R&S®FSMR3-K15
Avionics (VOR/ILS) Measurements
User Manual
(;Ý];2)
1179451102
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-K15 (1345.3143.02)
© 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.
Trade names are trademarks of the owners.
1179.4511.02 | Version 02 | R&S®FSMR3-K15
The following abbreviations are used throughout this manual: R&S®FSMR3000 is abbreviated as R&S FSMR3000. R&S®FSMR3K15 is abbreviated as R&S FSMR3-K15.
R&S®FSMR3-K15
1 Introduction............................................................................................ 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
2 Welcome to the R&S FSMR3000 Avionics (VOR/ILS) measurements
application............................................................................................ 10
2.1 Starting the R&S FSMR3000 Avionics (VOR/ILS) measurements application...... 10
2.2 Understanding the display information.................................................................... 11
3 Measurement basics............................................................................14
3.1 General information on ILS and VOR/DVOR............................................................ 14
3.1.1 The instrument landing system (ILS)............................................................................ 14
3.1.1.1 Localizer basics.............................................................................................................15
3.1.1.2 Glide slope basics......................................................................................................... 16
3.1.2 VHF omnidirectional radio range (VOR)....................................................................... 17
3.1.3 DVOR (doppler VHF omni-directional range)................................................................19
3.2 Description of the VOR/ILS measurement demodulator......................................... 20
3.2.1 Circuit description - block diagrams.............................................................................. 20
3.2.2 ILS demodulator............................................................................................................21
3.2.3 VOR demodulator......................................................................................................... 24
3.2.3.1 AM modulation depth.................................................................................................... 25
3.2.3.2 FM modulation depth.................................................................................................... 26
3.2.3.3 Azimuth (phase difference at 30 hz)..............................................................................26
3.2.3.4 AF frequencies.............................................................................................................. 26
3.3 Impact of specific parameters................................................................................... 26
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3.3.1 Demodulation bandwidth...............................................................................................26
3.3.2 Stability of measurement results................................................................................... 27
3.3.3 Phase notation in VOR measurements.........................................................................28
4 Measurements and result displays.................................................... 29
4.1 Result displays for VOR/ILS measurements............................................................ 29
4.2 Avionics parameters...................................................................................................34
4.2.1 Signal characteristics.................................................................................................... 34
4.2.2 ILS parameters..............................................................................................................34
4.2.3 VOR parameters........................................................................................................... 38
4.2.4 Harmonic distortion marker results (markers H1, F1, F2)............................................. 41
5 Configuration........................................................................................43
5.1 Configuration overview.............................................................................................. 43
Contents
5.2 Input, output and frontend settings...........................................................................45
5.2.1 Input source settings..................................................................................................... 45
5.2.1.1 Radio frequency input................................................................................................... 46
5.2.1.2 Settings for input from I/Q data files..............................................................................48
5.2.2 Frequency settings........................................................................................................49
5.2.3 Amplitude settings.........................................................................................................50
5.2.4 Output settings.............................................................................................................. 52
5.3 Trigger settings........................................................................................................... 55
5.4 Data acquisition and detection.................................................................................. 60
5.5 Sweep settings............................................................................................................ 61
5.6 Demodulation spectrum............................................................................................. 62
6 Analysis................................................................................................ 66
6.1 Display configuration................................................................................................. 66
6.2 Result configuration................................................................................................... 66
6.2.1 Y-Scaling....................................................................................................................... 66
6.2.2 Units.............................................................................................................................. 68
6.3 Markers........................................................................................................................ 69
6.3.1 Individual marker settings............................................................................................. 70
6.3.2 General marker settings................................................................................................74
6.3.3 Marker search settings..................................................................................................75
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6.3.4 Marker positioning functions......................................................................................... 76
6.4 Export functions..........................................................................................................77
7 How to perform VOR/ILS measurements...........................................80
8 Optimizing and troubleshooting the measurement.......................... 81
9 Remote commands to perform VOR/ILS measurements................. 84
9.1 Introduction................................................................................................................. 85
9.1.1 Conventions used in descriptions................................................................................. 85
9.1.2 Long and short form...................................................................................................... 86
9.1.3 Numeric suffixes............................................................................................................86
9.1.4 Optional keywords.........................................................................................................86
9.1.5 Alternative keywords..................................................................................................... 87
9.1.6 SCPI parameters...........................................................................................................87
Contents
9.1.6.1 Numeric values............................................................................................................. 87
9.1.6.2 Boolean......................................................................................................................... 88
9.1.6.3 Character data.............................................................................................................. 89
9.1.6.4 Character strings...........................................................................................................89
9.1.6.5 Block data..................................................................................................................... 89
9.2 Activating VOR/ILS measurements........................................................................... 89
9.3 Selecting the measurement type............................................................................... 92
9.4 Configuring VOR/ILS measurements........................................................................ 93
9.4.1 Input source settings..................................................................................................... 93
9.4.2 Configuring the outputs................................................................................................. 97
9.4.3 Frontend configuration.................................................................................................. 98
9.4.3.1 Frequency..................................................................................................................... 98
9.4.3.2 Amplitude settings.........................................................................................................99
9.4.3.3 Configuring the attenuation......................................................................................... 101
9.4.4 Triggering measurements........................................................................................... 102
9.4.4.1 Configuring the triggering conditions...........................................................................103
9.4.4.2 Configuring the trigger output......................................................................................106
9.4.5 Data acquisition...........................................................................................................109
9.4.6 Configuring the demodulation spectrum......................................................................111
9.5 Configuring and performing sweeps.......................................................................113
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9.6 Analyzing VOR/ILS measurements..........................................................................116
9.6.1 Configuring the result display...................................................................................... 116
9.6.1.1 General window commands........................................................................................ 116
9.6.1.2 Working with windows in the display........................................................................... 117
9.6.2 Configuring the Y-Axis scaling and units..................................................................... 123
9.6.3 Working with markers..................................................................................................127
9.6.3.1 Individual marker settings........................................................................................... 127
9.6.3.2 General marker settings..............................................................................................132
9.6.3.3 Positioning the marker................................................................................................ 133
9.6.3.4 Retrieving marker results............................................................................................ 137
9.7 Retrieving results......................................................................................................139
Contents
Positioning normal markers.........................................................................................133
Positioning delta markers............................................................................................135
9.7.1 Retrieving numeric results...........................................................................................139
9.7.2 Trace results................................................................................................................149
9.8 Status reporting system........................................................................................... 151
9.8.1 STATus:QUEStionable:SYNC<n> register.................................................................. 152
9.8.2 Querying the status registers...................................................................................... 153
9.9 Programming examples: performing VOR/ILS measurements............................ 155
9.9.1 Programming example: performing an ILS measurement.......................................... 155
9.9.2 Programming example: performing a VOR measurement.......................................... 157
Annex.................................................................................................. 160
A Abbreviations..................................................................................... 160
List of Commands (Avionics)........................................................... 161
Index....................................................................................................165
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1 Introduction
1.1 About this manual
Introduction
About this manual
This VOR/ILS 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 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 R&S FSMR3000 Avionics (VOR/ILS) measurements application
Introduction to and getting familiar with the application
●
About the measurement
General concept of the VOR/ILS measurement and typical applications
●
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
●
How to Perform Measurements in the R&S FSMR3000 Avionics (VOR/ILS)
measurements application
Step-by-step instructions to perform a basic VOR/ILS measurement
●
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 test setup
●
Remote Commands for VOR/ILS Measurements
Remote commands required to configure and perform VOR/ILS 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 FSMR3 User Manual)
Programming examples demonstrate the use of many commands and can usually
be executed directly for test purposes
●
Annex
Reference material
●
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
Introduction
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
Introduction
Documentation overview
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/
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2 Welcome to the R&S FSMR3000 Avionics
Welcome to the R&S FSMR3000 Avionics (VOR/ILS) measurements application
Starting the R&S FSMR3000 Avionics (VOR/ILS) measurements application
(VOR/ILS) measurements application
The R&S FSMR3-K15 is a firmware application that adds functionality to perform
VOR/ILS measurements to the R&S FSMR3.
The R&S FSMR3-K15 features:
●
Demodulation of avionics (VOR/ILS) signals
●
Modulation accuracy evaluation
●
Maximum accuracy and temperature stability due to digital down-conversion
●
No evidence of typical errors of analog down-conversion and demodulation like AM
⇔ FM conversion, deviation error, frequency response or frequency drift at DC coupling
This user manual contains a description of the functionality that the application provides, including remote control operation.
General R&S FSMR3 functions
The application-independent functions for general tasks on the R&S FSMR3 are also
available for VOR/ILS measurements and are described in the R&S FSMR3 user manual. In particular, this comprises the following functionality:
●
Data management
●
General software preferences and information
For further information see the Rohde & Schwarz Application Note 1MA193: "Aero-
nautical radio navigation measurement solutions".
2.1 Starting the R&S FSMR3000 Avionics (VOR/ILS) measurements application
The R&S FSMR3000 Avionics (VOR/ILS) measurements application adds a new application to the R&S FSMR3.
To activate the R&S FSMR3000 Avionics (VOR/ILS) measurements application
1. Press the [MODE] key on the front panel of the R&S FSMR3.
A dialog box opens that contains all operating modes and applications currently
available on your R&S FSMR3.
2. Select the "Avionics" item.
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Welcome to the R&S FSMR3000 Avionics (VOR/ILS) measurements application
Understanding the display information
The R&S FSMR3 opens a new measurement channel for the R&S FSMR3000
Avionics (VOR/ILS) measurements application.
The measurement is started immediately with the default settings. It can be configured
in the VOR/ILS "Overview" dialog box, which is displayed when you select the "Overview" softkey from any menu (see Chapter 5.1, "Configuration overview",
on page 43).
Multiple Measurement Channels and Sequencer Function
When you activate an application, a new measurement channel is created which determines the measurement settings for that application. 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 active channels are performed one after the other in the order of the tabs. The currently active measurement is
indicated by a
are updated in the tabs (including 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. The result displays of the individual channels
2.2 Understanding the display information
The following figure shows a measurement diagram during 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 R&S FSMR3000 Avionics (VOR/ILS) measurements application
Understanding the display information
1
6
5
1 = Channel bar for firmware and measurement settings
2+6 = Window title bar with diagram-specific (trace) information
3 = Diagram area with marker information
4 = Diagram footer with diagram-specific information, depending on measurement application
5 = Instrument status bar with error messages, progress bar and date/time display
2
3
Channel bar information
In the R&S FSMR3000 Avionics (VOR/ILS) measurements application, the
R&S FSMR3 shows the following settings:
Table 2-1: Information displayed in the channel bar in the R&S FSMR3000 Avionics (VOR/ILS) mea-
surements application
4
"Ref Level" Reference level
"Att" Mechanical and electronic RF attenuation
"Freq" Center frequency
"RBW" Resolution bandwidth
"Meas Time" Measurement time for data acquisition.
"Meas BW" Demodulation bandwidth
"Meas" Measurement type (ILS/VOR)
"SGL" The sweep is set to single sweep mode.
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.
Window title bar information
For diagrams, the header provides the following information:
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Welcome to the R&S FSMR3000 Avionics (VOR/ILS) measurements application
Understanding the display information
4
1 2
3
5 6
Figure 2-1: Window title bar information in the R&S FSMR3000 Avionics (VOR/ILS) measurements
1 = Window number
2 = Window type
3 = Trace color
4 = Trace number
5 = Detector
6 = Trace mode
application
Diagram footer information
The diagram footer (beneath the diagram) contains the frequency range.
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 basics
3.1 General information on ILS and VOR/DVOR
Measurement basics
General information on ILS and VOR/DVOR
Some background knowledge on basic terms and principles used in VOR/ILS measurements is provided here for a better understanding of the required configuration settings.
● General information on ILS and VOR/DVOR..........................................................14
● Description of the VOR/ILS measurement demodulator.........................................20
● Impact of specific parameters................................................................................. 26
The following topics summarize some background information on the related avionics
standards. The provided overview information is intended as explanation of the used
terms and does not aim to be comprehensive.
● The instrument landing system (ILS)...................................................................... 14
● VHF omnidirectional radio range (VOR)................................................................. 17
● DVOR (doppler VHF omni-directional range)..........................................................19
3.1.1 The instrument landing system (ILS)
An instrument landing system is used in aircraft during the landing approach to monitor
the correct approach path to the runway.
Using the globally standardized system ILS, an aircraft on a defined glide-path
receives highly accurate position information in reference to the glide-path during landing. This landing path is described by the intersection of a vertical glide-slope level and
a horizontal localizer plane.
Figure 3-1: Basics of the ILS
An ILS system consists of three independent subsystems:
●
A glide slope for vertical guidance.
●
A localizer for horizontal guidance.
●
(optional) marker beacons
● Localizer basics.......................................................................................................15
● Glide slope basics...................................................................................................16
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3.1.1.1 Localizer basics
Measurement basics
General information on ILS and VOR/DVOR
The localizer transmitter is located near the end of the runway (nearest to the start of
the aircraft approach). Typically, horizontally aligned antennas transmit two intersecting
main beams beside one another at carrier frequencies between 108 MHz and
112 MHz. As seen from the approaching aircraft coming in for a landing, the left beam
is usually modulated at 90 Hz and the right beam at 150 Hz.
The information on position is provided after demodulation of the beam signals by evaluating the difference in depth of modulation (DDM).
DDM = m(x90) – m(x150)
The following scenarios are possible:
●
Predominance of the 90 Hz beam: the aircraft is too far to the left and must turn to
the right
●
Predominance of the 150 Hz beam: the aircraft is too far to the right and must turn
to the left
●
The signal strength from both beams is equal: the aircraft is in the center, on the
right course.
Course and clearance signals
The landing path is divided into the region further away from the runway, referred to as
the course, and the runway itself, referred to as the clearance. Localizers are positioned in both areas, however they transmit their ILS signals using different frequencies, one that must travel farther, one for close-up. The frequencies differ only in a few
kilohertz. The aircraft always receives both signals, and cannot (and need not) distinguish the two. However, for test purposes, it can be useful to measure the signals individually.
Morse code identification signal
The localizer not only allows the aircraft to determine its position, it also provides identification of the ILS transmitter. The localizer periodically transmits a Morse code at
1020 Hz which uniquely identifies the transmitter. The receiver thus knows that the ILS
is operating correctly and that it is receiving the correct signal. The glide slope station
does not transmit an identification signal.
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3.1.1.2 Glide slope basics
Measurement basics
General information on ILS and VOR/DVOR
The following description is taken from the Rohde & Schwarz Application Note
1MA193: "Aeronautical radio navigation measurement solutions".
The glide slope transmitter is located near the end of the runway (nearest to the start of
the aircraft approach).
Figure 3-2: Approach navigation using instrument landing system (ILS)
Typically, vertically aligned antennas transmit two intersecting main beams on top of
one another at carrier frequencies between 329 MHz and 335 MHz. The top beam is
usually modulated at 90 Hz and the beam below at 150 Hz.
The information on position is provided after demodulation of the beam signals by evaluating the difference in depth of modulation (DDM). The following scenarios are possible:
●
Predominance of the 90 Hz beam: the aircraft is too high and must descend
●
Predominance of the 150 Hz beam: the aircraft is too low and needs to climb
●
The signal strength from both beams is equal: the aircraft is in the center, on the
right course.
If there is a predominance of the 90 Hz beam, then the aircraft is too high and must
descend. A predominant 150 Hz means that the aircraft is too low and needs to climb.
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3.1.2 VHF omnidirectional radio range (VOR)
Measurement basics
General information on ILS and VOR/DVOR
Very high frequency (VHF) omnidirectional radio range (VOR) is a radio navigation system for short and medium distance navigation. The VOR radio navigation aid supplies
the aircraft with directional information, angle information relative to the magnetic north
from the site of the beacon. Thus, it helps aircraft to determine their position and stay
on course. The range covered by a VOR station is ideally a circle around the VOR station with a radius depending on the flight altitude.
A VOR system consists of a ground transmission station and a VOR receiver on board
the aircraft.
Ground transmitter
The transmitter stations operate at VHF frequencies of 108 MHz to 118 MHz, with the
code identification (COM/ID) transmitting on a modulation tone of 1.020 kHz. It emits
two types of signals:
●
An omnidirectional reference signal (REF) that can consist of two parts:
– 30 Hz frequency modulated (FM) sine wave on subcarrier 9.96 kHz from ampli-
tude modulation (AM) carrier
– 1020 Hz AM modulated sine wave Morse code
●
A directional positioning signal, variable (VAR): 30 Hz AM modulated sine waves
with variable phase shift
VOR receiver
The VOR receiver obtains the directional information by measuring the phase difference of two 30 Hz signals transmitted by the beacon. A conventional VOR station
(CVOR) transmits with a rotating antenna. From the rotation, a sine wave AM signal
arises in the receiver, whose phase position depends on the present angle of rotation.
The rotation frequency of the antenna sets the modulation frequency at 30 Hz.
Instead of using a rotating antenna, DVOR stations (Doppler) divide the circumference
of the antenna into 48 or 50 segments, covering each segment by its own antenna.
Each antenna transmits the unmodulated subcarrier from one antenna to the next, so
that the signal completes the round trip 30 times per second.
To determine the radial, the phase difference to a reference phase must be measured.
This reference phase must be independent of the rotation of the antenna. Thus, it is
modulated with a frequency deviation of 480 Hz in FM onto a secondary carrier with
9.96 kHz. It is then emitted over a separate antenna with a round characteristic.
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Measurement basics
General information on ILS and VOR/DVOR
Figure 3-3: Basics of the VOR phase angles (Φ) depending on the azimuth angle (Θ)
The frequency modulated secondary carrier for the reference phase is itself again
modulated in AM on the RF carrier of the VOR station. In addition to the signals necessary for navigation, a Morse code with 1020 Hz can be transmitted on the VOR carrier.
Also, speech in the usual AF from 300 Hz to 3.3 kHz can be transmitted. Often the
voice channel of a VOR station is used for the transmission of ATIS (Automatic Terminal Information Service) messages. The Morse code can be used to identify the VOR
station, similar to the "Morse code identification signal" on page 15 in the ILS signal.
The spectrum of a VOR signal is therefore composed of the carrier and three modulated components.
Figure 3-4: Example of the VOR Spectrum
The identical modulation degree m = 0.3 for all three components was selected in
ICAO annex-10 [63] such that the total signal still contains 10% modulation reserve.
The carrier is therefore not suppressed at any time. The 9960 Hz reference carrier is
FM modulated with 480 Hz deviation. The VOR signal generation as under ICAO is
shown below.
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3.1.3 DVOR (doppler VHF omni-directional range)
Measurement basics
General information on ILS and VOR/DVOR
Figure 3-5: Basics of the VOR signal generation
Like a VOR beacon, a DVOR beacon transmits an RF signal in which the two phase
angles are coded. From the difference between these phases, the receiver can calculate its position in reference to the DVOR. In contrast to the VOR signal, the meaning
of the reference and azimuth-dependent phase is opposite. This means that the reference phase is no longer emitted in FM through the secondary carrier. Instead, the
30 Hz reference signal is emitted in AM from a fixed antenna.
In DVOR the azimuth-dependent phase is generated using the Doppler effect. The
Doppler effect is such that the receiving frequency frx increases when there is radial rel-
ative movement of a receiver with a speed vx towards the transmitter. Correspondingly,
it decreases when there is movement away from the transmitter.
The following figure shows the 50 circularly arranged single antennas of a DVOR station. The secondary carrier to be transmitted on (+9.96 kHz carrier) is distributed using
an electronic multiplexer on the circularly arranged antenna. Thus, the transmission
signal seems to revolve at 30 Hz in the circle.
Figure 3-6: Basics of a DVOR system
The circles shown in the above figure symbolize radial transmitters. The transmission
antenna in the center of the circle (M) transmits the reference phase in the form of the
30 Hz AM modulated carrier and the identifier of the station. The Doppler shift corresponds to the FM deviation.
In practice both sidebands of the secondary carrier (carrier + 9.96 kHz and carrier -
9.96 kHz) are created separately and fed into the antenna array spatially displaced by
180°. Therefore two super-imposed individual antennas are emitting at one period in
time, each being one sideband of the total signal. In the far field, there is the effect of
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Measurement basics
Description of the VOR/ILS measurement demodulator
an FM signal on the receiver. One sideband component always increases in frequency
due to the Doppler effect, while the other component decreases in frequency. The reason for this complex method of signal generation lies in the high accuracy which can
be obtained for the azimuth-dependent phase.
Figure 3-7: Basics of the DVOR signal generation
3.2 Description of the VOR/ILS measurement demodulator
The following chapter describes the functions of the VOR/ILS measurement demodulator in the R&S FSMR3000 Avionics (VOR/ILS) measurements application.
By sampling (digitization) already at the IF and digital down-conversion to the baseband (I/Q), the demodulator achieves maximum accuracy and temperature stability.
There is no evidence of typical errors of an analog down-conversion and demodulation
like AM ⇔ FM conversion, deviation error, frequency response or frequency drift at DC
coupling.
3.2.1 Circuit description - block diagrams
Figure 3-8: Block diagram of analyzer signal processing
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3.2.2 ILS demodulator
Measurement basics
Description of the VOR/ILS measurement demodulator
Figure 3-8 shows the analyzer's hardware from the IF to the processor. The A/D con-
verter samples the IF.
Lowpass filtering and reduction of the sampling rate follow the down-conversion to the
complex baseband. The decimation depends on the selected demodulation bandwidth.
Useless over-sampling at narrow bandwidths is avoided, saving calculating time and
increasing the maximum recording time.
The software demodulator runs on the main processor of the analyzer. The demodulation process is shown below. All calculations are performed simultaneously with the
same I/Q data set.
Figure 3-9: Block diagram of ILS software demodulator
The ILS demodulation basically comprises two bandpass filters with 90 Hz and 150 Hz
center frequencies. To meet the required selectivity with a reasonable filter order, the
AM signal must be decimated in frequency before filtering.
The optional ID signal is separated by a bandpass filter with a frequency range from
300 Hz to 4000 Hz.
A Morse decoder detects and decodes the ON and OFF periods in the identifier signal.
AM modulation depth
To obtain the AM depth, a lowpass filter must calculate the mean carrier power, while
suppressing all other signal components. The mean carrier power is then used to nor-
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Measurement basics
Description of the VOR/ILS measurement demodulator
malize the instantaneous magnitude of the I/Q signal. The result is the AM modulation
depth signal vs. time.
The following AM depths and their derivatives are calculated:
●
"Depth90": Modulation depth of the 90 Hz signal
●
"Depth
●
"DepthID": Modulation depth of the identification/voice signal.
": Modulation depth of the 150 Hz signal
150
– For a demodulation bandwidth of 12.5 kHz or larger: from 300 Hz to 4 kHz.
– For a demodulation bandwidth of 3.2 kHz: from 300 Hz to 1.6 kHz
– For a demodulation bandwidth of 800 Hz: not supported
●
"Sum90+150": Modulation depth of the signal containing both the 90 Hz and the
150 Hz component. Measured as peak-to-peak value after interpolating the signal.
●
"SDM90,150": Sum of modulation depths: "Depth90" + "Depth150"
●
"DDM90,150": Difference in modulation depths: "Depth90" - "Depth150"
AF frequencies
The following AF frequencies are calculated:
●
"Freq90": Modulating frequency of the 90 Hz signal
●
"Freq150": Modulating frequency of the 150 Hz signal
●
"FreqID": Modulating frequency of the identification/voice signal.
– For a demodulation bandwidth of 12.5 kHz or larger: from 300 Hz to 4 kHz.
– For a demodulation bandwidth of 3.2 kHz: from 300 Hz to 1.6 kHz
– For a demodulation bandwidth of 800 Hz: not supported
Phase angle 90/150 Hz
The phase angle is calculated using the estimated phases and frequencies of the
90 Hz and the 150 Hz signal. It describes the phase of the 150 Hz signal at the time
the 90 Hz signal crosses zero. If both involved frequencies have their ideal 3 to 5 ratio
the phase angle is valid. Phase angles exceeding ± 60° lead to ambiguous results. If
one of the two involved signals is turned off or if the frequency ratio is not 3 to 5, this
result does not make sense.
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Measurement basics
Description of the VOR/ILS measurement demodulator
Figure 3-10: Phase angle ambiguity
Example: ILS phase difference of 40 degrees
When the 90 Hz signal crosses zero, the 150 Hz signal has the following phase values:
-80 deg, +160 deg, +40 deg, -80 deg, etc.
If you add or subtract 120 degrees, the ambiguity is eliminated: all values become 40
degrees.
ILS distortion
The ILS software demodulator also analyzes AM AF distortions. The AM modulation
depth vs time signal is processed by an FFT, using a user-defined resolution bandwidth. The trace is displayed in the "Modulation Spectrum" display. The K2, K3 and
THD results of the AM components are calculated based on the FFT trace and the estimated modulation frequencies.
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3.2.3 VOR demodulator
Measurement basics
Description of the VOR/ILS measurement demodulator
Figure 3-11: Block diagram of the VOR software demodulator
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Measurement basics
Description of the VOR/ILS measurement demodulator
The VOR signal contains three AM modulated components that must be separated in a
first step:
●
Rotational signal (30 Hz)
●
Identification/voice part (300 Hz to 4 kHz)
●
FM modulated carrier (9960 Hz ± 700 Hz)
To obtain the AM depth, a lowpass filter must calculate the mean carrier power, while
suppressing all other signal components. The mean carrier power is then used to normalize the instantaneous magnitude of the I/Q signal. The result is the AM modulation
depth signal vs. time. The three AM components are separated using bandpass filters
covering the individual frequency ranges.
A Morse decoder detects and decodes the ON and OFF periods in the identifier signal.
The separated FM modulated carrier is passed through an FM demodulator. The FM
carrier frequency (nominal 9960 Hz) is calculated as the average output value of the
FM demodulator. To obtain the 30 Hz reference signal, the FM demodulator output is
filtered by the same narrow 30 Hz bandpass as the 30 Hz AM rotational component.
FM deviation is calculated using the estimated magnitude of the 30 Hz reference signal.
The azimuth is calculated as the phase difference of the 30 Hz reference signal and
the 30 Hz rotational signal.
VOR distortion
In the VOR software demodulator two kinds of signals are analyzed regarding distortions:
●
AM Distortion: The AM modulation depth vs time signal is processed by an FFT,
with a user-defined resolution bandwidth. The trace is displayed in the "Modulation
Spectrum" display. The K2, K3 and THD results of the AM components are calculated based on the FFT trace and the estimated modulation frequencies.
●
FM Distortion: The FM modulation depth vs time signal is processed by an FFT,
using a resolution bandwidth automatically set by the application. You cannot view
the resulting trace. The K2, K3 and THD results of the FM components are calculated based on the FFT trace and the estimated modulation frequencies.
3.2.3.1 AM modulation depth
To obtain the AM depth, a lowpass filter must calculate the mean carrier power, while
suppressing all other signal components. The mean carrier power is then used to normalize the instantaneous magnitude of the I/Q signal. The result is the AM modulation
depth signal versus time. It is then used to calculate the following AM modulation
depths:
●
Depth
●
Depth
●
DepthID: AM modulation depth of the identification/voice signal
: AM modulation depth of the FM carrier, typically at 9960 Hz
9960
: AM modulation depth of the 30 Hz rotational signal
AM30
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3.2.3.2 FM modulation depth
Measurement basics
Impact of specific parameters
The FM deviation Devia
(typically 480 Hz) is calculated by estimating the magni-
FM30
tude of the FM demodulated 30 Hz reference signal.
3.2.3.3 Azimuth (phase difference at 30 hz)
The phases of both the 30 Hz FM and 30 Hz AM signal are estimated at exactly the
same time instant. The azimuth (Phase FM-AM) is calculated as the phase difference
between the two.
3.2.3.4 AF frequencies
In the VOR demodulator the AF frequencies are calculated:
●
Freq
●
Freq
●
FreqID: voice / identification; From 300 Hz to 4 kHz, typically 1020 Hz
●
Freq
: 30 Hz Rotational-signal (AM)
AM30
: 30 Hz Reference-signal (FM)
FM30
: The carrier frequency of the FM carrier, typically 9960 Hz; Calculated as
9960
mean value of the FM demodulator output
3.3 Impact of specific parameters
● Demodulation bandwidth.........................................................................................26
● Stability of measurement results.............................................................................27
● Phase notation in VOR measurements...................................................................28
3.3.1 Demodulation bandwidth
The R&S FSMR3000 Avionics (VOR/ILS) measurements application captures I/Q data
using digital filters with quasi-rectangular amplitude responses. The demodulation
bandwidth defines the width of the filter's flat passband. This is not the 3 dB bandwidth,
but the useful bandwidth which is distortion-free with regard to phase and amplitude.
Small demodulation bandwidths have the following advantages:
●
Lower sample rate, less IQ data, higher measurement speed
●
Only the signal of interest is captured, no adjacent signals and less noise captured,
better SNR
Large demodulation bandwidths have the following advantages:
●
A high carrier frequency offset of the DUT is no longer critical because the whole
spectrum of the signal still falls in the filter's passband. FM to AM conversion is
avoided (VOR mode)
●
The "Modulation Spectrum" display allows for a wider span, showing harmonics of
a higher order
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Impact of specific parameters
It is recommended that you use the automatic configuration of the demodulation bandwidth, which applies the following settings:
●
ILS
DBW = 12.5 kHz, to capture the full identifier signal
●
VOR
DBW = 25 kHz, to capture the 9.96 kHz signal
If the demodulation bandwidth setting is changed, some demodulation results may not
be available due to bandwidth limitations. For harmonic distortion measurement, the
highest measured harmonic signal may be limited due to the demodulation bandwidth
(see also "Distortion Max Frequency" on page 64).
The following tables show the relationship between the available demodulation bandwidths and measurement times for the different measurements.
Table 3-1: Available demodulation bandwidths and measurement times for ILS measurements
Demodulation BW Meas time min Meas time max Meas time default
800 Hz 0.1 sec 133 sec 1 sec
3.2 KHz 0.1 sec 33.4 sec 1 sec
12.5 KHz 0.1 sec 8.356 sec 1 sec
50 KHz 0.1 sec 8.356 sec 1 sec
100 KHz 0.1 sec 8.356 sec 1 sec
Table 3-2: Available demodulation bandwidths and measurement times for VOR measurements
Demodulation BW Meas time min Meas time max Meas time default
25 KHz 0.1 sec 30 sec 1 sec
50 KHz 0.1 sec 30 sec 1 sec
100 KHz 0.1 sec 30 sec 1 sec
3.3.2 Stability of measurement results
The stability of the algorithms used to estimate the modulation depths and Azimuth rely
on a sufficient amount of data. This is achieved if at least five periods of the 30 Hz
basic modulation frequency are recorded. Since the R&S FSMR3000 Avionics (VOR/
ILS) measurements application automatically compensates for filter settling times internally, a measurement time of approximately 200 ms is required.
Note that the precision as specified in the data sheet is guaranteed only if the 30 Hz
AM rotational component can be identified properly in the VOR analysis case.
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3.3.3 Phase notation in VOR measurements
Measurement basics
Impact of specific parameters
In VOR measurements, the phase can be provided using two different notations, indicated in the following illustration:
Figure 3-12: Phase notation in VOR measurements
Phase is always counted counter-clockwise, starting at the reference.
The reference depends on the selected notation:
●
FROM: North direction at the VOR beacon
●
TO: North direction at the receiver/ aircraft
To convert one notation to the other, use the following equation:
PhaseTO = Phase
+ 180 deg
FROM
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4 Measurements and result displays
Measurements and result displays
Result displays for VOR/ILS measurements
The R&S FSMR3000 Avionics (VOR/ILS) measurements application provides two different measurements to determine the parameters described by the VOR/ILS specifications.
ILS measurement
The R&S FSMR3000 Avionics (VOR/ILS) measurements application demodulates the
AM components of the ILS signal at the RF input and calculates characteristic parameters such as the modulation depth and frequency or phase for specific components.
Furthermore, an FFT is performed on all components of the AF signal. The resulting
AF spectrum allows you to measure the required components and their distortions
(harmonics).
VOR measurement
The R&S FSMR3000 Avionics (VOR/ILS) measurements application demodulates the
AM and FM components of the VOR signal at the RF input. Then it calculates characteristic parameters, such as the modulation depth, and frequency or phase for specific
components and subcarriers. The VOR phase, i.e. the phase difference between the
AM and FM signal components, is also calculated. Furthermore, an FFT is performed
on all components of the AF signal. The resulting AF spectrum allows you to measure
the required components and their distortions (harmonics).
Selecting the measurement type
To select a different measurement type, do one of the following:
●
Select the "Overview" softkey. In the "Overview", select the "Select Measurement"
button. Select the required measurement.
●
Press the [MEAS] key. In the "Select Measurement" dialog box, select the required
measurement.
Remote command:
CALCulate<n>:AVIonics[:STANdard] on page 92
● Result displays for VOR/ILS measurements...........................................................29
● Avionics parameters................................................................................................34
4.1 Result displays for VOR/ILS measurements
Access: "Overview" ≥ "Display Config"
The captured VOR/ILS signal can be displayed using various evaluation methods. All
evaluation methods available for VOR/ILS measurements are displayed in the evaluation bar in SmartGrid mode.
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Measurements and result displays
Result displays for VOR/ILS measurements
For details see the R&S FSMR3 base unit user manual.
By default, the ILS measurement results are displayed in the following windows:
●
Signal Summary
●
Result Summary
●
Modulation Spectrum
The following evaluation methods are available for VOR/ILS measurements:
Signal Summary............................................................................................................30
Result Summary............................................................................................................30
Distortion Summary.......................................................................................................31
Modulation Spectrum.................................................................................................... 32
Marker Table................................................................................................................. 33
Signal Summary
Displays information on the input signal settings and measured values in one table.
A bargraph visualizes the signal strength compared to the current level settings. The
peak power measured during the current or most recent measurement is indicated by a
vertical yellow line in the graph. This is useful to detect underload or overload conditions at a glance.
Figure 4-1: Signal summary for ILS signal
For details on individual parameters, see Chapter 4.2.1, "Signal characteristics",
on page 34.
Remote command:
LAY:ADD? '1',RIGH,SSUM, see LAYout:ADD[:WINDow]? on page 117
Results:
CALCulate<n>:AVIonics:FERRor[:RESult]? on page 142
CALCulate<n>:AVIonics:RFFRequency[:RESult]? on page 143
CALCulate<n>:AVIonics:CARRier[:RESult]? on page 141
Result Summary
Displays the numerical measurement results for the demodulated signal components.
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