7BM63_2E

®
Products: R&S SFU
Phase Noise Profile Creator V. 1.2 for the
R&S®SFU
Basics and Applications of the
R&S®SFU-K41 Phase Noise Option
Application Note
This Application Note briefly explains the theoretical background regarding phase noise before describing
®
the phase noise option for the R&S SFU. You will see how the phase noise profile creator application
software can be used to approximate specific phase noise curves and how to output them with the aid of
®
the R&S SFU.
Subject to change – H. Gsoedl, B. Rott, T. Haberl 08.2007 – 7BM63_1E
Phase Noise Profile Creator for the R&S®SFU
Contents
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5
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Overview ................................................................................................. 3
Where to get the application software?................................................... 3
Software Features ................................................................................... 3
Hardware and Software Requirements ................................................... 4
PC Hardware Requirements .............................................................. 4
PC Software Requirements ............................................................... 4
®
R&S SFU Requirements ................................................................... 4
General Remarks on Phase Noise ......................................................... 5
Single Sideband Noise.................................................................. 6
Double Sideband Noise ................................................................ 6
®
R&S SFU-K41 Phase Noise Option ....................................................... 7
®
Graphical User Interface of the R&S SFU......................................... 7
Format of the Profile Files.................................................................. 7
Internal Phase Noise Generation ....................................................... 8
Installation Instructions for the Phase Noise Profile Creator................... 9
Installation of .NET Runtime 2.0 or Better ......................................... 9
Installation of the Actual Program Files ........................................... 10
Application: Phase Noise Profile Creator ............................................. 10
General Functional Description........................................................ 10
Procedure......................................................................................... 11
Checking the Phase Noise Curve ......................................................... 14
Additional Information ........................................................................... 15
Ordering Information ............................................................................. 16
2
Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
1 Overview
An important characteristic of an oscillator is its spectral purity. The spectral
purity, generally referred to as phase noise, is a measure of the short-term
stability of oscillators.
In the case of the
Rohde & Schwarz, the
characteristics.
®
R&S SFU Broadcast Test
oscillator has outstanding
System from
phase noise
At the receiver end, the quality of the received signal is mainly determined
by the phase noise of the oscillators used in the transmission path.
To allow manufacturers of receivers to thoroughly analyze the behavior of a
®
device under test (DUT), the R&S SFU offers a special feature: the
®
R&S SFU-K41 phase noise option.
This Application Note briefly explains the theoretical background regarding
®
phase noise before describing the phase noise option of the R&S SFU. You
will see how the phase noise profile creator application software of the
®
R&S SFU can be used to approximate specific phase noise curves and
®
how to output them with the aid of the R&S SFU.
2 Where to get the application software?
Please contact the Customer Support Center and provide the serial number
of your device. CS will grant you access to one of our file servers via HTTP.
Customer Support Europe
Telephone: +49 180 512 4242
Fax: +49 89 4129 63778
E-mail: [email protected]
3 Software Features
®
The phase noise profile creator software application of the R&S SFU allows
®
users of the R&S SFU to generate user-specific phase noise profiles with
®
the R&S SFU-K41 phase noise option.
For this purpose, the user defines five typical phase noise values with an
offset of 100 Hz, 1 kHz, 10 kHz, 100 kHz and 1 MHz from the actual carrier.
Based on these values, a phase noise curve is to some extent generated
automatically, can be adjusted manually afterwards and stored or loaded
®
into the R&S SFU.
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
4 Hardware and Software Requirements
PC Hardware Requirements
Minimum
CPU
Pentium II 450 MHz or better
RAM
128 Mbyte
Hard disk
50 Mbyte free hard disc space
Monitor
SVGA color monitor, resolution 1024 x 768 or better
PC Software Requirements
Recommended
OS
Windows 98 / 2000 / Me / XP
OS
add-ons
.NET Framework 2.0 or better
R&S®SFU Requirements
Software option
7BM63_1E
PHASE NOISE
4
®
R&S SFU-K41
2110.7660.02
Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
5 General Remarks on Phase Noise
Phase noise can be considered as a random frequency modulation around
an “ideal” carrier.
The following equation describes an ideal carrier:
s (t ) = A cos(2
f1 t )
As a result, a discrete spectral line is displayed in the frequency spectrum:
Fig. 1: Ideal oscillator
In reality, however, an oscillator cannot maintain this frequency .Thus, the
following equation describes the carrier:
s (t ) = A cos(2
f1 t +
n
(t ))
This kind of phase modulation (PM) results in a “broader” carrier in the
frequency spectrum.
Fig. 2: Real oscillator with phase noise
Two important parameters are used to determine phase noise:
Single sideband noise
Double sideband noise
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
Single Sideband Noise
The most frequently used phase noise parameter is single sideband noise
. It is defined as the spectral density of noise sidebands:
where:
N (f) = Noise power of a sideband
B
= Measurement bandwidth
Psig = Total signal power
Single sideband noise is typically specified by the unit dBc/Hz. This
®
parameter is used to describe the phase noise for the R&S SFU.
Double Sideband Noise
Double sideband noise is the basic noise parameter from which all other
noise parameters are derived. It is defined as the square of the phase
oscillation referenced to the measurement bandwidth.
(for small phase deviations)
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
6 R&S®SFU-K41 Phase Noise Option
Graphical User Interface of the R&S®SFU
®
Fig. 3: Phase noise generation with the R&S SFU
By using the SSB SHAPE PROFILE menu item, you can choose between
different profiles for the frequency response of single sideband phase
noise. Upon selection, a window opens where the profile files available on
®
the R&S SFU can be selected. These are coefficient sets for digital filters.
If a file is selected and confirmed with SELECT, the software configures the
phase noise generator with the corresponding data.
The indicated single sideband spectrum (SSB PHASENOISE) of the signal
carrier, or – in the case of multicarrier method – of all individual carriers,
then follows the characteristics of the filter curve from the profile file.
Format of the Profile Files
When needed, separate profile files can be created in accordance with the
example file in Fig. 4.
Fig. 4: Example of a profile file
ASCII text must be used as the file format, the file extensions *.fcf and *.txt
are permitted. The file is configured in such a way that after a random
number of comment lines with the keyword “SOS Matrix” (second-order
section matrix) there are two lines with six coefficients each, separated by
spaces. Each line corresponds to a second-order section (filter elements
with two zeros and two poles). The coefficients are in the sequence b0 b1
b2 a0 a1 a2 so that the following filter function applies to each line:
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
From the above display of coefficients, conversion into a zero and pole
display is possible.
The two sections, in turn, are cascaded. This corresponds to a
multiplication of the two functions. Thus, a digital filter must be designed to
generate a specific curve. Moreover, the individual coefficients must be
within the range of [-2; 2).
Internal Phase Noise Generation
The useful l and Q data is linked with the phase noise signal as follows:
Fig. 5: Generation principle
The above graphic shows that the generated noise signal is “genuine”
phase noise. The amplitude of the noise signal is maintained at a constant
level, the phase is varied.
The useful signal is converted from I and Q into phase (
(
). The noise phase (
n
) and amplitude
(t ) ) is then added to the signal phase. The total
signal is finally reconverted into its l and Q components.
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
7 Installation Instructions for the Phase Noise Profile Creator
Follow the installation steps below to install the phase noise profile creator
®
of the R&S SFU on your computer:
1. Installation of .NET Framework version 2.0 or better
2. Installation of the application from Rohde & Schwarz
Installation of .NET Runtime 2.0 or Better
The installation routine for the application from Rohde & Schwarz checks
whether .NET Framework version 2.0 is installed. If this is not the case, you
will be asked if the installation routine should be obtained from the Internet:
Fig. 6 Framework download window
If you confirm with YES, a browser window opens to the Microsoft web
server. A download link (free of charge) can be selected for .NET
Framework.
Fig. 7: Download page for .NET Framework
After the file is downloaded, start the Framework installation routine and
follow the directions on the screen.
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
Installation of the Actual Program Files
After carrying out the installation routine for the application from
Rohde & Schwarz, follow the directions on the screen. Before the
application can be installed, the general conditions of use from
Rohde & Schwarz have to be accepted.
The installation routine stores the program files in a user-selectable
directory. Links to the program and the documentation are added to the
start menu.
8 Application: Phase Noise Profile Creator
The following section describes how user-specific phase noise profiles can
®
be generated with the phase noise profile creator of the R&S SFU and
®
displayed by means of the R&S SFU.
The following screenshot shows the main application window:
Estimated phase
noise values
Automatic coefficient
determination
Desired phase noise
Export of phase noise files
Graphic display of
phase noise
- Red = desired
- Blue = estimated
Status bar: Warning when phase noise
profile is instable (coefficients exceed
boundaries) or might be instable (exceed
-10 dBc/Hz @ 100 Hz).
Gain, zeros and poles of filter function
General Functional Description
Based on five phase noise values at 100 Hz, 1 kHz, 10 kHz, 100 kHz and
1 MHz, an approximation of the phase noise characteristic is possible by
semi-automatically adjusting the filter transfer function. In the
®
implementation of the R&S SFU a fourfold Infinite Impulse Response (IIR)
filter is used. Through filter coefficients or respectively gain, zeros and poles
in the discussed application, the definition of the curve characteristic is
feasible.
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
Procedure
Generation is done essentially as follows:
1. Configuration of the optimization parameters via “Optimization
conditions” in the menu. These optimization values are used to
define an abort criterion for the phase noise curve calculation:
The abort criterion can either be the maximum permissible average
square error (see previous section) or the maximum number of
optimization loops.
The maximum average square error is defined as follows:
a, b, c, d, e: error value
a
b
c
100 Hz
Error =
1 kHz
10 kHz
d
100 kHz
e
Desired
Estimated
1 MHz
a2 + b2 + c 2 + d 2 + e2
5
The calculation does not always lead under all conditions to an
optimal phase noise curve. Therefore manual adjustment can be
carried out. See 5 and 6 for more details.
2. Entry of the desired phase noise values at 100 Hz, 1 kHz, 10 kHz,
100 kHz and 1 MHz:
3. Calculation of the automatic coefficient determination by selecting:
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
4. After optimization has been carried out, the current calculated
graph is displayed in blue in addition to the “desired” graph (defined
under 2).
5. If this optimization is not sufficient (see 1), you can adjust the zeros
and poles of the filter transfer function by manually configuring
them. Another alternative is to carry out optimization with altered
abort criteria. The “Manual Settings” selection must be activated to
manually change the filter curve:
6. The four pairs of zeros and poles can now be entered manually in
the activated range (Z1 to Z4, P1 to P4; Cartesian coordinate
system).
The parameters can have the following value ranges:
I. Gain: 0 < x < 4
II. Poles:
Radius: 0 <= x < 1 (polar coordinate system)
III. Zeros:
Radius: 0 <= x < 2 (polar coordinate system)
The results of the modified gain value and the zeros and poles are
immediately visible in the SSB graphic. Subsequent manual
optimization is now possible.
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
The relation between poles and coefficients (please refer to chapter
6) is as follows:
zx: Zero x (real)
zx_j: Zero x (imaginary)
px: Pole x (real)
px_j: Pole x (imaginary)
7. Press the “Transfer/Save Phase Noise Shape” button to transfer
the configured phase noise profile.
8. Now you can save the filter coefficients to a file. This file can later
be loaded through the measurement instrument.
Local saving
When you select “File”, a storage dialog opens, which specifies the
name of the file to be stored.
9. By clicking “Transfer/Save" the phase noise profile is written to the
specified site.
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
®
10. To start the specific phase noise profile on the R&S SFU, refer to
Section 6.
9 Checking the Phase Noise Curve
It is recommended to check the self-generated phase noise curves by
means of a spectrum analyzer with a phase noise measurement option.
®
®
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Spectrum analyzers such as the R&S FSP, R&S FSQ and R&S FSUP, for
example, are suitable:
Fig. 8: Test setup
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The “Noise only” mode on the R&S SFU must be selected to enable the
measurement.
®
Fig. 9: The R&S SFU noise menu
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
The phase noise personality of the spectrum analyzer allows a simple
determination of the phase noise behaviour of the carrier:
P HA SE NO IS E
Residual Nois e
Settings
Evaluation from 100 Hz
to 1 MHz
Spot Noise
Signal Freq:
442.000007 MHz
1 kHz
-62.37 dBc/Hz
Signal Level:
-19.24 dBm
Residual PM
3.128 °
10 kHz
-88.01 dBc/Hz
Signal Freq ?:
-5.02 Hz
Residual FM
383.475 Hz
100 kHz
-111.60 dBc/Hz
Signal Level ?:
0.01 dBm
RMS Jitter
19.6554 ps
1 MHz
-130.01 dBc/Hz
PH Noise
RF A tten
0 dB
Top -40 dBc/Hz
CHECK RESULT Fail
limi t
Fail
-50
A
-60
limit
-70
-80
1CLRWR
SMTH 1%
-90
2CLRWR
-100
-110
-120
-130
100 Hz
1 kHz
10 kHz
100 kHz
1 MHz
Running ...
Date: 25.SEP.2006
13:17:19
Fig. 10: Phase noise measurement using a spectrum analyzer
10 Additional Information
Our Application Notes are regularly revised and updated. Check for any
changes at http://www.rohde-schwarz.com.
Please send any comments or suggestions about this Application Note to
7BM63_1E
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Rohde & Schwarz
Phase Noise Profile Creator for the R&S®SFU
11 Ordering Information
ROHDE & SCHWARZ GmbH & Co. KG . Mühldorfstraße 15 . D-81671 Munich . P.O. Box 80 14 69 . D-81614 Munich . Tel
(089) 4129 -0 . Fax (089) 4129 - 13777 . Internet: http://www.rohde-schwarz.com
This application note and the supplied programs may only be used subject to the conditions of use set forth in the
download area of the Rohde & Schwarz website.
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Rohde & Schwarz

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