz
3.2 kHz 3.90625 kHz 12.8 kHz
6.4 kHz 7.8125 kHz 25.6 kHz
12.5 kHz 15.625 kHz 50 kHz
25 kHz 31.25 kHz 100 kHz
50 kHz 62.5 kHz 200 kHz
100 kHz 125 kHz 400 kHz
200 kHz 250 kHz 800 kHz
400 kHz 500 kHz 1.6 MHz
800 kHz 1 MHz 3.2 MHz
1.6 MHz 2 MHz 6.4 MHz
3 MHz 4 MHz 12 MHz
5 MHz 8 MHz 20 MHz
8 MHz 16 MHz 32 MHz
10 MHz 32 MHz 40 MHz
80 MHz
160 MHz
1)
2)
128 MHz 320 MHz
200 MHz 640 MHz
28User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurement Basics
Time Domain Zoom
Demodulation BW Sample Rate (Flat Top) Sample Rate (Gaussian Top)
320 MHz
1)
2)
2)
only available with option B80
only available with option B320
400 MHz 1280 MHz
Large numbers of samples
Principally, the R&S FSWP can handle up to 24 million samples. However, when
480001 samples are exceeded, all traces that are not currently being displayed in a
window are deactivated to improve performance. The traces can only be activated
again when the samples are reduced.
Effects of measurement time on the stability of measurement results
Despite amplitude and frequency modulation, the display of carrier power and carrier
frequency offset is stable.
This is achieved by a digital filter which sufficiently suppresses the modulation, provided, however, that the measurement time is ≥ 3 x 1 / modulation frequency, i.e. that at
least three periods of the AF signal are recorded.
The mean carrier power for calculating the AM is also calculated with a digital filter that
returns stable results after a measurement time of ≥ 3 x 1 / modulation frequency, i.e.
at least three cycles of the AF signal must be recorded before a stable AM can be
shown.
4.4 AF Triggers
The Analog Modulation Analysis application allows triggering to the demodulated signal. The display is stable if a minimum of five modulation periods are within the recording time.
Triggering is always DC-coupled. Therefore triggering is possible directly to the point
where a specific carrier level, phase or frequency is exceeded or not attained.
4.5 AF Filters
Additional filters applied after demodulation help filter out unwanted signals, or correct
pre-emphasized input signals. A CCITT filter allows you to evaluate the signal by simulating the characteristics of human hearing.
4.6 Time Domain Zoom
For evaluations in the time domain, the demodulated data for a particular time span
can be extracted and displayed in more detail using the "Time Domain Zoom" function.
29User Manual 1177.5691.02 ─ 08
R&S®FSWP-K7
Measurement Basics
Time Domain Zoom
This is useful if the measurement time is very large and thus each sweep point represents a large time span. The time domain zoom function distributes the available
sweep points only among the time span defined by the zoom area length. The time
span displayed per division of the diagram is decreased. Thus, the display of the
extracted time span becomes more precise.
Figure 4-2: FM time domain measurement with a very long measurement time (200 ms)
Figure 4-3: FM time domain measurement with time domain zoom (2.0 ms per division)
The time domain zoom area affects not only the diagram display, but the entire evaluation for the current window.
In contrast to the time domain zoom, the graphical zoom is available for all diagram
evaluations. However, the graphical zoom is useful only if more measured values than
trace points are available. The (time) span represented by each measurement point
remains the same.
30User Manual 1177.5691.02 ─ 08
Loading...