[time-nuts] Aside about Triangle Waveforms

Robert Atkinson robert8rpi at yahoo.co.uk
Tue Feb 2 19:48:52 UTC 2010

Modern radar altimeters also use triangular wave FM modulation but at around 4.2GHz. Mix the return signal with a sample of the transmitter and you get an audio tone directly proportional to the round trip delay and thus height. works down to a few feet, pretty good for a real time time interval measurement. Some old techniques are hard to beat :-)
Robert G8RPI. 

--- On Tue, 2/2/10, Brucekareen at aol.com <Brucekareen at aol.com> wrote:

From: Brucekareen at aol.com <Brucekareen at aol.com>
Subject: [time-nuts] Aside about Triangle Waveforms
To: time-nuts at febo.com
Date: Tuesday, 2 February, 2010, 15:14

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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