[time-nuts] Aside about Triangle Waveforms

Brucekareen at aol.com Brucekareen at aol.com
Tue Feb 2 15:14:11 UTC 2010


A widely used WW-II aircraft radio altimeter used a triangular waveform to  
FM modulate a 400 MHz oscillator, employing a mechanical variable capacitor 
 constructed similar to a permanent-magnet loudspeaker.  To get the  
capacitor's diaphragm to reverse accurately, at the positive peak of the  
trianglular waveform, required a sharp, negative-going impulse to be added to  the 
peak of the triangle, creating a sharp notch in the waveform about 30%  deep. 
 This makes me wonder about the limitations of speaker cones  attempting to 
reproduce complex waveforms.  If they had overall  feedback for positional 
correction, the spectrum of the resulting driving  waveform might contain 
some pretty complex components. 
 
Bruce Hunter


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