Tektronix 524A, 540A, 544A, TDS 520A Cursor Measurements of an FFT

Fast Fourier Transforms

Reference

Cursor Measurements of an FFT

Once you have displayed an FFT math waveform, use cursors to measure its

frequency amplitude or phase angle.

1. Be sure MORE is selected in the channel selection buttons and that the

FFT math waveform is selected in the More main menu.

2. Press CURSOR ➞ Mode (main) ➞ Independent (side) ➞ Func-

tion (main) ➞ H Bars (side).

3. Use the general purpose knob to align the selected cursor (solid line) to

the top (or to any amplitude on the waveform you choose).

4. Press SELECT to select the other cursor. Use the general purpose knob

to align the selected cursor to the bottom (or to any amplitude on the

waveform you choose).

5. Read the amplitude between the two cursors from the : readout. Read

the amplitude of the selected cursor relative to either 1 VRMS (0 dB),

ground (0 volts), or the zero phase level (0 degrees or 0 radians) from the

@: readout. (The waveform reference indicator at the left side of the

graticule indicates the level where phase is zero for phase FFTs.)

Figure 3-23 shows the cursor measurement of a frequency magnitude on

an FFT. The @: readout reads 0 dB because it is aligned with the 1 VRMS

level. The : readout reads 24.4 dB indicating the magnitude of the

frequency it is measuring is –24.4 dB relative to 1 VRMS. The source

waveform is turned off in the display.

The cursor units will be in dB or volts for FFTs measuring magnitude and

in degrees or radians for those FFTs measuring phase. The cursor unit

depends on the selection made for Set FFT Vert Scale to (side). See

step 7 on page 3-40 for more information.

6. Press V Bars (side). Use the general purpose knob to align one of the

two vertical cursors to a point of interest along the horizontal axis of the

waveform.

7. Press SELECT to select the alternate cursor.

8. Align the selected cursor to another point of interest on the math wave-

form.

9. Read the frequency difference between the cursors from the : readout.

Read the frequency of the selected cursor relative to the zero frequency

point from the @: readout.

The cursor units will always be in Hz, regardless of the setting in the

Time Units side menu. The first point of the FFT record is the zero

frequency point for the @: readout.

Contents

Main Page WARRANTY German Postal Information Certificate of the Manufacturer/Importer Bescheinigung des Herstellers/Importeurs EC Declaration of Conformity Page Welcome Related Manuals Getting Started Conventions Reference T able of Contents Getting Started Operating Basics Reference Appendices Glossary Index Safety Symbols and Terms CAUTION DANGER Specific Precautions Page Product Description Page Start Up Signal Path Compensation Signal Path Compensation (SPC) Signal Path Compensation Installation Front Cover Removal Power On Page Page Example 1: Displaying a Waveform main menus Resetting the Digitizing Oscilloscope side menus Display Elements trigger level bar trigger position indicator channel readout time base readout Adjusting the Waveform Display Using Autoset Page Page Example 2: Multiple Waveforms Adding a Waveform Page Changing Controls to Another Channel Removing a Waveform Example 3: Automated Measurements Displaying Automated Page Page Coarse Knobs The Numeric Keypad Displaying a Snapshot of Automated Page Example 4: Saving Setups Saving a Setup factory. Recalling a Setup Page Overview Page At a Glance At a Glance Front Panel Map Left Side Operating Basics Front Panel Map Right Side Rear Panel Map TDS 620A, 640A, & 644A User Manual Display Map Operating Basics To Operate a Menu TDS 620A, 640A, & 644A User Manual To Operate a Pop-Up Menu Menu Map Press these but- tons: To bring up these menus: Page Press these buttons: To bring up these menus: Page Triggering before, Trigger Sources slope level Types Trigger Modes Holdoff Coupling trigger position before after Trigger Position Slope and Level Delayed Trigger Acquisition Sampling and Digitizing Record Length Sampling Interleaving interpolation interleaving Equivalent-Time Sampling random equivalent-time sampling Selecting Sampling Mode Sample Peak Detect Hi Res Envelope Average Acquisition Modes, Bandwidth Acquisition Modes Bandwidth Coupling Page Scaling and Positioning Waveforms Offset Vertical System Horizontal System Aliasing aliasing Delayed Time Base FastFrame Autoset Zoom Autoset Page Measurements Sources Automated Measurements area amplitude Cursor Measurements Graticule Measurements Page Overview Welcome Conventions Page Acquisition Modes Description of Modes Sample Peak Detect Hi Res Envelope Average Sample Mode Peak Detect Mode Figure 3-1: How the Acquisition Modes Work Hi Res Mode Si = Sampling Interval for TDS 500A = Resolution Enhancement (bits) = ns t = Sample Interval ns Nd = Number of points per decimation interval Acquisition Readout Acquisition Mode Repetitive Signal Stop After Page Page Autoset Autoset Defaults Page Color (TDS 524A & TDS 644A) Display Choose Palette Change Palette Colors Set Math Waveform Color Set Reference Waveform Color Select Options Restore Colors Cursor Measurements Cursor Readouts tracking independent Function Mode Time Units Amplitude Units TDS Family Option 05 Video Trigger Interface, , Coarse Knobs Delayed Triggering delayed runs after main Delayed triggerable after main Delayed runs Delayed Runs After Main Delayed Triggering Reference Delayed Triggerable By Events Delayed Triggerable By Time Figure 3-14: How the Delayed Triggers Work Delayed Runs After Main Delayed Triggerable By Events/Time Delayed Triggerable Display Modes may Page Page Display Modes Color Display Style Intensity The Intensified setting for Timebase in the horizontal menu causes a zone on the waveform to be Display Readout Date/Time Stamping Your Hardcopy Filter Type Graticule Type Format Page Page Edge Triggering edge trigger Source Edge Trigger Coupling Slope Holdoff, Variable, Main Trigger Performance Verification Manual Triggering Specifications, Typical Characteristics Fast Fourier Transforms Offset, Position, and Scale, Considerations for Phase Displays, Selecting the Window, Adjust Phase Suppression, Cursor Measurements of an FFT Automated Measurements of an FFT Considerations for Using FFTs The FFT Frequency Domain Record FFTs May Not Use All of the Waveform Record FFTs Transform Time Records to Frequency Records FFT Frequency Range and Resolution Page Record Length Acquisition Mode Zoom and Interpolation Undersampling (Aliasing) Considerations for Phase Displays Establish a Zero Phase Reference Point . source FFT Windows Windowing Process Selecting a Window Displaying an FFT, Page Window Characteristics Page File System (Optional on TDS 620A & TDS 640A) Delete Rename Copy Print Create Directory Confirm Delete Overwrite Lock Format Hardcopy Hardcopy Formats Connection Strategies Setting Communication Parameters Setting Hardcopy Parameters Printing the Hardcopy while after last Date/Time Stamping Your Hardcopy Connection Strategies Printing Directly to a Hardcopy Device Using a Controller Page Page Help Horizontal Control Horizontal Knobs Record View Time Base readout Main and Delayed Time Base Horizontal Readouts Horizontal Menu Trigger Position Record Length and Fit To Screen Horizontal Scale Horizontal Position FastFrame FastFrame Interactions Scaling and Positioning Waveforms, Delayed Triggering Limit T esting Create Limit Test Template Page To view the waveform data as well as the template envelope, it might be useful to select the display style (see on page 3-28). Limit Test Sources Limit Test Setup Hardcopy The button labeled and specify one of the other choices in the Single and Multiple Waveforms Multiple Waveform Comparisons same acquisition Acquisition Modes, Acquisition, during the Logic Triggering pattern at the time state Pattern Logic Trigger Definitions all not all none Operations Common to Pattern and State Trigger When Set Thresholds Pattern Operations Define Inputs H Define Logic Define a Time Qualified Pattern Trigger at the point the logic condition became false. State Operations Define Inputs H Page Measurement System auto- matic measurements Definitions Snapshot of Measurements Cursor Measurements min/max histogram Page Selecting a Measurement Measurement Display low signal amplitude low resolution Removing Measurements Gated Measurements gated region not High-Low Setup Reference Levels Delay Measurement Delay Edges Creating the Delay Measurement once Snapshot of The snapshot display tells you the channel that the snapshot is being made on. Considerations When Taking Snapshots Tutorial Example 3: Automated Measurements Measurements Appendix B: Algorithms Probe Accessories C Ground Lead Inductance Retractable Hook Tip Standard Probe Probe Accessories Figure 3-53: Probe Accessories TDS 520A, 524A, 540A, & 544A User Manual Marker Rings Long Ground Leads Low-Inductance Ground Lead Probe-Tip-to-Circuit Board Adapters SMT KlipChip Optional Probe Probe-Tip-to-Chassis Adapter Compact-to-Miniature Probe Tip Adapter IC Protector Tip Dual-Lead Adapter Probe Cal Probe Cal vs. Probe Type Signal Path Compensation, Probe Offset Compensation Gain Offset Probe Gain Compensation, Offset Pass Prerequisites Changing Probes After a Probe Cal Re-use Probe Calibration data? Initialized Re-use Probe Calibration Data Initialized. Page Page Probe Compensation Probe Accessories Probe Selection Probe Selection General purpose (high input resistance) Low impedance (Z ) High voltage General Purpose (High Input Resistance) Probes Passive Voltage Probes Low Impedance (ZO) Probes High Voltage Probes High Speed Active Probes Differential Probes Fixtured Active Probes Active Voltage Probes Current Probes Optical Probes Time-to-Voltage Converter Probes by Type Probes by Application Pulse Triggering glitch width runt Page Source Operations Common to Glitch, Runt, and Width Glitch Operations Polarity & Width Glitch (Accept or Reject) Runt Operation Polarity Thresholds recrosses range Polarity Trig When Width Operation Remote Communication GPIB Protocol GPIB Interface Requirements Cables Connector GPIB Parameters mode Port Selection Page Saving and Recalling Setups Recalling a Setup .set all want Running File Utilities Saving and Recalling Waveforms active empty Page Autosave (TDS 640A and 644A only) Running File Utilities Selecting Channels File System Selecting Channels selected channel Ref Math channel selection Removing Waveforms From the Display Saving and Recalling Waveforms, Waveform Math, Signal Path Compensation Page Status Banner Triggering Operat- ing Basics For More Information . MAIN LEVEL Knob To Set to 50% Force Trigger Single Trigger Trigger Status Lights Trigger Display Readout Trigger Position and Level Indicators Trigger Menu Page Vertical Control Vertical readout Vertical Knobs Vertical Readouts Vertical Menu Coupling Bandwidth Fine Scale Scaling and Positioning Waveforms, Position Offset Waveform Differentiation wave- form differentiation Where: X is the source waveform Y is the derivative math waveform T is the time between samples Automated Measurements of a Derivative Waveform Cursor Measurement of a Derivative Waveform Considerations Zoom Automated Measurements of a Derivative Waveform Zoom Zoom Waveform Integration Cursor Measurements of an Integral Waveform Page long Considerations Automated Measurements of a Integral Waveform DC Offset Zoom Waveform Math Math1, Math2, and Math3 Single Wfm Math Dual Wfm Math Zoom sin(x)/x linear Zoom and Interpolation Setting Interpolation Reset Zoom Display Modes For Further Page Appendix A: Options and Accessories Options Options A1A5: International Power Cords Option B1: Service Manual Option 1K: K420 Scope Cart Page Page Probe Accessories Standard Optional Accessories Accessory Probes Probe Accessories Standard Accessories. The next four items below can only be used with the Compact-to- Miniature Probe Tip Adapter. Accessory Software Warranty Information Appendix B: Algorithms Variables High, Low Histogram Min-max HighRef, MidRef, LowRef, Mid2Ref HighRef MidRef LowRef Mid2Ref MCross Calculations MCross1, MCross2, and MCross3 MCross1Polarity StartCycle EndCycle Algorithms TSOFF Amplitude Area Cycle Area Burst Width Cycle Mean Cycle RMS Delay Fall Time Frequency High = Low Maximum Mean Waveform[ ] End Start Negative Width Peak to Peak Period Phase Positive Duty Cycle Positive Overshoot Positive Width Rise Time RMS: Integration Algorithm Measurements on Envelope Waveforms Missing or Out-of-Range Samples Page Appendix C: Packaging for Shipment Page Appendix D: Factory Initialization Settings Settings Page Page Page Page Page Page Glossary Page random equivalent time sampling Page linear sin(x)/x interpolation Page Page LowRef HighRef real-time sampling equivalent-time sampling. digitizing oscilloscope Page Page Index Numbers A B C D E F G H I K L M Page N O P Q R S T U V W X Y Z