[time-nuts] Why are 1PPS signals so skinny?

[shalimr9 at gmail.com]

The issue is that the overall power drawn at 1Hz can cause stability problems for all the power supplies, so in the example given by Tom, the power modulation probably affected the power supplies regulation and it affected the next pulse, not the first pulse. Since it is continuous pulse train, the perturbation affects potentially all the pulses.

This page shows the spectrum of pulses of constant frequency and amplitude, but varying width:
http://www.ko4bb.com/Test_Equipment/Pulse_Modulation/

You can see that when the duty cycle is changed from 10 to 50%, the amplitude of the first harmonic (the fundamental) goes up by 10dB.

So if you are only interested in the leading edge and there is appreciable power spent when the pulse is high, a longer pulse only draws more power at the fundamental without adding anything to the precision of the leading edge. If the fundamental is 1Hz, you will pulse the power drawn from the source at 1Hz, which is too low to be filtered out by most power supplies

Didier KO4BB

Sent from my BlackBerry Wireless thingy while I do other things...

-----Original Message-----
From: Mike S <mikes at flatsurface.com>
Sender: time-nuts-bounces at febo.com
Date: Tue, 15 May 2012 15:47:46 
To: <time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] Why are 1PPS signals so skinny?

On 5/15/2012 2:45 PM, shalimr9 at gmail.com wrote:
> The narrow pulses are easily filtered by the power supply because the
> frequency distribution of the power consumption has a much smaller
> component at 1Hz.

But, since PPS is the leading edge, if the power draw for a longer pulse 
width causes timing problems, then a short pulse would too, unless the 
edge can somehow see into the future to know how long the pulse will last.

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