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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