Fourier series
Play interactively with different waveforms, apply Fourier filters,
listen to them
http://www.falstad.com/dfilter
Convolution
Play interactively with convolution using functions that you can create yourself using the mouse.
http://www.jhu.edu/signals/convolve
The joy of convolution
Play interactively with convolution using different functions
http://www.jhu.edu/signals/convolve
Fourier Transform and Diffraction
Watch the behaviour of diffraction patterns using slits with varying sizes,
using light with different wavelengths
http://cnyack.homestead.com/files/afourtr/ftdiffraction.htm
Fourier Transform Experimentation
Play with Fourier transforms on 2-D images, where you may use your own
images; apply various filters in the Fourier domain and see the results
in the image domain
http://homepages.inf.ed.ac.uk/rbf/HIPR2/fftdemo.htm
Interactive Fourier Transform
Use gif images and play with the FFT. Filter them in various ways.
http://homepages.inf.ed.ac.uk/rbf/HIPR2/fftdemo.htm
Antenna applet
Watch the reception pattern of a linear array with a varying number of
elements, element separation, and phase shift
http://www.ee.siue.edu/~jchen/ee340/antenna_array.html
Virtual Radio Interferometer
Play interactively with various interferometers that actually exist.
Use different sources and (u,v)-coverages to see the effect of such
incomplete apertures on the resulting images.
http://www.narrabri.atnf.csiro.au/astronomy/vri.html