[time-nuts] Why are 1PPS signals so skinny?
SAIDJACK at aol.com
SAIDJACK at aol.com
Tue May 15 21:39:39 UTC 2012
QED: here is a phase noise plot of a 200ms 1PPS pulse showing up in the
phase noise spectrum of a 10MHz source (at 1Hz to 10Hz offsets) because the
unit was providing a 100mA current pulses into the cable, and power supply
modulation of the 10MHz output happened inside the unit.
The pulses would likely not be visible if they had been only microseconds
long, or the cable was not incorrectly end-terminated and causing the
massive DC current to flow. Yes, yes, the unit "could have been designed to
handle that scenario", but the point is: modulation is going to happen, and
could be "10's of Watts", and it will likely have some effect in one way or
another.
The discussion started with the question of why one would design short 1PPS
pulses versus long pulses. This is one reason why.
In a message dated 5/15/2012 14:24:07 Pacific Daylight Time,
mikes at flatsurface.com writes:
On 5/15/2012 5:14 PM, SAIDJACK at aol.com wrote:
> it is the effect of what follows after that leading edge, and propagates
> down the power supplies to cause side effects that is being discussed
here.
I'm asking "What side effects?" I haven't seen any mentioned. And
really, if an increase in power draw of 10 watts for an entire lab
environment causes any problems, I'd question the quality of the power
supplies, and ask what happens when you simply turn on the light?
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