Dear LF Group,
Although it may be possible to access the PC's internal clocks one
way or another, I can't see it would be much help for timing
accuracy - after all, it's all derrived from a very ordinary, un-
trimmed crystal on the motherboard somewhere.
I did some work at U of H a while ago with Dave Lauder, G0SNO,
investigating PC clocks. In fact, a lot of PCs (and other things) are
now using 'dithered clocks', where the clock is frequency
modulated to a deviation of a fraction of a percent, by a spiky
looking triangle wave. The reason for doing this is to spread
radiated noise emissions from the PC over a wider range of
frequencies, which in turn reduces the noise power seen by a
narrow band EMC receiver when noise emissions testing is being
performed. This slightly perverse idea is basically a fiddle to allow
PC's to generate more RF noise, while still passing the EMC
regulations. It saves the manufacturers some money on screening
and filter components. I'm sure it does not do much for timing
accuracy, though!
Cheers, Jim Moritz
73 de M0BMU
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