R&S®FPL1-K7
AM/FM/PM Modulation Analysis
Option
User Manual
(;ÜQê2)
1178339202
Version 10
This manual applies to the following R&S®FPL1000 models with firmware version 2.00 and later:
●
R&S®FPL1003 (1304.0004K03) - FPL1000 with maximum frequency 3 GHz
●
R&S®FPL1007 (1304.0004K07) - FPL1000 with maximum frequency 7.5 GHz
●
R&S®FPL1014 (1304.0004K14) - FPL1000 with maximum frequency 14 GHz
●
R&S®FPL1026 (1304.0004K26) - FPL1000 with maximum frequency 26.5 GHz
The following firmware options are described:
●
R&S FPL1-K7 (1323.1731.02)
© 2022 Rohde & Schwarz GmbH & Co. KG
Muehldorfstr. 15, 81671 Muenchen, Germany
Phone: +49 89 41 29 - 0
Email: info@rohde-schwarz.com
Internet: www.rohde-schwarz.com
Subject to change – data without tolerance limits is not binding.
R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG.
All other trademarks are the properties of their respective owners.
1178.3392.02 | Version 10 | R&S®FPL1-K7
Throughout this manual, products from Rohde & Schwarz are indicated without the ® symbol, e.g. R&S®FPL1000 is indicated as
R&S FPL1000.
R&S®FPL1-K7
1.1 Documentation overview..............................................................................................7
1.1.1 Getting started manual....................................................................................................7
1.1.2 User manuals and help................................................................................................... 7
1.1.3 Service manual............................................................................................................... 7
1.1.4 Instrument security procedures.......................................................................................8
1.1.5 Printed safety instructions............................................................................................... 8
1.1.6 Data sheets and brochures............................................................................................. 8
1.1.7 Release notes and open source acknowledgment (OSA).............................................. 8
1.1.8 Application notes, application cards, white papers, etc...................................................8
1.1.9 Calibration certificate.......................................................................................................9
Contents
Contents
1 Preface.................................................................................................... 7
1.2 Conventions used in the documentation....................................................................9
1.2.1 Typographical conventions..............................................................................................9
1.2.2 Conventions for procedure descriptions..........................................................................9
1.2.3 Notes on screenshots..................................................................................................... 9
2 Welcome to the R&S FPL1-K7 AM/FM/PM Modulation Analysis
application............................................................................................ 11
2.1 Starting AM/FM/PM Modulation Analysis..................................................................11
2.2 Understanding the display information.................................................................... 12
3 Measurements and result displays.................................................... 15
4 Measurement basics............................................................................26
4.1 Demodulation process............................................................................................... 26
4.2 Demodulation bandwidth........................................................................................... 28
4.3 Sample rate and demodulation bandwidth...............................................................29
4.4 AF triggers................................................................................................................... 30
4.5 AF filters.......................................................................................................................30
4.6 Time domain zoom......................................................................................................31
5 Configuration........................................................................................33
5.1 Configuration overview.............................................................................................. 33
5.2 Configuration according to standards......................................................................35
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5.3 Input and frontend settings........................................................................................37
5.3.1 Radio frequency input................................................................................................... 37
5.3.2 Settings for input from I/Q data files..............................................................................39
5.3.3 Amplitude settings.........................................................................................................40
5.3.4 Frequency..................................................................................................................... 44
5.4 Trigger configuration..................................................................................................45
5.4.1 Trigger source settings..................................................................................................45
5.5 Data acquisition.......................................................................................................... 48
5.5.1 Bandwidth settings........................................................................................................ 48
5.5.2 Sweep settings..............................................................................................................50
5.6 Demodulation display.................................................................................................53
5.7 Demodulation.............................................................................................................. 53
5.7.1 Basic demodulation measurement parameters (Demod)..............................................53
Contents
5.7.2 Demodulation spectrum................................................................................................ 56
5.7.3 AF filter..........................................................................................................................59
5.7.4 Scaling.......................................................................................................................... 62
5.7.5 Units.............................................................................................................................. 67
5.7.6 Result table settings......................................................................................................67
5.7.7 Settling time.................................................................................................................. 70
5.8 Output settings............................................................................................................72
5.9 Adjusting settings automatically...............................................................................72
6 Analysis................................................................................................ 76
6.1 Trace settings..............................................................................................................76
6.2 Spectrogram settings................................................................................................. 80
6.2.1 General spectrogram settings....................................................................................... 80
6.2.2 Color map settings........................................................................................................ 84
6.3 Trace / data export configuration.............................................................................. 85
6.4 Working with markers in the R&S FPL1-K7 AM/FM/PM Modulation Analysis appli-
cation............................................................................................................................88
6.4.1 Marker settings..............................................................................................................88
6.4.2 Marker search settings and positioning functions......................................................... 93
6.4.3 Marker search settings for spectrograms......................................................................96
6.4.4 Marker function configuration........................................................................................98
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8.1 How to export trace data and numerical results.................................................... 110
10 Optimizing and troubleshooting the measurement........................ 116
11 Remote commands for AM/FM/PM Modulation Analysis............... 117
11.1 Introduction............................................................................................................... 118
11.1.1 Conventions used in descriptions................................................................................118
11.1.2 Long and short form.................................................................................................... 119
11.1.3 Numeric suffixes..........................................................................................................119
11.1.4 Optional keywords.......................................................................................................120
Contents
7 I/Q data import and export................................................................ 108
8 How to perform measurements in the R&S FPL1-K7 AM/FM/PM
Modulation Analysis application...................................................... 109
9 Measurement example: demodulating an FM signal...................... 111
11.1.5 Alternative keywords................................................................................................... 120
11.1.6 SCPI parameters.........................................................................................................120
11.2 Common suffixes......................................................................................................123
11.3 Activating analog modulation analysis...................................................................123
11.4 Configuring the measurement.................................................................................126
11.4.1 Managing standard settings........................................................................................ 127
11.4.2 Configuring the input................................................................................................... 128
11.4.3 Configuring the output.................................................................................................132
11.4.4 Frequency settings......................................................................................................133
11.4.5 Configuring the vertical axis (amplitude, scaling)........................................................135
11.4.6 Configuring data acquisition........................................................................................141
11.4.7 Triggering.................................................................................................................... 145
11.4.8 Configuring demodulation........................................................................................... 151
11.4.9 Adjusting settings automatically.................................................................................. 171
11.5 Capturing data and performing sweeps................................................................. 175
11.6 Configuring the result display................................................................................. 179
11.6.1 General window commands........................................................................................179
11.6.2 Working with windows in the display...........................................................................180
11.7 Retrieving results......................................................................................................186
11.7.1 Retrieving trace results............................................................................................... 187
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11.7.2 Exporting trace results................................................................................................ 190
11.7.3 Retrieving result summary values............................................................................... 192
11.7.4 Formats for returned values: ASCII format and binary format.................................... 196
11.7.5 Reference: ASCII file export format............................................................................ 197
11.8 Analyzing results...................................................................................................... 199
11.8.1 Configuring spectrograms........................................................................................... 199
11.8.2 Configuring standard traces........................................................................................ 207
11.8.3 Working with markers remotely...................................................................................214
11.8.4 Marker search (spectrograms).................................................................................... 248
11.8.5 Defining limit checks................................................................................................... 257
11.9 Importing and exporting I/Q data and results........................................................ 272
11.10 Deprecated commands.............................................................................................274
11.11 Programming example............................................................................................. 275
Contents
Annex.................................................................................................. 278
A Predefined standards and settings.................................................. 278
List of commands (Analog Modulation Analysis)...........................280
Index....................................................................................................289
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1 Preface
1.1 Documentation overview
1.1.1 Getting started manual
Preface
Documentation overview
This chapter provides safety-related information, an overview of the user documentation and the conventions used in the documentation.
This section provides an overview of the R&S FPL1000 user documentation. Unless
specified otherwise, you find the documents at:
www.rohde-schwarz.com/manual/FPL1000
Introduces the R&S FPL1000 and describes how to set up and start working with the
product. Includes basic operations, typical measurement examples, and general information, e.g. safety instructions, etc.
A printed version is delivered with the instrument. A PDF version is available for download on the Internet.
1.1.2 User manuals and help
Separate user manuals are provided for the base unit and the firmware applications:
●
Base unit manual
Contains the description of all instrument modes and functions. It also provides an
introduction to remote control, a complete description of the remote control commands with programming examples, and information on maintenance, instrument
interfaces and error messages. Includes the contents of the getting started manual.
●
Firmware application manual
Contains the description of the specific functions of a firmware application, including remote control commands. Basic information on operating the R&S FPL1000 is
not included.
The contents of the user manuals are available as help in the R&S FPL1000. The help
offers quick, context-sensitive access to the complete information for the base unit and
the firmware applications.
All user manuals are also available for download or for immediate display on the Internet.
1.1.3 Service manual
Describes the performance test for checking compliance with rated specifications, firmware update, troubleshooting, adjustments, installing options and maintenance.
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1.1.4 Instrument security procedures
1.1.5 Printed safety instructions
1.1.6 Data sheets and brochures
Preface
Documentation overview
The service manual is available for registered users on the global Rohde & Schwarz
information system (GLORIS):
https://gloris.rohde-schwarz.com
Deals with security issues when working with the R&S FPL1000 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 FPL1000. 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/FPL1000
1.1.7 Release notes and open source acknowledgment (OSA)
The release notes list new features, improvements and known issues of the current
firmware version, and describe the firmware installation.
The software makes use of several valuable open source software packages. An opensource acknowledgment document provides verbatim license texts of the used open
source software.
See www.rohde-schwarz.com/firmware/FPL1000
1.1.8 Application notes, application cards, white papers, etc.
These documents deal with special applications or background information on particular topics.
See www.rohde-schwarz.com/application/FPL1000
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1.1.9 Calibration certificate
1.2 Conventions used in the documentation
1.2.1 Typographical conventions
Preface
Conventions used in the documentation
The document is available on https://gloris.rohde-schwarz.com/calcert. You need the
device ID of your instrument, which you can find on a label on the rear panel.
The following text markers are used throughout this documentation:
Convention Description
"Graphical user interface elements"
[Keys] Key and knob names are enclosed by square brackets.
Filenames, commands,
program code
Input Input to be entered by the user is displayed in italics.
Links Links that you can click are displayed in blue font.
"References" References to other parts of the documentation are enclosed by quota-
All names of graphical user interface elements on the screen, such as
dialog boxes, menus, options, buttons, and softkeys are enclosed by
quotation marks.
Filenames, commands, coding samples and screen output are distinguished by their font.
tion marks.
1.2.2 Conventions for procedure descriptions
When operating the instrument, several alternative methods may be available to perform the same task. In this case, the procedure using the touchscreen is described.
Any elements that can be activated by touching can also be clicked using an additionally connected mouse. The alternative procedure using the keys on the instrument or
the on-screen keyboard is only described if it deviates from the standard operating procedures.
The term "select" may refer to any of the described methods, i.e. using a finger on the
touchscreen, a mouse pointer in the display, or a key on the instrument or on a keyboard.
1.2.3 Notes on screenshots
When describing the functions of the product, we use sample screenshots. These
screenshots are meant to illustrate as many as possible of the provided functions and
possible interdependencies between parameters. The shown values may not represent
realistic usage scenarios.
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Preface
Conventions used in the documentation
The screenshots usually show a fully equipped product, that is: with all options installed. Thus, some functions shown in the screenshots may not be available in your particular product configuration.
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2 Welcome to the R&S FPL1-K7 AM/FM/PM
Welcome to the R&S FPL1-K7 AM/FM/PM Modulation Analysis application
Starting AM/FM/PM Modulation Analysis
Modulation Analysis application
The R&S FPL1-K7 AM/FM/PM Modulation Analysis application option converts the
R&S FPL1000 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 FPL1-K7 AM/FM/PM 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 R&S FPL1-K7 AM/FM/PM Modulation Analysis application
Using the R&S FPL1-K7 AM/FM/PM Modulation Analysis application requires the
optional AM/FM/PM Modulation Analysis firmware (R&S FPL1-K7).
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 FPL1000 User Manual. The latest version is available for download at the product homepage http://www.rohde-schwarz.com/product/FPL1000.
2.1 Starting AM/FM/PM Modulation Analysis
AM/FM/PM Modulation Analysis is a separate application on the R&S FPL1000.
To activate AM/FM/PM Modulation Analysis
1. Select the [MODE] key.
A dialog box opens that contains all operating modes and applications currently
available on your R&S FPL1000.
2. Select the "AM FM PM Analog Demod" item.
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Welcome to the R&S FPL1-K7 AM/FM/PM Modulation Analysis application
Understanding the display information
The R&S FPL1000 opens a new channel setup 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 "Overview" dialog box, which is displayed when you
select the "Overview" softkey from any menu (see Chapter 5.1, "Configuration over-
view", on page 33).
Multiple Channel setups and Sequencer Function
When you activate an application, a new channel setup is created which determines
the measurement settings for that application ("Channel"). The same application can
be activated with different measurement settings by creating several "Channel"s for the
same application.
The number of channel setups that can be configured at the same time depends on the
available memory on the instrument.
Only one measurement can be performed at any time, namely the one in the currently
active channel setup. However, 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 channel setups are updated in the tabs (as well as
the "MultiView") as the measurements are performed. Sequential operation itself is
independent of the currently displayed tab.
For details on the Sequencer function, see the R&S FPL1000 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.
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Welcome to the R&S FPL1-K7 AM/FM/PM Modulation Analysis application
Understanding the display information
1
2
3
4
5
1 = Channel setup bar for firmware and measurement settings
2 = Diagram area
3 = Window title bar with diagram-specific (trace) information
4 = Instrument status bar with error messages and date/time display
5 = Diagram footer with diagram-specific information, depending on result display
Channel setup bar information
In the Analog Modulation Analysis application, the R&S FPL1000 shows the following
settings:
Table 2-1: Information displayed in the channel setup bar in the application for analog modulation
Ref Level Reference level
Att RF attenuation applied to input
Offset Reference level offset
AQT Measurement time for data acquisition.
RBW Resolution bandwidth
DBW Demodulation bandwidth
Freq Center frequency for the RF signal
analysis
Window title bar information
For each diagram, the header provides the following information:
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Welcome to the R&S FPL1-K7 AM/FM/PM Modulation Analysis application
Understanding the display information
1 2 345 6 7 8 9
Figure 2-1: Window title bar information in the application for analog modulation analysis
1 = Window number
2 = Window 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.
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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 FPL1000 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 31.
AM Time Domain...........................................................................................................15
FM Time Domain...........................................................................................................16
PM Time Domain...........................................................................................................17
AM Spectrum................................................................................................................ 18
FM Spectrum.................................................................................................................19
PM Spectrum................................................................................................................ 20
RF Time Domain...........................................................................................................21
RF Spectrum.................................................................................................................22
Result Summary............................................................................................................23
Marker Table................................................................................................................. 25
Marker Peak List........................................................................................................... 25
AM Time Domain
Displays the modulation depth of the demodulated AM signal (in %) versus time.
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Measurements and result displays
Optionally, the settling time can be evaluated and displayed, see Chapter 5.7.7, "Set-
tling time", on page 70.
Remote command:
LAY:ADD? '1',RIGH,'XTIM:AM:REL'
(See LAYout:ADD[:WINDow]? on page 180)
FM Time Domain
Displays the frequency spectrum of the demodulated FM signal versus time.
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Measurements and result displays
Optionally, the settling time can be evaluated and displayed, see Chapter 5.7.7, "Set-
tling time", on page 70.
Remote command:
LAY:ADD? '1',RIGH,'XTIM:FM'
(See LAYout:ADD[:WINDow]? on page 180)
PM Time Domain
Displays the phase deviations of the demodulated PM signal (in rad or °) versus time.
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Measurements and result displays
Optionally, the settling time can be evaluated and displayed, see Chapter 5.7.7, "Set-
tling time", on page 70.
Remote command:
LAY:ADD? '1',RIGH,'XTIM:PM'
(See LAYout:ADD[:WINDow]? on page 180)
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.
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Measurements and result displays
Remote command:
LAY:ADD? '1',RIGH,'XTIMe:AM:REL:AFSPectrum1'
(see LAYout:ADD[:WINDow]? on page 180)
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.
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Measurements and result displays
Remote command:
LAY:ADD? '1',RIGH,'XTIMe:FM:AFSPectrum1'
(see LAYout:ADD[:WINDow]? on page 180)
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.
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Measurements and result displays
Remote command:
LAY:ADD? '1',RIGH,'XTIMe:PM:AFSPectrum1'
(see LAYout:ADD[:WINDow]? on page 180)
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.
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Measurements and result displays
Optionally, the settling time can be evaluated and displayed, see Chapter 5.7.7, "Set-
tling time", on page 70.
Remote command:
LAY:ADD? '1',RIGH,'XTIM:AM'
(see LAYout:ADD[:WINDow]? on page 180)
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.
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Measurements and result displays
Remote command:
LAY:ADD? '1',RIGH,'XTIM:SPECTRUM'
(see LAYout:ADD[:WINDow]? on page 180)
Result Summary
The "result summary" displays the results of the demodulation functions for all windows
in a table.
The following general results are provided:
For each demodulation, the following results are provided:
Label Description
"Carr Power" Measured carrier power
"Carr Offset" Carrier offset to nominal center frequency
"Mod. Depth" Modulation depth
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Measurements and result displays
Table 3-1: Result summary description
Label Description
"Settling Time" Time after which signal remains in a specified value range.
Only evaluated and displayed if enabled, see Chapter 5.7.7, "Settling time",
on page 70.
"+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
"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.
"DISTORT" Modulation distortion in %
(Calculated only if "SINAD" is also calculated)
Measures the distortion of the modulation in relation to the total power of the signal
inside the AF spectrum span. Indicates the quality of the modulation.
"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 5.7.6, "Result
table settings", on page 67.
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
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Measurements and result displays
Remote command:
LAY:ADD? '1',RIGH,RSUM, see LAYout:ADD[:WINDow]? on page 180
Results:
Chapter 11.7.3, "Retrieving result summary values", on page 192
Marker Table
Displays a table with the current marker values for the active markers.
This table is displayed automatically if configured accordingly.
(See "Marker Table Display" on page 92).
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 180
Results:
CALCulate<n>:MARKer<m>:X on page 216
CALCulate<n>:MARKer<m>:Y? on page 216
Marker Peak List
The marker peak list determines the frequencies and levels of peaks in the spectrum or
time domain. How many peaks are displayed can be defined, as well as the sort order.
In addition, the detected peaks can be indicated in the diagram. The peak list can also
be exported to a file for analysis in an external application.
Remote command:
LAY:ADD? '1',RIGH, PEAK, see LAYout:ADD[:WINDow]? on page 180
Results:
CALCulate<n>:MARKer<m>:X on page 216
CALCulate<n>:MARKer<m>:Y? on page 216
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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............................................................................................ 26
● Demodulation bandwidth.........................................................................................28
● Sample rate and demodulation bandwidth..............................................................29
● AF triggers...............................................................................................................30
● AF filters..................................................................................................................30
● Time domain zoom..................................................................................................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 FPL1000, refer to the reference
part of the I/Q Analysis remote control description in the R&S FPL1000 User Manual.
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Measurement basics
Demodulation process
Figure 4-1: Block diagram of software demodulator
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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 187.
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
regarding 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. The bandwidth must also be increased if FM or PM AC
coupling is selected.
In general, select the demodulation bandwidth 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 116.
A practical example is described in Chapter 9, "Measurement example: demodulating
an FM signal", on page 111.
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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
18 MHz* 32 MHz 72 MHz
28 MHz* 64 MHz 112 MHz
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Measurement basics
AF filters
Demodulation BW Sample Rate (Flat Top) Sample Rate (Gaussian Top)
40 MHz* 64 MHz 160 MHz
* Gaussian filter curve is limited by I/Q bandwidth
Flat top filters require an I/Q bandwidth at least the size of the demodulation bandwidth
on the R&S FPL1000. Gauss filters require at least twice the size of the demodulation
bandwidth on the R&S FPL1000. If necessary, install optional bandwidth extensions on
the R&S FPL1000 to use the required demodulation filter.
Large numbers of samples
Principally, the R&S FPL1000 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.
Stability is achieved by a digital filter which sufficiently suppresses the modulation. As
a prerequisite, the measurement time must be ≥ 3 x 1 / modulation frequency, i.e. 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.
The filter 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.
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