SigLab Tutorial
Contents
1. SLm scmeas 17 is invalid since SigLab only supports up to 16 input channels at the time of this writing Step 5 Extract the channel time data and assign it to the MATLAB variable y gt gt y SLm scmeas 1 tdmeas It s that simple Now extract the time domain x vector associated with the time data gt gt x SLm tdxvec If you understand what we have done so far then 90 of the battle 1s over Step 6 Let s go through a complete exercise together To get a quick plot of channel time domain data do this gt gt figure gt gt channel 1 gt gt x SLm tdxvec gt gt y SLm scmeas channel tdmeas gt gt plot x y 2 22 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Post Processing with MATLAB Step 7 To get a quick plot of the channel 1 autospectrum data do this gt gt x SLm fdxvec gt gt y 10 log10 abs SLm scmeas channel aspec gt gt plot x y SLm fdxvec stands for the frequency domain x vector associated with autospectrums For practice make a new measurement using vna and repeat the above steps Verify the plots reflect your new measurement Post Processing from a Setup File vna doesn t have to be open as a pre requisite for post processing If you saved your results to a setup file like default vna then you can extract that data on a machine without installing SigLab software Here s how you do it From the MATLAB Command Win2. TABLE OF CONTENTS SECTION 2 0 SECTION 2 0 GETTING ACQUAINTED WITH SIGLAB sssssssssssccccscecccccccccocccccsssssssssescccccccceeeecoscsssesssssse 1 NS A tia pas etna hb aa aoe va as waa wad ec aa wha wh clas ena AERA aa ea as 1 a A AAA too tice vam once oat vote tet eer am ces atonnce wun coerste de oan nceat ne ee eae 1 EXAMPLE 17 SINGLE CHANNEL MEASUREMENTS 0 sccuesevsvelescwos esseoway ond not ovononenovebsnewed orense 1 PCO MINIS Did o eds 4 ASUR PTE berce to Build A ah chee ea eah steed aie oes EI i ROR 13 EOSTEROCESSIN oasis castle 18 BUS AFECTE OVET VOW ror aE eA A AAA 18 POST PROCESSING WI MATEA B a 19 ABO DARA aces ET T E baleen altered ahs aeRO ets Rasen RG hal Sea ecite tab cake cee 20 POSt PIOCES SIO TOM O SEUD TC cee as esse TO AAA E E PO eves 23 TWo Shanmel MICGSUTCINCI IS A ts 24 POST PROCESSING OUTSIDE OF MATLAB 0 ao best e LS O Les 25 A BRIEF REVIEW OF THE VNA SETUP WINDOW cccccesssssscoeeeccccceeeeecesssssssssannonssssceceeeesesssoosstsnansneesaasaees 26 CHARCO OO iS AAA A AR A A ii 26 MC Setup Jor Multi L hannel USCIS A OE EA 28 ELEVEN ODIAN OE AS na N 29 PROCESS NE DIA O de o de ll eo 30 RALES R Cee eRe ne eee Ree ne eS ee eee Ty ee nee ete Ree eee 3 DSP Technology Inc SigLab User Guide I 09 17 98INSL3 Goals Section 2 0 Getting Acquainted 11 DSP Technology Inc User Guide 09 17 98INSL3 SECTION 2 0 GETTING ACQUAINTED WITH SIGLAB Goals e Learn the basic controls of the dynamic sig
3. cha M M E firs Ch5 El gt lor A o o Click here to set all multiple channels at Click here to enforce the lf arai or 7 Set Ch2 thru Ch8 Ch2 Multi Channel PreView Apply Undo Save As Figure 2 20 The multi channel setup window as called from VNA once Key points to be aware of when using the MC Setup Window 1 No changes take affect until the Apply button is pushed The Apply button is disabled until you change some parameter in the MC Setup window 2 After you push the Apply button you cannot Undo the changes The Undo button only un does changes since the last Apply Channel 1 is always on It cannot be disabled Channels 2 thru N can be turned on at once as indicated in Figure 20 5 The Invert checkbox is a display feature that applies to the Engineering Units fields only If unchecked the engineering units are displayed as EU per Volt If checked they are displayed as Volts per EU Ea 2 28 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted A Brief Review of the VNA Setup Window Frequency Dialog The frequency controls are similar to the so called horizontal controls on stand alone oscilloscopes The frequency controls impact your entire system not just a particular channel or set of channels In other words you can t set the bandwidth on channel to 20 kHz and the bandwidth on channel 2 to something different like 100 Hz All channels must acqui
4. Command Window 8 Where did the data come from In the vna plot window noticed that plots appear You may wonder where that data came from since we haven t actually acquired any data yet This plot is data from a file called default vna a name you Il see listed in the title bar We call default vna a setup file Setup files contain data the screen position and setup parameters as well like voltage ranges sample rate triggering coupling averaging mode etc All of this information is stored in one concise setup file for easy recall Setup files make good memories far less important DSP Technology Inc SigLab User Guide 2 3 09 17 98IHSL3 Example 1 Single Channel Measurements Section 2 0 Getting Acquainted 9 v g Window The vfg is your knob to controlling SigLab s output channels It lets you generate different waveforms for excitation of the device under test in real time using vna Currently you should have a connection from SigLab output channel 1 to Siglab input channel 1 Let s take a closer look at the vfg settings EMA a ee x Currently vfg is set to generate a File Help 1 414 Volts Peak O volts offset 1000 Hz sine wave on channel 1 You BE an should set the All On All Off toggle button to read All On as in Figure 2 3 Frequency Volts Peak If your settings appear as in Figure 2 3 your SigLab 1s now outputting a volte Offeat 1000 Hz 1 414 volts peak sine wave i 10 Excitation Independent In the v
5. To export your data to an ascii text file 1 Select the Export menu pick under File in the vna setup window 2 Select the data type of interest 3 Click SaveAs and indicate the filename Time Series y Transfer Function C k Auto S pectrum nee pecto Soto orre ation Eoss Pone atan Eoherente a Comules EE gt Impulse Response i Fapte HUNE 3 Saves to Text Send to Excel To export your data to Excel 1 Select the Export menu pick under File in the vna setup window 2 Check the data type of interest 3 Click Send to Excel When you do this a text file is automatically created The text file name is the same as the currently opened vna file but with a txt extension How to customize the Excel interface is described in the Common Element of Section Section 4 0 of this User Guide DSP Technology Inc SigLab User Guide 22 09 17 98IHSL3 A Brief Review of the VNA Setup Window Section 2 0 Getting Acquainted A Brief Review of the VNA Setup Window This section gives a quick introduction to all the controls in the vna setup window For an in depth explanation see the vna section of the user manual The vna setup window is divided into 4 control sections or dialogs as they re frequently referred to Channel Dialog For those familiar with using a stand alone oscilloscope channel controls are similar to vertical controls Only one channel s setup is viewable at any give time First
6. and or digital alias filters Use the overload indicators as your ultimate judge for overloaded conditions not the plot e The front panel of the SigLab hardware also monitors and displays overloads This LED turns red if an overload occurs on any input channel 2 6 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Example 1 Single Channel Measurements Ctrl U w Dual Grids Ltrl l Overlay Upper Ctrl U Overlay Lower Chrl L Analysis Windows Ctra Print Ctrl F Default size Chrl 7 Bode Plot Ctrl B Kill Tooltips Cirk 3 Changing Display Mode Change to single display in the vna plot window using the menu selection Display Single You should see one large plot of a sine wave Figure 2 6 Changing the display from time to autospectrum 4 Viewing Spectrum Change the data type from time to autospectrum using the y data type popup in the upper left hand corner of the vna plot window You should see the plot change from the time domain to the frequency domain You should see a O dB spectral peak at 1 kHz vna displays the autospectrum aspec of the acquired data The autospectrum computation is implemented on SigLab s C31 DSP Because we have a pure sine wave we do not see significant harmonics or spurious components in the autospectrum DSP Technology Inc SigLab User Guide 2 7 09 17 98IHSL3 Example 1 Single Channel Measurements Section 2 0 Getting Acquainted Figure 2 7 The S
7. generator menu item in the vna setup window You ll find vfg next to the File and Excitation menus This menu item 2 2 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Example 1 Single Channel Measurements behaves like a pushbutton in the sense that no submenu items appear but instead vfg is invoked directly 7 Importance of a Well Organized Workspace Before we get into pushing buttons and acquiring data the most important thing to do is establish an efficient working space Otherwise you ll spend more time mousing and keyboarding around and less time doing real work Setting the workspace is a highly individual thing but there is one feature that most people can agree upon the more visibility the better See Figure 2 2 for one particular way to organize your workspace Resize the vna plot window and MATLAB window if necessary We suggest you maintain some visibility with the MATLAB workspace even if it s only a few lines for debugging purposes Your screen resolution is the biggest factor limiting what organizational scheme you choose The minimum recommended is 1024x768 we pla ad Spee altre last west dad dd EL joint wr DP 2 CEA Pp BATLAR Corra rd ye Fo PAB Ta get ataertes bye ae of Eh Pelada Belpdeek ar dea Far profe Lean week eee mi eerie co Figure 2 2 One possible workspace organization for easy access to the vna plot window vna setup window vfg window and the MATLAB
8. hair The right boxes indicate the relative position with respect to the marked location f Click on the Mark button again to remove it The Mark button is a toggle button A0 H 100 1000 UU UU 400 5O00 linear Hertz Figure 2 14 The difference between the fundamental and the third harmonic is measured using the Mark and peak finder buttons The third harmonic is 1975 Hz to the right of the fundamental and 8 79 dB smaller 2 16 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Example 1 Single Channel Measurements 9 You must be exhausted now Let s save the work so we don t have to remember all these steps the next time we setup SigLab Select File SaveAs and save to the file excercisel vna The data and the setup information are now contained in one concise file It s not necessary to enter the vna extension It will be applied automatically 10 Congratulations you are done with the first Getting Started exercise Select File Quit in the vna setup window or click on the Windows 95 98 NT X button in the upper right hand corner to close vna and fg DSP Technology Inc SigLab User Guide 2 17 09 17 98IHSL3 Post Processing Section 2 0 Getting Acquainted Post Processing In this section we investigate the different options available for post processing There are two main approaches to processing your measurement data depending on your MATLAB programming level 1 For th
9. i 0 005 0 01 0 015 me 0 025 0 03 0 035 pl ot r epr es ents chann el asf stop 7 1 time data displayed in green The bottom plot represents channel 2 displayed in time blue You should see a flat line on channel 2 because we are not injecting a signal real volts Making Changes On the Fly One of SigLab s primary strengths is the ability to react to your changing demands on the fly You can modify almost every control in the user interface while SigLab is acquiring data Some people say that it feels very analog To get a feel for this real time interaction do the following while it s acquiring data r i Y AA Filters On Record Length 64 512 8192 4 a oom OFF Set bandwidth Channel Label Eu onfi 0d 1 Changing Bandwidth Change the bandwidth from 5 kHz to 10 kHz to 20 kHz via the Frequency Rng dialog in the vna setup window This popup has values from 20 kHz down to 2 Hz for a 20 kHz SigLab Change it back to 5 kHz 2 Changing Full Scale Range Change the full scale voltage level on channel 1 from 5 0 volts to 10 0 volts to 63 volts via the Channel Setup dialog in the vna setup window This popup has values from 10 0 volts down to 20 mv Notice that you saturated the analog front end circuitry of SigLab when you changed to 0 63 volts The waveform DSP Technology Inc SigLab User Guide 22 09 17 98IHSL3 Example 1 Single Channel Measurements Section 2 0 Getting Acquainted
10. of the signal is displayed above the plot in volts rms The RMS level meter updates in real 1 3648 Y rms time as the signal level changes 7 Let s say you d like to know the difference between the fundamental and the third harmonic in the spectrum You could visually ascertain that the third harmonic is at approximately 3000 Hz and is about 10 dB down from the fundamental However here s how to get exact answers DSP Technology Inc SigLab User Guide 2 15 09 17 98IHSL3 Example 1 Single Channel Measurements Section 2 0 Getting Acquainted Left single click anywhere in the plot window Initialize mouse cursor in plot window b Hit the peak finder button You should see the small yellow cross hair jump to the fundamental c Hit the mark button The Mark button hasn t been discussed up to this point The small yellow cross hair should turn into a large red Marker cross hair Now you have established a reference point All subsequent cursored data points will be measured with respect to this x y location Left boxes are absolute positions z aaan 1975 000 Right boxes are relative positions d Hit the peak finder button again You ll see the yellow cross hair jump to the third harmonic and the x y readout will update as in Figure 2 14 e Interpret the x y readout Four boxes appear next to the x y after you cursored the third harmonic The left two boxes indicate the absolute position of the yellow cross
11. we ll look at Channel only To view channel setup information at a glance use the MC Multi Channel Setup menu selection in the vna Setup window Input Offset F Channel Label Figure 2 16 A sample channel setup dialog found in the VNA setup window Find the following settings in Figure 2 16 A Channel 1 is ON Note that Channel 1 cannot be turned off All others channels can be turned off B Full Scale Voltage Range 5 volts peak All voltage ranges are implied bipolar although not listed that way in the user interface You can set the full scale range from 20 mv to 10 volts peak C Coupling DC Your other choices are AC and ICP D DC Offset 0 volts The range of offset values depends on the full scale voltage range Full Scale Voltage Range Maximum DC Offset 8 0 volts 2 5 volt to 20 mv scales 2 26 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted A Brief Review of the VNA Setup Window E Channel Label Channel 1 You can edit the channel label to read any text string If the string is too long it will scroll to the left F EU engineering units are Off This toggle button controls the state of engineering units When engineering units are off the units are based on volts When engineering units are on the units are based on your entries See Figure 2 18 G 0 dB reference 1 volt RMS You can changed the 0 dB reference point to any value The d
12. ap or Max Overlap 93 75 F Boxcar Window You can choose numerous FFT analysis windows to control spectral leakage The boxcar window is equivalent to no window at all 2 30 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted A Brief Review of the VNA Setup Window Triggering Dialog The triggering controls are more relevant to time domain measurements and less relevant to spectrum measurements Most spectrum measurements don t require triggering If this is the case set triggering to Off Free Run You may only see Off Free Ru depending on your font size and type settings o oe co a loz oz oz zijo Delay Delay Delay Delay 100 oo 100 f 100 oo 100 100 o0 100 100 0 0 100 4 4 d 4 b 4 A B D E Figure 2 23 The many different triggering modes from A to E Only the controls relevant to your particular triggering mode are displayed This helps avoid confusion x Trigger mode A is Free Run and is equivalent to no triggering at all The data is displayed as it is acquired in Record Length blocks Trigger mode B is Every Frame triggering Data is displayed triggered in Record Length blocks every time a positive going signal crosses through 0 of full scale on channel 1 Trigger mode C is 1 Frame triggering It is equivalent to Trigger mode B Every Frame on the first block of data and Trigger mode A Free Run thereafter Trigger mode D
13. de 2 Connect channel 1 output directly to channel 1 input using the RCA cables and connectors provided with SigLab Or you may use one of your own BNC cables 3 Start MATLAB 4 Start SigDemo Invoke SigDemo from the MATLAB Command Window gt gt sigdemo lt enter gt Note that MATLAB is case sensitive in general but typing Sigdemo or even SIGDEMO will work under later versions of MATLAB 5 DSP Technology Inc SigLab User Guide 2 1 09 17 98INSL3 Example 1 Single Channel Measurements Section 2 0 Getting Acquainted 4 SigLab Demo i on abe epa papal CO ET fy Figure 2 1 The vna setup window left and the vna plot window right are both initialized here using the default vna file After some time you should see the something very similar to Fig 2 1 appear 8 Input Channels Pentium 90 MHz Pentium II 350 MHz Pre hardware Init Post hardware Init Table 2 1 The time required to initialize SigLab instruments depends on whether the hardware has been pre initialized On a 90 MHz Pentium computer approximately 28 seconds is required to initialize vna for 8 channels The first session requires more time since neither the software nor the hardware was initialized Once you have initialized the hardware subsequent invocations of vna will be substantially faster 6 Start vfg We will use the function generator as our source of excitation Bring up the function generator by clicking on the vfg virtual function
14. dow gt gt load default vna mat Now SLm exists in the MATLAB workspace for post processing as before To verify this type gt gt who Your variables are CenterFreq ch_ptr vdlgl_sl ChanLabel exdlg2_sl vdlgl_s2 ChanStat exdlg2_vis vdlg2_sl Cmprssd_Notes grids vi_timestamp EULabel hdlgl_sl vna_pos SLm hdlg2_s1 xplot_axes SampleRate hdlg2_vis xplot_sl SystemCIk key xplot_s2 UniformFlg num_io DSP Technology Inc SigLab User Guide 2223 09 17 98THSL3 Post Processing with MATLAB Section 2 0 Getting Acquainted Ignore the other variables as they are internal vna file details The only variable of interest is SLm You can repeat steps 1 through 7 using SLm Two Channel Measurements Post processing two channel measurements is a more involved task and as such needs more explanation Refer to SLm section Section 2 0 of the Programming Guide for how to extract and plot transfer function cross spectrum correlation and coherence data 2 24 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Post Processing Outside of MATLAB Post Processing Outside of MATLAB You may have already developed a set of routines for post processing data independent of MATLAB In that case you ll need to export the data to your environment SigLab exports data by way of ascii text files For Excel users we have developed a set of templates and Visual Basic scripts optimized for processing these ascii files
15. e More precisely scmeas is an array of structures On the other hand tdxvec is a vector This will all become clear after we look at some examples Step 3 To get a quick plot of channel 1 time domain data do this gt gt figure gt gt channel 1 gt gt x SLm tdxvec gt gt y SLm scmeas channel tdmeas gt gt plot x y After typing SLm scmeas it reported a 1x16 struct array with fields If you are familiar with C language this is called an array of structures Each element of the array is a data structure containing that channel s single channel measurement data Step 4 To make the concept of an array of structures more clear let s look at one element in the array First let s look at channel 1 s single channel measurment data gt gt SLm scmeas 1 ans tdmeas 512x1 double aspec 201x1 double fft acor label Channel 1 eu_on off 0 euscale fac 1 eu_string Gs DSP Technology Inc SigLab User Guide 2 21 09 17 98IHSL3 Post Processing with MATLAB Section 2 0 Getting Acquainted eu_val 1 fs_val 5 db ref 1 Note that whereas SLm scmeas 1s an array of structures SLm scmeas 1 is just a structure or one element in the array Equivalently we can type gt gt SLm scmeas 2 to see channel 2 data gt gt SLm scmeas 3 to see channel 3 data gt gt SLm scmeas 16 to see channel 16 data gt gt SLm scmeas 17 27 Index exceeds matrix dimensions
16. e experienced MATLAB programmer post process in the MATLAB environment using the SLm data structure 2 For the non MATLAB programmer post process in another environment like Excel using the data Export selection from the File menu Regardless of which approach you take it s important to understand how SigLab stores data in the MATLAB environment Brief Architecture Overview When you the push the Inst or Avg buttons in vna you re actually causing the following events to happen 1 MATLAB requests new data from SigLab hardware via a DLL function call 2 New data if available is returned to MATLAB as a MATLAB variable 3 This MATLAB variable vector is plotted in the vna plot window 4 Goto step 1 The above process continues until the user hits the Stop button Even though the data is returned as a MATLAB variable it is hidden from the user by design Your data is a local variable to the vna m M file not a global variable If you type who at the MATLAB prompt you ll find no indication that a new MATLAB variable or variables exists after running vna In fact hundreds of new variables actually do exist but they are all local variables Why this approach We hide the data for two reasons 1 Ifit s not hidden it s very easy to accidentally erase it or modify it by hacking in the MATLAB command window 2 Ifit s not hidden your MATLAB workspace would be filled with hundreds of meaningless variables that
17. eady is not gt gt vna lt enter gt Data is now available in the MATLAB environment although you can t see it as discussed above The data is local to the vna M file To access the data namely the SLm data structure use the data access method listed above The vna get meas command extracts the most recent measurement data from vna s local variable space What happens if you haven t made a measurement yet Do we have any measurement data The answer is Yes In this case vna s local measurement variables have already been set by reading from the current setup file in this case default vna Step 1 gt gt SLm vna get meas If you accidentally omit the trailing semi colon you 11 quickly understand why it s commonly used Omitting the semi colon is tantamount to saying Show me the data Step 2 To see all the fields of SLm do this gt gt SLm SLm scmeas 1x16 struct xcmeas 4x16 struct xcstate 1x1 struct tdxvec 1x512 double fdxvec 1x201 double clist 1 2 numin 8 wincor winsel rbw 25 nave 20 2 20 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Post Processing with MATLAB zpad 0 ovld O zoomcf 0 filestor 1x1 struct The first field listed above in SEm 1s semeas semeas contains single channel measurement data Here we will investigate both semeas and tdxvec semeas 1s also a structure Essentially scmeas is also structur
18. efault value is O dB 1 0 volt RMS Refer to the VNA section on engineering units for a complete description of this field s capabilities Figure 2 17 Two faces of the Channel Setup dialog with AC coupling A and DC coupling B With AC coupling the DC offset slider is not visible With DC coupling a slider appears for selecting the DC offset Figure 2 18 Two faces of the Channel Setup dialog without engineering units A and with engineering units B With EU Off the two fields to enter engineering units are not visible With EU On you have to enter both an engineering unit and multiplying factor DSP Technology Inc SigLab User Guide 2 21 09 17 98THSL3 A Brief Review of the VNA Setup Window Section 2 0 Getting Acquainted MC Setup for Multi Channel Users For SigLab users in the 4 to 16 channel range using the Channel Setup dialog can be quite tedious for both channel setup and interrogation To make life easier we have provided a Multi Channel Setup utility MC Setup It has all the functionality of the Channel Setup dialog but it lets you see all channels at a glance You ll find a main menu link to MC Setup in both the VNA Setup and Plot Windows yna plot cAisiglabivnaidefault vna Setup MC Setup Cross Channel Display Preview File Storage Figure 2 19 The VNA plot window has a link to the MC Setup window HC Setup 22008 fesov foc IA 0 IO font Y ch2 Fl E Jor Y Ch3 M E for gt
19. g Acquainted Processing Dialog Processing controls are less associated with oscilloscopes than they are with spectrum analyzers or network analyzers Unlike the channel and frequency controls which affect the way the analog data is acquired the processing controls manipulate the data only after it has been digitized fad FZ Peak pli ze Adaptive yl Time I Zp a ae 1al oT To 4 P No Overlap v NoQverlap v Boxcar x Hanning zj Aa Bt Cc D E E Figure 2 22 The many different faces of the Processing Dialog Each dialog shows different configurations for averaging type overload rejection overlap and FFT window OvidRe Off Refer to Figure 2 22 part A for the following settings A Additive Averaging In the processing control you will only see Add to signify additive averaging See the VNA section of the user s manual for a complete explanation and the equations used in the different averaging modes B Zero Padding Zp is Off Zero padding is generally only set to On for correlation measurements C Stop at Count 20 The acquisition and averaging will automatically stop after 20 averages are complete D Overload Reject is Off In this state even overloaded data i e saturated corrupted bogus data is included in the averaging process If Overload Reject is on then overloaded frames of data are not included E No Overlap You can set the overlap to be No Overlap 0 50 Overl
20. ingle Display mode after changing from time to autospectrum Notice the plot is not autoscaled initially 5 Pre Autoscaled You probably noticed that the noise floor of the sine wave is not initially visible Let s fix that Right single click anywhere in the plot window Continue right clicking until you see the noise floor appear Right single clicking 1s a way to autoscale the plot limits to the data 6 Post Autoscaled After autoscaling you should see something like Figure 2 8 2 8 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Example 1 Single Channel Measurements Sep AC Sehe CrocrCharral Depim Breer Foe Siege Figure 2 8 After autoscaling you can see the signal and the noise floor across the entire spectrum Notice the excellent dynamic range attained even without the use of averaging 7 Left single click on the Stop button in the vna plot window before proceeding with steps 8 through 14 8 Display Expansion At times it s necessary to zoom on parts of the spectrum for a closer look Here s how to do this a Position the mouse cursor in the plot window to start the upper left portion of your Zoom box b Left double click and hold after the second click c While holding down drag the mouse down and to the right A yellow box will appear as illustrated in Figure x d Enclose the region of interest in the yellow zoom box and then release the mouse e Left single click again in
21. is Manual Arm triggering It is equivalent to Trigger mode B except that you must arm press the Arm button before trigger events are monitored The trigger is armed when the arm led is green Trigger mode E is 1 Frame Manual Arm triggering It is equivalent to Trigger mode C except that you must arm press the Arm button before trigger events are monitored DSP Technology Inc SigLab User Guide 2 31 09 17 98IHSL3 A Brief Review of the VNA Setup Window Section 2 0 Getting Acquainted DAD DSP Technology Inc User Guide 09 17 98INSL3
22. na setup window under the Excitation menu ensures that the Quit Independent selection is checked Figure 2 3 The default VFG window is set to a 1000 Hz sine wave on channel one Excitation Vlg MC Setup Help e ER A gt Linked to Measurement Ctrl a ent gives you tuli use O Independent wfhg Ctrl Acquiring Data This section lets you get hands on experience with the instrument You will be able to generate acquire and display real data A brief overview of every control will be covered in the following sections For in depth coverage of each control in vna and vfg refer to Sections 5 0 and 6 0 of this manual To get started switch to the vna plot window and hit the Inst button bottom left hand corner Inst stands for Instantaneous which means no averages are to be taken 2 4 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Example 1 Single Channel Measurements lyna plot c simglab4 yna default vna Ml ES Figure 2 4 The vna Setup MC Setup Cross Channel Display Preview File Storage ee plot window appears as Sees above after hitting the Inst button to acquire and display the sine wave generated by SigLab output channel 1 Notice that while you are acquiring the Inst and Avg buttons are greyed out disabled while the adjacent Stop button is black enabled 0 01 0 015 TRIE 0 025 0 03 sec Eo E The plots should begin to update with newly acquired data The top
23. nal analyzer and function generator e Make measurements showing SigLab s excellent dynamic range and spectral purity e Extract the just acquired data and post process in MATLAB Introduction Most experts would agree The best way to learn is by example The hardest part of learning any new product is mastering the user interface This section will accelerate you up the learning curve and have you taking full advantage of the SigLab user interface So just relax and follow the instructions By the time you finish this section you 11 have a good feel for what SigLab can do for you and just as importantly what it cannot This section introduces two commonly used Vis virtual instruments the SigLab network analyzer and the function generator There are many other VIs which you may find useful in your work and we encourage you to use these as well In any case the goals we outlined above are relevant regardless of the instrument You must always set up your instrument acquire data and finally post process the data to make inferences and generate reports This section assumes that you have successfully completed the SigLab and SCSI installation Example 1 Single Channel Measurements 1 Turn on SigLab and verify its connection to the PC The front panel Status should briefly flash OK and then change to TS Terminated at SCSI ID 5 or similar If you do not see this make sure you have completed the SCSI Installation per the Quick Start Gui
24. plot This plot extends from 500 Hz to 3000 Hz in the x direction and from 120 dB to 80 dB in y direction Getting the Plot Limits At times you also may want to know what the current plot limits are To do this you can just look at the plot itself or you can left single click on the x and y buttons and the x y limits will appear beneath the plot Clicking the button finds successive peaks A Finding Peaks Frequently you ll want to know where the largest signal or response resides in the spectrum Sometimes your eyes will tell you but it s much easier to let the computer do comparisons for you To do this left single click on the peak finder beside the x y readout boxes The peak finder appears like the up carrat symbol or Shift 6 on most keyboards Clicking on the peak finder again finds the second largest peak Clicking again finds the third largest peak and so on until you wrap around to the largest peak again Give it a try until you get the hang of it Notice that each time you find a peak the corresponding x y peak values are readout beneath the plot Finding Valleys Some people also call these valleys by a different name nulls depending on the application In any case once you mastered finding peaks finding 2 12 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Example 1 Single Channel Measurements valleys is a snap To find the lowest valley in your plot left
25. re data at the same bandwidth and the same frequency resolution 4 4 d Zoom Off 1000 1900 4 Fring 3000 11000 dF 50_000Hz dF _ 500Hz Figure 2 21 Sample Frequency Range Dialogs Part A is setup for baseband analysis Part B is setup for zoom analysis with the center set to 10 kHz and a bandwidth of 1 0 kHz Refer to Figure 2 21 part A for the following settings A BW Bandwidth 10 kHz The sample rate is always 2 56 Bandwidth In this case Fs 25 6 kHz The range of bandwidths is 2 Hz to 20 kHz for a 20 kHz system B AA Anti Alias Filters are On AA Filters may be toggled on and off Only the digital AA filters may be toggled on off The 20 kHz AA filter is analog and is always on C Record Length 512 samples For spectral analysis the record length is equivalent to the FFT size which is always a power of 2 The range of FFT sizes 1s 64 to 8192 D Zoom Processing is Off When Zoom is off we are said to be processing in baseband Zoom processing 1s equivalent to shifting the center frequency of analysis from O Hz baseband to some center frequency of interest E dF 50 Hz The FFT bin width 50 Hz The terms dF FFT bin width and frequency resolution all refer to the same thing In generic terms dF Sample_rate Record_Length For our current setup dF 25 600 Hz 512 50 Hz DSP Technology Inc SigLab User Guide 2 29 09 17 98IHSL3 A Brief Review of the VNA Setup Window Section 2 0 Gettin
26. s cursored Notice that it s at 2000 Hz as expected and 92 2 dB down from the fundamental 1 harmonic 2 10 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Example 1 Single Channel Measurements 11 Setting the Plot Limits Most of the time display expansion using the mouse is acceptable However at times you ll want to set the plot x y limits to some exact values In other words sometimes you want to set Xmin Xmax and Ymin Ymax explicitly Here s how you do this Clicking on x allows entry of user defined X limits a Set the X limits Left single click on the x button A second edit box will appear next to the already present one Enter Xmin and Xmax in the left and right hand edit boxes respectively b Set the Y limits Left single click on the y button Enter Ymin and Ymax in the left and right hand boxes respectively As you enter the numbers you will a box drawn in the plot window marking the new limits Clicking on y allows entry of user defined Y limits p c Left single click in the plot window to accept these new x y limits Verify the limits actually changed as in Fig 2 11 DSP Technology Inc SigLab User Guide 2 11 09 17 98IHSL3 Example 1 Single Channel Measurements Section 2 0 Getting Acquainted 12 13 14 I I 1000 1500 2000 2500 3000 ar A linear Hertz Figure 2 11 You can set x y limits manually via the x and y controls beneath the
27. saturated at 0 63 volts and the overload indicators turned red See Figure 2 5 Change back to 5 0 volts Ch 1 amp 2 enabled no overloads Ovid OULU Uy Ch 3 thru 8 are disabled no overload Ch 1 and 2 enabled overload on Ch 1 i I L U U U U U U Ch 3 thru 8 are disabled no overload Ch 1 thru 8 are enabled no overloads Figure 2 5 The SigLab overload Ovld indicators appear above the Inst Avg and Stop buttons in the vna plot window Here are 3 possible states of the many you could see the overload indicators in for an 8 channel system Some Facts about Overload Monitoring e Green indicates channel is enabled with no overloads e Red indicates channel is enabled with an overload e Clear indicates channel is not enabled with no overloads e lt c ow indicates that the channel is not enabled data is not being acquired or processed on this channel BUT there is an overload condition The overload condition should be addressed by either removing the input signal or increasing the full scale range e There is one overload indicator per input channel Channel 1 s overload indicator is on the far left and they number sequentially from left to right If you have a 16 channel system you will see 16 overload indicators e Overload monitoring occurs before any filtering takes place You may not see obvious saturated data in the plot window if the frequency components causing the overload are being heavily attenuated by the analog
28. single click on the v valley finder beside the x y readout boxes It appear like a lower case letter v Clicking the v button finds successive valleys Mark Clicking on the valley finder again finds the second lowest valley Clicking again finds the third lowest and so on until you wrap around to the beginning Give it a try until you get the hang of it Notice that each time you find a valley the corresponding x y valley values are readout A Simple Exercise to Build On Let s incorporate all we have learned so far into a simple exercise This will give you some practice using the cursor functions which can be a little awkward at first 1 Left single click on the Stop button in the vna plot window if you haven t already done SO PA JA vna ae vfg should be gual vna is set as follows 1 Bandwidth 5 kHz 2 Record Length 512 samples 3 Channel 1 Full Scale 5 volts 4 Boxcar window 5 Additive Averaging Stop Count 20 6 Autospectrum Single Display 3 Set vfg to output a square wave on channel 1 Use the default settings of 984 Hz and 1 414 volts peak DSP Technology Inc SigLab User Guide 2 13 09 17 98IHSL3 Example 1 Single Channel Measurements Section 2 0 Getting Acquainted 4 Hit the Avg average button in the vna plot window You will see the average counter count up from 1 to 20 in the vna plot window You should see the first 3 harmonics of a bo pas ceda ide Aia FS File Help The average coun
29. ter updates as the averaging 1s being performed Yolts Offset 10 0000 10 4 H square wave Figure 2 12 Remember to autoscale right click if the plot is not already autoscaled Since the square wave harmonics do not lie on FFT lines and the Boxcar window is being used the noise floor is swamped by spectral leakage Let s fix that we DOUG AN E Ge Figure 2 12 The first 3 harmonics of a 984 Hz square wave processed with a boxcar window The dynamic range is greatly reduced by the spectral leakage of harmonic components into adjacent fft bins 2 14 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Example 1 Single Channel Measurements 5 In the vna setup window change the FFT window from Boxcar to Hanning In the vna plot window menu check Display Overlay Upper Hit Avg and observe the reduction in spectral leakage in Figure 2 13 Again autoscale right click in the plot window if necessary 6 In the vna plot window menu uncheck Display Overlay Upper such that you only see the most recent measurement Figure 2 13 Though the fundamental 3rd and 5th harmonics of the 984 Hz square wave are clearly visible there is substantial spectral leakage since they do not happen to lie exactly on FFT analysis lines The dynamic range is greatly enhanced due to reduced spectral leakage The mouse pointer points to the hanning windowed measurement The total RMS energy in the displayed portion
30. the plot window to accept the new plot limits Repeat the above process until you have it mastered Don t get frustrated if you don t get the knack right away It s not easy at first to get the hang of display expansion In one sentence it s left double click hold drag release left single click to accept or right click to reject DSP Technology Inc SigLab User Guide 2 9 09 17 98IHSL3 Example 1 Single Channel Measurements Section 2 0 Getting Acquainted E TAr YW rme mean BE s iiai 3007143 Figure 2 9 The yellow zoom box appears indicating the region of interest 9 Viewing Previous Expansions Make successive right single clicks in the plot window and you will see the plots scroll through the previous display expansions Four different expansions are stored When you hear a small click from your system speaker this means you have cycled through the 4 expansions The next click will autoscale the plot limits to the data as discussed in step 5 above 10 Cursoring Data You can cursor any point in the plot by left single clicking on it with the mouse The corresponding x y readout for that data point appears beneath the plot WN i h A i l i Jj j ey V 1 N Y i y AU yi 7 i 1000 2000 30 A m 2000 000 linear Hertz 92 2164 Figure 2 10 The x y readout under each plot gives the current value of the cursored data point In this figure the second harmonic of a 1 414 volt 1000 Hz sine wave wa
31. would leave you either very perplexed or very angry at the vendor 2 18 DSP Technology Inc User Guide 09 17 98INSL3 Section 2 0 Getting Acquainted Post Processing with MATLAB Post Processing with MATLAB There exists a single data access method It is a function call of the following form SIm vna get meas SLm is a MATLAB data structure containing measurement related information including the data itself The vna get meas command extracts the most recent measurement data from vna s local variable space The SLm data structure contains the data listed in Table 1 For a complete description of how to use SLm see Section 2 0 of the Programming Guide SLm fields Description Description Winsel 1 Overload Status ovld O Overload Status Zoomct O Zoom Center Frequency Filestor 1x1 struct File Storage Menu Information Table 2 2 The SLm data structure DSP Technology Inc SigLab User Guide 2 19 09 17 98IHSL3 Post Processing with MATLAB Section 2 0 Getting Acquainted A Brief SLm example Although the SLm section does an exhaustive job of explaining it contents and uses a few quick examples should serve to get you over the hump of using SLm The following steps were performed from the MATLAB command window You ll find yourself understanding how the SLm data structure works if you go through these examples Afterwards please review Section 2 0 of the Programming Guide Open vna if it alr
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