Sunday, October 3, 2010

Frequency Modulation

Here's a GIF Animation of the modulating signal (top) and the corresponding frequency modulated signal (bottom) captured on an analog Cathode Ray Oscilloscope.
The modulating signal is a very low frequency sine wave fed from signal generator to an ICL8038 FSK trainer kit. You can see the frequency of the carrier wave change as the voltage level of the modulating signal changes slowly.

The video was shot using a digital camera. The location is VESIT, Mumbai's Communications Laboratory.




Here's how the GIF animation was created on a Windows based PC using free tools:
  1. The video was originally in .MOV (Quicktime) format. It was converted to uncompressed AVI using Rad Tools (free version of QuickTime must be installed on your system before you can convert the MOV to AVI).
  2. The uncompressed AVI was then loaded into VirtualDub and Image Sequence of a selected duration of video was exported. This particular time period of the video consisted of a sequence of 14 frames. The frame sequences were selected such that the waveform in the start frame and the end frame were almost in phase (i.e. looked the same) so that when the 14 images when displayed one after another should give an impression of a continuous loop.
  3. The exported images (or frames) were converted in a batch job from BMP to GIF using IrfanView.
  4. The GIF animation was created using Microsoft GIF Animator.The GIF images were imported into it, the animation was set to loop forever and the delay between each image was set to 3/100 seconds since the video was originally shot at 30 frames per second.
  5. The GIF animation was saved and ulpoaded to Picasa which now supports GIF images with animations.
The above steps can be used to convert any AVI file to GIF Animation. You do not need to used RAD Tools in case your video is not in MOV format as VirtualDub can directly import video files encoded with popular Codecs like MPEG or DivX or XviD. Now days are many websites which help you create a GIF by uploading individual images for each frame. Some of these are:
GIFup (can import images from flickr) 
gifninja (allows conversion of video to GIF)

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