Manual for the program SpectrumSLC

Program Files

The program is a single exe-file that can be started directly on your computer without installation. The only additional file that is needed is bass.dll. It should be in the same directory, where the exe-file is located or in a directory where Windows is searching for dll-files by default. Take care that you use the correct bass.dll file. Different versions of SpectrumSLC need different versions of bass.dll.


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Configure Input

After starting the program, you should check, which channel of your sound-card is used as input. Open in the menu "Configure" -> "Configure Sound Card". In the window that opens up, you can select the input channel and adjust the volume. You may use "Line-in" or "Microphone" depending on how you have connected the experiment to your sound-card. The sum of both input channels (left and right) is used as input signal. Please take care that your sound card does not use any filters that may screw-up the input signal.


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Measure a spectrum

Choose the start and stop frequencies, the frequency steps in Hz and the time per step in milliseconds. When pressing on the button "Measure" the programs plays a frequency-sweep with a continuously increasing frequency. At same time the input-signal is recorded and analyzed. The mean amplitude is extracted from the AC-signal using a fast Fourier transformation to apply a very narrow band-pass filter that makes the signal insensitive to other noise sources. You may display the Fourier-transformation of the current signal in a separate window (see below). You may also display the current signal as function of time in a separate window (see below) to check the quality of the signal. 

The computer uses the time between two step for drawing the spectrum and for other interrupts. If this time is not sufficient, the sweep is stopped internally, rewinded and restarted at the proper position. This, however, needs a lot of extra time. Such a situation is indicated by a red text "Sweep rewinded" above the "Measure"-button. If this text is visible more or less continuously while taking a spectrum, you should reduce other tasks of the computer or choose a longer "Time per Step". Using thin lines for the spectra helps to reduce drawing time.

The vertical scale in the spectra is an arbitrary scale. The numbers are proportional to the sound amplitude, however, the absolute value depends on the soundcard settings. The signal starts to saturate at values above 100. Take care that you measure in the linear range below 100.


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Active spectrum

The program is organized in a way that four different spectra can be handled and displayed simultaneously in different colours. This can be used to compare spectra with each other. All activities like "Measure", "Clear Spectrum", "Fit Spectrum" or "Save Spectrum" refer to the spectrum chosen to be active. Use the buttons in the top left corner to choose the index of the "Active Spectrum".


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Save Data

The measured data can be saved as an ASCII-file. Go to "File" -> "Save Spectrum". The data of the active spectrum are saved in two columns with frequency in Hz and amplitude in arbitrary units.


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Open Data

To reload data go to "File" -> "Open Spectrum". The data are loaded into the currently active spectrum (index 1 .. 4).


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Save as Image

The currently displayed image can be saved as a graphic file (bmp or jpg format for example). Go to the menu item "File" -> "Save as Image". This feature can be used by students to create figures for their report easily. 

The currently displayed image can also be saved in the EPS file-format. This format produces the best quality for presentations. It is easy to use together with Latex.  Go to the menu item "File" -> "Save as EPS".

You may alternatively click with the right mouse button on the figure and use the popup-menu.


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Print Image

The currently displayed image can be printed directly. You can choose the printer settings "File" -> "Printer Setup" and than print the image "File" -> "Print". You may alternatively click with the right mouse button on the figure and use the popup-menu.


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Zoom Spectrum

To look at details in a spectrum you can magnify the spectrum with respect to the frequency scale by choosing "Zoom Spectrum" to 200%, 400% or 800%. The image is then displayed in a scroll box. In this case, saving and printing of the image refers to the hole image not only to the visible part.


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Style


With menu item "Set Color", the colour of the current spectrum can be changed.

With menu item "Set Linestyle", the line-width and the style of the data points can be changed. Lines, circles, squares and a filled polygon are availible.

With menu item "Set Font", the size and style of the font can be changed. (In EPS-figure output special fonts are replaced by standard fonts.)

Pen color and style can be set for each of of the four spectra separately. A change is applied to the active spectrum.


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Life FFT of Signal

The menu-item "Windows" -> "Life FFT of Signal" opens a separate window that displays the Fourier-transformation of the current input signal (Amplitude as function of frequency). It stays active even when no measurement is running. If there are any problems with the input signal, it might help to identify any unusual frequency.

You may click with the right mouse button on the figure and use the popup-menu to change style or save the current image.


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Life Image of Signal

The menu-point "Windows" -> "Life Image of Signal" opens a separate window that displays the current input signal as function of time (like an oscilloscope).

You may click with the right mouse button on the figure and use the popup-menu to change style or save the current image.


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Measure a wave function

Click with the left mouse button exactly on the position (frequency) in the spectrum, where you want to measure the wave function. To get usefull results you should not use an overview spectrum but a careful measurement of a single peak to click in. Since there are transient phenomena in the resonator, you need to sweep slowly enough over the peak (1 Hz, 100 ms for example). Check if the amplitude of the peak is smaller than 100 to avoid saturation effects, that would distort the measured wavefunction.

After clicking on the peak, the chosen frequency is played for 10 seconds. Then go to the menu-item "Windows" -> "Measure Wave Function". The "Angle between Hemispheres" refers to the angle on the scale mounted at the top hemisphere. This angle is called alpha in the manual. In the case of a spherical resonator "Lifted degeneracy" must not be checked. The angle alpha is converted correctly into the polar angle theta as described in the manual. In the case of lifted degeneracy or experiments with the molecule the checkbox "Lifted degeneracy" must be checked. In this case the angle is not converted and represents the azimuthal angle phi.

Rotate the hemispheres to the highlighted angle and click on "Measure value". A single amplitude is measured at the chosen angle with the frequency chosen before (When starting the measurement, the first data-point is not displayed - continue and you see how it works). Continue this procedure for all angles 0°-180°. The amplitude as function if angle theta or phi is displayed in blue or green, respectively.

The figure is a radial plot. You may complete the figure by symmetry and show the polar grid by checking the checkboxes. The data can be saved as ASCII-file and the current image can be saved or printed. The ASCII-data are saved in a two-column format with angle and amplitude in the first and second column, respectively. Style and color of the figure can be changed using the menu-item "Style" or with the popup-menu opened with a right-click on the figure.


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Fit

Spectra can be fitted by a maximum of 8 peaks. The peak shapes that are used can be found in the manual. To open the Window for peak fitting choose the spectrum that you want to fit as the "Active Spectrum" and go to "Windows" -> "Fit Spectrum".

The spectrum is shown in a separate window. Move your mouse to the top of the first peak and click the left mouse button. This puts the first peak to its position. Use the mouse wheel to adjust the peak width (on touch-pads you may use the two-finger scroll-function) or you may use the +/- buttons on the left to change the width. Then choose "2. Peak" in the top left corner of the window, move to the next peak and click on the left mouse button. Continue for the other peaks.

For the shape of the total spectrum the phase of the (complex) peaks with respect to each other is important. The phase of each peak can be changed by the slider on the left. The contribution of the active peak can be displayed in gray. If you want to fit only part of the total spectrum you may specify the "Fit Range". Then press "Start Fit" and wait until the spectrum has been fitted. In case that your starting parameter were not good enough you have to adjust the peaks better before starting the automatic fit. The fitted parameters can be read on the left for each peak and can be saved as ASCII-File.


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