Agilent X-Series Signal Analyzer This manual provides documentation for the following X-Series Analyzers: MXA Signal Analyzer N9020A EXA Signal Analyzer N9010A N9020A/N9010A Spectrum Analyzer Mode Measurement Guide
Notices © Agilent Technologies, Inc. 2008 Manual Part Number No part of this manual may be reproduced in any form or by any means (including electronic storage and retrieval or translation into a foreign language) without prior agreement and written consent from Agilent Technologies, Inc. as governed by United States and international copyright laws. N9060-90022 Supersedes:N9060-90022, August 2008 March 2009 Printed in USA Agilent Technologies, Inc.
Warranty This Agilent technologies instrument product is warranted against defects in material and workmanship for a period of one year from the date of shipment. During the warranty period, Agilent Technologies will, at its option, either repair or replace products that prove to be defective. For warranty service or repair, this product must be returned to a service facility designated by Agilent Technologies.
Contents 2. Front and Rear Panel Features Front-Panel Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Display Annotations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Rear-Panel Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Front and Rear Panel Symbols . . . . . . . . . . . . . . . . . . . .
Table of Contents Contents Improving Phase Noise Measurements by Subtracting Signal Analyzer Noise . . . . . . . . . .89 9. Making Time-Gated Measurements Generating a Pulsed-RF FM Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94 Connecting the Instruments to Make Time-Gated Measurements . . . . . . . . . . . . . . . . . . . .99 Gated LO Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 Getting Started with the Spectrum Analyzer Measurement Application This chapter provides some basic information about using the Spectrum Analyzer and IQ Analyzer Measurement Application Modes. It includes topics on: “Making a Basic Measurement” on page 8. • “Recommended Test Equipment” on page 12. • “Accessories Available” on page 13.
Getting Started with the Spectrum Analyzer Measurement Application Making a Basic Measurement Making a Basic Measurement Refer to the description of the instrument front and rear panels to improve your understanding of the Agilent Signal Analyzer measurement platform. This knowledge will help you with the following measurement example. Getting Started with the Spectrum Analyzer Measurement Application This section includes: • “Using the Front Panel” on page 9.
Getting Started with the Spectrum Analyzer Measurement Application Making a Basic Measurement Using the Front Panel Entering Data When setting measurement parameters, there are several ways to enter or modify the value of the active function: Increments or decrements the current value. Arrow Keys Increments or decrements the current value. Numeric Keypad Enters a specific value. Then press the desired terminator (either a unit softkey, or the Enter key).
Getting Started with the Spectrum Analyzer Measurement Application Making a Basic Measurement Presetting the Signal Analyzer The preset function provides a known starting point for making measurements. The analyzer has two main types of preset: User Preset Restores the analyzer to a user-defined state. Mode Preset This type of preset restores the currently selected mode to a default state. For details, see the help or User’s and Programmer’s Reference.
Getting Started with the Spectrum Analyzer Measurement Application Making a Basic Measurement Improving Frequency Accuracy 9. To increase the accuracy of the frequency reading in the marker annotation, turn on the frequency count function. • Press Marker, More, Marker Count. The Marker Count softkeys appear. Note softkey Counter On Off. If Off is underlined, press the softkey to toggle marker count on. The marker active function annotation changes from Mkr1 to Cntr1.
Getting Started with the Spectrum Analyzer Measurement Application Recommended Test Equipment Recommended Test Equipment The following table lists the test equipment you will need to perform the example measurements described in this manual. Getting Started with the Spectrum Analyzer Measurement Application NOTE To find descriptions of specific analyzer functions for the N9060A Spectrum Analyzer Measurement Application refer to the Agilent Technologies User’s and Programmer’s Reference.
Getting Started with the Spectrum Analyzer Measurement Application Accessories Available Accessories Available A number of accessories are available from Agilent Technologies to help you configure your analyzer for your specific applications. They can be ordered through your local Agilent Sales and Service Office and are listed below. NOTE For the latest information on Agilent signal analyzer options and upgrade kits, visit the following Internet URL: http://www.agilent.com/find/sa_upgrades.
Getting Started with the Spectrum Analyzer Measurement Application Accessories Available Broadband Preamplifiers and Power Amplifiers Getting Started with the Spectrum Analyzer Measurement Application Preamplifiers and power amplifiers can be used with your signal analyzer to enhance measurements of very low-level signals. • The Agilent 8447D preamplifier provides a minimum of 25 dB gain from 100 kHz to 1.3 GHz. • The Agilent 87405A preamplifier provides a minimum of 22 dB gain from 10 MHz to 3 GHz.
Getting Started with the Spectrum Analyzer Measurement Application Accessories Available Static Safety Accessories 9300-1367 Wrist-strap, color black, stainless steel. Four adjustable links and a 7 mm post-type connection. 9300-0980 Wrist-strap cord 1.5 m (5 ft.
Getting Started with the Spectrum Analyzer Measurement Application Getting Started with the Spectrum Analyzer Measurement Application Accessories Available 16 Chapter 1
Front and Rear Panel Features 2 Front and Rear Panel Features • “Front-Panel Features” on page 18. • “Display Annotations” on page 22. • “Rear-Panel Features” on page 24. • “Front and Rear Panel Symbols” on page 26.
Front and Rear Panel Features Front and Rear Panel Features Front-Panel Features Front-Panel Features Item Description # Name 1 Menu Keys Key labels appear to the left of the menu keys to identify the current function of each key. The displayed functions are dependent on the currently selected Mode and Measurement, and are directly related to the most recent key press. 2 Analyzer Setup Keys These keys set the parameters used for making measurements in the current Mode and Measurement.
Item Description # Name 9 Delete Key Press this key to delete files, or to perform other deletion tasks. 10 USB Connectors Standard USB 2.0 ports, Type A. Connect to external peripherals such as a mouse, keyboard, DVD drive, or hard drive. 11 Local/Cancel/(Esc) Key If you are in remote operation, Local: • • • returns instrument control from remote back to local (the front panel). turns the display on (if it was turned off for remote operation). can be used to clear errors.
Front and Rear Panel Features Front and Rear Panel Features Front-Panel Features Item Description # Name 21 Full Screen Key Pressing this key turns off the softkeys to maximize the graticule display area. Press the key again to restore the normal display. 22 Help Key Initiates a context-sensitive Help display for the current Mode. Once Help is accessed, pressing a front panel key brings up the help topic for that key function.
Some menu keys have multiple choices on their label, such as On/Off or Auto/Man. The different choices are selected by pressing the key multiple times. For example, the Auto/Man type of key. To select the function, press the menu key and notice that Auto is underlined and the key becomes highlighted. To change the function to manual, press the key again so that Man is underlined. If there are more than two settings on the key, keep pressing it until the desired selection is underlined.
Front and Rear Panel Features Front and Rear Panel Features Display Annotations Display Annotations This section describes the display annotation as it is on the Spectrum Analyzer Measurement Application display. Other measurement application modes will have some annotation differences. Item 1 Description Measurement bar - Shows general measurement settings and information. Function Keys All the keys in the Analyzer Setup part of the front panel. Indicates single/continuous measurement.
Item Description 3 Banner - shows the name of the selected measurement application and the measurement that is currently running. Mode, Meas 4 Measurement title (banner) - shows title information for the current Measurement, or a title that you created for the measurement. Meas 5 Function Keys View/Display, Display, Title Settings panel - displays system information that is not specific to any one application. • • • • Input/Output status - green LXI indicates the LAN is connected.
Front and Rear Panel Features Front and Rear Panel Features Rear-Panel Features Rear-Panel Features MXA and EXA with Option PC2 EXA Item # 1 Description Name EXT REF IN Input for an external frequency reference signal: For MXA – 1 to 50 MHz For EXA – 10 MHz.
Item # 2 Description Name GPIB A General Purpose Interface Bus (GPIB, IEEE 488.1) connection that can be used for remote analyzer operation. 3 USB Connector USB 2.0 port, Type B. USB TMC (test and measurement class) connects to an external pc controller to control the instrument and for data transfers over a 480 Mbps link. 4 USB Connectors Standard USB 2.0 ports, Type A. Connect to external peripherals such as a mouse, keyboard, printer, DVD drive, or hard drive.
Front and Rear Panel Features Front and Rear Panel Features Front and Rear Panel Symbols Front and Rear Panel Symbols This symbol is used to indicate power ON (green LED). This symbol is used to indicate power STANDBY mode (yellow LED). This symbol indicates the input power required is AC. The instruction documentation symbol. The product is marked with this symbol when it is necessary for the user to refer to instructions in the documentation.
3 Measuring Multiple Signals Measuring Multiple Signals 27
Measuring Multiple Signals Comparing Signals on the Same Screen Using Marker Delta Comparing Signals on the Same Screen Using Marker Delta Using the analyzer, you can easily compare frequency and amplitude differences between signals, such as radio or television signal spectra. The analyzer delta marker function lets you compare two signals when both appear on the screen at one time.
Measuring Multiple Signals Comparing Signals on the Same Screen Using Marker Delta Press Marker, Delta. The symbol for the first marker is changed from a diamond to a cross (5) with a label that now reads 2, indicating that it is the fixed marker (reference point). The second marker symbol is a diamond labeled 1Δ2, indicating it is the delta marker. When you first press the Delta key, both markers are at the same frequency with the symbols superimposed over each other.
Measuring Multiple Signals Comparing Signals not on the Same Screen Using Marker Delta Comparing Signals not on the Same Screen Using Marker Delta Measure the frequency and amplitude difference between two signals that do not appear on the screen at one time. (This technique is useful for harmonic distortion tests when narrow span and narrow bandwidth are necessary to measure the low level harmonics.
Measuring Multiple Signals Comparing Signals not on the Same Screen Using Marker Delta Step 6. Activate the marker delta function: Press Marker, Delta. Step 7. Increase the center frequency by 10 MHz: Press FREQ Channel, Center Freq, ↑ . The first marker and delta markers move to the left edge of the screen, at the amplitude of the first signal peak. Step 8. Move the delta marker to the new center frequency: Press Peak Search.
Measuring Multiple Signals Resolving Signals of Equal Amplitude Resolving Signals of Equal Amplitude In this procedure a decrease in resolution bandwidth is used in combination with a decrease in video bandwidth to resolve two signals of equal amplitude with a frequency separation of 100 kHz. Notice that the final RBW selection to resolve the signals is the same width as the signal separation while the VBW is slightly narrower than the RBW. Step 1.
Measuring Multiple Signals Resolving Signals of Equal Amplitude Figure 3-6 Unresolved Signals of Equal Amplitude Step 6. Change the resolution bandwidth (RBW) to 100 kHz so that the RBW setting is less than or equal to the frequency separation of the two signals and decrease the video bandwidth to 10 kHz: Press BW, Res BW, 100, kHz. Press Video BW, 10, kHz Notice that the peak of the signal has become two peaks separated by a 2.5 dB dip indicating that two signals may be present. Refer to Figure 3-7.
Measuring Multiple Signals Resolving Signals of Equal Amplitude Step 7. Decrease the resolution bandwidth (RBW) to 10 kHz: Press BW, Res BW, 10, kHz. Two signals are now visible as shown in Figure 3-8. You can use the front-panel knob or step keys to further reduce the resolution bandwidth and better resolve the signals. Figure 3-8 Resolving Signals of Equal Amplitude As the resolution bandwidth is decreased, resolution of the individual signals is improved and the sweep time is increased.
Measuring Multiple Signals Resolving Signals of Equal Amplitude Figure 3-9 Resolving Signals of Equal Amplitude Measuring Multiple Signals Chapter 3 35
Measuring Multiple Signals Resolving Small Signals Hidden by Large Signals Resolving Small Signals Hidden by Large Signals This procedure uses narrow resolution bandwidths to resolve two input signals with a frequency separation of 50 kHz and an amplitude difference of 60 dB. Step 1. Connect two sources to the analyzer RF INPUT as shown in Figure 3-10. Figure 3-10 Setup for Obtaining Two Signals Step 2. Setup the signal sources as follows: Set signal generator #1 to 300 MHz at −10 dBm.
Measuring Multiple Signals Resolving Small Signals Hidden by Large Signals Step 6. Set the 300 MHz signal peak to the reference level: Press Peak Search, Mkr →Ref Lvl. NOTE The Signal Analyzer 30 kHz filter shape factor of 4.1:1 has a bandwidth of 123 kHz at the 60 dB point. The half-bandwidth, or 61.5 kHz, is NOT narrower than the frequency separation of 50 kHz, so the input signals can not be resolved. Refer to Figure 3-11. Figure 3-11 Signal Resolution with a 30 kHz RBW Step 7.
Measuring Multiple Signals Resolving Small Signals Hidden by Large Signals Signal Resolution with a 10 kHz RBW Measuring Multiple Signals Figure 3-12 38 Chapter 3
Measuring Multiple Signals Decreasing the Frequency Span Around the Signal Decreasing the Frequency Span Around the Signal Using the analyzer signal track function, you can quickly decrease the span while keeping the signal at center frequency. This is a fast way to take a closer look at the area around the signal to identify signals that would otherwise not be resolved. This procedure uses signal tracking with span zoom to view the analyzer 50 MHz reference signal in a 200 kHz span. Step 1.
Measuring Multiple Signals Decreasing the Frequency Span Around the Signal Step 8. Turn off signal tracking: Press SPAN X Scale, Signal Track (Off).
Measuring Multiple Signals Easily Measure Varying Levels of Modulated Power Compared to a Reference Easily Measure Varying Levels of Modulated Power Compared to a Reference This section demonstrates a method to measure the complex modulated power of a reference device or setup and then compare the result of adjustments and changes to that or other devices.
Measuring Multiple Signals Easily Measure Varying Levels of Modulated Power Compared to a Reference Step 6. Enable trace averaging and the Band/Interval Power Marker function for measuring the total power of the reference 4-carrier W-CDMA signal. Press Trace/Detector, Select Trace, Trace 1, Trace Average Press Marker Function, Band/Interval Power Step 7. Center the frequency of the Band/Interval Power marker on the 4-carrier reference signal envelope: Press Select Marker, Marker 1, 1.96, GHz Step 8.
Measuring Multiple Signals Easily Measure Varying Levels of Modulated Power Compared to a Reference Step 10. Simulate a varying power level resulting from either adjustments, changes to the reference DUT, or a different DUT by lowering the signal source power. Set the source amplitude to –20 dBm. Note the Delta Band Power Marker value displayed in the Marker Result Block showing the 10 dB difference between the modulated power of the reference and the changed power level. Refer to Figure 3-16.
Measuring Multiple Signals Measuring Multiple Signals Easily Measure Varying Levels of Modulated Power Compared to a Reference 44 Chapter 3
Measuring a Low−Level Signal 4 Measuring a Low−Level Signal 45
Measuring a Low−Level Signal Measuring a Low−Level Signal Reducing Input Attenuation Reducing Input Attenuation The ability to measure a low-level signal is limited by internally generated noise in the signal analyzer. The measurement setup can be changed in several ways to improve the analyzer sensitivity. The input attenuator affects the level of a signal passing through the instrument. If a signal is very close to the noise floor, reducing input attenuation can bring the signal out of the noise.
Step 6. Move the desired peak (in this example, 300 MHz) to the center of the display: Press Peak Search, Marker ?, Mkr ? CF. Step 7. Reduce the span to 1 MHz (as shown in Figure 4-2) and if necessary re-center the peak: Press Span, 1, MHz. Step 8. Set the attenuation to 20 dB: Press AMPTD Y Scale, Attenuation, Mech Atten (Man), 20, dB. Note that increasing the attenuation moves the noise floor closer to the signal level.
Measuring a Low−Level Signal Measuring a Low−Level Signal Reducing Input Attenuation Step 9. To see the signal more clearly, set the attenuation to 0 dB: Press AMPTD Y Scale, Attenuation, Mech Atten (Man), 0, dB. See Figure 4-3 shows 0 dB input attenuation. Figure 4-3 Measuring a Low-Level Signal Using 0 dB Attenuation CAUTION When you finish this example, increase the attenuation to protect the analyzer RF input: Press AMPTD Y Scale, Attenuation, Mech Atten (Auto) or press Auto Couple.
Decreasing the Resolution Bandwidth Resolution bandwidth settings affect the level of internal noise without affecting the level of continuous wave (CW) signals. Decreasing the RBW by a decade reduces the noise floor by 10 dB. Step 1. Setup the signal sources as follows: Set the frequency of the signal source to 300 MHz. Set the source amplitude to −80 dBm. Step 2. Connect the source RF OUTPUT to the analyzer RF INPUT as shown in Figure 4-4. Figure 4-4 Setup for Measuring a Low-Level Signal Step 3.
Measuring a Low−Level Signal Measuring a Low−Level Signal Decreasing the Resolution Bandwidth Figure 4-5 Default Resolution Bandwidth Step 6. Decrease the resolution bandwidth: Press BW, 47, kHz. The low-level signal appears more clearly because the noise level is reduced. Refer to Figure 4-6. Figure 4-6 Decreasing Resolution Bandwidth A “#” mark appears next to the Res BW annotation in the lower left corner of the screen, indicating that the resolution bandwidth is uncoupled.
RBW Selections You can use the step keys to change the RBW in a 1−3−10 sequence. All the signal analyzer RBWs are digital and have a selectivity ratio of 4.1:1. Choosing the next lower RBW (in a 1−3−10 sequence) for better sensitivity increases the sweep time by about 10:1 for swept measurements, and about 3:1 for FFT measurements (within the limits of RBW). Using the knob or keypad, you can select RBWs from 1 Hz to 3 MHz in approximately 10% increments, plus 4, 5, 6 and 8 MHz.
Measuring a Low−Level Signal Measuring a Low−Level Signal Using the Average Detector and Increased Sweep Time Using the Average Detector and Increased Sweep Time When the analyzer noise masks low-level signals, changing to the average detector and increasing the sweep time smooths the noise and improves the signal visibility. Slower sweeps are required to average more noise variations. Step 1. Setup the signal source as follows: Set the frequency of the signal source to 300 MHz.
Step 7. Increase the sweep time to 100 ms: Press Sweep/Control, Sweep Time (Man), 100, ms. Note how the noise smooths out, as there is more time to average the values for each of the displayed data points. Step 8. With the sweep time at 100 ms, change the average type to log averaging: Press Meas Setup, Average Type, Log-Pwr Avg (Video). Note how the noise level drops.
Measuring a Low−Level Signal Measuring a Low−Level Signal Trace Averaging Trace Averaging Averaging is a digital process in which each trace point is averaged with the previous average for the same trace point. Selecting averaging, when the analyzer is autocoupled, changes the detection mode from normal to sample. Sample mode may not measure a signal amplitude as accurately as normal mode, because it may not find the true peak.
Step 6. Turn trace averaging on: Press Trace/Detector, Trace Average. As the averaging routine smooths the trace, low level signals become more visible. Avg/Hold >100 appears in the measurement bar near the top of the screen. Refer to Figure 4-10. Step 7. With trace average as the active function, set the number of averages to 25: Press Meas Setup, Average/Hold Number, 25, Enter. Annotation above the graticule in the measurement bar to the right of center shows the type of averaging, Log-Power.
Measuring a Low−Level Signal Measuring a Low−Level Signal Trace Averaging 56 Chapter 4
5 Improving Frequency Resolution and Accuracy Improving Frequency Resolution and Accuracy 57
Improving Frequency Resolution and Accuracy Using a Frequency Counter to Improve Frequency Resolution and Accuracy Using a Frequency Counter to Improve Frequency Resolution and Accuracy This procedure uses the signal analyzer internal frequency counter to increase the resolution and accuracy of the frequency readout. Improving Frequency Resolution and Accuracy Step 1. Set the analyzer to the Spectrum Analyzer mode and enable the spectrum analyzer measurements: Press Mode, Spectrum Analyzer. Step 2.
Improving Frequency Resolution and Accuracy Using a Frequency Counter to Improve Frequency Resolution and Accuracy Step 6. The marker counter remains on until turned off. Turn off the marker counter: Press Marker, More, Marker Count, Count (Off) Or Press Marker, Off.
Improving Frequency Resolution and Accuracy Improving Frequency Resolution and Accuracy Using a Frequency Counter to Improve Frequency Resolution and Accuracy 60 Chapter 5
6 Tracking Drifting Signals Tracking Drifting Signals 61
Tracking Drifting Signals Measuring a Source Frequency Drift Measuring a Source Frequency Drift The analyzer can measure the short- and long-term stability of a source. The maximum amplitude level and the frequency drift of an input signal trace can be displayed and held by using the maximum-hold function. You can also use the maximum-hold function if you want to determine how much of the frequency spectrum a signal occupies.
Tracking Drifting Signals Measuring a Source Frequency Drift Step 7. Reduce the span to 500 kHz: Press SPAN, 500, kHz. Notice that the signal is held in the center of the display. Step 8. Turn off the signal track function: Press SPAN X Scale, Signal Track (Off). Step 9. Measure the excursion of the signal with maximum hold: Press Trace/Detector, Max Hold. As the signal varies, maximum hold maintains the maximum responses of the input signal.
Tracking Drifting Signals Tracking a Signal Tracking a Signal The signal track function is useful for tracking drifting signals that drift relatively slowly by keeping the signal centered on the display as the signal drifts. This procedure tracks a drifting signal. Note that the primary function of the signal track function is to track unstable signals, not to track a signal as the center frequency of the analyzer is changed.
Tracking Drifting Signals Tracking a Signal Step 7. Turn the delta marker on to read signal drift: Press Marker, Delta. Step 8. Tune the frequency of the signal generator in 100 kHz increments. Notice that the center frequency of the analyzer also changes in 100 kHz increments, centering the signal with each increment.
Tracking Drifting Signals Tracking Drifting Signals Tracking a Signal 66 Chapter 6
7 Making Distortion Measurements Making Distortion Measurements 67
Making Distortion Measurements Identifying Analyzer Generated Distortion Identifying Analyzer Generated Distortion High level input signals may cause internal analyzer distortion products that could mask the real distortion measured on the input signal. Using trace 2 and the RF attenuator, you can determine which signals, if any, are internally generated distortion products. Using a signal from a signal generator, determine whether the harmonic distortion products are generated by the analyzer. Step 1.
Making Distortion Measurements Identifying Analyzer Generated Distortion Figure 7-2 Harmonic Distortion Step 6. Change the center frequency to the value of the first harmonic: Press Peak Search, Next Peak, Mkr→CF. Step 7. Change the span to 50 MHz and re-center the signal: Press SPAN X Scale, Span, 50, MHz. Press Peak Search, Mkr→CF. Step 8. Set the attenuation to 0 dB: Press AMPTD Y Scale, Attenuation, 0, dB. Step 9.
Making Distortion Measurements Identifying Analyzer Generated Distortion Step 11. Increase the RF attenuation to 10 dB: Press AMPTD Y Scale, Attenuation, 10, dB. Notice the ΔMkr1 amplitude reading. This is the difference in the distortion product amplitude readings between 0 dB and 10 dB input attenuation settings. If the ΔMkr1 amplitude absolute value is approximately ≥1 dB for an input attenuator change of 10 dB, the distortion is being generated, at least in part, by the analyzer.
Making Distortion Measurements Third-Order Intermodulation Distortion Third-Order Intermodulation Distortion Two-tone, third-order intermodulation distortion is a common test in communication systems. When two signals are present in a non-linear system, they can interact and create third-order intermodulation distortion products that are located close to the original signals. These distortion products are generated by system components such as amplifiers and mixers.
Making Distortion Measurements Third-Order Intermodulation Distortion Press Mode Preset. Step 5. Set the analyzer center frequency and span: Press FREQ Channel, Center Freq, 300.5, MHz. Press SPAN X Scale, Span, 5, MHz. Step 6. Set the analyzer detector to Peak: Press Trace/Detector, Detector, Peak. Step 7. Set the mixer level to improve dynamic range: Press AMPTD Y Scale, Attenuation, Max Mixer Lvl, –10, dBm.
Making Distortion Measurements Third-Order Intermodulation Distortion Figure 7-5 Measuring the Distortion Product Making Distortion Measurements Chapter 7 73
Making Distortion Measurements Making Distortion Measurements Third-Order Intermodulation Distortion 74 Chapter 7
Measuring Noise Measuring Noise 8 75
Measuring Noise Measuring Noise Measuring Signal-to-Noise Measuring Signal-to-Noise Signal-to-noise is a ratio used in many communication systems as an indication of noise in a system. Typically the more signals added to a system adds to the noise level, reducing the signal-to-noise ratio making it more difficult for modulated signals to be demodulated. This measurement is also referred to as carrier-to-noise in some communication systems.
Measuring Noise Measuring Signal-to-Noise Measuring Noise Figure 8-1 Measuring the Signal-to-Noise Read the signal-to-noise in dB/Hz, that is with the noise value determined for a 1 Hz noise bandwidth. If you wish the noise value for a different bandwidth, decrease the ratio by 10 × log ( BW ) . For example, if the analyzer reading is −70 dB/Hz but you have a channel bandwidth of 30 kHz: S/N = – 70 dB/Hz + 10 × log ( 30 kHz ) = – 25.
Measuring Noise Measuring Noise Measuring Noise Using the Noise Marker Measuring Noise Using the Noise Marker This procedure uses the marker function, Marker Noise, to measure noise in a 1 Hz bandwidth. In this example the noise marker measurement is made near the 50 MHz reference signal to illustrate the use of Marker Noise. Step 1. Set the analyzer to the Spectrum Analyzer mode and enable the spectrum analyzer measurements: Press Mode, Spectrum Analyzer. Step 2. Preset the analyzer: Press Mode Preset.
Measuring Noise Measuring Noise Using the Noise Marker Measuring Noise Step 7. To adjust the width of the noise marker relative to the span: Press Marker Function, Band Adjust, Band/Interval Span, and adjust the value to the desired marker width. Notice that the marker does not go to the peak of the signal unless the Band/Interval Span is set to 0 Hz because otherwise there are not enough points at the peak of the signal.
Measuring Noise Measuring Noise Measuring Noise Using the Noise Marker Figure 8-3 Noise Marker with Zero Span 80 Chapter 8
Measuring Noise Measuring Noise-Like Signals Using Band/Interval Density Markers Band/Interval Density markers let you measure power over a frequency span. The markers allow you to easily and conveniently select any arbitrary portion of the displayed signal. However, while the analyzer, when autocoupled, makes sure the analysis is power-responding (rms voltage-responding), you must set all of the other parameters. Step 1.
Measuring Noise Measuring Noise Measuring Noise-Like Signals Using Band/Interval Density Markers Figure 8-4 Band/Interval Density Measurement Step 8. Set the Band/Interval Density Markers to enable moving the markers (set at 40 kHz span) around without changing the Band/Interval span. Use the front-panel knob to move the band power markers and note the change in the power reading: Press Marker Function, Band/Interval Density, then rotate front-panel knob. Refer to Figure 8-5.
Measuring Noise Measuring Noise-Like Signals Using the Channel Power Measurement You may want to measure the total power of a noise-like signal that occupies some bandwidth. Typically, channel power measurements are used to measure the total (channel) power in a selected bandwidth for a modulated (noise-like) signal. Alternatively, to manually calculate the channel power for a modulated signal, use the noise marker value and add 10 × log ( channel BW ) .
Measuring Noise Measuring Noise Measuring Noise-Like Signals Using the Channel Power Measurement Figure 8-6 Measuring Channel Power The power reading is essentially that of the tone; that is, the total noise power is far enough below that of the tone that the noise power contributes very little to the total. The algorithm that computes the total power works equally well for signals of any statistical variant, whether tone-like, noise-like, or combination.
Measuring Noise Measuring Signal-to-Noise of a Modulated Carrier Signal-to-noise (or carrier-to-noise) is a ratio used in many communication systems as indication of the noise performance in the system. Typically, the more signals added to the system or an increase in the complexity of the modulation scheme can add to the noise level. This can reduce the signal-to-noise ratio and impact the quality of the demodulated signal.
Measuring Noise Measuring Noise Measuring Signal-to-Noise of a Modulated Carrier Step 6. Enable the Band Power Marker function for measuring the total power of the 4 carrier W-CDMA signal. Press Marker Function, Band/Interval Power Step 7. Center the frequency of the Band Power marker on the signal: Press Select Marker 1, 1.96, GHz Step 8. Adjust the width (or span) of the Band Power marker to encompass the entire 4 carrier W-CDMA signal.
Measuring Noise Measuring Signal-to-Noise of a Modulated Carrier Measuring Noise Figure 8-9 Noise Marker Measuring System Noise Step 12. Measure carrier-to-noise by making the Noise Marker relative to the carrier's Band Power Marker.
Measuring Noise Measuring Noise Measuring Signal-to-Noise of a Modulated Carrier Step 13. Simultaneously measure carrier-to-noise on a second region of the system by enabling another Noise Marker (up to 11 available). Press Marker Function, Select Marker, Marker 3, Marker Noise Press Select Marker 3, 1.941, GHz Press Return, Band Adjust, Band/Interval, 5, MHz Press Marker, Properties, Select Marker, Marker 3, Relative to, Marker 1 Step 14.
Measuring Noise Improving Phase Noise Measurements by Subtracting Signal Analyzer Noise Making noise power measurements (such as phase noise) near the noise floor of the signal analyzer can be challenging where every dB improvement is important.
Measuring Noise Measuring Noise Improving Phase Noise Measurements by Subtracting Signal Analyzer Noise Figure 8-13 Measurement of DUT and Analyzer Noise Step 7. Measure only the analyzer noise using trace 2 (blue trace) with trace averaging (allow time for sufficient averaging).
Measuring Noise Improving Phase Noise Measurements by Subtracting Signal Analyzer Noise Measuring Noise Step 8. Subtract the noise from the DUT phase noise measurement using the Power Diff math function and note the phase noise improvement at 100 kHz offset between trace 1 (yellow trace) and trace 3 (magenta trace).
Measuring Noise Measuring Noise Improving Phase Noise Measurements by Subtracting Signal Analyzer Noise Figure 8-16 Improved Phase Noise Measurement with Delta Noise Markers 92 Chapter 8
9 Making Time-Gated Measurements Making Time-Gated Measurements 93
Making Time-Gated Measurements Generating a Pulsed-RF FM Signal Generating a Pulsed-RF FM Signal Making Time-Gated Measurements Traditional frequency-domain spectrum analysis provides only limited information for certain signals.
Making Time-Gated Measurements Generating a Pulsed-RF FM Signal Table 9-2 ESG #2 Internal Function Generator (LF OUT) Settings FuncGen LF Out Waveform Pulse LF Out Period 5 ms LF Out Width (pulse width) 4 ms LF Out Amplitude 2.5 Vp LF Out On RF On/Off Off Mod On/Off On Step 2. Set up ESG #1 to transmit a pulsed-RF signal with frequency modulation.
Making Time-Gated Measurements Generating a Pulsed-RF FM Signal Step 3. If you are using your Agilent X-Series Signal Analyzer (using Gate View), set up the analyzer to view the gated RF signal (see Figure 9-1 and Figure 9-2 for examples of the display): 1. Set the analyzer to the Spectrum Analyzer mode: Press Mode, Spectrum Analyzer, Mode Preset. 2. Set the analyzer center frequency, span and reference level: Making Time-Gated Measurements Press FREQ Channel, Center Freq, 40, MHz.
Making Time-Gated Measurements Generating a Pulsed-RF FM Signal 7. Set the RBW to auto, gate view to off, gate method to LO, and gate to on: Press Sweep/Control, Gate, Gate View (Off). Press BW, Res BW (Auto). Press Sweep/Control, Gate, Gate Method, LO. Press Gate (On). Figure 9-2 Gated RF Signal with Auto RBW Making Time-Gated Measurements Step 4.
Making Time-Gated Measurements Generating a Pulsed-RF FM Signal Making Time-Gated Measurements Figure 9-3 Viewing the Gate Timing With an Oscilloscope Figure 9-3 oscilloscope channels: 1. Channel 1 (left display, top trace) - the trigger signal. 2. Channel 2 (left display, bottom trace) - the gate signal (gate signal is not active until the gate is on in the spectrum analyzer). 3. Channel 3 (right display) - the RF output of the signal generator.
Making Time-Gated Measurements Connecting the Instruments to Make Time-Gated Measurements Connecting the Instruments to Make Time-Gated Measurements Figure 9-4 shows a diagram of the test setup. ESG #1 produces a pulsed FM signal by using an external pulse signal. The external pulse signal is connected to the front of the ESG #1 to the EXT 2 INPUT to control the pulsing. The pulse signal is also used as the trigger signal.
Making Time-Gated Measurements Connecting the Instruments to Make Time-Gated Measurements Instrument Connection Diagram without Oscilloscope Making Time-Gated Measurements Figure 9-5 100 Chapter 9
Making Time-Gated Measurements Gated LO Measurement Gated LO Measurement This procedure utilizes gated LO to gate the FM signal. For concept and theory information about gated LO see “How Time Gating Works” on page 149. Step 1. Set the analyzer to the Spectrum Analyzer mode: Press Mode, Spectrum Analyzer, Mode Preset. Step 2. Set the analyzer center frequency, span and reference level: In Figure 9-7 (left), the moving signals are a result of the pulsed signal.
Making Time-Gated Measurements Gated LO Measurement Making Time-Gated Measurements Figure 9-6 Viewing the Gate Settings with Gated LO In Figure 9-6 the blue vertical line (the far left line outside of the RF envelope) represents the location equivalent to a zero gate delay. In Figure 9-6 the vertical green parallel bars represent the gate settings. The first (left) bar (GATE START) is set at the delay time while the second (right) bar (GATE STOP) is set at the gate length, measured from the first bar.
Making Time-Gated Measurements Gated LO Measurement Figure 9-7 Pulsed-RF FM Signal Making Time-Gated Measurements Step 7. Enable the gate settings (see Figure 9-8): Press Gate (On). Figure 9-8 Pulsed and Gated FM Signal Step 8. Turn off the pulse modulation on ESG #1 by pressing Pulse, Pulse so that Off is selected. Notice that the gated spectrum is much cleaner than the ungated spectrum (as seen in Figure 9-7).
Making Time-Gated Measurements Gated Video Measurement Gated Video Measurement This procedure utilizes gated video to gate the FM signal. For concept and theory information about gated video see “How Time Gating Works” on page 149. Step 1. Set the analyzer to the Spectrum Analyzer mode: Press Mode, Spectrum Analyzer, Mode Preset. Making Time-Gated Measurements Step 2. Set the analyzer center frequency, span and reference level: Press FREQ Channel, Center Freq, 40, MHz. Press SPAN X Scale, Span, 500, kHz.
Making Time-Gated Measurements Gated Video Measurement Figure 9-9 Viewing the Pulsed-RF FM Signal (without gating) Making Time-Gated Measurements Step 4. Set the gate delay to 2 ms and the gate length to 1 ms. Check that the gate control is set to edge: Press Sweep/Control, Gate, More, Control (Edge). Press More, Gate Delay, 2, ms. Press Gate Length, 1, ms. Step 5. Turn the gate on: Press Sweep/Control, Gate, Gate Method, Video Press Gate (On).
Making Time-Gated Measurements Gated Video Measurement Step 6. Notice that the gated spectrum is much cleaner than the ungated spectrum (as seen in Figure 9-9). The spectrum you see is the same as a frequency modulated signal without being pulsed. To prove this, turn off the pulse modulation on ESG #1 by pressing Pulse, Pulse so that Off is selected. The displayed spectrum does not change. Making Time-Gated Measurements Step 7.
Making Time-Gated Measurements Gated FFT Measurement Gated FFT Measurement This procedure utilizes gated FFT to gate the FM signal. For concept and theory information about gated FFT see “How Time Gating Works” on page 149. Step 1. Set the analyzer to the Spectrum Analyzer mode: Press Mode, Spectrum Analyzer, Mode Preset. Step 2. Set the analyzer center frequency, span and reference level: Making Time-Gated Measurements Press FREQ Channel, Center Freq, 40, MHz. Press SPAN X Scale, Span, 500, kHz.
Making Time-Gated Measurements Gated FFT Measurement With the above analyzer settings, the RBW should be 4.7 kHz. Note that the measurement speed is faster than the gated LO example. Typically gated FFT is faster than gated LO for spans less than 10 MHz. Vary the RBW settings and note the signal changes shape as the RBW transitions from 1 kHz to 300 Hz. Making Time-Gated Measurements NOTE If the trigger event needs to be delayed use the Trig Delay function under the Trigger menu.
10 Measuring Digital Communications Signals The signal analyzer makes power measurements on digital communication signals fast and repeatable by providing a comprehensive suite of power-based one-button automated measurements with pre-set standards-based format setups. The automated measurements also include pass/fail functionality that allow the user to quickly check if the signal passed the measurement.
Measuring Digital Communications Signals Channel Power Measurements Channel Power Measurements This section explains how to make a channel power measurement on a W-CDMA (3GPP) mobile station. (A signal generator is used to simulate a base station.) This test measures the total RF power present in the channel. The results are displayed graphically as well as in total power (dB) and power spectral density (dBm/Hz). Measurement Procedure Step 1.
Measuring Digital Communications Signals Channel Power Measurements Step 7. Initiate the channel power measurement: Press Meas, Channel Power. The Channel Power measurement result should look like Figure 10-2 The graph window and the text window showing the absolute power and its mean power spectral density values over 5 MHz are displayed. Figure 10-2 Channel Power Measurement Result Measuring Digital Communications Signals Step 8.
Measuring Digital Communications Signals Occupied Bandwidth Measurements Occupied Bandwidth Measurements This section explains how to make the occupied bandwidth measurement on a W-CDMA (3GPP) mobile station. (A signal generator is used to simulate a base station.) The instrument measures power across the band, and then calculates its 99.0% power bandwidth. Measurement Procedure Step 1.
Measuring Digital Communications Signals Occupied Bandwidth Measurements Figure 10-4 Occupied Bandwidth Measurement Result Troubleshooting Hints Shoulders on either side of the spectrum shape indicate spectral regrowth and intermodulation. Rounding or sloping of the top shape can indicate filter shape problems. Chapter 10 113 Measuring Digital Communications Signals Any distortion, such as harmonics or intermodulation for example, produces undesirable power outside the specified bandwidth.
Measuring Digital Communications Signals Making Adjacent Channel Power (ACP) Measurements Making Adjacent Channel Power (ACP) Measurements The adjacent channel power (ACP) measurement is also referred to as the adjacent channel power ratio (ACPR) and adjacent channel leakage ratio (ACLR). We use the term ACP to refer to this measurement. ACP measures the total power (rms voltage) in the specified channel and up to six pairs of offset frequencies.
Measuring Digital Communications Signals Making Adjacent Channel Power (ACP) Measurements Step 7. Select the adjacent channel power one-button measurement from the measure menu and then optimize the attenuation setting suitable for the ACP measurement (see Figure 10-6): Press Meas, ACP. Press Meas Setup, AMPTD, Attenuation, Adjust Atten for Min Clip.
Measuring Digital Communications Signals Making Adjacent Channel Power (ACP) Measurements Step 9. View the results using the full screen: Press Full Screen. NOTE Press the Full Screen key again to exit the full screen display without changing any parameter values. Step 10. Define a new third pair of offset frequencies: Press Meas Setup, Offset/Limits, Offset, C, Offset Freq (On), 15, MHz. This third pair of offset frequencies is offset by 15.
Measuring Digital Communications Signals Making Adjacent Channel Power (ACP) Measurements Figure 10-8 Setting Offset Limits NOTE You may increase the repeatability by increasing the sweep time.
Measuring Digital Communications Signals Making Statistical Power Measurements (CCDF) Making Statistical Power Measurements (CCDF) Complementary Cumulative Distribution Function (CCDF) curves characterize a signal by providing information about how much time the signal spends at or above a given power level. The CCDF measurement shows the percentage of time a signal spends at a particular power level. Percentage is on the vertical axis and power (in dB) is on the horizontal axis.
Measuring Digital Communications Signals Making Statistical Power Measurements (CCDF) Step 7. Select the CCDF one-button measurement from the measure menu and then optimize the attenuation level and attenuation settings suitable for the CCDF measurement: Press Meas, Power Stat CCDF. Press AMPTD, Attenuation, Adjust Atten for Min Clip. Figure 10-10 Power Statistics CCDF Measurement on a W-CDMA Signal Press Trace/Detector, Store Ref Trace.
Measuring Digital Communications Signals Making Statistical Power Measurements (CCDF) Figure 10-11 Storing and Displaying a Power Stat CCDF Measurement Measuring Digital Communications Signals NOTE If you choose a measurement bandwidth setting that the analyzer cannot display, it automatically sets itself to the closest available bandwidth setting. Step 11. Change the number of measured points from 10,000,000 (10.0Mpt) to 1,000 (1kpt): Press Meas Setup, Counts, 1, kpt.
Measuring Digital Communications Signals Making Statistical Power Measurements (CCDF) Figure 10-12 Reducing the Measurement Points to 1 kpt Step 12. Change the scaling of the X-axis to 1 dB per division to optimize your particular measurement: Measuring Digital Communications Signals Press SPAN X Scale, Scale/Div, 1, dB. Refer to Figure 10-13.
Measuring Digital Communications Signals Making Burst Power Measurements Making Burst Power Measurements The following example demonstrates how to make a Burst Power measurement on a Bluetooth™ signal broadcasting at 2.402 GHz. (A signal generator is used to simulate a Bluetooth™ signal.) Step 1. Setup the signal sources as follows: Setup a Bluetooth™ signal transmitting DH1 packets. Set the source frequency to 2.402 GHz. Set the source amplitudes to −10 dBm. Set Burst on. Step 2.
Measuring Digital Communications Signals Making Burst Power Measurements Step 8. View the results of the burst power measurement using the full screen (See Figure 10-15): Press Full Screen. Figure 10-15 Full Screen Display of Burst Power Measurement Results Measuring Digital Communications Signals NOTE Press the Full Screen key again to exit the full screen display without changing any parameter values. Refer to Figure 10-16.
Measuring Digital Communications Signals Making Burst Power Measurements Step 9. Select one of the following three trigger methods to capture the bursted signal: Periodic Timer Triggering, Video, or RF Burst Wideband Triggering (RF Burst is recommended, if available): Press Trigger, RF Burst. For more information on trigger selections see “Trigger Concepts” on page 148.
Measuring Digital Communications Signals Making Burst Power Measurements Figure 10-18 Bar Graph Results with Measured Burst Width Set If you set the burst width manually to be wider than the screen's display, the vertical white lines move off the edges of the screen. This could give misleading results as only the data on the screen can be measured. NOTE The Bluetooth™ standard states that power measurements should be taken over at least 20% to 80% of the duration of the burst. Step 12.
Measuring Digital Communications Signals Making Burst Power Measurements Figure 10-19 Displaying Multiple Bursts Measuring Digital Communications Signals NOTE Although the burst power measurement still runs correctly when several bursts are displayed simultaneously, the timing accuracy of the measurement is degraded. For the best results, including the best trade-off between measurement variations and averaging time, it is recommended that the measurement be performed on a single burst.
Measuring Digital Communications Signals Spurious Emissions Measurements Spurious Emissions Measurements The following example demonstrates how to make a Spurious Emissions measurement on a multitone signal used to simulate a spurious emission in a measured spectrum. Measurement Procedure Step 1. Setup the signal sources as follows: Setup a multitone signal with 8 tones with a 2.0 MHz frequency spacing. Set the source frequency to 1.950 GHz. Set the source amplitudes to −50 dBm. Step 2.
Measuring Digital Communications Signals Spurious Emissions Measurements Step 7. You may focus the display on a specific spurious emissions signal: Press Meas Setup, Spur, 1, Enter (or enter the number of the spur of interest). Press Meas Type to highlight Examine. The Spurious Emission result should look like Figure 10-21. The graph window and a text window are displayed. The text window shows the list of detected spurs.
Measuring Digital Communications Signals Spectrum Emission Mask Measurements Spectrum Emission Mask Measurements This section explains how to make the Spectrum Emission Mask measurement on a W-CDMA (3GPP) mobile station. (A signal generator is used to simulate a mobile station.) SEM compares the total power level within the defined carrier bandwidth and the given offset channels on both sides of the carrier frequency, to levels allowed by the standard.
Measuring Digital Communications Signals Spectrum Emission Mask Measurements Step 7. Initiate the spectrum emission mask measurement. Press Meas, More, Spectrum Emission Mask. Measuring Digital Communications Signals Figure 10-23 Spectrum Emission Mask Measurement Result - (Default) View The Spectrum Emission Mask measurement result should look like Figure 10-23.
11 Demodulating AM Signals Demodulating AM Signals 131
Demodulating AM Signals Measuring the Modulation Rate of an AM Signal Measuring the Modulation Rate of an AM Signal This section demonstrates how to determine parameters of an AM signal, such as modulation rate and modulation index (depth) by using frequency and time domain measurements (see the concepts chapter “AM and FM Demodulation Concepts” on page 168 for more information).
Demodulating AM Signals Measuring the Modulation Rate of an AM Signal Step 8. Use the video trigger to stabilize the trace: Press Trigger, Video. Since the modulation is a steady tone, you can use video trigger to trigger the analyzer sweep on the waveform and stabilize the trace, much like an oscilloscope. See Figure 11-1. NOTE If the trigger level is set too high or too low when video trigger mode is activated, the sweep stops.
Demodulating AM Signals Measuring the Modulation Rate of an AM Signal Figure 11-2 Measuring Time Parameters with Inverse Time Readout Demodulating AM Signals Another way to calculate the modulation rate would be to view the signal in the frequency domain and measure the delta frequency between the peak of the carrier and the first sideband.
Demodulating AM Signals Measuring the Modulation Index of an AM Signal Measuring the Modulation Index of an AM Signal This procedure demonstrates how to use the signal analyzer as a fixed-tuned (time-domain) receiver to measure the modulation index as a percent AM value of an AM signal. Step 1. Connect an Agilent ESG RF signal source to the analyzer RF INPUT. Setup the signal sources as follows: Set the source frequency to 300 MHz. Set the source amplitudes to −10 dBm. Set the AM depth to 80%.
Demodulating AM Signals Measuring the Modulation Index of an AM Signal Step 10. Increase the sweep time and decrease the VBW so that the waveform is displayed as a flat horizontal signal: Press Sweep/Control, Sweep Time, 5, s. Press BW, Video BW, 30, Hz. Step 11. Center the flat waveform at the mid-point of the y-axis and then widen the VBW and decrease the sweep time to display the waveform as a sine wave: Press AMPTD Y Scale, Ref Level, (rotate front-panel knob). Press BW, Video BW, 100, kHz.
IQ Analyzer Measurement 12 IQ Analyzer Measurement 137
IQ Analyzer Measurement IQ Analyzer Measurement Capturing Wideband Signals for Further Analysis Capturing Wideband Signals for Further Analysis This section demonstrates how to capture complex time domain data from wide bandwidth RF signals. This mode preserves the instantaneous vector relationships of time, frequency, phase and amplitude contained within the selected digitizer span or analysis BW, at the analyzer's center frequency, for output as IQ data.
Complex Spectrum Measurement This section explains how to make a waveform (time domain) measurement on a W-CDMA signal. (A signal generator is used to simulate a base station.) The measurement of I and Q modulated waveforms in the time domain disclose the voltages which comprise the complex modulated waveform of a digital signal. Step 1. Setup the signal source as follows: Set the mode to W-CDMA 3GPP with 4 carriers. Set the frequency of the signal source to 1.0 GHz. Set the source amplitude to -10 dBm.
IQ Analyzer Measurement IQ Analyzer Measurement Complex Spectrum Measurement Figure 12-2 Spectrum and I/Q Waveform (Span 10 MHz) Figure 12-3 Spectrum and I/Q Waveform (Span 25 MHz) NOTE A display with both an FFT derived spectrum in the upper window and an IQ Waveform in the lower window will appear when you activate a Complex Spectrum measurement. The active window is outlined in green. Changes to Frequency, Span or Amplitude will affect only the active window.
IQ Waveform (Time Domain) Measurement This section explains how to make a Waveform (time domain) measurement on a W-CDMA signal. (A signal generator is used to simulate a base station.) The measurement of I and Q modulated waveforms in the time domain disclose the voltages which comprise the complex modulated waveform of a digital signal. Step 1. Setup the signal source as follows: Set the mode to W-CDMA 3GPP with 4 carriers. Set the frequency of the signal source to 1.0 GHz.
IQ Analyzer Measurement IQ Analyzer Measurement IQ Waveform (Time Domain) Measurement Step 9. Set the analysis bandwidth: Press BW, Info BW, 10, MHz (25 MHz if option B25 installed) This view provides a waveform display of power versus time of the RF signal in the upper window with metrics for mean and peak-to-mean in the lower window. Refer to Figure 12-5 or Figure 12-6.
Step 10. View the IQ Waveform: Press View/Display, IQ Waveform Step 11. Set the time scale: Press Span X Scale, Scale/Div, 100, ns Step 12. Enable markers: Press Marker, Properties, Marker Trace, IQ Waveform, 500, ns This view provides a display of voltage versus time for the I and Q waveforms. Markers enable measurement of the individual values of I and Q. Refer to Figure 12-7.
IQ Analyzer Measurement IQ Analyzer Measurement IQ Waveform (Time Domain) Measurement 144 Chapter 12
13 Concepts Concepts 145
Concepts Resolving Closely Spaced Signals Resolving Closely Spaced Signals Resolving Signals of Equal Amplitude Concepts Two equal-amplitude input signals that are close in frequency can appear as a single signal trace on the analyzer display. Responding to a single-frequency signal, a swept-tuned analyzer traces out the shape of the selected internal IF (intermediate frequency) filter (typically referred to as the resolution bandwidth or RBW filter).
Concepts Resolving Closely Spaced Signals The digital filters in the analyzer have filter widths about one-third as wide as typical analog RBW filters. This enables you to resolve close signals with a wider RBW (for a faster sweep time).
Concepts Trigger Concepts Trigger Concepts NOTE The trigger functions let you select the trigger settings for a sweep or measurement. When using a trigger source other than Free Run, the analyzer will begin a sweep only with the selected trigger conditions are met. A trigger event is defined as the point at which your trigger source signal meets the specified trigger level and polarity requirements (if any). In FFT measurements, the trigger controls when the data is acquired for FFT conversion.
Concepts Trigger Concepts 6. Periodic Timer Triggering This feature selects the internal periodic timer signal as the trigger. Trigger occurrences are set by the Periodic Timer parameter, which is modified by the Sync Source and Offset. Figure 13-2 shows the action of the periodic timer trigger. A second way to use this feature would be to use Sync Source temporarily, instead of Offset.
Concepts Trigger Concepts a. Period Sets the period of the internal periodic timer clock. For digital communications signals, this is usually set to the frame period of your current input signal. In the case that sync source is not set to OFF, and the external sync source rate is changed for some reason, the periodic timer is synchronized at the every external synchronization pulse by resetting the internal state of the timer circuit. Press Trigger, Periodic Timer. b.
Concepts Time Gating Concepts Time Gating Concepts Introduction: Using Time Gating on a Simplified Digital Radio Signal This section shows you the concepts of using time gating on a simplified digital radio signal. The section on Making Time-Gated Measurements demonstrates time gating examples. Figure 13-3 shows a signal with two radios (radio 1 and radio 2) that are time-sharing a single frequency channel. Radio 1 transmits for 1 ms, then radio 2 transmits for 1 ms.
Concepts Time Gating Concepts Concepts Time gating allows you to see the separate spectrum of radio 1 or radio 2 to determine the source of the spurious signal, as shown in Figure 13-5. Figure 13-5 Time-Gated Spectrum of Radio 1 Figure 13-6 Time-Gated Spectrum of Radio 2 Time gating lets you define a time window (or time gate) of when a measurement is performed. This lets you specify the part of a signal that you want to measure, and exclude or mask other signals that might interfere.
Concepts Time Gating Concepts How Time Gating Works Time gating is achieved by the signal analyzer selectively interrupting the path of the detected signal, with a gate, as shown in Figure 13-8 and Figure 13-9 The gate determines the times at which it captures measurement data (when the gate is turned “on,” under the Gate menu, the signal is being passed, otherwise when the gate is “off,” the signal is being blocked).
Concepts Time Gating Concepts Gated Video Concepts Gated video may be thought of as a simple gate switch, which connects the signal to the input of the signal analyzer. When the gate is “on” (under the Gate menu) the gate is passing a signal. When the gate is “off,” the gate is blocking the signal. Whenever the gate is passing a signal, the analyzer sees the signal.
Concepts Time Gating Concepts Figure 13-9 Gated LO Signal Analyzer Block Diagram Concepts Gated FFT Concepts Gated FFT (Fast-Fourier Transform) is an FFT measurement which begins when the trigger conditions are satisfied. The process of making a spectrum measurement with FFTs is inherently a “gated” process, in that the spectrum is computed from a time record of short duration, much like a gate signal in swept-gated analysis.
Concepts Time Gating Concepts Concepts Figure 13-10 Gated FFT Timing Diagram Time Gating Basics (Gated LO and Gated Video) The gate passes or blocks a signal with the following conditions: • Trigger condition - Usually an external transistor-transistor logic (TTL) periodic signal for edge triggering and a high/low TTL signal for level triggering. • Gate Delay - The time after the trigger condition is met when the gate begins to pass a signal.
Concepts Time Gating Concepts The timing interactions between the three signals are best understood if you observe them in the time domain (see Figure 13-11). The main goal is to measure the spectrum of signal 1 and determine if it has any low-level modulation or spurious signals. Because the pulse trains of signal 1 and signal 2 have almost the same carrier frequency, their spectra overlap. Signal 2 will dominate in the frequency domain due to its greater amplitude.
Concepts Time Gating Concepts Figure 13-13 Using Time Gating to View Signal 1 (spectrum view) Concepts Moving the gate so that it is positioned over the middle of signal 2 produces a result as shown in Figure 13-15. Here, you see only the spectrum within the pulses of signal 2; signal 1 is excluded.
Concepts Time Gating Concepts Step 1. Determine how your signal under test appears in the time domain and how it is synchronized to the trigger signal. You need to do this to position the time gate by setting the delay relative to the trigger signal. To set the delay, you need to know the timing relationship between the trigger and the signal under test.
Concepts Time Gating Concepts Step 2. Set the signal analyzer sweep time: Gated LO: Sweep time does not affect the results of gated LO unless the sweep time is set too fast. In the event the sweep time is set too fast, Meas Uncal appears on the screen and the sweep time will need to be increased. Concepts Gated Video: Sweep time does affect the results from gated video. The sweep time must be set accordingly for correct time gating results.
Concepts Time Gating Concepts There is flexibility in positioning the gate, but some positions offer a wider choice of resolution bandwidths. A good rule of thumb is to position the gate from 20 % to 90 % of the burst width. Doing so provides a reasonable compromise between setup time and gate length. Figure 13-18 Best Position for Gate As an example, if you want to use a 1 kHz resolution bandwidth for measurements, you will need to allow a setup time of at least 3.84 ms.
Concepts Time Gating Concepts Step 5. The resolution bandwidth will need to be adjusted for gated LO and gated video. The video bandwidth will only need to be adjusted for gated video. Resolution Bandwidth: The resolution bandwidth you can choose is determined by the gate position, so you can trade off longer setup times for narrower resolution bandwidths. This trade-off is due to the time required for the resolution-bandwidth filters to fully charge before the gate comes on.
Concepts Time Gating Concepts signal parameters you chose in Step 1. If necessary, adjust span, but do not decrease resolution bandwidth, video bandwidth, or sweep time. “Quick Rules” for Making Time-Gated Measurements This section summarizes the rules described in the previous sections.
Concepts Time Gating Concepts Most control settings are determined by two key parameters of the signal under test: the pulse repetition interval (PRI) and the pulse width (τ ). If you know these parameters, you can begin by picking some standard settings. Table 2 summarizes the parameters for a signal whose trigger event occurs at the same time as the beginning of the pulse (in other words, SD is 0). If your signal has a non-zero delay, just add it to the recommended gate delay.
Concepts Time Gating Concepts Table 3 If You Have a Problem with the Time-Gated Measurement Symptom Possible Causes Suggested Solution Erratic analyzer trace with dropouts that are not removed by increasing analyzer sweep time; oscilloscope view of gate output signal jumps erratically in time domain. Gate delay may be greater than trigger repetition interval. Reduce gate delay until it is less than trigger interval. Gate does not trigger. 1) Gate trigger voltage may be wrong.
Concepts Time Gating Concepts Using the Edge Mode or Level Mode for Triggering Depending on the trigger signal that you are working with, you can trigger the gate in one of two separate modes: edge or level. This gate-trigger function is separate from the normal external trigger capability of the signal analyzer, which initiates a sweep of a measurement trace based on an external signal. Edge Mode Edge mode lets you position the gate relative to either the rising or falling edge of a trigger signal.
Concepts Time Gating Concepts Noise Measurements Using Time Gating Time gating can be used to measure many types of signals. Noise and noise-like signals are often a special case in spectrum analysis. With the history of gated measurements, these signals are especially noteworthy. The average detector is the best detector to use for measuring noise-like signals because it uses all the available noise power all the time in its measurement.
Concepts AM and FM Demodulation Concepts AM and FM Demodulation Concepts Demodulating an AM Signal Using the Analyzer as a Fixed Tuned Receiver (Time-Domain) The Zero Span mode can be used to recover amplitude modulation on a carrier signal. The following functions establish a clear display of the waveform: • Concepts • • • Triggering stabilizes the waveform trace by triggering on the modulation envelope.
Concepts IQ Analysis Concepts IQ Analysis Concepts Purpose IQ Analysis (Basic) mode is used to capture complex time domain data from wide bandwidth RF signals. This mode preserves the instantaneous vector relationships of time, frequency, phase and amplitude contained within the selected digitizer span or analysis BW, at the analyzer's center frequency, for output as IQ data. This IQ data can then be utilized internally or output over LAN, USB or GPIB for use with external analysis tools.
Concepts IQ Analysis Concepts IQ Waveform Measurement Purpose The IQ Waveform measurement provides a time domain view of the RF signal envelope with power versus time or an IQ waveform with the I and Q signal waveforms in parameters of voltage versus time. The RF Envelope view provides the power verses time display, and the I/Q Waveform view provides the voltage versus time display.
Concepts Spurious Emissions Measurement Concepts Spurious Emissions Measurement Concepts Purpose Spurious signals can be caused by different combinations of signals in the transmitter. The spurious emissions from the transmitter should be minimized to guarantee minimum interference with other frequency channels in the system. Harmonics are distortion products caused by nonlinear behavior in the transmitter. They are integer multiples of the transmitted signal carrier frequency.
Concepts Spectrum Emission Mask Measurement Concepts Spectrum Emission Mask Measurement Concepts Purpose Concepts The Spectrum Emission Mask measurement includes the in-band and out-of-band spurious emissions. As it applies to W-CDMA (3GPP), this is the power contained in a specified frequency bandwidth at certain offsets relative to the total carrier power. It may also be expressed as a ratio of power spectral densities between the carrier and the specified offset frequency band.
Concepts Occupied Bandwidth Measurement Concepts Occupied Bandwidth Measurement Concepts Purpose Occupied bandwidth measures the bandwidth containing 99.0 of the total transmission power. The spectrum shape of a signal can give useful qualitative insight into transmitter operation. Any distortion to the spectrum shape can indicate problems in transmitter performance. Measurement Method The total absolute power within the measurement frequency span is integrated for its 100% of power.
Concepts Concepts Occupied Bandwidth Measurement Concepts 174 Chapter 13
14 Programming Examples • The programming examples were written for use on an IBM compatible PC. • The programming examples use C, Visual Basic, or VEE programming languages. • The programming examples use VISA interfaces (GPIB, LAN, or USB). • Some of the examples use the IVI-COM drivers. Interchangeable Virtual Instruments COM (IVI-COM) drivers: Develop system automation software easily and quickly.
Programming Examples X-Series Spectrum Analyzer Mode Programing Examples X-Series Spectrum Analyzer Mode Programing Examples The following examples work with Spectrum Analyzer mode. These examples use one of the following programming languages: Visual Basic® 6, Visual Basic.NET®, MS Excel®, C++, ANSI C, C#.NET, and Agilent VEE Pro.
Programming Examples X-Series Spectrum Analyzer Mode Programing Examples Programming using C++, ANSI C and C#.NET: • Serial Poll for Sweep Complete using C++ This example demonstrates how to: 1. Perform an instrument sweep. 2. Poll the instrument to determine when the operation is complete. 3. Perform an instrument sweep. File name: _Sweep.c • Service Request Method (SRQ) determines when a measurement is done by waiting for SRQ and reading Status Register using C++. This example demonstrates how: 1.
Programming Examples X-Series Spectrum Analyzer Mode Programing Examples • Phase Noise using C++ This example demonstrates how to: 1. Remove instrument noise from the phase noise 2. Calculate the power difference between 2 traces File name: _phasenoise.c Programming using Agilent VEE Pro: • Transfer Screen Images from my Spectrum Analyzer using Agilent VEE Pro This example program stores the current screen image on the instrument flash memory as “D:\scr.png”.
Programming Examples 89601X VXA Signal Analyzer Programming Examples 89601X VXA Signal Analyzer Programming Examples The following examples work with 89601X VXA Signal Analyzer Mode. These examples use one of the following programming languages: Visual Basic® 6, Visual Studio 2003 .NET®, and Agilent VEE Pro. These examples are available in either the “progexamples” directory on the Agilent Technologies 89601X VXA documentation CD-ROM or the “progexamples” directory in the analyzer.
Programming Examples 89601X VXA Signal Analyzer Programming Examples Programming using Agilent VEE Pro: • Setting up a VSA Measurement on your 89601X VXA using VEE. This example program: — Sets up the VSA Mode. — Sets the Vector Measurement. — Configures the Vector Measurement. — Starts the Vector Measurement. — Reads the trace data in Real 32, Real 64 and ASCII data format File name: VXA-MeasDemo.vee • Setting up a Digital Demod Measurement on your 89601X VXA VEE.
Programming Examples 89601X VXA Signal Analyzer Programming Examples • Setting up a Digital Demod Measurement on your 89601X VXA using Visual Basic 6. This example program: — Sets up the VSA Mode. — Sets the Digital Demod Measurement. — Configures the Digital Demod Measurement. — Starts the Digital Measurement. — Reads the trace data, EVM, and demodulated bits. File name: VXA-DigDemodDemo.
Programming Examples 89601X VXA Signal Analyzer Programming Examples 182 Chapter 14
Index Numerics 10 MHz reference, turning on 10 50 ohm load 13 50 ohm/75 ohm minimum loss pad 13 75 ohm matching transformer 13 A AC probe 13 Accessories 13 accessories 50 ohm load 13 50 ohm/75 ohm minimum loss pad 13 75 ohm matching transformer 13 AC probe 13 broadband preamplifiers 14 GPIB cable 14 power splitters 14 RF limiters 14 transient limiters 14 ACP key MEAS key 115 Meas key 115 ACP measurement 114 active function 20 Adjacent Channel Power measurement 114 AM demodulation time-domain demodulation,
Index H harmonic distortion measuring low-level signals 30 hold, maximum 63 I identifying distortion products 68 initial setting for time gating 164 input attenuation, reducing 46 intermodulation distortion, third order 71 interval power marker function 41 iq waveform measurement 170 K key overview 20 keypad, using 9 keys 18 knob, using 9 Index L limiters RF and transient 14 load, 50 ohm 13 low-level signals harmonics, measuring 30 input attenuation, reducing 46 resolution bandwidth, reducing 49 sweep ti
Index on-screen, comparing 28 resolving, overview 146 separating, overview 146 signals, increasing accuracy 11 signals, viewing 10 softkeys, auto and man mode 9 softkeys, basic types 9 Span Zoom key 63 Spectrum (Frequency Domain) key 169 Spectrum analysis measurement application 109 channel power 83 spectrum emission mask in-band and out-of-band spurious emissions 172 integration bandwidth method 172 measurement method 172 offset or region frequency pairs 172 purpose 172 reference channel integration bandw
Index Index 186
