Rohde&Schwarz FMU36 Operating Manual

Operating Manual

Baseband Signal Analyzer



R&S

1303.3500.02

Printed in Germany

FMU36

Test and Measurement Division

1303.3545.12-01- 1

Dear Customer,

R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG.
Trade names are trademarks of the owners.

1303.3545.12-01- 2

R&S FMU Tabbed Divider Overview

Tabbed Divider Overview

Contents

Safety Instructions
Certificate of Quality
EU Certificate of Conformity
List of R&S Representatives

Manuals for Baseband Signal Analyzer R&S FMU

Tabbed Divider

1 Chapter 1: Putting into Operation (s. Quick Start Guide)

2 Chapter 2: Getting Started

3 Chapter 3: Menu Overview

4 Chapter 4: Functional Description

5 Chapter 5: Remote Control – Basics

6 Chapter 6: Remote Control – Commands

7 Chapter 7: Remote Control – Program Examples

8 Chapter 8: Maintenance and Hardware Interfaces

9 Chapter 9: Error Messages

10 Index

1303.3545.12 RE E-1

Certificate No.: 2006-76

This is to certify that:

EC Certificate of Conformity

Equipment type

Stock No. Designation

FMU36 1303.3500.02 Baseband Signal Analyzer

complies with the provisions of the Directive of the Council of the European Union on the
approximation of the laws of the Member States

- relating to electrical equipment for use within defined voltage limits
(73/23/EEC revised by 93/68/EEC)

- relating to electromagnetic compatibility
(89/336/EEC revised by 91/263/EEC, 92/31/EEC, 93/68/EEC)

Conformity is proven by compliance with the following standards:

EN 61010-1 : 2001
EN 55011 : 1998 + A1 : 1999 + A2 : 2002, Klasse B
EN 61326 : 1997 + A1 : 1998 + A2 : 2001 + A3 : 2003
EN 61000-3-2 : 2000 + A2 : 2005
EN 61000-3-3 : 1995 + A1 : 2001

For the assessment of electromagnetic compatibility, the limits of radio interference for Class
B equipment as well as the immunity to interference for operation in industry have been used
as a basis.

Affixing the EC conformity mark as from 2006

ROHDE & SCHWARZ GmbH & Co. KG
Mühldorfstr. 15, D-81671 München

Munich, 2006-11-23 Central Quality Management MF-QZ / Radde

1303.3500.02 CE E-2

R&S FMU Manuals

Contents of Manuals for Baseband Signal Analyzer

R&S FMU

Operating Manual R&S FMU

The operating manual describes the following models and options of baseband signal analyzer '
R&S FMU:

• R&S FMU36

This operating manual contains information about the technical data of the instrument, the setup
functions and about how to put the instrument into operation. It informs about the operating concept
and controls as well as about the operation of the R&S FMU via the menus and via remote control.
Typical measurement tasks for the R&S FMU are explained using the functions offered by the menus
and a selection of program examples.

Additionally the operating manual includes information about maintenance of the instrument and
about error detection listing the error messages which may be output by the instrument. It is subdi­vided into 9 chapters:

The data sheet informs about guaranteed specifications and characteristics of the instrument.

Chapter 1 see Quick Start Guide chapter 1 and 2 (describes the control elements and con-

nectors on the front and rear panel as well as all procedures required for putting
the R&S FMU into operation and integration into a test system.)

Chapter 2 gives an introduction to typical measurement tasks of the R&S FMU which are

explained step by step.

Chapter 3 describes the operating principles, the structure of the graphical interface and of-

fers a menu overview.

Chapter 4 forms a reference for manual control of the R&S FMU and contains a detailed

description of all instrument functions and their application. The chapter also lists
the remote control command corresponding to each instrument function.

Chapter 5 describes the basics for programming the R&S FMU, command processing and

the status reporting system.

Chapter 6 lists all the remote-control commands defined for the instrument. At the end of the

chapter a alphabetical list of commands and a table of softkeys with command
assignment is given.

Chapter 7 contains program examples for a number of typical applications of the R&S FMU.

Chapter 8 describes preventive maintenance and the characteristics of the instrument’s in-

terfaces.

Chapter 8 gives a list of error messages that the R&S FMU may generate.

Chapter 9 contains a list of error messages.

Chapter 10 contains an index for the operating manual.

Service Manual - Instrument

The service manual - instrument informs on how to check compliance with rated specifications, on
instrument function, repair, troubleshooting and fault elimination. It contains all information required
for the maintenance of R&S FMU by exchanging modules.

1303.3545.12 0.1 E-1

R&S FMU Putting into Operation

1 Putting into Operation

or details refer to the Quick Start Guide chapters 1, "Front and Rear Panel", and 2, "Preparing for

F
Use".

1303.3545.12 1.1 E-1

R&S FMU Contents– Getting Started

Contents - Chapter 2 "Getting Started"

2 Getting Started .................................................................................................... 2.1

Basic Spectrum Measurements....................................................................................................2.1

Setting the Input Impedance and Signal Source.........................................................................2.1

Intermodulation Measurements ..................................................................................................2.2

Measurement Example – Measuring the R&S FMU’s intrinsic intermodulation ....................2.4

Measuring Signals in the Vicinity of Noise .................................................................................2.7

Measurement example – Measuring a sinewave signal at low S/N ratios.............................2.9

Measurements in the Frequency Domain..................................................................................2.12

Measurement example – Spectrum of a GSM signal in the complex baseband .....................2.12

Measurement example – Function of the RECALC Softkey.....................................................2.18

Noise Measurements ...................................................................................................................2.22

Measuring noise power density.................................................................................................2.22

Measurement example – Measuring the intrinsic noise power density of the R&S FMU...2.22

Measurement of Noise Power within a Transmission Channel ................................................2.25

Measurement Example – Measuring the intrinsic noise of the R&S FMU with the

channel power function...............................................................2.25

Measuring Phase Noise............................................................................................................2.29

Measurement Example - Measuring the phase noise of a signal generator.............................2.29

Measuring Channel Power and Adjacent Channel Power ........................................................2.31

Power measurements..................................................................................................................2.32

Measurement Example - ACPR measurement on an IS95 CDMA Signal ..........................2.32

Measuring the S/N Ratio of Burst Signals.................................................................................2.34

Measurement Example – Time domain analysis of an 8PSK signal ...................................2.34

1303.3545.12 I-2.1 E-1

R&S FMU Basic Spectrum Measurements

2 Getting Started

hapter 2 explains how to operate the R&S FMU using typical measurements as examples. This

C
chapter is split up in two parts, basic spectrum measuremnts and measurements on modulated signals.
Chapter 3 describes the basic operating steps such as selecting the menus and setting parameters, and
explains the screen structure and displayed function indicators. Chapter 4 describes all the menus and
R&S FMU functions.

All of the following examples are based on the standard settings of the analyzer. These are set with the
PRESET key. A complete listing of the standard settings can be found in chapter 4, section "Preset
settings of the R&S FMU – PRESET key". Examples of more basic character are provided in the Quick
Start Guide, chapter 5, as an introduction.

Basic Spectrum Measurements

Though the R&S FMU is a baseband signal analyzer, it can also perform basic spectrum measurements
up to 36 MHz. Measuring the frequency and level of a signal is one of the most common purposes for
the use of a spectrum analyzer. On the R&S FMU, spectrum measurements can be performed usign the
FFT mode. For unknown signals, the FFT default settings (PRESET) are a good starting point for the
measurement.
In general, modulated signals can be connected to either the I or Q baseband input of the R&S FMU,
whereas baseband signals usually require two connections, one each for the I and Q component.
If the input impedance is set to 50 C, the total incident power at either input port may not exceed 30
dBm (= 1 W). Power attenuators can be used to measure stronger signals. With the input impedance
set to 1 MC, the maximum voltage at the input ports is 5 V. Exceeding these limits can destroy
attenuators or amplifiers.

Setting the Input Impedance and Signal Source

The following examples are all performed with the input impedance set to 50 C.

1. Set the input impedance to 50 

 Press FFT hotkey.

 Press SIGNAL SOURCE.

 Press I/Q INPUT until 50 C is selected.

In the default state (PRESET key) the input impedance is set to 50 C.

Unlike spectrum analyzers, the R&S FMU can not only display positive frequencies but also the negative
part of the spectrum in its FFT frequency domain. This is necessary as complex signals may have a
non-symmetric spectrum.
Depending on the choice made for the I/Q path (complex or either I or Q path), the spectrum is
displayed in full for a complex signal, or only positive frequencies are displayed for I or Q path only.

In the following examples for all spectrum measurements, the selection I path (I ONLY) shall be used.
In the default state (PRESET key) the baseband input is set up for complex signals (I+jQ).

2. Select real input signal on the I port

 Press the FFT hotkey.

 Press the SIGNAL SOURCE softkey.

 Press the softkey I/Q PATH and select I ONLY.

1303.3545.12 2.1 E-1

Basic Spectrum Measurements R&S FMU

Intermodulation Measurements

If several signals are applied to a DUT with non-linear characteristics, unwanted mixing products are
generated – mostly by active components such as amplifiers or mixers. The products created by 3

rd

order intermodulation are particularly troublesome as they have frequencies close to the useful signals
and, compared with other products, are closest in level to the useful signals. The fundamental wave of
one signal is mixed with the 2

s1 = 2  f u1 – f u2 (1)

f

s2 = 2  f u2 - f u1 (2)

f

nd

harmonic of the other signal.

where fs1 and fs2 are the frequencies of the intermodulation products and fu1 and fu2 the frequencies of
the useful signals.

The following diagram shows the position of the intermodulation products in the frequency domain.

Level

1

P

u

2

u

P

a

D3

P

Fig. 2-1 3

s1



f

s1

f

rd

order intermodulation products

f

u1



f

f

u2

P

s2



f

f

s2

Frequency

1 = 10 MHz, f u2 = 10.03 MHz

Example:

f u

s1 = 2  f u1 - f u2 = 2  10 MHz – 10.03 MHz = 9.97 MHz

f

f

s2 = 2  f u2 - f u1 = 2  10.03 MHz – 10 MHz = 10.06 MHz

The level of the intermodulation products depends on the level of the useful signals. If the level of the
two useful signals is increased by 1 dB, the level of the intermodulation products is increased by 3 dB.

The intermodulation distance d

is, therefore, reduced by 2 dB. Fig. 2-2 shows how the levels of the

3

useful signals and the 3rd order intermodulation products are related.

1303.3545.12 2.2 E-1

R&S FMU Basic Spectrum Measurements

Output

level

Intercept

point

Compression

Carrier

level

3

a

D

1

1

1

Intermodulation

products

3

Input level

Fig. 2-2 Level of the 3rd order intermodulation products as a function of the level of the useful

signals

The behavior of the signals can explained using an amplifier as an example. The change in the level of
the useful signals at the output of the amplifier is proportional to the level change at the input of the
amplifier as long as the amplifier is operating in linear range. If the level at the amplifier input is changed
by 1 dB, there is a 1 dB level change at the amplifier output. At a certain input level, the amplifier enters
saturation. The level at the amplifier output does not increase with increasing input level.

The level of the 3
signals. The 3

rd

order intermodulation products increases 3 times faster than the level of the useful

rd

order intercept is the virtual level at which the level of the useful signals and the level of
the spurious products are identical, i.e. the intersection of the two straight lines. This level cannot be
measured directly as the amplifier goes into saturation or is damaged before this level is reached.

rd

The 3
distance d

order intercept can be calculated from the known slopes of the lines, the intermodulation

and the level of the useful signals.

2

TOI = a

/ 2 + P

D3

n

(3)

with TOI (T

hird Order Intercept) being the 3rd order intercept in dBm and Pnthe level of a carrier in

dBm.

With an intermodulation distance of 60 dB and an input level, P

of –20 dBm, the following 3rd order

w,

intercept is obtained:

TOI = 60 dBm / 2 + (-20 dBm) = 10 dBm.

1303.3545.12 2.3 E-1

Basic Spectrum Measurements R&S FMU

Measurement Example – Measuring the R&S FMU’s intrinsic intermodulation

Test setup:

In order to measure the intermodulation performance of the R&S FMU the test signal must be largely
free of intermodulation. To avoid intermodulation inside the signal generators, use a 3 dB power
combiner (for example Mini Circuits ZFSC-2 series) instead of a common 6 dB splitter. Also the
automatic level control (ALC) of the signal generators must be switched off. Recommended signals
generators are R&S SMIQs.

Signal generator settings (e.g. R&S SMIQ):

Level Frequency

Signal Generator 1 +7 dBm

Signal Generator 2

ALC off

+7 dBm

ALC off

21.35 MHz

21.45 MHz

Measurement using the R&S FMU:

1. Set the spectrum analyzer to its default settings.

 Press the PRESET key.

The R&S FMU is in the its default state.

2. Set center frequency to 21.4 MHz and the frequency span to 900 kHz.

 Press the FREQ key and enter 21.4 MHz.

 Press the SPAN key and enter 900 kHz.

3. Set the reference level to +10 dBm.

 Press the AMPT key and enter 10 dBm.

The input attenuator setting is coupled to the reference level setting. The attenuator is
automatically set to 0 dB with a reference level setting of +10dBm.

4. Set the resolution bandwidth to 500 Hz.

 Press the BW key.

 Press the RES BW MANUAL softkey and enter 500 Hz.

By reducing the bandwidth, the noise is reduced and the intermodulation products can be clearly
seen.

1303.3545.12 2.4 E-1

R&S FMU Basic Spectrum Measurements

. Measuring intermodulation by means of the 3

5

rd

order intercept measurement function

 Press the MEAS key.

 Press the NEXT key.

 Press the TOI softkey.

The R&S FMU activates four markers. Two markers are positioned on the wanted signals and two
on the intermodulation products. The 3

d

r

order intercept is calculated from the level difference

between the wanted signals and the intermodulation products. It is then displayed on the screen:

Fig. 2-3 Result of intrinsic intermodulation measurement on the R&S FMU. The 3rd order

intercept (TOI) is displayed at the top right corner of the grid

Calculation method:

The method used by the R&S FMU to calculate the intercept point takes the average wanted signal level

in dBm and calculates the intermodulation d3in dB as a function of the average value of the levels

P

uw

of the two intermodulation products. The third order intercept (TOI) is then calculated as follows:

TOI/dBm = ½ d

3

+ Pu

w

The level of the intrinsic intermodulation products depends on the level of the useful signals at the input
amplifier. When the input attenuation is added, the level is reduced and the intermodulation ratio is
increased. With an additional attenuation of 5 dB, the levels of the intermodulation products are reduced
by 10 dB.

6. Increasing input attenuation to 5 dB by setting the reference level to +15 dBm to reduce

intermodulation products.

 Press the AMPT key and enter 15 dBm.

The attenuator setting is coupled to the reference level setting. The attenuator is automatically set
to 5dB with a reference level of 15 dBm.

1303.3545.12 2.5 E-1

Basic Spectrum Measurements R&S FMU

Fig. 2-4 If the baseband input attenuation is increased, the R&S FMU’s intrinsic

intermodulation products are reduced. In the shown example the intermodulation
products disappear below the noise floor of the signal genarators.

1303.3545.12 2.6 E-1

R&S FMU Measuring Signals in the Vicinity of Noise

Measuring Signals in the Vicinity of Noise

The minimum signal level a signal analyzer can measure is limited by its intrinsic noise. Small signals
can be swamped by noise and therefore cannot be measured. For signals that are just above the
intrinsic noise, the accuracy of the level measurement is influenced by the intrinsic noise of the signal
analyzer.

The displayed noise level of a FFT signal analyzer depends on its noise figure, the selected reference
level, the selected resolution bandwidth and the detector. The effect of the different parameters is
explained in the following.

Impact of the reference level setting

If the reference level is changed, the R&S FMU changes the gain and the input attenuation so that the
voltage at the A/D converter is always the same for signal levels corresponding to the reference level.
This ensures that the dynamic range of the A/D converter is fully utilized. Therefore, the total gain of the
signal path is low at high reference levels and the noise figure of the amplifier makes a substantial
contribution to the total noise figure of the R&S FMU. Fig. 2-5 below shows the change in the displayed
noise depending on the set reference level.

40

35

30

25

20

15

rel. noise level / dB

10

5

0

-20 -15 -10 -5 0 5 10 15 20 25

reference level / dBm

Fig. 2-5 Change in displayed noise as a function of the selected reference level

Impact of the resolution bandwidth

The sensitivity of a signal analyzer also depends directly on the selected bandwidth. The highest
sensitivity is obtained for the smallest bandwidth (for the R&S FMU: 0.5 Hz). If the bandwidth is
increased, the reduction in sensitivity is proportional to the change in bandwidth. Increasing the
bandwidth by a factor of 3 increases the displayed noise by approx. 5 dB (4.77 dB precisely). If the
bandwidth is increased by a factor of 10, the displayed noise increases by 10 dB.

Impact of the detector

Noise is evaluated differently by the different detectors. The noise display is therefore influenced by the
choice of detector. Sinewave signals are weighted in the same way by all detectors, i.e. the level display
for a sinewave signal does not depend on the selected detector, provided that the signal-to-noise ratio is
high enough. The measurement accuracy for signals in the vicinity of intrinsic spectrum analyzer noise
is also influenced by the detector which has been selected. The R&S FMU has the following detectors:

1303.3545.12 2.7 E-1

Measuring Signals in the Vicinity of Noise R&S FMU

Maximum peak detector
If the max. peak detector is selected, the largest noise display is obtained, since the spectrum analyzer
displays the highest value of the baseband input in the frequency range assigned to a pixel at each pixel
in the trace. In the time domain, with longer sweep times, the trace indicates higher noise levels since
the probability of obtaining a high noise amplitude increases with the dwell time on a pixel. For short
sweep times, the display approaches that of the sample detector since the dwell time on a pixel is only
sufficient to obtain an instantaneous value.

Minimum peak detector

The min. peak detector indicates the minimum voltage of the baseband input in the frequency range
assigned to a pixel at each pixel in the trace. The noise is strongly suppressed by the minimum peak
detector since the lowest noise amplitude that occurs is displayed for each test point. If the signal-to­noise ratio is low, the minimum of the noise overlaying the signal is displayed too low.
Inn the time domain at longer sweep times, the trace shows smaller noise levels since the probability of
obtaining a low noise amplitude increases with the dwell time on a pixel. For short sweep times, the
display approaches that of the sample detector since the dwell time on a pixel is only sufficient to obtain
an instantaneous value.

Autopeak detector

The Autopeak detector displays the maximum and minimum peak value at the same time. Both values
are measured and their levels are displayed on the screen joint by a vertical line.

Sample detector
The sample detector samples the signal for each pixel of the trace only once and displays the resulting
value. If the frequency span of the spectrum analyzer is considerably higher than the resolution
bandwidth (span/RBW >500), there is no guarantee that useful signals will be detected. They are lost
due to undersampling. This does not happen with noise because in this case it is not the instantaneous
amplitude that is relevant but only the probability distribution.

RMS detector
For each pixel of the trace, the RMS detector outputs the RMS value of the baseband input for the
frequency range assigned to each test point. It therefore measures noise power. The display for small
signals is, however, the sum of signal power and noise power. In the time domain, for short sweep
times, i.e. if only one uncorrelated sample value contributes to the RMS value measurement, the RMS
detector is equivalent to the sample detector. If the sweep time is longer, more and more uncorrelated
values contribute to the RMS value measurement. The trace is, therefore, smoothed. In the frequency
domain, the level of sinewave signals is only displayed correctly if the selected span / resolution
bandwidth ratio is less than 200 (RBW). At a resolution bandwidth of 1 kHz, this means that the
frequency display range (SPAN) must not exceed 200 kHz.

Average detector
For each pixel of the trace, the average detector outputs the average value of the linear baseband input
for the frequency range assigned to each test point. It therefore measures the linear average noise. The
level of sinewave signals is only displayed correctly if the selected span / resolution bandwidth ratio is
less than 200 (RBW).

1303.3545.12 2.8 E-1

R&S FMU Measuring Signals in the Vicinity of Noise

Measurement example – Measuring a sinewave signal at low S/N ratios

The example shows the different factors influencing the S/N ratio.

Test setup:

Settings on the signal generator (e.g. R&S SMIQ):
Frequency: 10 MHz
Level: -60 dBm

Measurement using R&S FMU:

1. Set the spectrum analyzer to its default state.

 Press the PRESET key.

The R&S FMU is in its default state.

2. Set the center frequency to 10 MHz and the frequency span to 10 MHz.

 Press the FREQ key and enter 10 MHz.

 Press the SPAN key and enter 10 MHz.

3. Set the reference level to 25 dBm to attenuate the input signal and to increase the intrinsic

noise.

 Press the AMPT key.

 Press the REF LEVEL softkey and enter 25 dBm.

The high input attenuation reduces the signal level which can no longer be detected in noise.

Fig. 2-6 Sinewave signal with low S/N ratio. The signal is completely swamped by the intrinsic

noise of the spectrum analyzer.

1303.3545.12 2.9 E-1

Measuring Signals in the Vicinity of Noise R&S FMU

. To suppress noise spikes the trace can be averaged.

4

 Press the TRACE key.

 Press the AVERAGE softkey.

he traces of consecutive sweeps are averaged. To perform averaging, the R&S FMU

T
automatically switches on the sample detector. The signal, therefore, can be more clearly
distinguished from noise.

Fig. 2-7 Sinewave signal with low S/N ratio if the trace is averaged.

1303.3545.12 2.10 E-1

R&S FMU Measuring Signals in the Vicinity of Noise

. By reducing the resolution bandwidth by a factor of 10, the noise is reduced by 10 dB.

5

 Press the BW key.

 Press the RES BW MANUAL softkey and enter 20 kHz.

he displayed noise is reduced by approx. 10 dB. The signal, therefore, emerges from noise by

T
about 10 dB.
The noise floor is outside the displayed level range. In order to display the noise, the level range
must be set to 120 dB.

 Press the AMPT key.

 Press the RANGE LOG MANUAL softkey and enter 120 dB.

Fig. 2-8 Sinewave signal at a smaller resolution bandwidth

1303.3545.12 2.11 E-1

Measurements in the Frequency Domain R&S FMU

Measurements in the Frequency Domain

Measurement example – Spectrum of a GSM signal in the complex

baseband

Test setup:

Settings on the signal generator (e.g. R&S SMIQ or R&S SMU)

Frequency: not relevant, because the baseband output is used
Level: not relevant, because the baseband output is used
Modulation: GSM standard; PRBS data is used

The I baseband output of the signal generator is connected to the I baseband input of the R&S FMU.
The Q baseband output of the signal generator is connected to the Q baseband input of the R&S FMU.

1. Set the R&S FMU to its default state:

 Press the PRESET key.

2. Change to the FFT Analyzer:

 Press the FFT hotkey.

3. Configure the baseband input:

 Press the SIGNAL SOURCE softkey.

 Select the appropriate input impedance using the I/Q INPUT softkey (usually 50 C, depends on

the signal generator).

 Use the BALANCED softkey to set the measurement mode (balanced / referenced to ground to

match the signal generator's output).

4. Set the span to 1 MHz:

 Press the SPAN key and enter 1 MHz.

5. Set the resolution bandwidth to 10 kHz:

 Press the FREQ key, then the RES BW MANUAL softkey and enter 10 kHz.

1303.3545.12 2.12 E-1

R&S FMU Measurements in the Frequency Domain

. Switch on averaging:

6

 Press the TRACE key and then the AVERAGE softkey.

You can see the typical spectrum of a GSM signal (see Fig. 2-9). The center frequency is 0 Hz.
Positive and also negative frequencies are shown. This is meaningful, because the spectrum of a

omplex input signal is in most cases not symmetrical to 0 Hz.

c

Fig. 2-9 Typical spectrum of a GSM signal (PRBS data is used)

1303.3545.12 2.13 E-1

Measurements in the Frequency Domain R&S FMU

We want to generate a complex rotating phasor now.

1. Switch the signal generator to bit pattern "11111..." or "00000....":

 Operator interactions depend on the signal generator used.

Important: Differential coding must be used.

2. Use the marker to measure the frequency and the level of the rotating phasor:

Press the MKR  key, then the PEAK softkey.



You can see (Fig. 2-10) the spectrum of a complex rotating phasor. Its frequency is a quarter of
the GSM symbol frequency of 270.833 kHz (=67.708 kHz). You can read the frequency and the
level of the rotating phasor in the marker information field.

A complex rotating phasor is defined as:

with a positive or negative R, which determines the direction of rotation and the frequency.
The above formula can be rewritten as:



and



A sine or cosine can be split into two complex rotating phasors. We will need this fact later.

tj









1



2

j

1
2

=

+=

tjtj

)()sin(

eet





tjtj

)()cos(

eet

)sin()cos()( tjtets

+==



Fig. 2-10 Spectrum with pattern "11111..." or "00000..." used.

Note: In the spectrum you can see a small DC offset around 0 Hz and a few harmonics at multiples of

67.708 kHz.

1303.3545.12 2.14 E-1

R&S FMU Measurements in the Frequency Domain

We now want to generate a complex rotating phasor with the opposite direction of rotation:

1. Switch the signal generator to alternating bit pattern "10101..."

 Operator interactions depend on the signal generator used.

Important: Differential coding must be used.

2. Use the marker to measure the frequency and the level of the rotating phasor:

 Press the MKR  key, then the PEAK softkey.

Now you can see (Fig. 2-11) the spectrum of the same complex rotating phasor, but with the
opposite direction of rotation. The level measured by the marker stays the same.

Fig. 2-11 Spectrum with pattern "101010..." used.

1303.3545.12 2.15 E-1

Measurements in the Frequency Domain R&S FMU

We now want to switch from a complex to a real input signal:

. Use the signal generator's I output as a real signal

1

 Disconnect the cable from the Q input of the R&S FMU.

Fig. 2-12 Spectrum after disconnecting the Q signal. Misconfiguration of the FFT analyzer!

You can see (Fig. 2-12) the complex spectrum of a real carrier. The level of the carrier measured
by the marker is 6 dB lower now. This is because half of the input power is now missing (one
cable disconnected). Due to the complex FFT, the remaining power is additionally split into equal
shares on a rotating phasor with a negative frequency and another one with a positive frequency.





Expressed mathematically:



1
2

+=

tjtj

)()cos(

eet

Conclusion: When measuring real signals, you should not use the configuration I+j*Q.

1303.3545.12 2.16 E-1

R&S FMU Measurements in the Frequency Domain

We configure the R&S FMU to get the correct spectrum of the signal applied to the I input:

1. Switch to real input signals:

 Press the FFT HOME hotkey, then SIGNAL SOURCE, then IQ PATH, then I ONLY

. Use the marker to measure the frequency and the level of the rotating phasor:

2

 Press the MKR  key, then the PEAK softkey.

The FFT analyzer omits the range of negative frequencies due to the selection of real input
signals. The correct level is now shown in the range of positive frequencies (see Fig. 2-13).

Fig. 2-13 Spectrum after switching to real input signals.

1303.3545.12 2.17 E-1

Measurements in the Frequency Domain R&S FMU

Measurement example – Function of the RECALC Softkey

This measurement example shall demonstrate the application possibilities of the RECALC function. We
are using it in this example to measure the phase difference between the sine oscillations at the I and Q
inputs. As in the previous example, a complex phasor is used as the input signal.

Test setup:

Settings on the signal generator (e.g. R&S SMIQ or R&S SMU)

Frequency: not relevant, because the baseband output is used
Level: not relevant, because the baseband output is used

Modulation: GSM standard; "1111..." or "0000...." pattern is used

The I baseband output of the signal generator is connected to the I baseband input of the R&S FMU.
The Q baseband output of the signal generator is connected to the Q baseband input of the R&S FMU.

1. Set the R&S FMU to its default state:

 Press the PRESET key.

2. Change to the FFT analyzer:

 Press the FFT hotkey.

3. Activate the "Capture Both Domains" mode:

 Press the CAPTURE BOTH DOM softkey.

4. Configure the baseband input:

 Press the SIGNAL SOURCE softkey.
 Select the appropriate input impedance using the I/Q INPUT softkey (usually 50 C, depends on

the signal generator).

 Use the BALANCED softkey to set the measurement mode (balanced / referenced to ground to

match the signal generator's output).

5. Initiate capturing of data:

 Press the SWEEP key, then the SINGLE SWEEP softkey.

The memory was now filled completely with sampled data of the signals applied to the I and Q
inputs (because the CAPTURE BOTH DOMAINS softkey was active).
All following measurements of this measurement example are completely based on this data,
since the RECALC softkey will be used each time. You could already disconnect both cables now
or connect a new device under test.

We already know the frequency of the rotating phasor from the previous measurement example.
It is 270.8333 kHz / 4 = 67.708 kHz.

6. Set the span to 200 Hz and the center frequency to 67.708 kHz and start a recalculation

 Press the SPAN key and enter 200 Hz.

 Press the FREQ key and enter 67.708 kHz.

 Press the SWEEP key

 Press the RECALC softkey

1303.3545.12 2.18 E-1

R&S FMU Measurements in the Frequency Domain

. Switch on the phase information:

7

 Press the FFT HOME hotkey, then FREQUENCY DOMAIN, then the MAGNITUDE PHASE

softkey.

.

8. Measure the phase of the signal applied to the I input:

 Press the FFT HOME hotkey, then SIGNAL SOURCE, then the IQ PATH softkey,

then the I-ONLY softkey.

 Press the SWEEP key

 Press the RECALC softkey

 Press the MKR key. Then enter 67.708 kHz.

In the marker information field you can read the phase of the sine wave applied to the I input
(see Fig. 2-14).

Fig. 2-14 Example of the measurement of the phase of the sine wave applied to the I input.

1303.3545.12 2.19 E-1

Measurements in the Frequency Domain R&S FMU

. Measure the phase of the signal applied to the Q input:

9

 Press the FFT HOME hotkey, then SIGNAL SOURCE, then the IQ PATH softkey,

then the Q-ONLY softkey.

 Press the SWEEP key
 Press the RECALC softkey

Fig. 2-15 Example of the measurement of the phase of the sine wave applied to the Q input.

In the marker information field you can read the phase of the sine wave applied to the Q input
(see Fig. 2-15).

The phase difference between the I and the Q input is 155.89T - (-114.16T) = 270.05T = -89.95T.

1303.3545.12 2.20 E-1

R&S FMU Measurements in the Frequency Domain

Now we want to observe both signals in the time domain:

1. Switch to time domain. Show both signals simultaneously:

 Press the FFT HOME hotkey, then SIGNAL SOURCE, then the I+j*Q softkey.
 Press the FFT HOME hotkey, then TIME DOMAIN, then the VOLTAGE softkey.

2. Switch off the mixer and set up the sweep time:

 Press the FREQ key, then enter 0 Hz.
 Press the SWEEP key, then enter 20 Us.
 Press the RECALC soft key

3. Search for the maximum of the signal applied to the I input:

 Press the MKR key. The marker searches for the maximum of the trace of the I input

automatically. The other marker is automatically moved synchronously on the trace of the Q input.

At the found maximum of the I signal, you can see (Fig. 2-16) a zero crossing of the sine wave applied
to the Q input. The phase difference is therefore again about -90°.

Note: This measurement in the time domain does not reach the accuracy of the previous one in the

frequency domain. It should only show that you can also switch between time domain and
frequency domain when using CAPTURE BOTH DOMAINS and RECALC.

Fig. 2-16 Both signals shown simultaneously in the time domain.

1303.3545.12 2.21 E-1

Noise Measurements R&S FMU

Noise Measurements

Noise measurements play an important role in signal analysis. Noise for example affects the sensitivity
of radiocommunication systems and their components.

Noise power is specified either as the total power in the transmission channel or as the power referred
to a bandwidth of 1 Hz. The sources of noise are, for example, amplifier noise, or noise generated by
oscillators used for the frequency conversion of useful signals in receivers or transmitters. The noise at
the output of an amplifier is determined by its noise figure and gain.

The noise of an oscillator is determined by phase noise near the oscillator frequency and by thermal
noise of the active elements far from the oscillator frequency. Phase noise can mask weak signals near
the oscillator frequency and make them impossible to detect.

Measuring noise power density

To measure noise power referred to a bandwidth of 1 Hz at a certain frequency, the R&S FMU has an
easy-to-use marker function. This marker function calculates the noise power density from the
measured marker level.

Measurement example – Measuring the intrinsic noise power density of the

R&S FMU

The frequency of interest is 100 kHz.

1. Set the spectrum analyzer to its default state.

 Press the PRESET key.

The R&S FMU is in its default state.

2. Set the center frequency to 98 kHz and the span to 10 kHz.

 Press the FREQ key and enter 98 kHz.

 Press the SPAN key and enter 10 kHz.

3. Set the reference level to the most sensitive value

 Press the AMPT key.

 Press the REF LEVEL softkey and enter -20 dBm.

4. Set the display range 140 dB

 Press the AMPT key.

 Press the RANGE LOG MANUAL softkey and enter 140 dB.

5. Switch on the noise marker function.

 Press the MKR FCTN key.

 Press the NOISE MEAS softkey and enter 100 kHz.

The R&S FMU displays the noise power density at 100 kHz in dBm/Hz (dBm in 1Hz bandwidth).

Since noise is random, a sufficiently long measurement time has to be selected to obtain stable
measurement results. This can be achieved by averaging the trace.

1303.3545.12 2.22 E-1

R&S FMU Noise Measurements

. The measurement result is stabilized by averaging the trace

6

 Press the TRACE key.

 Press the AVERAGE softkey.

he R&S FMU performs sliding averaging over 10 traces from consecutive sweeps. The

T
measurement result becomes more stable.

Fig. 2-17 Measurement of the intrinsic noise power density of the R&S FMU

Conversion to other reference bandwidths

The result of the noise measurement is normalized to 1 Hz bandwidth. Using the Noise Marker yields
therefore a result, which is bandwidth independent.
If the noise power is read out using a standard marker, the conversion can be done manually. This is
done by subtracting 10 * log (BW) of the measurement result, BW being the resolution bandwidth.

Example:

A noise power of -120 dBm measured with a resolution bandwidth of 1 kHz shall be converted to 1 Hz
normalized noise power.

= -120 - 10 * log (1000) = -120 -30 = -150 dBm/Hz

P

[Noise]

Calculation method:

The following method is used to calculate the noise power:

If the noise marker is switched on, the R&S FMU automatically activates the sample detector.

To calculate the noise, the R&S FMU takes an average over 17 adjacent pixels (the pixel on which the
marker is positioned and 8 pixels to the left, 8 pixels to the right of the marker). The measurement result
is stabilized by averaging over 17 pixels.

Since averaging over 17 trace points is performed in the log display mode, the result would be 2.51 dB
too low (difference between logarithmic noise average and noise power). The R&S FMU, therefore,
corrects the noise figure by 2.51 dB.

To standardize the measurement result to a bandwidth of 1 Hz, the result is also corrected by –10 * log
(RBW). RBW is the equivalent noise power bandwidth of the selected resolution filter.

1303.3545.12 2.23 E-1

Noise Measurements R&S FMU

Correction

Detector selection

The noise power density is measured in the default setting with the sample detector and using
averaging. Other detectors that can be used to perform a measurement giving true results are the

verage detector or the RMS detector. The R&S FMU automatically corrects the measurement result of

a
the noise marker display depending on the selected detector (+1.05 dB for the average detector, 0 d
for the RMS detector).

The Pos Peak, Neg Peak or Auto Peak detectors are not suitable for measuring noise power density.

Determining the noise figure:

The noise figure of an amplifier can be obtained from the noise power measured at the amplifier's
output. Based on the known thermal noise power of a 50  resistor at room temperature (-174 dBm
(1Hz)) and the measured noise power P

the noise figure (NF) is obtained as follows:

noise

NF = P

+ 174 – g,

noise

where g = gain of D UT in dB

Noise figure of the R&S FMU:

The R&S FMU displays the noise power density at the baseband input connector. Internal gain is
already included in the result. The noise figure (NF) of the R&S FMU is obtained as follows from the
displayed noise power P

NF = P

noise

+ 174

:

oise

n

Example: The measured internal noise power of the R&S FMU is found to be –157.2 dBm / Hz. The

noise figure of the R&S FMU is obtained as follows

NF = -157.2 + 174 = 16.8 dB

Note: If noise power is measured at the output of an amplifier, for example, the sum of the

internal noise power of the R&S FMU and the noise power at the output of the DUT is
measured. The noise power of the DUT can be obtained by subtracting the internal noise
power from the total power (subtraction of linear noise powers). By means of the following
diagram, the noise level of the DUT can be estimated from the level difference between the
total and the internal noise level.

0

factor in dB

-1

-2

-3

-4

-5

-6

-7

-8

-9

-10
012345678910111213141516

Total power/intrinsic noise power in dB

Fig. 2-18 Correction factor for measured noise power as a function of the ratio of total power to the

intrinsic noise power of the spectrum analyzer.

1303.3545.12 2.24 E-1

R&S FMU Noise Measurements

Measurement of Noise Power within a Transmission Channel

Noise in any bandwidth can be measured with the channel power measurement functions. Thus the
noise power in a communication channel can be determined, for example. If the noise spectrum within
the channel bandwidth is flat, the noise marker from the previous example can be used to determine the
noise power in the channel by considering the channel bandwidth. If, however, phase noise and noise
that normally increases towards the carrier is dominant in the channel to be measured, or if there are
discrete spurious signals in the channel, the channel power measurement method must be used to
obtain correct measurement results.

Measurement Example – Measuring the intrinsic noise of the R&S FMU with the

channel power function

The frequency band of interest is centered at 10 MHz, the channel bandwidth is 1.23 MHz.

Test setup:

The baseband input of the R&S FMU remains open-circuited or is terminated with 50 .

Measurement with the R&S FMU:

1. Set the analyzer to its default state.

 Press the PRESET key.

The R&S FMU is in its default state.

2. Set the center frequency to 10 MHz and the span to 3 MHz.

 Press the FREQ key and enter 10 MHz.

 Press the SPAN key and enter 3 MHz.

3. To obtain maximum sensitivity, set the reference level to -20 dBm.

 Press the AMPT key.

 Press the REF LEVEL softkey and enter -20 dBm.

4. Switch on and configure the channel power measurement.

 Press the MEAS key.

 Press the CHAN POWER / ACP softkey.

The R&S FMU activates the channel or adjacent channel power measurement according to the
currently set configuration.



 Press the CP/ACP CONFIG

The R&S FMU enters the submenu for configuring the channel.

 Press the CHANNEL BANDWIDTH softkey.

 Confirm the TX channel using the ENTER button and enter 1.23 MHz.

The R&S FMU displays the 1.23 MHz channel as two vertical lines which are symmetrical to the
center frequency.

softkey.

 Press the ADJUST SETTINGS softkey.

The settings for the frequency span, the bandwidth (RBW) and the detector are automatically set
to the optimum values required for the measurement.

1303.3545.12 2.25 E-1

Noise Measurements R&S FMU

Fig. 2-19 Measurement of the R&S FMU’s intrinsic noise power in a 1.23 MHz channel

bandwidth.

5. Referring the measured channel power to a bandwidth of 1 Hz

 Press the CHAN PWR / Hz softkey.

The channel power is referred to a bandwidth of 1 Hz. The measurement is corrected by -10 * log
(ChanBW), with ChanBW being the channel bandwidth that was selected.

Method of calculating the channel power

When measuring the channel power, the R&S FMU integrates the linear power which corresponds to
the levels of the pixels within the selected channel. The analyzer uses a resolution bandwidth which is
far smaller than the channel bandwidth.

The following steps are performed:

• The linear power of all the trace pixels within the channel is calculated.

(Li/10)

= 10

P

i

where P

L

= power of the trace pixel i

i

= displayed level of trace point i

i

• The powers of all trace pixels within the channel are summed up and the sum is divided by the
number of trace pixels in the channel.

• The result is multiplied by the quotient of the selected channel bandwidth and the noise bandwidth of
the resolution filter (RBW).

Since the power calculation is performed by integrating the trace within the channel bandwidth, this
method is also called the IBW method (I

ntegration Bandwidth method).

1303.3545.12 2.26 E-1

R&S FMU Noise Measurements

Bandwidth selection (RBW)

For channel power measurements, the resolution bandwidth (RBW) must be small compared to the
channel bandwidth so that the channel bandwidth can be defined precisely. If the resolution bandwidth

hich has been selected is too wide, this may have a negative effect on the selectivity of the simulated

w
channel filter and result in the power in the adjacent channel being added to the power in the transmit
channel. A resolution bandwidth equal to 1% to 3% of the channel bandwidth should, therefore, be
selected. If the resolution bandwidth is too small, the required measurement time increases
considerably.

Detector selection

Since the power of the trace is measured within the channel bandwidth, only the sample detector and
RMS detector can be used. These detectors provide measured values that make it possible to calculate
the real power. The peak detectors (Pos Peak, Neg Peak and Auto Peak) are not suitable for noise
power measurements as no correlation can be established between the peak value of the voltage and
power. The R&S FMU automatically uses the RMS detector when the channel power measurement is
switched on.

Repeatability

Repeatability can be estimated from the following diagram:

max. error/dB

0

95 % Confidence

0.5

1

1.5

2

2.5

3

10

level

100

99 % Confidence

level

1000

10000

Number of samples

100000

Fig. 2-20 Repeatability of channel power measurements as a function of the number of samples

used for power calculation

The curves in Fig. 2-20 indicate the repeatability obtained with a probability of 95% and 99% depending
on the number of samples used.
The repeatability depends on the averaging effect when summing up the noise powers within the
channel bandwidth. Since only uncorrelated samples cause averaging, the number of samples is not
equal to the number of pixels! Samples can be assumed to be uncorrelated if sampling is performed at

intervals of 1/RBW. The number of uncorrelated samples (N

) is calculated as follows:

decorr

N

= Channel Bandwidth / RBW

decor

r

1303.3545.12 2.27 E-1

Noise Measurements R&S FMU

Example:

At a resolution bandwidth of 10 kHz and a channel bandwidth of 1 MHz, 100 uncorrelated samples are
obtained. For the channel power measurement, a repeatability of 1.3 dB with a confidence level of 99%
is the estimate that can be derived from Fig. 2-20.

Averaging

To increase the stability of measurement results, the trace average mode can be used. With the trace
set to average, sweep count sets the number of sweeps that are averaged. In sweep continuous mode,
a sliding average is calculated over 10 sweeps, if sweep count is 0. For sweep count equalling 1,
averaging is switched off, as the number of sweeps is set to 1.

The repeatability is improved by a factor of

N with

avg

Example:
The repeatability (without averaging) is estimated from Fig. 2-20 to be 1.3 dB. With trace averaging with

sweep count set to 100, the repeatability is improved by a factor of
averages is 0.13 dB.

N = sweep count (number of averages).

avg

100 =10. The repeatability after 100

1303.3545.12 2.28 E-1

R&S FMU Noise Measurements

Measuring Phase Noise

The R&S FMU has an easy-to-use marker function for phase noise measurements. This marker
function indicates the phase noise of an oscillator at any carrier offset in dBc in a bandwidth of 1 Hz.

Measurement Example - Measuring the phase noise of a signal generator

The phase noise at 10 kHz carrier offset shall be measured.

Test setup:

Settings on the signal generator (e.g. R&S SMIQ):
Frequency: 10 MHz
Level: 0 dBm

Measurement using R&S FMU:

1. Set the spectrum analyzer to its default state

 Press the PRESET key.

The R&S FMU is in its default state.

2. Set the center frequency to 10 MHz and the span to 50 kHz.

 Press the FREQ key and enter 10 MHz.

 Press the SPAN key and enter 50 kHz.

3. Enable phase noise measurement

 Press the MKR FCNT key.



 Press the PHASE NOISE

The R&S FMU activates phase noise measurement. Marker 1 (=main marker) and marker 2 (=
delta marker) are positioned on the signal maximum. The position of the marker is the reference
(level and frequency) for the phase noise measurement. A horizontal line represents the level of
the reference point and a vertical line the frequency of the reference point. Data entry for the delta
marker is activated so that the frequency offset at which the phase noise is to be measured can
be entered directly.

4. Set 10 kHz frequency offset for determining phase noise.

 Enter 10 kHz.

The R&S FMU displays the phase noise at a frequency offset of 10 kHz . The magnitude of the
phase noise in dBc/Hz is displayed in the delta marker output field at the top right of the screen
(delta 2 [T1 PHN]).

softkey.

1303.3545.12 2.29 E-1

Noise Measurements R&S FMU

. Stabilize the measurement result by activating trace averaging.

5

 Press the TRACE key.

 Press the AVERAGE softkey.

Fig. 2-21 Measuring phase noise with the phase-noise marker function

The frequency offset can be varied by moving the marker with the spinwheel or by entering a new
frequency offset as a number.

1303.3545.12 2.30 E-1

R&S FMU Noise Measurements

Measuring Channel Power and Adjacent Channel Power

Measuring channel power and adjacent channel power is one of the most important tasks in the field of
digital transmission for a spectrum analyzer with the necessary test routines. While, theoretically,
channel power could be measured at highest accuracy with a power meter, its low selectivity means that
it is not suitable for measuring adjacent channel power as an absolute value or relative to the transmit
channel power. The power in the adjacent channels can only be measured with a selective power meter.

A spectrum analyzer cannot be classified as a true power meter, because it displays the IF envelope
voltage. However, it is calibrated such as to correctly display the power of a pure sinewave signal
irrespective of the selected detector. This calibration is not valid for non-sinusoidal signals. Assuming
that the digitally modulated signal has a Gaussian amplitude distribution, the signal power within the
selected resolution bandwidth can be obtained using correction factors. These correction factors are
normally used by the spectrum analyzer's internal power measurement routines in order to determine
the signal power from IF envelope measurements. These factors are valid if and only if the assumption
of a Gaussian amplitude distribution is correct.
Apart from this common method, the R&S FMU also has a true power detector, i.e. an RMS detector. It
correctly displays the power of the test signal within the selected resolution bandwidth irrespective of the
amplitude distribution, without additional correction factors being required. With an absolute
measurement uncertainty of < 0.3 dB and a relative measurement uncertainty of < 0.1 dB (each with a
confidence level of 95%), the R&S FMU comes close to being a true power meter.

The R&S FMU utilizes the IBW method (I
adjacent channel power. The spectrum analyzer measures with a resolution bandwidth that is less than
the channel bandwidth and integrates the level values of the trace versus the channel bandwidth. This
method is described in the section on noise measurements.

The R&S FMU has test routines for simple channel and adjacent channel power measurements. These
routines give quick results without any complex or tedious setting procedures.

ntegration Bandwidth Method) for measuring channel and

1303.3545.12 2.31 E-1

Power measurements R&S FMU

Power measurements

Measurement Example - ACPR measurement on an IS95 CDMA Signal

Test setup:

Settings on the signal generator (e.g. R&S SMIQ):
Modulation: CDMA IS 95

Measurement with the R&S FMU:

1. Set the spectrum analyzer to its default state.

 Press the PRESET key.

The R&S FMU is in its default state.

2. Make sure I and Q path are activated

 Press the FFT key.
 Press the SIGNAL SOURCE softkey.
 Press the I/Q PATH softkey and select I+j*Q.

3. Configuring the adjacent channel power for the CDMA IS95 reverse link.

 Press the MEAS key.



 Press the CHAN PWR ACP

 Press the CP/ACP STANDARD softkey.

From the list of standards, select CDMA IS95A REV using the spinwheel or the cursor down key
below the spinwheel and press ENTER.
The R&S FMU sets the channel configuration according to the IS95 standard for mobile stations
with 2 adjacent channels above and below the transmit channel. The baseband spectrum is
displayed in the upper part of the screen, the numeric values of the results and the channel
configuration in the lower part of the screen. The various channels are represented by vertical
lines on the graph.
The frequency span, resolution bandwidth and detector are selected automatically to give correct
results.
The repeatability of the results in the adjacent channels is very poor. The resolution bandwidth
equals the adjacent channel bandwidth, consequently only one uncorrelated sample is obtained.
To get stable results - especially in the adjacent channels, which are narrow in comparison with
the transmission channel – the R&S FMU automatically uses trace averaging with sweep count =

20.
Note that the channel power for this baseband measurement is only a characteristic number for
the I/Q output of the generator or DUT.

softkey.

1303.3545.12 2.32 E-1

R&S FMU Power measurements

Fig. 2-22 Adjacent channel power measurement on a CDMA IS95 signal

1303.3545.12 2.33 E-1

Power measurements R&S FMU

Measuring the S/N Ratio of Burst Signals

The R&S FMU has easy-to-operate functions for measuring power during a given time interval.

For TDMA transmission methods, the S/N ratio or the switch-off range can be measured by comparing
the powers during the switch-on and switch-off phase of the transmission burst. The R&S FMU,
therefore, has a function to perform absolute and relative power measurements in the time domain. The
measurement is carried out as follows, using a GSM burst as an example.

Measurement Example – Time domain analysis of an 8PSK signal

Test setup:

Settings on the signal generator (e.g. R&S SMIQ):
Modulation: 8PSK
Data Source: Data List: 000 001 010 011 100 101 110 111
Filter: Rectangular
Symbol Rate: 10 000 sym/s

Measurement with the R&S FMU:

1. Set the spectrum analyzer to its default state.

 Press the PRESET key.

The R&S FMU is in its default state.

2. Make sure I and Q path are activated

 Press the FFT key.

 Press the SIGNAL SOURCE softkey.

 Press the I/Q PATH softkey and select I+j*Q.

3. Switch to Time Domain

 Press the FFT key

 Press the TIME DOMAIN softkey.

 Press the VOLTAGE softkey.

4. Adjust the sweep time and setup the trigger

 Press the SWEEP key and enter 800 µs.

 Press the TRIG key.

 Press the I LEVEL softkey and enter 0.4 V.

1303.3545.12 2.34 E-1

R&S FMU Power measurements

Fig. 2-23 Real and imaginary part of an 8PSK vector rotating counter-clockwise

Fig. 2-23 shows the counter-clockwise rotating 8PSK vector. It starts from the I-axis, as the trigger
was set to the maximum I level. The necessary trigger level may vary depending on the I/Q output
of the signal generator.

1303.3545.12 2.35 E-1

R&S FMU Menu Overview

Contents - Chapter 3 " "Menu Overview"

3 Menu Overview................................................................................................ 3.1

FFT Analyzer ................................................................................................................................ 3.1

FREQ Key ..................................................................................................................................... 3.2

SPAN Key ..................................................................................................................................... 3.3

AMPT Key..................................................................................................................................... 3.4

MKR Key....................................................................................................................................... 3.5

MKR-> Key ................................................................................................................................... 3.6

MKR FCTN Key ............................................................................................................................ 3.7

BW Key ......................................................................................................................................... 3.8

SWEEP Key .................................................................................................................................. 3.9

MEAS Key................................................................................................................................... 3.10

TRIG Key .................................................................................................................................... 3.11

TRACE Key................................................................................................................................. 3.12

LINES Key .................................................................................................................................. 3.13

DISP Key..................................................................................................................................... 3.14

FILE Key ..................................................................................................................................... 3.15

CAL Key...................................................................................................................................... 3.16

SETUP Key ................................................................................................................................. 3.17

HCOPY Key ................................................................................................................................ 3.18

Hotkey Menu .............................................................................................................................. 3.19

LOCAL Menu.............................................................................................................................. 3.19

1303.3545.12 I-3.1 E-1

R&S FMU Menu Overview

3 Menu Overview

he following section gives a graphical overview of the R&S FMU menus. Side menus are marked by an

T
arrow directed to the left/right, submenus by an arrow showing upwards.
The menus appear in the order corresponding to the arrangement of keys on the front panel. The
available hotkeys and the LOCAL menu appearing during the remote control of the instrument are also
displayed.

The functions of menus are described in detail in Chapter 4. The IEC/IEEE-bus command associated
with each softkey is indicated. In addition, the softkey list at the of Chapter 6 gives the assignment of
IEC/IEEE-bus commands to softkeys.

FFT Analyzer

FFT HOME

BASEBAND

ANALOG

IQ PATH

(I+J*Q)

I/Q INPUT

50 1M

BALANCED

ON OFF

LOW PASS

36 MHz

I+J*Q

I ONLY

Q ONLY

FREQUENCY

DOMAIN

TIME

DOMAIN

CAPTURE

BOTH DOM

SIGNAL
SOURCE

ZOOM

ADJUST

REF LVL

MAGNITUDE

VOLTAGE

MAGNITUDE

MAGNITUDE

PHASE

REAL
IMAG

WINDOWFCT

(FLATTOP)

FLATTOP

GAUSSIAN

RECT

HAMMING

HANN

CHEBYCHEV

DITHER

ON OFF

1303.3545.12 3.1 E-1

Menu Overview R&S FMU

FREQ Key

1303.3545.12 3.2 E-1

R&S FMU Menu Overview

SPAN Key

1303.3545.12 3.3 E-1

Menu Overview R&S FMU

AMPT Key

AMPT

REF LEVEL

RANGE

LOG 100 dB

RANGE

LOG MANUAL

RANGE

LINEAR

UNIT

REF LEVEL

POSITION

REF LEVEL

OFFSET

PHASE

SETTINGS

AUTOSCALE

Y-AXIS

/DIV

Y-AXIS

REF VALUE

Y-AXIS

REF POS

PHASE

OFFSET

PHASE

RAD DEG

PHASEWRAP
ON OFF

dBm

dBmV

dB+V

dBuV

dB+A

dBuA

dBpW

dBpW

VOLT

AMPERE

WATT

RANGE

LINEAR %

RANGE

LINEAR dB

Y-AXIS

/DIV

Y-AXIS

REF VALUE

Y-AXIS

REF POS

1303.3545.12 3.4 E-1

R&S FMU Menu Overview

MKR Key

1303.3545.12 3.5 E-1

Menu Overview R&S FMU

MKR-> Key

SPAN

MKR

AMPL

MKR

FCTN

LEFT

LIMIT

RIGHT
LIMIT

THRESHOLD

SEARCH LIM

OFF

SELECT
MARKER

PEAK

CENTER

=MKR FREQ

REF LEVEL

=MKR LVL

NEXT PEAK

NEXT PEAK

RIGHT

NEXT PEAK

LEFT

SEARCH
LIMITS

MRK->TRACE

MIN

NEXT MIN

NEXT MIN

RIGHT

NEXT MIN

LEFT

EXCLUDE

DC

PEAK

EXCURSION

AUTO MAX

PEAK

AUTO MIN

PEAK

1303.3545.12 3.6 E-1

R&S FMU Menu Overview

MKR FCTN Key

PH NOISE

SPAN

MKR

AMPT

MKR

FCTN

SELECT
MARKER

PEAK

N

OISE MEAS

P

HASE

NOISE

N DB DOWN

PEAK

S

HAPE FACT

LIST

60:3 60:6

NEW

SEARCH

SORT MODE

FREQ LEVEL

PEAK

EXCURSION

L

EFT

LIMIT

RIGHT
LIMIT

THRESHOLD

ON OFF

REF POINT

LEVEL

R

EF POINT

LVL OFFSET

R

EF POINT

FREQUENCY

PEAK

SEARCH

A

UTO PEAK

SEARCH

SIGNAL ID

MRK->TRACE

PEAK LIST

OFF

1303.3545.12 3.7 E-1

Menu Overview R&S FMU

BW Key

BW

MEAS

SWEEP

TRIG

RES BW

MANUAL

SWEEPTIME

MANUAL

RESB BW

AUTO

SWEEPTIME

AUTO

COUPLING

RATIO

DEFAULT

COUPLING

SPAN / RBW

SPAN / RBW
AUTO [ 50 ]

AUTO [50]

SPAN / RBW

MANUAL

RES BW

1-2-3-5

1303.3545.12 3.8 E-1

R&S FMU Menu Overview

SWEEP Key

BW

MEAS

SWEEP

TRIG

CONTINUOUS

S

WEEP

SINGLE

SWEEP

CONTINUE

SGL SWEEP

SWEEPTIME

MANUAL

SWEEPTIME

AUTO

SWEEP
COUNT

SWEEP

POINTS

RECALC

SGL SWEEP

DISP OFF

RECALC

AUTO OFF

1303.3545.12 3.9 E-1

Menu Overview R&S FMU

MEAS Key

S

P

OWER

ON OFF

CP / ACP

ON OFF

C

P / ACP

M

EAS

TIME DOM

POWER

OI

T

CHAN PWR

CP

A

MULT CARR

ACP

CCUPIED

O

BANDWIDTH

SIGNAL

TATISTIC

S

C/N

STANDARD

CP / ACP

CONFIG

SET CP

REFERENCE

O

F

F

NOISE CORR

O

FF

O

N

NOISE

CORR

DIAGRAM

FULL SIZE

P

EAK

RMS

M

EAN

S

TANDARD

DEVIATION

LIMITS

ON OFF

START
LIMIT

STOP

L

IMIT

C/No

ODULATION

M

DEPTH

ET

REFERENCE

POWER

ABS REL

MAX HOLD

ON OFF

AVERAGE

O

N OFF

NUMBER OF

SWEEPS

APD

ON OFF

CCDF

ON OFF

SELECT

PERCENT

MARKER

MARKER

RES BW

NO OF

SAMPLES

SCALING

CONT
MEAS

SINGLE

MEAS

ELECT

S
MARKER

X-AXIS

REF LEVEL

X-AXIS

RANGE

Y-UNIT

% ABS

Y-AXIS

MAX VALUE

Y-AXIS

MIN VALUE

DEFAULT

SETTINGS

C/N

C/No

CHANNEL

BANDWIDTH

ADJUST

SETTINGS

OCCUP BW

ON OFF

% POWER

BANDWIDTH

CHANNEL

BANDWIDTH

ADJUST

SETTINGS

CLEAR/

WRITE

MAX HOLD

NO. OF

ADJ CHAN

NO. OF

TX CHAN

CHANNEL

BANDWIDTH

CHANNEL
SPACING

ACP REF
SPACING

CP/ACP

ABS REL

CHAN PWR

/ HZ

POWER

MODE

ADJUST

SETTINGS

ACP LIMIT

CHECK

EDIT

ACP LIMIT

SELECT

TRACE

1303.3545.12 3.10 E-1

R&S FMU Menu Overview

TRIG Key

TRI G

FREE RUN

EXTERN

I LEVEL

Q LEVEL

I

/Q LEVEL

TRIGGER

OFFSET

POLARITY

POS NEG

1303.3545.12 3.11 E-1

Menu Overview R&S FMU

TRACE Key

AUTO

SELECT

TRACE

SELECT

TRACE

CLEAR/

WRITE

MAX HOLD

AVERAGE

VIEW

BLANK

SWEEP
COUNT

DETECTOR

TRACE
MATH

MIN HOLD

HOLD CONT

ON OFF

AVG MODE

LOG LIN

ASCII FILE

EXPORT

DECIM SEP

. ,

COPY

TRACE

T1-T2->T1

T1-T3->T1

TRACE

POSITION

TRACE MATH

OFF

DETECTOR

AUTO PEAK

DETECTOR
MAX PEAK

DETECTOR
MIN PEAK

DETECTOR

SAMPLE

DETECTOR

RMS

DETECTOR

AVERAGE

1303.3545.12 3.12 E-1

R&S FMU Menu Overview

LINES Key

LINES

SELECT

LIMIT LINE

NEW LIMIT

LINE

EDIT LIMIT

LINE

COPY

LIMIT LINE

DELETE

LIMIT LINE

X OFFSET

Y OFFSET

DISPLAY

LINES

RESTORE

GSM LINES

DISPLAY

LINE 1

DISPLAY

LINE 2

FREQUENCY

LINE 1

FREQUENY

LINE 2

TIME

LINE 1

TIME

LINE 2

PHASE

LINE 1

PHASE

LINE 2

NAME

VALUES

INSERT

VALUE

DELETE

VALUE

SHIFT X

LIMIT LINE

SHIFT Y

LIMIT LINE

SAVE

LIMIT LINE

1303.3545.12 3.13 E-1

Menu Overview R&S FMU

DISP Key

LINE S

DISP

FILE

FULL

SCREEN

SPLIT

SCREEN

CONFIG

DISPLAY

SCREEN

TITLE

TIME+DATE

ON OFF

LOGO

ON OFF

ANNOTATION

ON OFF

DATA ENTRY

OPAQUE

DEFAULT

COLORS 1

DEFAULT

COLORS 2

DISPLAY
PWR SAVE

SELECT
OBJECT

BRIGHTNESS

TINT

SATURATION

PREDEFINED

COLORS

1303.3545.12 3.14 E-1

R&S FMU Menu Overview

FILE Key

FILE

SAVE

RECALL

EDIT

PATH

EDIT

COMMENT

ITEMS TO
SAVE/RCL

DATA SET

LIST

DATA SET

CLEAR

STARTUP

RECALL

FILE

MANAGER

ASCII FILE

XPORT

E

DECIM SEP

. ,

NAME

DATE

EDIT

PATH

NEW

FOLDER

COPY

RENAME

CUT

PASTE

DELETE

SORT MODE

2

FILE LISTS

SCII FILE

A

XPORT

E

DECIM SEP

. ,

FORMAT

DISK

SELECT

ITEMS

ENABLE

ALL ITEMS

DISABLE

ALL ITEMS

DEFAULT

CONFIG

EXTENSION

SIZE

1303.3545.12 3.15 E-1

Menu Overview R&S FMU

CAL Key

AL

C

SETUP

PROBE CAL

PROBE CORR

ON OFF

PROBE DATA

SELECT

SORT BY

NAME DATE

PROBE DATA

SELECT

SORT BY

NAME DATE

PROBE CAL

RESULTS

CAL TOTAL

CAL ABORT

CAL CORR

ON OFF

CAL RESULTS

PAGE UP

PAGE DOWN

PROBE CAL

START

PROBE COMP

ON OFF

GAIN&OFFS

ON OFF

FREQ RESP

ON OFF

IQ PATH

( I ONLY)

IQ INPUT

50 1M

BALANCED

ON OFF

PROBE DATA

RENAME

PROBE DATA

DELETE

PROBE DATA
DELETE ALL

PROBE CAL

DC

PROBE CAL

PULSE

PROBE CAL

COMP

I + J*Q

I ONLY

Q ONLY

1303.3545.12 3.16 E-1

R&S FMU Menu Overview

SETUP Key

SETUP

REFERENCE
INT EXT

SIGNAL
SOURCE

GENERAL

SETUP

SYSTEM

INFO

SERVICE

SELFTEST

SELFTEST

RESULTS

FIRMWARE

UPDATE

STATISTICS

HARDWARE

INFO

SYSTEM

MESSAGES

CLEAR ALL

MESSAGES

FIRMWARE

UPDATE

RESTORE

FIRMWARE

UPDATE

PATH

BASEBAND

ANALOG

I/Q INPUT
50

BALANCED
ON OFF

LOW PASS

36 MHz

DITHER

ON OFF

GPIB

COM

INTERFACE

TIME +

DATE

CONFIGURE

NETWORK

NETWORK

LOGIN

VIE

W

1M

FSP-

B16

I+j*Q

I ONLY

Q ONLY

SOFT

FRONTPANEL

FSP-

B16

ADDRESS

ID STRING

FACTORY

ID STRING

FSP

B1

6

FSP

-

B1

6

INSTALL

OPTION

REMOVE

OPTION

GPIB

USER

-

OPTIONS

ENTER

PASSWORD

1303.3545.12 3.17 E-1

Menu Overview R&S FMU

HCOPY Key

HCOPY

PRINT

SCREEN

PRINT
TRACE

PRINT
TABLE

DEVICE

SETUP

DEVICE
1 2

COLORS

COMMENT

INSTALL
PRINTER

COLOR

ON OFF

SCREEN
COLORS

OPTIMIZED

COLORS

USER

DEFINED

SELECT

OBJECT

BRIGHTNESS

TINT

SATURATION

PREDEFINED

COLORS

SET TO

DEFAULT

1303.3545.12 3.18 E-1

R&S FMU Menu Overview

Hotkey Menu

LOCAL Menu

LOCAL

1303.3545.12 3.19 E-1

R&S FMU Contents

Contents - Chapter 4 "Instrument Functions"

4 Instrument Functions ..................................................................................... 4.1

Functional Description ...............................................................................................................4.2

Block Diagram.....................................................................................................................4.2

Digital Down Converter for Low Carrier Frequency (IF)......................................................4.5

Level display........................................................................................................................4.7

Error correction ...................................................................................................................4.7

FFT Analyzer ................................................................................................................................4.8

Overview .............................................................................................................................4.8

Operating principle of the FFT Analyzer..............................................................................4.8

Operating principle in the Time Domain mode..........................................................4.9

Operating principle in the Frequency Domain mode ..............................................4.10

General Operation .....................................................................................................................4.11

Settings of the Baseband Inputs .......................................................................................4.12

Input impedance .....................................................................................................4.12

Measurement mode ................................................................................................4.13

Lowpass Filter.........................................................................................................4.14

Dithering..................................................................................................................4.14

Measurement range................................................................................................4.16

Using Probes .............................................................................................................................4.17

Connecting the Probes......................................................................................................4.18

Measuring with Probes......................................................................................................4.18

Calibrating Probes.............................................................................................................4.19

Probe Calibration Procedure.............................................................................................4.20

Operation Menu .........................................................................................................................4.21

R&S FMU Initial Configuration – PRESET Key.......................................................................4.22

Selecting the Operating Mode – HOTKEY bar........................................................................4.23

Return to manual control – LOCAL Menu ...............................................................................4.24

Operation of the FFT Analyzer .................................................................................................4.25

Overview of menus ...........................................................................................................4.25

Main menu of the FFT Analyzer........................................................................................4.26

Frequency Domain submenu of the FFT Analyzer ...........................................................4.27

Time Domain submenu of the FFT Analyzer ....................................................................4.31

SIGNAL SOURCE submenu of the FFT Analyzer ............................................................4.32

Frequency and Span Selection – FREQ Key ..........................................................................4.34

Setting the frequency span – SPAN Key.................................................................................4.38

Setting the level display and configuring the diagrams – AMPT key ..................................4.40

Setting the Bandwidths and Sweep Time – BW Key .............................................................4.44

Setting the Sweep – SWEEP Key .............................................................................................4.48

Triggering the Sweep – TRIG Key............................................................................................4.51

Selection and Setting of Traces – TRACE Key.......................................................................4.53

Selection of Trace Function ..............................................................................................4.53

1303.3545.12 I-4.1 E-1

Contents R&S FMU

Selection of Detector.........................................................................................................4.60

Mathematical Functions for Traces...................................................................................4.63

Correction Data Acquisition of R&S FMU – CAL Key ............................................................4.64

Markers and Delta Markers – MKR Key...................................................................................4.74

Marker Functions – MKR FCTN Key........................................................................................4.80

Activating the Markers.......................................................................................................4.81

Measurement of Noise Density .........................................................................................4.81

Phase Noise Measurement...............................................................................................4.83

Measurement of the Filter or Signal Bandwidth ................................................................4.86

Measurement of a Peak List .............................................................................................4.87

Selecting the Trace ...........................................................................................................4.89

Change of Settings via Markers – MKR  Key .....................................................................4.90

Power Measurements – MEAS Key .........................................................................................4.96

Power Measurement in Time Domain...............................................................................4.97

Channel and Adjacent-Channel Power Measurements ..................................................4.102

Setting the Channel Configuration ..................................................................................4.107

Measurement of Occupied Bandwidth ............................................................................4.117

Measurement of Signal Amplitude Statistics...................................................................4.120

Measurement of Signal Amplitude Statistics...................................................................4.120

Measurement of Carrier/Noise Ratio C/N and C/No........................................................4.126

Measurement of the AM Modulation Depth.....................................................................4.128

Measurement of the Third Order Intercept (TOI) ............................................................4.129

Setup of Limit Lines and Display Lines – LINES Key ..........................................................4.132

Selection of Limit Lines ...................................................................................................4.133

Entry and Editing of Limit Lines.......................................................................................4.137

Display Lines...................................................................................................................4.142

Configuration of Screen Display – DISP Key........................................................................4.145

Instrument Setup and Interface Configuration – SETUP Key .............................................4.149

External Reference .........................................................................................................4.150

SIGNAL SOURCE Submenu ................................................................................4.151

Programming the Interface Configuration and Time Setup ............................................4.153

Selecting the IEC/IEEE-Bus Address ...................................................................4.153

Serial Interface Configuration ...............................................................................4.154

Setting Date and Time ..........................................................................................4.156

Configuration of Network Settings R&S FMU .......................................................4.157

Enabling Firmware Options...................................................................................4.158

Emulation of the Instrument Front Panel ..............................................................4.159

System Information .........................................................................................................4.160

Display of Module Data.........................................................................................4.161

Display of Device Statistics...................................................................................4.162

Display of System Messages................................................................................4.163

Service Menu ..................................................................................................................4.164

General Service Functions....................................................................................4.165

Selftest ..................................................................................................................4.165

Hardware Adjustment ...........................................................................................4.166

Firmware Update.............................................................................................................4.166

Saving and Recalling Data Sets – FILE Key .........................................................................4.167

1303.3545.12 I-4.2 E-1

R&S FMU Contents

Overview .........................................................................................................................4.167

Storing a Device Configuration .......................................................................................4.168

Storing a Complete Device Configuration.............................................................4.168

Storing Parts of a Device Configuration................................................................4.169

Loading a Data Set:.........................................................................................................4.169

Automatic Loading of a Data Set during Booting ............................................................4.170

Copying Data Sets to Disk ..............................................................................................4.171

Description of the Individual Softkeys .............................................................................4.172

Operating Concept of File Managers..........................................................................4.177

Measurement Documentation – HCOPY Key .......................................................................4.182

HCOPY menu: ................................................................................................................4.182

Selecting Printer, Clipboard and File Formats ................................................................4.185

File formats ...........................................................................................................4.185

Clipboard...............................................................................................................4.185

Printer ...................................................................................................................4.186

Selecting Alternative Printer Configurations .........................................................4.187

Selecting Printer Colours ................................................................................................4.187

1303.3545.12 I-4.3 E-1

R&S FMU Functional Description

4 Instrument Functions

he baseband input is used for direct measurement of complex baseband signals (normally modulation

T
signals) or IF signals .

Measurements in both the time domain and frequency domain are possible.

Alternatively you can also extract data: To do so, the R&S FMU digitizes the analog input signals at a
user-selectable sampling rate.
The samples can be transferred via IEC/IEEE bus or LAN interface to an external computer for analysis.
They are not displayed (Baseband IQ Data Grabbing).

Note: Baseband IQ data grabbing denotes the following:

The TRACE:IQ subsystem (see chapter 6.1) is used by an external computer via IEC/IEEE
bus or LAN interface. That is, the R&S FMU digitizes the signals applied at the baseband
input, then filters, decimates and transfers them to the external computer, where they are
further processed by a program (e.g. Matlab) to be written by the customer. No results are
displayed by the R&S FMU.
The user must explicitly select the sampling rate (thereby automatically selecting the filter
bandwidth) and the data length.

1303.3545.12 4.1 E-1

Functional Description R&S FMU

Functional Description

Block Diagram

1303.3545.12 4.2 E-1

R&S FMU Functional Description

DUT Connection

The device under test, e.g. a complex modulation source, is connected to baseband inputs I and Q . By
definition, I is the real part (in phase) and Q the imaginary part (quadrature phase).
A real signal source, like the IF output of a device under test, is connected to the baseband input I.

ifferential sources are connected to baseband inputs I /

D

I and Q / Q respectively, while the inverted

signal being connected to
At the

BALANCED OFF position only the I / Q input is through-connected and at the BALANCED ON

position the difference between the I -

I and Q resp.

I and Q - Q inputs is through-connected for further processing.

Attenuator and Preamplifier

There is an attenuator to –15 dB at the input. This means that higher input voltages are attenuated to
<1 V so that the A/D converter is not overloaded. Voltages of ±1 V can be measured at the 0 dB
position. In sensitive measurement ranges, a preamplifier to +30 dB ensures adequate drive level of the
A/D converter and thus a low noise figure.
The attenuator and preamplifier settings are permanently coupled to the setting of the

LEVEL

and not user accessible.

REFERENCE

RANGE 5.62 V 3.16 V 1.78 V 1 V 562 mV 316 mV 178 mV 100 mV 56.2 mV 31.6 mV

Attenuator -15 dB -10 dB -5 dB 0 dB 0 dB 0 dB 0 dB 0 dB 0 dB 0 dB

Preamplifier 0 dB 0 dB 0 dB 0 dB +5 dB +10 dB +15 dB +20 dB +25 dB +30 dB

The attenuator and preamplifier have an impedance of 50 . The switchable 1 M



input is reached by

inserting a high-impedance 1:1 amplifier directly behind the input sockets. In this instance the maximum
measurement range is 1.78 V.

Antialiasing Filter

An analog anti-aliasing filter follows with a cutoff frequency of 36MHz. It is active by default and can be
switched off. With

LOWPASS ON / OFF the amplitude and group delay flatness is specified up to 30

MHz / 36 MHz.

Dithering

If required, a dither signal can be added to the test signal, DITHER ON/OFF. This improves the linearity
of the A/D converter at low drive levels.

A to D conversion

The test signal (with dither signal if necessary) is sampled by a 14 bit A/D converter with 81.6 MHz.
The anti-aliasing filter is optimized for this fixed ADC sampling rate.

Sampling rate and bandwidth

The user must specify the output sampling rate when data is extracted. It is user-definable but must be
between 400 Hz and 100 MHz.
With the FFT Analyzer, the user never selects the output sampling rate directly but always indirectly
using other parameters (span, RBW, etc). The firmware always selects the appropriate output sampling
rate.
In both cases, the sampling rate is not changed at the A/D converter but by means of digital signal
processing using a resampler and subsequent integer decimation. Digital filters limit the signal before
decimation to the bandwidth which can still be displayed without aliasing at the output sampling rate.

If the sampling rate is set too low for the test signal, the bandwidth of the signal is limited; but this does
not result in aliasing (folding back of high frequencies to the useful band).

The bandwidths available for the given sampling rate are specified in the following table. Reference is
made to the useful bandwidth, without limitation of the data (flat response of the digital filters).
This table is only relevant if data is extracted (Baseband IQ Data Grabbing).

1303.3545.12 4.3 E-1

Functional Description R&S FMU

With the FFT Analyzer, the sampling rate is calculated by the firmware. In this case, the
interdependencies from Chapter “FFT Analyzer” must be observed.

Table 4-1 Available bandwiths

Sampling rate
from to

100 MHz >81.6 MHz 0.343 sampling rate

81.6 MHz >40.8 MHz 0.441 sampling rate

40.8 MHz >20.4 MHz 0.34 sampling rate

20.4 MHz 400 Hz 0.4 sampling rate

Max. flat bandwidth
I and Q in each case

but L 30 MHz for
Lowpass = ON

but L 30 MHz for
Lowpass = ON

These bandwidths apply to I and Q, and are therefore the equivalent lowpass filter bandwidths.
The complex signal formed by I and Q is a bandpass signal having a center frequency of zero.
The bandpass filter bandwidth is twice the size of the lowpass filter bandwidth shown in the table.
The maximum bandpass filter bandwidth is therefore 72 MHz (with sampling rate 81.6 MHz,
Lowpass = OFF).

Sample length and format

When data is extracted, the samples (I/Q data) are written with the selected sampling rate to a
16 Mword memory (16 Mword for both I and Q). The number of measurement values (samples) to be
acquired is user-selectable.
The FFT Analyzer, however, selects the data volume automatically such that the data volume is always
just large enough for the requirements of the user-selected measurement task. The "Capture both
domains" mode is an exception; here the complete memory volume of 16 Mwords is filled.

If data is extracted, the acquisition and output of I/Q samples are controlled using the commands of the
TRACe:IQ subsystem.
In this case the measurement results are output in list form, with the list of I data and the list of Q data
immediately following each other in the output buffer. You can use the FORMAT command to choose
between binary output (32 bit IEEE 754 floating-point numbers) and output in ASCII format
For further details, refer to chapter 6 onwards.

1303.3545.12 4.4 E-1

R&S FMU Functional Description

Digital Down Converter for Low Carrier Frequency (IF)

The R&S FMU is capable of mixing signals from low carrier frequencies (e.g. low IF signals) into the
complex baseband. The maximum allowed center frequency range is -35 MHz to +35 MHz. Both real­valued and complex-valued signals are supported.
The baseband signal is sampled, mixed from desired center frequency into the complex baseband and
resampled to the requested output sampling rate.

Limitation of center frequency range depending on signal bandwidth for real-valued signals:

Center frequency and sampling rate are adjustable independently, though there are some restrictions to
observe:
The lower limit of the center frequency depends on the sideband suppression that is needed for a
particular measurement application. To avoid overlapping of the two sidebands of a real-valued signal,
the theoretical lower limit of the intermediate frequency is half the signal bandwidth.

Fig. 4-1 Dependency between signal bandwidth and carrier frequency

The carrier frequency f
overlap. The carrier frequency f

in Fig. 4-1 - a) is lower than half the signal bandwidth, resulting in sideband

c

in Fig. 4-1 - b) is high enough to separate the two sidebands.

c

In practice, the intermediate frequency must be increased for lower sideband crosstalk (limited filter
edge steepness). All spectral components of the opposite sideband must be above the decimation filter
stop band frequency. Thus, the center frequency must be higher than 0.5 x ( stop band frequency +

0.5 x signal bandwidth).The stop band frequency depends on the desired output sampling rate and is
specified in the following table:

Table 4-2 Stop band frequency of equivalent lowpass filter

Sampling rate
from to

100 MHz >81.6 MHz 0.54 sampling rate

81.6 MHz >40.8 MHz 0.55 sampling rate

40.8 MHz >20.4 MHz 0.42 sampling rate

20.4 MHz 400 Hz 0.53 sampling rate

Stop band frequency of
equivalent lowpass filter

1303.3545.12 4.5 E-1

Functional Description R&S FMU

Real-valued signals shifted to complex baseband

Fig. 4-2 Real-valued signals shifted to complex baseband

In the signal shown in Fig. 4-2 - a) an unwanted part of the opposite sideband remains after decimation
filtering, while figure Fig. 4-2 - b) depicts a decimation filtered signal free from sideband crosstalk.

Signal bandwidth dependency on the maximum baseband input bandwidth

The upper limit of the carrier frequency is specified by the available baseband input bandwidth. The
entire signal spectrum must fit into the baseband input bandwidth, so the carrier frequency may not
exceed

± 0.5 x (baseband input bandwidth – signal bandwidth )

Fig. 4-3 Signal bandwidth dependency on the maximum baseband input bandwidth

In Fig. 4-3 - a) signal spectrum is cut, because it exceeds the baseband input bandwidth.
Fig. 4-3 - b) shows a signal fitting entirely into the baseband input bandwidth.

Signal bandwidth limitation for real-valued input signals:

A theoretical upper bandwidth limit for an input signal on the lowest possible intermediate frequency
(= 0.5 x signal bandwidth) is defined by the half of the baseband input.

1303.3545.12 4.6 E-1

R&S FMU Functional Description

Level display

When extracting data (I/Q data grabbing) the I/Q data specifies the voltages at the I/Q inputs at the
sampling instants in volts.

In the Time Domain Voltage display of the FFT Analyzer, the I/Q voltages versus time are displayed.

In the Time Domain Magnitude or Frequency Domain Magnitude display, the result is displayed as RMS
value (e.g.. RMS value of voltage or power in dBm).

Examples of the Frequency Domain Magnitude display:

Input Signal

I only I + j*Q

cw signal, 0 dBm, freq. = f at input I signal at freq. = f

0 dBm
cw signal, 0 dBm, freq. = f, phase 0° at input I
cw signal, 0 dBm, freq. = f, phase -90° at input Q
cw signal, 0 dBm, freq. = f, phase 0° at input I
cw signal, 0 dBm, freq. = f, phase +90° at input Q

signal at freq. = +f , +3 dBm

signal at freq. = -f , +3 dBm

Selected I/Q Input Mode

signal at freq. = +f , -3 dBm
signal at freq. = -f , -3 dBm

Error correction

The R&S FMU automatically corrects all important parameters of the baseband input provided that a
valid total calibration has been performed (total calibration status passed).

Baseband input parameters corrected after total calibration

Offset:

Gain:

Frequency
response:

Phase
difference:

Trigger offset:

Compensated for by means of a D/A converter before the A/D converters. This
ensures that the measurement range of the A/D converters is retained even at high
offset voltages (at high gain).

Digitally corrected by a RAM with a correction table (lookup table) downstream of
the A/D converters.

Constant amplitude and group delay (linear phase) over the frequency are achieved
by means of digital compensation filters.

The delay difference (and thus the phase difference) between I and Q is
compensated for by means of digital filters.

The different propagation delays (depending on the sampling rate and filters in the
signal path) are automatically corrected so that the time reference between the test
signal and an external trigger signal is retained.

1303.3545.12 4.7 E-1

FFT Analyzer R&S FMU

FFT Analyzer

Overview

The FFT Analyzer provides a convenient way of analyzing the signals at the analog baseband input in
both the time domain and the frequency domain. This does not require an external computer. The R&S
FMU is used to process the data and to display the results.

In contrast to usual spectrum analyzers, the FFT Analyzer does not determine the spectrum using the
sweep principle but instead by performing a FFT (Fast Fourier Transform) on the input data. For this
reason, some parameter interdependencies are completely different. There are also a number of new
setting options, such as the window functions.

In the FFT Analyzer, a distinction is made between the two operating modes Time Domain and
Frequency Domain. They differ with respect to signal processing and the internal parameter
interdependencies.

Operating principle of the FFT Analyzer

This chapter contains a brief description of the signal processing steps for the two operating modes of
the FFT Analyzer.

The processing sequence depends on the following parameters:

• Is the Time Domain or Frequency Domain mode active?

• Which input signal am I expecting?

- I+j*Q mode: Signals at the I and Q input are regarded as components of a complex signal.

- I ONLY mode: A signal at the I input is regarded as a single, real signal. A signal at the Q input
is ignored.

- Q ONLY mode: A signal at the Q input is regarded as a single, real signal. A signal at the I input
is ignored.

• Is the CAPTURE BOTH DOMAINS mode active?
This mode allows measurements with completely different configurations to be performed repeatedly
using data which needs to be acquired once only. Initial acquisition of the data must, however, be
performed directly to the memory. In the first step, the samples of both the I and Q input are always
recorded regardless of the input signal setting.

• How large is the span in the Frequency Domain mode?
If the span is larger than 27.5 MHz, initial acquisition of the data must once again be performed
directly to the memory.

The input signals are processed in the following sequence corresponding to the functional block
diagram on page 4.2:

1. Provision of the appropriate input impedance (50 R or 1 MR).

2. Attenuation of signal depending on the REFERENCE LEVEL. Both inputs do, however, always
experience the same level of attenuation.

3. Amplification of signal depending on the REFERENCE LEVEL. Both inputs do, however, always
experience the same level of gain.

4. Adaptation of the measurement mode (balanced / referenced to ground). Has the same effect on
both inputs.

5. Activation of analog anti-aliasing filter or not. Has the same effect on both inputs.

1303.3545.12 4.8 E-1

R&S FMU FFT Analyzer

6. Possible addition of shaped dither signal.

7. Sampling of both paths at constant 81.6 MHz.

8. The I and Q samples are then written directly to the memory, but only if this is necessary. Bypassing
of switch S1 and S2 using the signal processing block.

9. The samples from both the I and Q input are passed on to the mixer. They either come from the
current data acquisition process (i.e. directly from the two A/D converters) or are read out of the two
memories if the samples were written directly to these memories beforehand, e.g. because the
CAPTURE BOTH DOMAINS mode is active.
Reading out of the raw data and all subsequent signal processing steps can also be triggered by a
manual or automatic RECALC process. Signal processing starts here for every RECALC process.

10. The samples pass through the complex mixer. The mixer has a complex input and output.
Depending on the IQ PATH setting, the mixer performs the following internal processes:

- I + J*Q mode: The samples from the I input are passed on to the real part of the mixer input
and the samples from the Q input to the imaginary part.

- I ONLY mode: The samples from the I input are passed on to the real part of the mixer input.
The samples from the Q input are discarded. The imaginary part of the mixer
input is instead set to zero.

- Q ONLY mode: The samples from the Q input are passed on to the real part of the mixer input.
The samples from the I input are discarded. The imaginary part of the mixer

11. The resulting real or complex signal at the mixer input is multiplied in the mixer by a complex
rotating phasor. This causes a shift in the frequency domain which is directly proportional to the
rotational frequency of the rotating phasor. The rotational frequency can also be 0 Hz; there is then
no shift. The rotational frequency is calculated automatically by the firmware on the basis of the
measurement settings. The output signal of the mixer is normally complex. If the input signal was
real and has not been mixed, it remains real.

The next processing steps are different for the two operating modes Time Domain and Frequency
Domain.

input is instead set to zero.

Operating principle in the Time Domain mode

The resampler processing block is not active in the Time Domain mode.

An identical digital lowpass filter in both signal paths allows only low-frequency signal components to
pass. However, these signal components had a completely different frequency position prior to mixing.
The mixing process should have shifted the frequency domain of interest to the range around 0 Hz. It is
not attenuated by the filter.
In the Time Domain mode, the filter always has a Gaussian characteristic. Its bandpass filter bandwidth
(twice the cutoff frequency) corresponds to the RESOLUTION BANDWIDTH (RBW) selected by the
user.
The filter also performs integer decimation. With small filter bandwidths, the effect of decimation may be
greater than with large filter bandwidths. The output sampling rate for small and medium RBWs is
always approx. 20 times that of the selected RBW; with very large RBWs the output sampling rate drops
to approx. twice that of the selected RBW.

The two filtered signals are then stored in the memory The output sampling rate of the signal processing block
determines the period during which the memory is completely full. As a result, the maximum observation time
in the Time Domain mode usually depends on the selected RBW. If, however, CAPTURE BOTH DOMAINS
and SINGLE SWEEP are active, the acquisition time is always max. 0.16 seconds (16 Mwords / 81.6 MHz
minus settling time) irrespective of the RBW since the data is initially recorded in the memory without
decimation. See Chapter “Setting the bandwidths and sweep time – BW key", softkey SWT MANUAL”.

1303.3545.12 4.9 E-1

FFT Analyzer R&S FMU

The data is then read out of the memory for analysis. This cannot be performed until data acquisition
and processing has been completed. The result trace is therefore not continuously plotted on the display

n the case of long observation times. Instead, the trace only appears after the observation time has

i
elapsed. With very large data volumes (i.e. large RBW and/or long observation time), the data is read
out in blocks and, as a result, the trace is plotted bit by bit.

The read-out measurement data can be analyzed in a number of different ways:

• MAGNITUDE diagram: The magnitude of the measurement data is plotted over time.

• VOLTAGE diagram: The real and imaginary part of the read-out measurement data is plotted. If

the mixer was not active, this corresponds to the operating principle of a
digital single-channel or dual-channel storage oscilloscope. If, however, the
mixer was active, the information contained in this diagram will not be
conclusive.

Note: The upper and lower diagram display the real part and the imaginary part of the selected

complex or real input signal AFTER the input signal has passed through the signal
processing modules. The two diagrams DO NOT normally represent the I and Q inputs.

A Gaussian filter is always used for Time Domain measurements. The user-definable

window functions from the Frequency Domain mode are completely irrelevant here.

Operating principle in the Frequency Domain mode

The resampler processing block is active in the Frequency Domain mode. It performs fractional
resampling of the sampling rate. Combined with the subsequent integer decimation in the digital filters,
this allows the output sampling rate to be varied steplessly over a very broad range.

An identical digital lowpass filter (approximately rectangular in form) in both signal paths removes high­frequency signal components. Only slightly more than the span selected by the user is allowed through
unchanged. The mixing process should have shifted the center of the selected span to the frequency 0 Hz.
This permits the largest possible decimation (here integer decimation) to be performed following
filtering, i.e. the sampling rate is reduced.

The two filtered signals are then stored in the memory. The output sampling rate of the signal
processing block determines the period during which the memory is completely full. This gives rise to
the interdependencies and minimum/maximum values described in chapter “Setting the bandwidths and
sweep time – BW key”. Other values apply in the CAPTURE BOTH DOMAINS mode since the
acquisition time is max. 0.16 seconds (16 Mwords / 81.6 MHz minus settling time). In this mode, data is
always initially recorded in the memory without decimation.

The samples are then read out of the memory. They are multiplied using the selected window function.
A complex FFT transforms the data from the time domain to the frequency domain.

The FFT results can be analyzed in a number of different ways:

• MAGNITUDE diagram: Only the magnitude of the FFT results is displayed.

• MAGNITUDE PHASE diagram: The upper diagram corresponds to the upper MAGNITUDE diagram.

The phase information is, however, also displayed in the lower diagram. The phase trace only
provides conclusive information if a single measurement (SINGLE SWEEP) was performed, or if a
periodic signal is analyzed in the CONTINUOUS SWEEP using a trigger.

• REAL IMAG diagram: The real and imaginary parts of the FFT results are displayed on a linear

scale. These can also be negative. This diagram is generally of little relevance. As with the
MAGNITUDE PHASE diagram, a single measurement should be performed or, alternatively, a trigger
should be used.

1303.3545.12 4.10 E-1

R&S FMU General Operation

General Operation

The following diagrams explain which settings must be made to allow the hardware to process the input
signals correctly. The operating principle is the same for all operating modes; configuration, however,
takes place at different locations.

The configurations for the baseband inputs are kept separate for the following operating modes:

• Baseband IQ Data Grabbing (extraction of data by means of IEC/IEEE bus or LAN interface,

TRACE:IQ)

• FFT Analyzer

• every option which can use the baseband inputs

For configuration, the FFT Analyzer provides:

• a separate submenu

• or, alternatively, the submenu which can be called up using the SIGNAL SOURCE softkey in the

SETUP menu.

All options which can use the baseband inputs provide the following for configuration:

• the submenu, which can be called up using the SIGNAL SOURCE softkey in the SETUP menu.

Please also refer to the operating manual for the respective option.

Note: Both paths (I and Q) are always taken into consideration when data is extracted. The

possibility of ignoring a path is only available in the FFT Analyzer (IQ PATH softkey).

1303.3545.12 4.11 E-1

General Operation R&S FMU

Settings of the Baseband Inputs

Input impedance

IEC/IEEE bus command: INP:IQ:IMP LOW  HIGH

LOW corresponds to 50 ; HIGH corresponds to 1 M.
The default setting is 50 .

Equivalent input circuit



50

1 M



Note: It should be remembered that at the 50 setting there is always a 50 DC path to ground,

even when the input is switched to BALANCED.

1303.3545.12 4.12 E-1

R&S FMU General Operation

Measurement mode

IEC/IEEE bus command: INP:IQ:BAL ON OFF

Used to toggle the measurement mode between balanced (BALANCED ON) and referenced to ground
(BALANCED OFF).
The default setting is OFF.

Connecting the signal sources (device under test)

BALANCED OFF

The connection to ground is run via the shield of the coaxial cable.

BALANCED ON

A connection to ground is not necessary.

1303.3545.12 4.13 E-1

General Operation R&S FMU

Lowpass Filter

IEC/IEEE bus command: IQ:LPAS ON OFF

Used to switch the anti-aliasing filters upstream of the A/D converters on and off (cutoff frequency
36 MHz).
The default setting is ON.

0

d
B

10

-

-20

30

-

40

-

-50

-60

70

-

-80

-90

100

­0Hz 10MH z 20MHz 30MHz 40M Hz 50MHz 60MHz 70 MHz 80MH z 90MHz 100MHz

DB(C24:2)

V

Frequency

Fig. 4-4 Anti-aliasing lowpass filter, typical frequency response

Note:

• The filter prevents frequencies above the usable frequency range (>36 MHz) from
being mixed into the usable frequency range (DC to 36 MHz) as a result of sampling
(sampling frequency 81.6 MHz). It should therefore always be switched on. It should
bear in mind that, for example, harmonics and other spurious emissions of the device
under test might be in the disallowed frequency range.

• Amplitude response and phase response (or group delay) of the filter are
compensated for up to 30 MHz.

• With the filter switched off, amplitude response and phase response (or group delay)
of the filter are compensated for up to 36 MHz. This setting is only recommended if
the higher bandwidth is required. In this case, it is important to ensure that the
spectrum of the device under test has adequately decayed >45.6 MHz since these
spectral components appear in the useful band <= 36 MHz.

Dithering

IEC/IEEE bus command: IQ:DITH ON OFF

Used to switch the dither signal on and off. The dither signal is added to the signal to be measured
before the A to D conversion.
The default setting is OFF.

The dither signal distinctly improves the linearity of the A/D converter at low signal levels (low drive level
at the A/D converter) and thus the accuracy of the level displayed.

Note: The dither signal is necessary only if the total AC voltage applied to the input (up to

36 MHz) is more than 46 dB less than the set REFERENCE LEVEL. The DC component is
not taken into account.

1303.3545.12 4.14 E-1

R&S FMU General Operation

Relative Input Level / dB

The dither signal has no effect with signals applied having levels higher than measurement range –46 dB. A

isadvantage, however, is that it might have to be removed from the spectrum as a result of post-processing

d
(filters).

Baseband Level Linearity (sine wave)

0.50

0.40

0.30

0.20

0.10

0.00

-0.10

-0.20

Linearity Error/ dB

-0.30

-0.40

-0.50
0 -10 -20 -30 -40 -50 -60 -7 0 -80 -90

Fig. 4-5 Typical linearity error with and without dither signal

Characteristics of the dither signal:

Band-limited noise, center frequency 38.93 MHz (in the I/Q spectrum), 3 dB bandwidth approx. 2 MHz, peak
voltage 7 %, rms 1 % of measurement range of A/D converter.

Dither Off

D

ither On

Fig. 4-6 Dither signal, spectrum (complex FFT of I/Q data)

The entire spectrum is outside the usable frequency range (>36 MHz) and can therefore be removed by
means of digital filters without affecting the useful signal. If data is extracted by means of IEC/IEEE bus
or LAN interface, at lower sampling rates (<40.8 MHz) the dither signal will already have been removed
by the internal digital filters and therefore no longer appears in the I/Q data.

In the FFT Analyzer the dither signal is almost completely removed by the internal digital filters.

1303.3545.12 4.15 E-1

General Operation R&S FMU

Measurement range

IEC/IEEE bus command: VOLT:IQ:RANG 5.623.161.7810.5620.316 ...

The unit for input is volts.

The default setting is 1 V.

The measurement range specifies the measurable peak voltage, at the I and Q inputs in each case.
For example, voltages between –1 V and +1 V can be measured with a setting of 1 V.
With the BALANCED ON setting, the measurement range defines the measurable differential voltage.

The measurement range can be changed in steps of 5 dB.
Permissible settings:

0.0316 V

0.0562 V

0.1 V

0.178 V

0.316 V

0.562 V
1 V

1.78 V

3.16 V only with IMPEDANCE LOW (50 )

5.62 V only with IMPEDANCE LOW (50 )

Headroom: Typically 3 dB (with dither 2 dB) higher voltages can still be measured. The A/D

converter is overloaded when the headroom is exceeded, then the overload display
appears: OVLD.

The measurement range depends on the REFERENCE LEVEL. By setting the REFERENCE LEVEL,
the same or the next higher measurement range is selected automatically.

1303.3545.12 4.16 E-1

R&S FMU Using Probes

Using Probes

As a special feature, the R&S FMU allows you to perform measurements using high-impedance probes,
since the input impedance can be switched to 1 MR.

10:1 probes

1:1 probes

Automatic probe detection

Automatic switchover to 1 MD

Preset

Conventional 10 MR/10:1 oscilloscope probes can be used if their
compensation range includes 8 pF. Appropriate probes are available
as an accessory (R&S FMU-Z1, order no. 1409.7508.00).

You can also measure with 1:1 probes. But due to their high input
capacitance of typ. 50 pF, these probes are only suitable for
frequencies up to approx. 6 MHz.
However, the 1:1 probes are only advantageous with weak signals
(approx. <180 mV peak voltage), since they attain a higher signal-to­noise ratio in the R&S FMU than 10:1 probes.

All modern probes have a coding pin. This pin is connected to ground
via a resistor. A certain resistance value is assigned to a variety of
attenuation factors (examples: 1:1, 2:1, 10:1, 100:1). By means of this
resistance coding, the R&S FMU detects a connected probe and
automatically takes into account the respective attenuation factor in
the display. The attenuation factors must be between 1:1 and 100:1.
Example: A measurement range of 1 V is set on the R&S FMU. A
10:1 probe is connected. The measurement range automatically
changes to 10 V.

As soon as a probe is connected, the R&S FMU automatically
switches the input impedance to 1 MR, since passive probes cannot
be operated at a 50 R input. The automatic switchover thus simplifies
operation.
When you remove the probe, the 1 MR setting is maintained.

The blue PRESET key
without taking connected probes into account. The default state of the
baseband input is I + j*Q, unbalanced, input impedance 50 R . Probe
calibration is switched off.
The PRESET FFT key
PRESET key, as long as no probes are connected.
If probes are connected, the following settings remain unchanged:
I/Q path (I only, Q only, I+j*Q)
Balanced ON/OFF
Input impedance 1 MR
An active probe calibration is not switched off.

resets the instrument to the default state

in the hot key bar has the same effect as the

1303.3545.12 4.17 E-1

Using Probes R&S FMU

Connecting the Probes

Before connecting the probes, it is advisable to carry out the following configuration as desired:

I/Q path (I only, Q only, I+j*Q)
Balanced ON/OFF

By doing so, the active inputs are defined. Active inputs are indicated by illuminated LEDs.

Note! Probes with identical attenuation factor must be connected on all active inputs.

If more than one input is active, the following message will appear after the first probe has been
connected:

As soon as you have connected probes on all active inputs, the message will disappear automatically. If
the configuration (e.g. Balanced = OFF) is not to be set correctly until after the probes have been
connected, then you must first acknowledge this message by pressing ESC or ENTER.

Measuring with Probes

Usually, you have 50 R interfaces at instrument outputs (e.g. I/Q output of a signal generator). In
development, it is often necessary to measure within printed boards – i.e. at spots that do not support 50
R. For this purpose, you can switch the R&S FMU to 1 MR input impedance. If you use a coaxial cable
(e.g. BNC cable) for connecting the DUT, this cable will put considerable strain on the measuring point
due to its capacitance (typ. 100 pF/m). This will lead to incorrect measurement results. Due to the high
impedance (10 MR // 10 pF) of high-quality probes (such as the R&S FMU-Z1), you can perform virtually
distortion-free measurements. Owing to their fine probe tip, adaptation is also much easier than
with a cable.

1303.3545.12 4.18 E-1

R&S FMU Using Probes

Calibrating Probes

In principle, a connected probe leads to a larger measurement uncertainty. The tolerance of the
attenuation factor is usually specified, allowing you to at least calculate the resulting measurement
uncertainty. Although it is practically impossible to make a quantitative statement with respect to the
frequency response, this is no problem for the R&S FMU. The R&S FMU is able to measure all errors of
the probe and mathematically correct them afterwards. For this purpose, the probe is connected to the
calibration source of the R&S FMU and automatically calibrated by pressing a button. For safe
adaptation, you should make sure to use a BNC adapter. The R&S FMU-Z1 probes are supplied with a
BNC adapter.

Probe calibration is explained in detail in the description of the PROBE CAL menu. The following gives
you an overview of the procedure.

It is presumed that the I/Q input is set as desired and that all probes have been connected appropriately.

The PROBE CAL menu provides the following options:

• Gain & Offset

• Frequency Response

• Probe Compensation

In the default setting, all three functions are active.

This function measures the probe attenuation and then mathematically
corrects it. In connection with the probe, the DC offset of the input gain is
compensated to zero.

This function measures the frequency response of the overall system
(probe, amplifier, filter, etc) and then compensates it with a digital filter.

The R&S FMU provides a 1 kHz squarewave signal that allows you to
adjust the probe to the input capacitance of the R&S FMU. It is the same
procedure as usual with oscilloscopes. The R&S FMU automatically sets a
time domain display that matches the signal so that you only have to make
the adjustment.

1303.3545.12 4.19 E-1

Using Probes R&S FMU

Probe Calibration Procedure

After pressing the PROBE CAL START softkey, you are requested to connect the probes to the
calibration source (PROBE CAL BNC connector).

After pressing the ENTER key, calibration is started. The first step (if selected) is the probe
compensation.

After the probe has been adjusted, the calibration is continued by pressing the ENTER key.

If more than one probe is to be calibrated, then this procedure, beginning with the request to connect
this probe, is repeated for each probe.

Finally, after all probes have been calibrated the following message will appear:

If you acknowledge this message with YES, the calibration data will be saved to the hard disk as a file
and can be reactivated at any time.
However, if you acknowledge with NO, the data will only be available in the memory. After each step that
renders the data invalid (e.g. disconnecting a probe, changing the Balanced ON /OFF configuration), the
calibration data is lost.

Taking the data into account (Probe Correction = ON) is automatically switched on after the calibration
or after a saved file has been loaded.

1303.3545.12 4.20 E-1

R&S FMU Operation Menu

Operation Menu

All functions of the baseband signal analyzer and their application are explained in detail in this chapter.
The sequence of the described menu groups depends on the procedure selected for the configuration
and start of a measurement:

1. Resetting the instrument - PRESET key

2. Setting the mode – hotkey bar and LOCAL key

3. Configuring the FFT Analyzer – softkeys FREQUENCY DOMAIN, TIME DOMAIN, SIGNAL
SOURCE

4. Setting the measurement parameters - keys FREQ, SPAN, AMPT, BW, SWEEP, TRIG, TRACE,
CAL

5. Selecting and configuring the measurement function - keys MKR, MKR->, MKR FCTN, MEAS,
LINES

The instrument functions for general settings, printout and data management are described at the end
of this chapter – keys DISP, SETUP, FILE and HCOPY.

The different softkeys of a menu are described from top to bottom and from the left to the right side
menu. The submenus are marked by an indentation or displayed in a separate section. The whole path
(key - softkey - ...) is indicated in the line above the menu display.

An overview of the menus is given in chapter 3 which also contains the description of the operating
concept.

The IEC/IEEE-bus commands (if any) are indicated for each softkey. For a fast overview a list of
softkeys with the associated IEC/IEEE-bus commands is given at the end of Chapter 6.

An index at the end of the handbook serves as further help for the user.

1303.3545.12 4.21 E-1

R&S FMU Initial Configuration – PRESET Key R&S FMU

R&S FMU Initial Configuration – PRESET Key

PRESET

Using the PRESET key, the R&S FMU can be set to a predefined initial state.

Notes: The initial instrument state set by the PRESET key can be

adapted to arbitrary applications using the STARTUP RECALL

CAL

function. With this function the STARTUP RECALL dataset is
loaded upon pressing the PRESET key. For further information
refer to section "Saving and Recalling Data Sets".

Pressing the PRESET key causes the R&S FMU to enter its initial state according to the following table:

Table 4-3 Initial State of R&S FMU

Parameter Settings

Mode FFT Mode
Capture domain Frequency domain magnitude

Center frequency 0 Hz

Center frequency step size 0.1 * center frequency

Span 72 MHz

Reference level +10 dBm ( peak 1.0 V)

Level range 100 dB log

Level unit dBm

Sweep time 3.8852 µs

Resolution bandwidth auto (1 MHz)

Span / RBW auto (50)

Sweep continuous

Trigger free run

Trace 1 clr write

Trace 2/3 blank

Detector auto select (auto peak)

Trace math off

Frequency offset 0 Hz

Reference level offset 0 dB

Reference level position 100 %

Grid abs

Cal correction on

Probe correction off

Display Full screen, active screen A

Type of signal at baseband input (IQ Path) I+jQ

I/Q Input Impedance 50 Ohm

Balanced Input Off

Lowpass 36 MHz On

Dither Off

Sweep count 0

Sweep points 625

The PRESET key also sets all other applications (e.g. VSA) to their default state.

The PRESET FFT key (in the hotkey bar) only sets the FFT Analyzer to a predefined default state.

IEC/IEEE bus command: SENS:FFT:PRES

1303.3545.12 4.22 E-1

R&S FMU Selecting the Operating Mode – HOTKEY bar

Selecting the Operating Mode – HOTKEY bar

The R&S FMU has seven keys ("hotkeys") below the display to allow fast selection of the various
operating modes. These keys may have different functions depending on the available instrument
options.
The illustration below shows how the hotkey bar may look if the instrument is in the FFT mode (Preset

setting).

The EXIT FFT hotkey enables the R&S FMU main hotkey bar that allows the

EXIT FFT

selection of different operation modes.

IEC/IEEE bus command: INST:SEL <other>

The main hotkey bar allows the activation of another operation mode.

FFT

PRESET FFT

HOME FFT

SCREEN A

VSA

The PRESET FFT hotkey sets the FFT Analyzer to a predefined state.
IEC/IEEE bus command: SENS:FFT:PRES

The HOME FFT hotkey opens the main menu of the FFT Analyzer.

Real split-screen mode is not possible with the R&S FMU. Although there are
measurements with a split screen, these measurements cannot display the
results of two completely independent measurements. The
SCREEN A / SCREEN B hotkey can only be used in measurements that
automatically display split-screen diagrams. Marker operations and the
configuration of the diagram axes can be switched between the upper diagram
(SCREEN A) and the lower one (SCREEN B) with this hotkey.

IEC/IEEE-bus command: DISP:WIND<1|2>:SEL

SCREEN B

The meaning of the other keys is described in the chapter describing the various options.

1303.3545.12 4.23 E-1

Return to manual control – LOCAL Menu R&S FMU

blanked out (they can be activated using the remote control command

Return to manual control – LOCAL Menu

The menu LOCAL is displayed on switching the instrument to remote control
mode.

At the same time, the HOTKEY bar is blanked out and all keys are disabled
except the PRESET key. The diagram, traces and display fields are then

SYSTem:DISPlay:UPDate ON).

The menu contains only one softkey, the LOCAL key. The LOCAL key
switches the instrument from remote to manual control, with the assumption
that the remote controller has not previously set the LOCAL LOCKOUT
function.

A change in the control mode consists of:

- Enabling the Front Panel Keys
Returning to manual mode enables all inactive keys and turns on the
hotkey menu. The soft key menu which is displayed is the main menu of
the current mode.

Inserting the measurement diagrams
The blanked diagrams, traces and display fields are inserted.

LOCAL

- Generating the message OPERATION COMPLETE
If, at the time of pressing the LOCAL softkey, the synchronisation
mechanism via *OPC, *OPC? or *WAI is active, the currently running
measurement procedure is aborted and synchronisation is achieved by
setting the corresponding bits in the registers of the status reporting
system.

- Setting Bit 6 (User Request) of the Event Status Register
With a corresponding configuration of the status reporting system, this
bit immediately causes the generation of a service request (SRQ)

is used to inform the control software

front-panel control. This information can be used, e.g., to interrupt the
control program so that the user can make necessary manual
corrections to instrument settings. This bit is set each time the LOCAL
softkey is pressed.

Note: If the LOCAL LOCKOUT function is active in the remote control

mode, the front-panel PRESET key is also disabled. The LOCAL
LOCKOUT state is left as soon as the process controller de­activates the REN line or the IEC/IEEE-bus cable is

disconnected

from the instrument.

that the user wishes to return to

which

1303.3545.12 4.24 E-1

R&S FMU Operation of the FFT Analyzer

Operation of the FFT Analyzer

Overview of menus

FFT HOME

BASEBAND

ANALOG

IQ PATH

(I+J*Q)

I/Q INPUT

50 1M

BALANCED

ON OFF

LOW PASS

36 MHz

I+J*Q

I ONLY

Q ONLY

FREQUENCY

DOMAIN

TIME

DOMAIN

CAPTURE

BOTH DOM

SIGNAL
SOURCE

ZOOM

ADJUST
REF LVL

MAGNITUDE

VOLTAGE

MAGNITUDE

MAGNITUDE

PHASE

REAL
IMAG

WINDOWFCT

(FLATTOP)

FLATTOP

GAUSSIAN

RECT

HAMMING

HANN

CHEBYCHEV

DITHER

ON OFF

1303.3545.12 4.25 E-1

Operation of the FFT Analyzer R&S FMU

Main menu of the FFT Analyzer

This softkey main menu appears on the right-hand side of the display immediately after the
FFT Analyzer mode is started or whenever the HOME FFT hotkey is pressed.

The FREQUENCY DOMAIN softkey opens a submenu in which various types of
spectrum measurements can be selected. The softkey activates the
Frequency Domain mode and deactivates the Time Domain mode.

Note: The Frequency Domain mode can also be activated by entering a

SPAN larger than 0 Hz (see chapter "Setting the frequency span –
SPAN ")

IEC/IEEE bus command: SENS:FREQ:SPAN 10MHz

The TIME DOMAIN softkey opens a submenu in which various types of time­domain measurements can be selected.
The softkey activates the Time Domain mode and deactivates the
Frequency Domain mode.

Note: The Time Domain mode can also be activated by entering a SPAN

of 0 Hz (see Chapter "Setting the frequency span – SPAN ”).

IEC/IEEE bus command: SENS:FREQ:SPAN 0Hz

1303.3545.12 4.26 E-1