FFT Spectrum Analyser Demo applet
(Java 1.1 Version)
- Note
- This is a Java 1.1 applet. It should work with HotJava 1.1,
Internet Explorer 4.0 or Netscape Navigator 4.0 with the Java 1.1 upgrade patch
applied.
Java 1.1 version features
The following features are new in the Java 1.1 version of the FFT Spectrum
Analyser applet:
- The signal is plotted in either the time domain (signal) or the frequency
domain (spectrum), rather than both together.
- When you move the cursor over the signal plot area, the cursor coordinates
are displayed as voltage and time or voltage and frequency values. Voltages
are shown in volts, times in milliseconds, and frequencies in Hertz.
- You can select a tapered data window to be applied to the sampled signal
to show the effect on spectral
leakage and resolution.
- A digital
anti-aliasing filter can be applied to the signal prior to determining its
frequency spectrum using the FFT. This virtually eliminates any frequency
components of the sampled signal above the folding frequency (in this case,
4000 Hz, i.e. half the sampling frequency of 8000 Hz), so as to prevent aliasing
of these components.
Outline instructions
Operation of the applet is similar to the 1.02 version. Apart from minor
changes to the control panel layout, the main differences are the addition of
the data window choice box, the anti-aliasing filter checkbox and the use of a
single Plot button to update the display when changes are made to the
signal settings. The Signal / Spectrum radio buttons select whether the signal
is displayed in the time or frequency domain.
If all you can see is a grey rectangle, try the Java 1.02 version
of the applet.
Download source code
(zip archive)
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