[time-nuts] Aside about Triangle Waveforms
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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Aside about Triangle Waveforms
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, brucekar...@aol.com brucekar...@aol.com wrote: From: brucekar...@aol.com brucekar...@aol.com Subject: [time-nuts] Aside about Triangle Waveforms To: time-nuts@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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Aside about Triangle Waveforms
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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
