[time-nuts] Aside about Triangle Waveforms
J. Forster
jfor at quik.com
Tue Feb 2 22:11:14 UTC 2010
It's the AN/APN-1 in the USAAC version. There is also a USN version with
slight differences.
-John
==============
> 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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