"Maarten Wiltink" <maar...@kittensandcats.net> writes: >"Unruh" <unruh-s...@physics.ubc.ca> wrote in message >news:6rmxm.46378$db2.43...@edtnps83... >> "Maarten Wiltink" <maar...@kittensandcats.net> writes: >>> "Unruh" <unruh-s...@physics.ubc.ca> wrote in message >>> news:k8yxm.46291$db2.44...@edtnps83...
>>>> No idea what "spread spectrum " means for a clock. >> >>> That there is a certain jitter explicitly introduced in its >>> effective frequency. Probably in the form of a random offset, >>> that averages to zero, to every tick, so you're certain that >>> the long-term frequency doesn't change. >> >> I am afraid I am left as confused as before. HOw introducing random >> offsets would stop the frequency from changing I have no idea. >Say you have a clock running at 1 Hz. One tick per second. Naively, >you might "spread its spectrum" by changing the frequency. Let it >run at 0.5 Hz some seconds, 1.5 Hz some others. That's two ticks >some seconds, two thirds of one others. The average frequency works >out to 0.75 Hz. Not what you want. >Alternatively, instead of ticking at the top of every second, add >a random offset to the time when every tick happens. After an hour, >there will have been 3,600 ticks. Still 1 Hz. >> It sounds like a terrible idea, but that may be ignorance. >If you want the best clock possible, it is. But that's not the only >consideration. Say you add plus or minus .5 sec at every tick. Yes, after an hour, you will still have 3600 ticks, but when you measure the time at any particular point in the hour, you will never know the time to better than .5 sec. This will set an ultimate limit on the accuracy of your clock. All to save a few cents in copper to shield your system properly. And your system is till polluting the airwaves with the same amount of energy, only spread around slightly in frequency. >Groetjes, >Maarten Wiltink _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
