Hamming and Vonn Hann weighting are good general purpose windows with good sidelobe suppression and nominal broadening. This is because the weighting is uniform over the acquired record. In general Rectangular weighting is used for transient signals that can occur anywhere in the acquisition. The effects of the weighting Windows on the spectral response Use the Vertical offset knob on the front panel to move the FFT display vertically until the spectral peak is just below the top of the display as shown in Figure 6. Touch or click on the Vertical Center box, it will be highlighted in inverse video. Touch or click on the Vertical Scale/div box, enter the value 12 to set the vertical scale to 12 dB/div. In the Vertical zoom area check the Var(iable) check box this will allow us to set a scale outside of the normal 1-2- 5 progression. The FFT display should now have a horizontal scale of 200 Hz per division centered at 1 kHz.
This will again bring up a pop up keypad. Touch or click on the Scale/Div box twice. Enter the desired center frequency of 1 kHz then press OK. Touch or click on the Center Frequency box in the Horizontal zoom area twice. We are going to view the spectral line at 1 kHz. Touch or click on the Math dialog box Zoom tab. You can use the zoom setting of the math trace to select a center frequency and horizontal scale for the FFT display. The FFT span, as we discussed previously, is one half of the scopes sample rate. Using the Zoom Tab to Set Displayed Center Frequency and Horizontal Scale Turn off the channel 1 display by pressing the button marked 1 in the vertical control group on the front panel. Restore the Time/division setting to 20 ms. The resolution bandwidth has decreased from 5 Hz to 2 Hz because the capture time increased to 500 ms (1/500 ms = 2 Hz). Note that the span is now 100 kHz again, one half of the sample rate. The sample rate will decrease to 200kS/s. Increase the Time/Division setting from 20 ms/division to 50 ms/ division. Open the timebase dialog box by touching or clicking on the timebase annotation box. In our setup the sample rate is 500 kS/s so the span is 250 kHz. The span or the total range of frequencies in the FFT spectrum is one half of the oscilloscopes sample rate. The resulting resolution bandwidth is 1/200ms or 5 Hz. The example in Figure 7 has acquired 200 ms of data (20 ms/division times 10 divisions). Resolution bandwidth, Δf, is the reciprocal of the acquisition or capture time of the scope. How FFT Resolution Bandwidth and Span are DeterminedĪs we have seen in the previous section, the resolution bandwidth of the FFT is dependent on the acquisition or record length. Uncheck the Suppress DC box, note that the Span now reads: “DC-250 kHz”, indicating the addition of the DC point. The user can elect to add the DC point by un-checking this box. The default is not to compute the DC point. The Suppress DC check box determines if the FFT computes the DC point in the FFT. This reports a span of Δf to one half of the sample rate or 250 kHz. In our example that is 200 ms, hence the resolution bandwidth of 5 Hz. New mask test criteria can be added by simply editing this file to include the data rate, mask and any pulse finding criteria.Δf is the resolution bandwidth of the FFT, it is the reciprocal of the scope’s acquisition or capture time.
#Wavesurfer mxs software
The LeCroy ET-PMT software mask, alignment and pulse location functions are completely defined by a single Microsoft access 2000 database. In addition, many new applications for pulse mask tests are being developed for proprietary interfaces. As telecom standards evolve, new pulse types and data rates are defined. The test can be programmed to terminate after a defined number of sweeps or to run indefinitely. Any combination of these actions can be set to occur on a failure. These includes storage of the failed waveform, outputting a pulse, printing a screen image, stopping the test, or generating an audible alarm. Unattended or long term testing is supported through the use of automated actions on failure. Signals are tested against standard masks and the software keeps track of the number of failures (signal excursions outside the compliance mask) as well as the percentage of failures relative to the number of sweeps. This electrical pulse mask testing software for LeCroy oscilloscopes performs automated compliance mask tests on a wide range of electrical telecom standards.
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