PAD-T-M: 3574.3259.02/01.00/CI/1/EN
R&S®FS-K15
VOR/ILS Avionics Measurements
Software Manual
Software Manual
Test and Measurement
1302.0942.42 – 04
© 2013 Rohde & Schwarz GmbH & Co. KG
Muehldorfstr. 15, 81671 Munich, Germany
Phone: +49 89 41 29 - 0
Fax: +49 89 41 29 12 164
E-mail: info@rohde-schwarz.com
Internet: http://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.
The following abbreviations are used throughout this manual:
R&S®FS-K15 is abbreviated as R&S FS-K15
R&S FS-K15 Contents
Software Manual 1302.0942.42 - 04 3
Contents
1 Installation and Enabling ................................................................... 5
1.1 Installation .................................................................................................................... 5
1.2 Enabling ........................................................................................................................ 5
1.3 General information about ILS and VOR/DVOR ....................................................... 6
1.3.1 ILS (Instrument Landing System) .................................................................................. 6
1.3.2 VOR (VHF Omni directional Radio Range) ................................................................... 6
1.3.3 DVOR (Doppler VHF Omni directional Range) ............................................................. 8
1.4 Description of the Avionics Measurement Demodulator ........................................ 9
1.4.1 Circuit Description - Block Diagrams ...........................................................................10
1.4.2 ILS demodulator...........................................................................................................10
1.4.3 VOR demodulator ........................................................................................................12
1.5 Further Characteristics .............................................................................................13
1.5.1 IF Bandwidth ................................................................................................................13
1.5.2 Demodulation Bandwidth .............................................................................................13
1.5.3 Stability of Measurement Results ................................................................................14
2 Configuration of the Avionics Demodulator ................................... 15
2.1 Getting Started ...........................................................................................................15
2.2 Test Setup for Measurements ..................................................................................16
2.3 Selecting the Operating Mode – HOTKEY Bar ........................................................16
2.4 Avionics Demodulator Mode ....................................................................................17
2.5 Result Display – RF level and frequency counter result .......................................18
2.6 Avionics Demodulator Main Menu ...........................................................................19
2.7 FREQ Key ...................................................................................................................26
2.8 SPAN Key ...................................................................................................................29
2.9 AMPT Key ...................................................................................................................30
2.9.1 Setting the Level Display and Configuring the RF Input – AMPT Key ........................30
2.9.2 Setting the Level Display at the Baseband Input – AMPT Key ...................................33
2.10 BW Key .......................................................................................................................34
2.10.1 Setting the Bandwidths and the Measurement Time – BW Key ..................................34
2.11 SWEEP Key ................................................................................................................37
2.11.1 Setting the Sweep – SWEEP/MEAS Keys ..................................................................37
2.12 TRIG Key .....................................................................................................................40
2.13 MKR Key .....................................................................................................................41
2.14 MKR -> Key .................................................................................................................41
2.15 MKR FCTN Key ...........................................................................................................42
R&S FS-K15 Contents
Software Manual 1302.0942.42 - 04 4
2.16 TRACE Key .................................................................................................................42
2.17 DISP Key .....................................................................................................................43
2.18 Other Keys ..................................................................................................................43
3 Remote Control Commands ............................................................ 44
3.1 Common Commands .................................................................................................44
3.2 CALCulate Subsystem ..............................................................................................44
3.2.1 CALCulate:AVIonics Subsystem .................................................................................44
3.2.2 CALCulate:FEED - Subsystem ....................................................................................50
3.3 DISPlay Subsystem ...................................................................................................50
3.4 INITiate Subsystem ....................................................................................................53
3.5 INPut Subsystem .......................................................................................................54
3.6 INSTrument Subsystem ............................................................................................58
3.7 SENSe Subsystem ....................................................................................................59
3.7.1 [SENSe:]ADEMod Subsystem .....................................................................................59
3.7.2 SENSe:BANDwidth Subsystem ...................................................................................61
3.7.3 SENSe:FREQuency Subsystem ..................................................................................62
3.7.4 SENSe:SWEep Subsystem .........................................................................................64
3.7.5 SENSe:VOLTage Subsystem ......................................................................................65
3.8 UNIT Subsystem ........................................................................................................66
3.9 Softkeys Assignment to IEC/IEEE Bus Commands ...............................................67
3.9.1 AVIONICS Hotkey........................................................................................................67
3.9.2 FREQ Key ....................................................................................................................68
3.9.3 SPAN Key ....................................................................................................................68
3.9.4 AMPL Key ....................................................................................................................69
3.9.5 BW Key ........................................................................................................................70
3.9.6 SWEEP Key .................................................................................................................70
4 Performance Test ............................................................................. 71
4.1 Test Instructions ........................................................................................................71
4.2 Measuring Equipment and Accessories .................................................................72
4.3 Performance Test FS-K15 .........................................................................................73
4.3.1 Checking the ILS Demodulation (AM) .........................................................................73
4.3.2 Checking the VOR Demodulation (AM, FM) ................................................................80
4.3.3 Checking the Audio Input Characteristics (only in case of FSMR and FSQ-B71) .......86
4.4 Performance Test Report FS-K15 ............................................................................88
5 Index .................................................................................................. 95
R&S FS-K15 Installation and Enabling
Software Manual 1302.0942.42 - 04 5
1 Installation and Enabling
Instrument type
Firmware version
R&S FSMR
4.26
R&S FSU
4.31
R&S FSQ
4.35
1.1 Installation
Application Firmware R&S FS-K15 is part of the basic firmware of the base unit. The
application is available starting with the following minimum firmware version of the
instruments:
If the firmware has to be updated, start the update of the firmware by SETUP → NEXT
→ FIRMWARE UPDATE.
1.2 Enabling
Installation
Application Firmware R&S FS-K15 is enabled in the SETUP → GENERAL SETUP
menu by entering a keyword. The keyword is supplied together with the application
firmware. After enabling the application firmware a performance verification test is
required to check the measurement accuracy.
If the application firmware is installed at the factory, it will already be enabled and
tested against the specifications.
SETUP menu:
GENERAL SETUP
The GENERAL SETUP softkey opens a submenu in which the general instrument
parameters can be set up. In addition to the configuration of the digital interfaces
(IECBUS, COM), the date and time may be entered.
OPTIONS
The OPTIONS softkey opens a submenu in which you can enter the keywords for the
application firmware. The existing applications are displayed in a table that opens
when you enter the submenu.
INSTALL OPTION
The INSTALL OPTION softkey enables entry of the keyword for application firmware.
If the keyword is valid, the message OPTION KEY OK is displayed and the application
firmware is entered in the FIRMWARE OPTIONS table.
If an invalid keyword is entered, OPTION KEY INVALID is displayed.
R&S FS-K15 Installation and Enabling
General information about ILS and VOR/DVOR
Software Manual 1302.0942.42 - 04 6
Centerline
Course
DDM >0
DDM <0
Clearance
LLZ
150 Hz
90 Hz
150 Hz
90 Hz
1.3 General information about ILS and VOR/DVOR
1.3.1 ILS (Instrument Landing System)
Through the globally standardized ILS an aircraft on a defined glidepath receives
highly accurate position information in reference to the glidepath during landing. This
landing path is described by the intersection of a vertical glideslope level and a
horizontal localizer plane.
Figure 1-1: Basics of the ILS landing
The ILS frequency range covers 108 to 118.MHz for the LLZ (localizer) and 320 to 340
MHz for the GS (Glideslope). The ILS is based on the interpretation of two amplitude
modulated coherent carrier signals, each of which is emitted through an antenna array.
If the aircraft is on the landing line both signals are received with the same modulations
depth. If the aircraft deviates from the landing line, either the 90 Hz- or the 150 Hzcomponents predominates after the AM demodulation. The ILS-interpretation is done
by measuring the modulation depth of both emitted signals, the difference allows the
calculation of the DDM (Difference in Depth of Modulation).
DDM = m(x90) – m(x150)
The ICAO (International Civil Aviation Organization) prescribes the way in which the
DDM values must be generated for different distances from the runway threshold.
According to this the corresponding antenna diagrams of the landing course transmitter
LLZ (Localizer) and the glide path transmitter GS (Glideslope) are calibrated.
Figure 1-2: Basic antenna diagrams of the ILS localizer
1.3.2 VOR (VHF Omni directional Radio Range)
VOR is a radio navigation system for short and medium distance navigation. VOR
transmitter systems work in the VHF range from 108 to 118 MHz. The VOR radio
navigation aid supplies the aircraft with directional information, angle information
relative to the magnetic north from the site of the beacon. The range covered by a
VOR station is ideally a circle around the VOR station with a radius depending on the
flight altitude.
R&S FS-K15 Installation and Enabling
General information about ILS and VOR/DVOR
Software Manual 1302.0942.42 - 04 7
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
transmits with a rotating antenna. From the rotation a sinewave AM modulated 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. In order
to determine the radial the phase difference to a reference phase must be measured.
Because this reference phase must be independent of the rotation of the antenna it is
modulated with a frequency deviation of 480 Hz in FM onto a secondary carrier with
9,96 kHz and emitted over a separate antenna with round characteristic.
Figure 1-3: Basics of the VOR phase angles () depending on the azimuth angle ()
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 or speech in the usual AF from
300 Hz to 3.3 kHz can be transmitted on the VOR carrier. Often the voice channel of a
VOR station is used for the transmission of ATIS (Automatic Terminal Information
Service) messages. The spectrum of a VOR signal is therefore composed of the carrier
and three modulated components.
Figure 1-4: 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
R&S FS-K15 Installation and Enabling
General information about ILS and VOR/DVOR
Software Manual 1302.0942.42 - 04 8
1
2
3
4
5
50
26
25
M
24
23
27
28
29
23
49
48
47
FM modulated with 480 Hz deviation. The VOR signal generation as under ICAO is
shown below.
Figure 1-5: Basics of the VOR signal generation
1.3.3 DVOR (Doppler VHF Omni directional Range)
A DVOR beacon transmits like a VOR a RF signal in which the two phase angles are
coded from whose difference the receiver can calculate it´s position in reference to the
DVOR. In contrast to the VOR the meaning of the reference and azimuth depending
phase is interchanged. This means that the reference phase is no longer emitted in FM
through the secondary carrier, but rather 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
relative movement of a receiver with a speed vx towards the transmitter, and
correspondingly 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 (carrier + 9,96 kHz) is distributed
using an electronic multiplexer on the circularly arranged antenna, such that the
transmission signal seems to revolve at 30 Hz in the circle.
Figure 1-6: 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
R&S FS-K15 Installation and Enabling
Description of the Avionics Measurement Demodulator
Software Manual 1302.0942.42 - 04 9
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 a
FM on the receiver, because one sideband component always increases in frequency
because of 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 1-7: Basics of the DVOR signal generation
1.4 Description of the Avionics Measurement Demodulator
The following chapter describe the functions of the Avionics measurement
demodulator. In the case of functions identical to those of the base unit, reference is
made to the relevant chapter in the base unit manual.
The digital signal processing used in the analyzer mode for digital IF filters are also
ideally suited for demodulating VOR and ILS navigation aid signals.
By sampling (digitization) already at the IF and digital downconversion to the baseband
(I/Q), the demodulator achieves maximum accuracy and temperature stability. There is
no evidence of typical errors of an analog downconversion and demodulation like AM
FM conversion, deviation error, frequency response or frequency drift at DC
coupling. Only the characteristics of the analog IF filter ahead of the A/D converter
needs to be taken into consideration.
R&S FS-K15 Installation and Enabling
Description of the Avionics Measurement Demodulator
Software Manual 1302.0942.42 - 04 10
I Memory
128 k
Processor
Analog
IF filter
Bandwidth
300 kHz
Analyzer IF
20.4 MHz
A
D
A/D
converter
32 MHz
sampling
clock
Digital down conversion
+ decimation
cos
sin
decimation
filters
NCO
20.4 MHz
Q Memory
128 k
sampling rate
VOR: 31250 Hz
ILS: 15625 Hz
Data aquisition hardware
I data
Q data
Trigger
1.4.1 Circuit Description - Block Diagrams
Figure 1-8: Block diagram of analyzer signal processing
Figure 1-8 shows the analyzer’s hardware from the IF to the processor. The IF filter is
the resolution filter of the spectrum analyzer, with a bandwidth range from 300 kHz to
10 MHz for ILS and VOR measurement. The A/D converter samples the IF (20.4 MHz)
at 32 MHz.
Lowpass filtering and reduction of the sampling rate follow the downconversion to the
complex baseband. The decimation depends on the selected demodulation bandwidth.
The output sampling rate is set in powers of 2 between 800 Hz and 31.250 kHz.
Useless oversampling at narrow bandwidths is avoided, saving computing time and
increasing the maximum recording time.
The I/Q data is stored in memories each comprising 512 k words in case of FSU, FSQ
and FSMR. The hardware triggering (external, IF power) controls the memory.
1.4.2 ILS demodulator
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.
R&S FS-K15 Installation and Enabling
Description of the Avionics Measurement Demodulator
Software Manual 1302.0942.42 - 04 11
I2 + Q
2
AM demodulator
I/Q data
BP 90 Hz
decimation
filter
BP ID
LP 0 Hz
BP 150 Hz
Inter-
polation
Inter-
polation
Zero-
crossing
Detectors
Frequency
Phase-
difference
Amplitude
Freq
90
Sum
90+150
Depth
90
Freq
150
Depth
150
carrier power
Psi
90,150
DDM
90,150
Zero-
crossing
Frequency
Amplitude
Freq
ID
Depth
ID
fs=15625 Hz fs=976.5625 Hz
fs=15625 Hz
ILS Software Demodulator
Figure 1-9: Block diagram of ILS software demodulator
The ILS demodulation basically comprises of two bandpass filters with center
frequencies of 90 and 150 Hz. In order to meet the required selectivity with a
reasonable filter order the AM signal must be decimated in frequency before filtering
and interpolated thereafter.
The optional ID signal is separated by a bandpass filter with a frequency range from
300 to 4000 Hz.
1.4.2.1 AM Modulation Depth
To obtain the AM depth the mean carrier power must be calculated by an lowpass
filter. Since modulation depths are computed by using the RMS method, the averaging
length is crucial and must be multiples of the period length. Thus zero crossing
detector results are used to derive the appropriate averaging lengths. In this way the
following AM depths and their derivates are computed
● 90 Hz / 150 Hz
● 300 Hz -4KHz (Identification/Voice)
● DDM Difference in Depths of Modulation (90 Hz and 150 Hz)
● SDM Sum of Depths of Modulation (90 Hz and 150 Hz)
● Sum90/150 Hz (vectorial) sum amplitude of the 90 and 150 Hz signals
(peak-to-peak method, no RMS)
1.4.2.2 AF frequencies
Interpolated results of the zero crossing detectors are used to determine the
frequencies of the AM signal components 90 Hz, 150 Hz and 1020 Hz (Identification).
1.4.2.3 Phase angle 90/150 Hz
The phase angle is computed by the differences of the interpolated results of the
90/150 Hz zero crossing detectors. Since the frequencies having a ratio of 3 to 5,
phase angles exceeding ± 60° will lead to ambiguous results.
R&S FS-K15 Installation and Enabling
Software Manual 1302.0942.42 - 04 12
1.4.3 VOR demodulator
I2+Q
2
AM
demodulator
I/Q
data
BP 30 Hz
decimation
filters
BP 9960
Hz
LP 0 Hz
Inter-
polation
Inter-
polation
Averaging
Scaling
Freq
FM30
Depth
AM30
Freq
AM30
carrier power
Phase
FM-AM
Zero-
crossing
Frequency
Amplitude
Freq
ID
Depth
ID
fs=31250 Hz
fs=3906.25 Hz
fs=15625 Hz
VOR Software Demodulator
BP ID
FM
demod
Phase-
estimation
Phase-
estimation
d/dt
d/dt
+
-
Freq
9960
Devia
FM30
Zero-
crossing
Depth
9960
BP 30 Hz
Description of the Avionics Measurement Demodulator
Figure 1-10: Block diagram of VOR software 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 – 4 kHz)
● FM component (9960 ± 700 Hz)
This is done by means of bandpass filters covering the given frequency ranges.
However, like in the case of the ILS demodulator, the low frequency component of 30
Hz must be computed on an downsampled version of the AM demodulated signal in
order to obtain the required selectivity with a reasonable filter order.
The separated FM component is passed through a FM demodulator. To obtain the 30 Hz
reference-signal the FM demodulator output is processed with the same procedure as the
AM 30 Hz rotational-component (downsampling, 30 Hz bandpass filter and interpolation).
FM deviation is computed using the RMS value of the 30 Hz reference signal.
Both signals, the 30 Hz reference and the rotational signal are fed to a phase
estimation procedure for the azimuth processing.
1.4.3.1 AM Modulation Depth
To obtain the AM depth the mean carrier power must be calculated by an lowpass
filter. Since modulation depths are computed by using the RMS method, the averaging
length is crucial an must be multiple of the period length. Thus zero crossing detector
result of the AM 30 Hz rotational component is used to derive the appropriate
averaging length. Note that the precision as specified in the FS-K15 data sheet will be
guaranteed only if the AM 30 Hz rotational component can be identified properly.
R&S FS-K15 Installation and Enabling
Software Manual 1302.0942.42 - 04 13
The following AM depths are computed:
● 30 Hz (Rotational-signal)
● 300 Hz – 4KHz (Identification/Voice)
● 9960 Hz (FM)
1.4.3.2 Azimuth (Phase difference at 30 Hz)
In order to meet the resolution requirements the phase of the 30 Hz rotational- (AM)
and reference- (FM) components are computed by means of an Hilbert transform
based phase estimation algorithm. The azimuth is obtained by the difference of both
estimator results and the frequency results are obtained from the differential phase.
1.4.3.3 AF frequencies
In the VOR demodulator the AF frequencies are computed using different methods:
● 30 Hz Rotational-signal (AM), differential of the phase estimator result
● 30 Hz Reference-signal (FM), differential of the phase estimator result
● 1020 Hz (Identification), interpolated results of the zero crossing detector
● 9960 Hz (FM carrier frequency), mean value for the FM demodulator output
Further Characteristics
1.5 Further Characteristics
1.5.1 IF Bandwidth
The analog IF filter improves the selectivity, but also may cause signal distortion. The
filter is negligible if the IF bandwidth is wider than the highest modulation frequency.
In general, the IF bandwidth should be set to auto coupling.
1.5.2 Demodulation Bandwidth
Digital filters determine the demodulation bandwidth. This is not the 3 dB bandwidth
but the useful bandwidth which is distortion-free with regard to phase and amplitude.
Therefore the following automated settings are applied:
● ILS: demodulation bandwidth set to 12.5 kHz, in order to capture the full
identifier signal
● VOR: demodulation bandwidth set to 25 kHz, in order to capture the 9.96 kHz
signal
● DIST demodulation bandwidth set to same value as selected demodulator (ILS or
VOR)
R&S FS-K15 Installation and Enabling
Software Manual 1302.0942.42 - 04 14
If the demodulation bandwidth setting is changed, some demodulation results may not
be available due to bandwidth limitations. In case of harmonic distortion measurement
the highest measured harmonic signal may be limited due to the demodulation
bandwidth.
In general, the demodulation bandwidth should be set to auto coupling.
1.5.3 Stability of Measurement Results
Stability of the mean-squares method involved for of computation of the modulation
depths and Azimuth estimation rely on a sufficient length for the averaging.
This is achieved if at least five periods of the 30 Hz basic modulation frequency are
recorded. To this time the summed filter settling times must, be added, thus a minimum
recording time of 400 ms is needed to meet the required precision.
Note, that the precision as specified in FS-K15 data sheet will be guaranteed only if the
AM 30 Hz rotational component can be identified properly in the VOR analysis case.
Due to rounding effects of the phase estimation algorithm, the systematic error is
limited to 10E-8 for the Azimuth- and frequency results.
Further Characteristics
R&S FS-K15 Configuration of the Avionics Demodulator
Getting Started
Software Manual 1302.0942.42 - 04 15
2 Configuration of the Avionics Demodulator
2.1 Getting Started
Before measurements, you must adjust the instrument settings to the properties of the
device under test. The following procedure is recommended:
1. Set the spectrum analyzer to its default state.
─ Press the PRESET button.
The device is now in its default state. If the instrument is not in the spectrum
analyzer mode, the mode has to be changed to the spectrum analyzer mode:
Press the SPECTRUM hotkey.
2. Activate measurements with avionics demodulator.
─ Press the AVIONICS hotkey.
Measurements with the avionics demodulator will be activated and the menu
with the settings for the avionics demodulator will be opened.
3. Set the frequency
─ In the default setting, the frequency of the avionics demodulator is coupled
with the center frequency of the analyzer, i.e. when the center frequency of
the analyzer is set (FREQ button), the avionics demodulator is automatically
set to the frequency to be measured.
4. Set the measurement mode.
─ In the avionics demodulator main menu, press the VOR softkey for
measurements in the VOR standard (VHF Omnidirectional Radio Range), or
press the ILS softkey for measurements in the ILS standard (Instrument
Landing System)
5. Set the unit
─ Press the SETTINGS softkey to select the harmonic distortion readings in %
or dB values.
Additional setting options are described in the following reference section of the
manual.
R&S FS-K15 Configuration of the Avionics Demodulator
Software Manual 1302.0942.42 - 04 16
2.2 Test Setup for Measurements
Instrument damage caused by disregarding the following precautions
Before the instrument is put into operation, make sure the following are done:
● The ventilation openings are unobstructed.
● No signal voltage levels exceed permitted limits.
The instrument outputs are not overloaded or improperly connected
SCREEN B
MRECEIVER
SPECTRUM
NETWORK PWR METER
AVIONICS
SPECTRUM
The SPECTRUM hotkey sets the instrument to spectrum analysis mode.
Remote: INST:SEL SAN
AVIONICS
The AVIONICS hotkey sets the instrument to avionics demodulation mode.
Remote: INST:SEL AVI
This chapter describes the basic settings for the analyzer for measurements. Before
measurements can be started, the analyzer must be correctly configured and powered
as described in Chapter 1 of the operating manual for the base unit. Furthermore,
Application Firmware R&S FS-K15 must be enabled. Chapter 1 of this manual
describes how to install and enable the application firmware.
Test Setup for Measurements
2.3 Selecting the Operating Mode – HOTKEY Bar
The base instrument has seven hotkeys below the display for fast mode selection.
These hotkeys can be differently assigned depending on the available instrument
options and instrument modes.
The keys after instrument preset: ( in spectrum analysis mode, further keys may be
available).
The operating manual of the base instrument or of the other options describes the
meaning of the other keys.
R&S FS-K15 Configuration of the Avionics Demodulator
Software Manual 1302.0942.42 - 04 17
2.4 Avionics Demodulator Mode
SPECTRUM
AVIONICS
MRECEIVER
NETWORK
SCREEN B
AVIONICS
VOR
MODULATION
SPECTRUM .
AVIONICS
SETTINGS
DISTORT
ON OFF
DISTORTION
MAX FREQ
FUND FREQ
90/150 HZ
FSMR
FSQ with opt.
B71
(baseband
input)
Instrument Model
FUND FREQ
150 HZ
THD UNIT
% DB
ILS
BASEBAND
DDM UNIT
% [1]
FUND FREQ
90 HZ
BASEBAND
ON OFF
BASEBAND
SENSITIVTI
INPUT LEV
4V 400mV
BASEBAND
ANALOG
BALANCED
ON OFF
RF PATH
FUND FREQ
IDENT
FUND FREQ
90/150 HZ
FUND FREQ
90 HZ
FUND FREQ
150 HZ
FUND FREQ
IDENT
BASEBAND
SENSITIVTI
HARMONIC
FREQ
INPUT IMP
1MΩ 50Ω
INPUT IMP
1MΩ 50Ω
The softkeys visible in the BASEBAND submenu depend on the instrument type. The
BASEBAND submenu is only available in the R&S FSMR and R&S FSQ equipped
with baseband inputs (option R&S FSQ-B71).
The application firmware R&S FS-K15 (avionics demodulation measurements) is
activated with the AVIONICS hotkey.
The AVIONICS hotkey allows the access to the avionics measurement capabilities
(VOR/ILS) of the instrument.
A softkey menu suitable for the currently selected operating mode is simultaneously
displayed and allows the setting of the measurement parameters.
Avionics Demodulator Mode
Simultaneously, the VOR demodulator is activated (default after Preset).
The individual settings are explained in the following menus.
R&S FS-K15 Configuration of the Avionics Demodulator
Result Display – RF level and frequency counter result
Software Manual 1302.0942.42 - 04 18
ATT
Setting of the RF attenuator. Manual or Coupled to Reference level
AQT
This is the measurement time or capture time.
RBW
Display of actual resolution bandwidth for distortion measurement
AUTO
TUNE
Enhancement label for Autotune = ON.
AUTOL
Enhancement label for level Autorange.
The main measurement functions of the avionics demodulator are:
● VOR VOR Measurements
● ILS ILS Measurements
● MODULATION SPECTRUM Modulation Distortion measurements
In the avionics demodulator mode the base instrument is equipped with a high
performance avionics demodulator. In order to display the measurement results the
screen is divided in two halves.
The frequency setting, the frequency counter result and the RF or baseband input level
is displayed in the upper half of the screen. The measurement results of the avionics
demodulator are displayed in a table in the lower half of the screen. The modulation
spectrum can be displayed in the lower half as a trace.
Signal parameters such as modulation depth and frequency deviation can be
determined.
2.5 Result Display – RF level and frequency counter result
The upper screen shows the level readings and the frequency settings and frequency
counter result.
Example for upper screen:
Figure 2-1: RF Level measurement display
Screen description:
● RF frequency Result from the frequency counter
● Carrier Offset Frequency offset between measured frequency and tuned
frequency
● Tuned Frequency RF Frequency setting
● RF level RF level reading (Baseband input level in case of baseband
operation)
● Bargraph for visual information about the input level
Status information flags for Power Splitter, Auto Tune, Average, AutoLevel etc.:
R&S FS-K15 Configuration of the Avionics Demodulator
Software Manual 1302.0942.42 - 04 19
EVEL
SPLITTER
Enhancement label for Power Splitter Sensor head. The insertion loss of
the splitter will be taken into account in the RF level reading
VOR
The VOR softkey switches the VOR demodulator on. The VOR demodulator default
setting is OFF. When the AVIONICS mode is selected after preset, the demodulator is
switched on automatically.
Remote: CALC:AVI:STAN VOR
Figure 2-2: VOR measurement display
The settings of the spectrum analyzer active before the demodulator is switched on
will be restored when the demodulator is switched off. The center frequency setting is
coupled between the operating modes.
The trace operating mode and detector are restored (the VOR/ILS demodulator has
separate trace settings).
The individual measured values are read out with the following commands:
RF frequency CALC:AVI:RFFR:RES?
Carrier Offset CALC:AVI:FERR:RES?
RF level CALC:AVI:CARR:RES?
2.6 Avionics Demodulator Main Menu
The AVIONICS hotkey opens the menu for setting the VOR/ILS demodulator functions.
Avionics Demodulator Main Menu
R&S FS-K15 Configuration of the Avionics Demodulator
Avionics Demodulator Main Menu
Software Manual 1302.0942.42 - 04 20
Screen description:
30 Hz AM Selective modulation depth and AF frequency measurement of VOR 30
Hz signal component.
9.96 kHz AM Selective modulation depth and AF frequency measurement of
frequency modulated VOR 9960 Hz signal component.
IDENT AM Modulation depth and frequency measurement of Identifier signal and
speech band 300 Hz to 4 kHz without influence by the actual VOR
signal component.
30 Hz FM Frequency deviation and AF frequency measurement at the frequency
modulated VOR 9960 Hz signal component.
THD Ident Distortion measurement at the identifier signal component.
THD 30 Distortion measurement at the 30 Hz AM signal component.
VOR Phase Phase measurement between 30 Hz AM signal and 30 Hz FM
demodulated signal (= reference signal), measurement range 0 to 360
degree.
The individual measured values are read out with the following commands:
30 Hz AM Depth CALC:AVI:AM:DEPT? ‘30’
30 Hz AM Frequency CALC:AVI:AM:FREQ? ‘30’
9.96 kHz AM Depth CALC:AVI:AM:DEPT? ‘9960’
9.96 kHz AM Freq. CALC:AVI:AM:FREQ? ‘9960’
IDENT AM depth CALC:AVI:AM:DEPT? ‘ID’
IDENT AM Frequency CALC:AVI:AM:FREQ? ‘ID’
30 Hz FM deviation CALC:AVI:FM:DEV?
30 Hz FM Frequency CALC:AVI:FM:FREQ?
THD Ident CALC:AVI:THD:RES? 'ID'
THD 30 CALC:AVI:THD:RES? '30'
VOR Phase CALC:AVI:PHAS?
ILS
The ILS softkey switches the ILS demodulator on.
Remote: CALC:AVI:STAN ILS
R&S FS-K15 Configuration of the Avionics Demodulator
Avionics Demodulator Main Menu
Software Manual 1302.0942.42 - 04 21
Figure 2-3: ILS measurement display
The settings of the spectrum analyzer active before the demodulator is switched on
will be restored when the demodulator is switched off. The center frequency setting is
transferred between the operating modes.
Similarly, the trace operating mode and detector are restored (the VOR/ILS
demodulator has separate trace settings).
Screen description:
90 Hz AM Selective modulation depth and AF frequency measurement of
90 Hz ILS signal component.
150 Hz AM Selective modulation depth and AF frequency measurement of
150 Hz ILS signal component.
ILS Phase Phase angle measurement between 90 Hz and 150 Hz AM signal
(90 Hz = reference signal), measurement range ±60 degree.
90+150 Hz AM Total modulation depth of the 90 Hz and the 150 Hz components
taking the phase between the components into account.
IDENT AM Modulation depth and frequency measurement of Identifier
signal and speech band 300 Hz to 4 kHz without influence by
the actual ILS signal components.
SDM Selective measurement of the sum-modulation depth (SDM =
Sum in Depth of Modulation); arithmetic sum of the modulation
depth of the 90 Hz and the 150 Hz components without any
influence of the phase between the components.
THD Ident Distortion measurement at the identifier signal component.
DDM DDM (= difference in depth of modulation) between 90 Hz and
150 Hz AM signal (m90 Hz – m150 Hz).
The individual measured values are read out with the following commands:
R&S FS-K15 Configuration of the Avionics Demodulator
Avionics Demodulator Main Menu
Software Manual 1302.0942.42 - 04 22
90 Hz AM depth CALC:AVI:AM:DEPT? ‘90’
90 Hz AM Frequency CALC:AVI:AM:FREQ? ‘90’
150 Hz AM depth CALC:AVI:AM:DEPT? ‘150’
150 Hz AM Frequency CALC:AVI:AM:FREQ? ‘150’
90+150 Hz AM depth CALC:AVI:AM:DEPTh? ‘90+150’
ILS Phase CALC:AVI:PHAS?
IDENT AM depth CALC:AVI:AM:DEPT? ‘ID’
IDENT AM Frequency CALC:AVI:AM:FREQ? ‘ID’
SDM CALC:AVI:SDM?
THD CALC:AVI:THD:RES? ‘’
DDM CALC:AVI:DDM?
MODULATION
SPECTRUM
The MODULATION SPECTRUM softkey opens the submenu for the distortion meter
operation and selects the display of the AF spectrum. The AF spectrum is calculated
from the ILS signal or the VOR signal depending on the mode which was active before
selecting the distortion/spectrum measurement.
Remote:: CALC:FEED 'XTIM:SPEC'
To switch back to the demodulation summary screen:
Remote: CALC:FEED 'XTIM:AMS'
Figure 2-4: Distortion measurement display
Similarly to the spectrum analyzer operation, the markers can be used for selective
harmonic measurements on any arbitrary frequencies within the audio spectrum
range. The spectrum is limited to the half of the demodulation bandwidth setting
(default: 12.5 kHz in ILS mode and 25 kHz in VOR mode).
R&S FS-K15 Configuration of the Avionics Demodulator
Avionics Demodulator Main Menu
Software Manual 1302.0942.42 - 04 23
Screen description:
DIST Distortion measurement at the selected signal component.
The measured value are read out with the following command:
Remote: CALC:AVI:SHD:RES?
DISTORTION
ON OFF
The DISTORTION ON OFF softkey activates the harmonic distortion measurement.
Remote: CALC:AVI:SHD:STAT ON | OFF
HARMONIC
FREQUENCY
The HARMONIC FREQUENCY softkey sets the measurement frequency of the
harmonic distortion measurement. This setting is only taken into account for the
distortion reading in the distortion screen.
Remote: CALC:AVI:SHD:FREQ 300HZ
The result of the manual distortion measurement is available with the following
command:
Remote: CALC:AVI:SHD:RES?
FUND FREQ
90/150HZ
The FUND FREQ 90/150HZ softkey sets the reference frequency for the harmonic
distortion reading to the 90 Hz and 150 Hz signal. Both modulation tones will be
measured and the average level will be used as reference. This allows THD
measurements at signals with non-equal tone modulation (DDM not zero). All
harmonics at N * 30 Hz will be measured and the distortion result is calculated in % or
dB to the average of the 90 Hz and 150 Hz signal level.
Remote: CALC:AVI:THD:FREQ:FUND '90_150'
FUND FREQ 90
HZ
The FUND FREQ 90 HZ softkey sets the reference frequency for the harmonic
distortion reading to the 90 Hz signal. All harmonics at N * 90 Hz will be measured and
the distortion result is calculated in % or dB to the 90 Hz signal level.
Remote CALC:AVI:THD:FREQ:FUND '90'
FUND FREQ
150 HZ
The FUND FREQ 150 HZ softkey sets the reference frequency for the harmonic
distortion reading to the 150 Hz signal. All harmonics at N * 150 Hz will be measured
and the distortion result is calculated in % or dB to the 150 Hz signal level.
Remote: CALC:AVI:THD:FREQ:FUND '150'
FUND FREQ
IDENT
The FUND FREQ IDENT softkey sets the fundamental frequency for the harmonic
distortion reading to the Identifier signal. The THD measurement will use the highest
signal in the frequency range from 300 Hz to 4 kHz as the fundamental signal
reference.
Remote: CALC:AVI:THD:FREQ:FUND 'ID'
SETTINGS
The SETTINGS softkey opens the submenu for setting the measurement parameters
of the selected measurement function.
DDM UNIT
% [1]
The DDM UNIT %/1 softkey selects between % and unitfree for displaying the DDM
measurement results of the ILS demodulator.
Remote: UNIT:DDM PCT | UNIT
R&S FS-K15 Configuration of the Avionics Demodulator
Avionics Demodulator Main Menu
Software Manual 1302.0942.42 - 04 24
DISTORTION
MAX FREQ
The DISTORTION MAX FREQ softkey sets the upper frequency limit of the total
harmonic distortion measurement.
Remote: CALC:AVI:THD:FREQ:UPP
DIST UNIT %/DB
The DIST UNIT %/DB softkey selects between % and dB for displaying the THD
measurement results.
Remote: UNIT:THD PCT
FUND FREQ
90/150HZ
The FUND FREQ 90/150HZ softkey sets the reference frequency for the harmonic
distortion reading to the 90 Hz and 150 Hz signal. Both modulation tones will be
measured and the average level will be used as reference. This allows THD
measurements at signals with non-equal tone modulation (DDM not zero). All
harmonics at N * 30 Hz will be measured and the distortion result is calculated in % or
dB to the average of the 90 Hz and 150 Hz signal level.
Remote: CALC:AVI:THD:FREQ:FUND '90_150'
FUND FREQ 90
HZ
The FUND FREQ 90 HZ softkey sets the reference frequency for the harmonic
distortion reading to the 90 Hz signal. All harmonics at N * 90 Hz will be measured and
the distortion result is calculated in % or dB to the 90 Hz signal level.
Remote: CALC:AVI:THD:FREQ:FUND '90'
FREQ 150 HZ
The FUND FREQ 150 HZ softkey sets the reference frequency for the harmonic
distortion reading to the 150 Hz signal. All harmonics at N * 150 Hz will be measured
and the distortion result is calculated in % or dB to the 150 Hz signal level.
Remote: CALC:AVI:THD:FREQ:FUND '150'
FUND FREQ
IDENT
The FUND FREQ IDENT softkey sets the fundamental frequency for the harmonic
distortion reading to the Identifier signal. The THD measurement will use the highest
signal in the frequency range from 300 Hz to 4 kHz as the fundamental signal
reference.
Remote: CALC:AVI:THD:FREQ:FUND 'ID'
BASEBAND
FUND FREQ IDENT (present at the RF input of the instrument) the modulation signal
at the audio input or the baseband input is analyzed. The input level range is fixed (no
autorange). In all VOR/ILS modulation depth measurements the selectively measured
voltages are converted into modulation depth and read out in %AM, the sensitivity
entered under Baseband Sensitivity in Volöts/100% being used as a reference. This
applies also to the ILS measurements DDM, SDM and m(90+150)Hz derived from the
90 and 150 Hz tones modulation depth measurements. When baseband
measurements are selected, the RF input is switched off.
The baseband menu is only available when the instrument is equipped with an audio
input (R&S FSMR) or with the option baseband inputs (R&S FSQ-B71).
The baseband signal shall be connected to the “I” baseband input on the R&S FSQ.
R&S FS-K15 Configuration of the Avionics Demodulator
Avionics Demodulator Main Menu
Software Manual 1302.0942.42 - 04 25
Figure 2-5: Screen display of measurements on the audio input
Screen description:
RF frequency Not available in Baseband mode
Carrier Offset Not available in Baseband mode
Tuned Frequency Not available in Baseband mode
Input level Peak input level of the modulation signal
Bargraph for visual information about input level
The following commands are used for reading out the individual measured value:
Input Level(Pk) CALC:AVI:POW:AC:RES?
R&S FSQ with
R&S FSQ-B71
R&S FSMR
BASEBAND
ANALOG
BASEBAND
ON/OFF
The BASEBAND ON/OFF or BASEBAND ANALOG softkey in the
avionics mode switches the audio or baseband input to active.
Remote: ON: INP1:SEL AIQ| AUD
Remote: OFF: INP1:SEL RF
BASEBAND
SENSITIVITY
BASEBAND
SENSITIVITY
The BASEBAND SENSITIVITY softkey enables the entry of the
sensitivity of an (external) AM modulator that could be or is driven by
the applied baseband signal. The entered sensitivity [Vpeak/100%AM]
is used to convert the measured voltages into modulation depth.
Default value: 1 V peak voltage corresponds to 100 % AM.
Remote: SENS1:VOLT:AC:SENS 2V
R&S FS-K15 Configuration of the Avionics Demodulator
FREQ Key
Software Manual 1302.0942.42 - 04 26
Use reference
level setting in
amplitude menu.
INP LEVEL
4V/400mV
The INP LEVEL 4V/400mV softkey switches the input voltage range of
the audio input between 4 V and 400 mV.
In the default setting, the 4 V range is switched on.
Remote: SENS1:VOLT:AC:RANG:UPP 0.4V
I/Q INPUT
50Ω/1MΩ
INPUT IMP
50Ω/1MΩ
The INPUT IMP 50Ω/1MΩ or I/Q INPUT 50Ω/1MΩ softkey switches the
input impedance of the audio input between 50 Ω and 1 MΩ.
Note: The baseband input impedance on the R&S FSQ depends on the
model. Older models offer 50Ω/1kΩ impedance settings.
In the default setting, the input impedance is set to 1 MΩ.
Remote: INP1:IMP 50OHM
BALANCED
ON/OFF
The BALANCED ON/OFF softkey switches the baseband input between
balanced and unbalanced mode. (only R&S FSQ-B71).
In the default setting, the balanced mode is switched on.
Remote: INP1:IQ:BAL ON
2.7 FREQ Key
The FREQ key opens the RF frequency menu. The menu allows to set the RF
frequency tuning mode on the instrument. In the default status the analyzer is set to
manual tuning mode and 100 MHz receiver frequency. The keys for the RF frequency
variation are not available in the baseband mode.
R&S FS-K15 Configuration of the Avionics Demodulator
FREQ Key
Software Manual 1302.0942.42 - 04 27
FREQ
RECEIVER
FREQUENCY
STEPSIZE
SIGNAL
TRACK
TRACKING
ON OFF
AUTO
COARSE
AUTO
FINE
STEPSIZE
=FREQ
STEPSIZE
MANUAL
AF START
AF STOP
AF CENTER
SINGLE
AUTOTUNE
AUTOTUNE
THRESHOLD
TRACK
ONCE
RECEIVER
FREQUENCY
The RECEIVER FREQUENCY softkey activates the window for entering the receiver
frequency.
The receiver frequency resolution is 0.1 Hz.
Setting range: 20 Hz fREC fmax
Remote: SENS:FREQ:CENT 300MHz
STEPSIZE
The STEPSIZE softkey opens a submenu for setting the step size of the receive
frequency. The step size can either be coupled to the set frequency or be manually set
to a fixed value. The menu softkeys are selection switches, and only one of them at a
time can be active.
AUTO AUTO
COARSE
COARSE
The AUTO COARSE softkey sets the step size of the receive frequency to coarse. In
this setting, the fourth position of the set frequency is varied.
Remote: ---
AUTO
FINE
The AUTO FINE softkey sets the step size of the receive frequency to fine. The
seventh position of the set frequency is varied in this setting.
Remote: ---
STEPSIZE
MANUAL
The STEPSIZE MANUAL softkey activates the window for entering a fixed value for
the step size.
Remote: FREQ:CENT:STEP 50 kHz
R&S FS-K15 Configuration of the Avionics Demodulator
FREQ Key
Software Manual 1302.0942.42 - 04 28
STEPSIZE
= FREQ
The STEPSIZE = FREQ softkey sets the step size to the receive frequency value. This
function is particularly useful for measuring the harmonics of a signal. If the receiver is
first tuned to the fundamental, the frequency of another harmonic is set with each
frequency variation by using the rotary knob or the STEP keys.
Remote: ---
AUTOTUNE
THRESHOLD
The AUTOTUNE THRESHOLD softkey activates the window for entering the threshold
level of the autotune function. This function is only available for instrument models up
to a maximum frequency of 26.5 GHz.
The autotune threshold default setting is -40 dBm.
Setting range -50 dBm Threshold level 0 dBm
Remote: SENS:FREQ:CW:AFC:THR <numeric_value>
SINGLE
AUTOTUNE
This softkey activates a single automatic signal search.Q
Remote: SENS:FREQ:CW:AFC ONCE
SIGNAL
TRACK
This softkey activates a function to track a drifting signal. If the measured signal
frequency is too far away from the tuned center frequency and the level is above the
threshold, the center frequency of the receiver will be changed to the new signal
frequency.
Remote: SENS:FREQ:CW:AFC ON
TRACK
ONCE
This softkey activates a single frequency setting to align the tuned frequency to the
signal. If the measured signal frequency is too far away from the tuned center
frequency and the level is above the threshold, the center frequency of the receiver will
be changed to the new signal frequency.
Remote: SENS:FREQ:CW:AFC ON'
SENS:FREQ:CW:AFC:STR ONCE
AF CENTER
The AF CENTER softkey allows the user to select the center frequency within the AF
spectrum.
Remote: SENS:ADEM:AF:CENT 1KHZ
AF START
The AF START softkey allows the user to select the start frequency within the AF
spectrum.
Remote: SENS:ADEM:AF:STAR 0HZ
AF STOP
The AF STOP softkey allows the user to select the stop frequency within the AF
spectrum.
The maximum AF stop frequency corresponds to half the demodulation bandwidth.
Remote: SENS:ADEM:AF:STOP 2KHZ
R&S FS-K15 Configuration of the Avionics Demodulator
Software Manual 1302.0942.42 - 04 29
2.8 SPAN Key
DEMOD
BW
AF
FULL SPAN
AF SPAN
SPAN
The Span softkey is only available when the modulation spectrum is active.
AF SPAN
The AF SPAN softkey allows the user to select the frequency range if the modulation
spectrum display is active.
Values between the sampling rate/200 and the demodulation bandwidth/2 can be
selected.
Remote: SENS:ADEM:AF:SPAN 2.5 kHz
AF
FULL SPAN
The AF FULL SPAN softkey sets the maximum frequency range if the AF spectrum
displays are active.
The maximum frequency range corresponds to half the demodulation bandwidth.
Remote: SENS:ADEM:AF:SPAN:FULL
DEMOD
BW
The demodulation bandwidth of the avionics demodulator is selected using the
DEMOD BW softkey. The demodulation bandwidth determines the sampling rate for
recording the signal to be analyzed. The DEMOD BW MANUAL softkey is only
available in ILS demodulation mode. The bandwidth can be set to 12.5 kHz, 3.2 kHz
and 800 Hz. This function can be used to suppress adjacent transmitters.
Remote: SENS:BAND:DEM 3.2KHZ
SPAN Key
The SPAN menu allows the user to select the frequency range to be displayed.
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