® 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 1 2 3 4 5 6 7 8 9 10 11 7BM63_1E 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. 7BM63_1E 3 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 7BM63_1E 5 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) 7BM63_1E 6 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: 7BM63_1E 7 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. 7BM63_1E 8 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. 7BM63_1E 9 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. 7BM63_1E 10 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: 7BM63_1E 11 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. 7BM63_1E 12 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. 7BM63_1E 13 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. ® ® ® Spectrum analyzers such as the R&S FSP, R&S FSQ and R&S FSUP, for example, are suitable: Fig. 8: Test setup ® The “Noise only” mode on the R&S SFU must be selected to enable the measurement. ® Fig. 9: The R&S SFU noise menu 7BM63_1E 14 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 15 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. 7BM63_1E 16 Rohde & Schwarz

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