On Sun, 8 Mar 2020 at 14:01, Chris Olson via CentOS <centos@xxxxxxxxxx>
wrote:
> A few years ago, one of our interns was curious about system
> time keeping features in computer systems. This intern was
> also the proud owner of an inexpensive Radio-Controlled Clock.
> The intern wondered why computer motherboards were not just
> equipped with a chip like the ones in the RCC so that their
> system time would always be correct.
>
>
One issue is that the radio clock frequencies are based on the country they
are in. They are also dependent on different characteristics of those
frequencies. In the US, the clock measurement which reaches the entire
country is the 60 kHz WWWVB. It hugs the ground so does not miss places
like the WWV frequencies of 5,10,15 MHz. However WWWVB needs a very long
antennae to be used and it can get masked by anything from a kitchen
blender or a lot of computer parts. This means that the antennae need to be
away from most equipment. The frequencies that most US radio clocks use are
the WWV 5, 10 and 15 Mhz. The problem with these frequencies are many:
1. They are shortwave frequencies which bounce off the ionosphere. You may
get areas of the country skipped over all different times of day or year or
sun sponts.
2. The frequencies are used by a lot of chips. That means you are going
drown out a lot of talk from computers.
3. The data in the signals are different per country but due to the
ionosphere skipping you might get a different clock source.
4. There is only one signal per country so you can drift out of time easier
for various reasons.
https://en.wikipedia.org/wiki/Radio_clock
https://en.wikipedia.org/wiki/WWVB
The radiation pattern of WWVB antennas is designed to present a field
strength of at least 100 μV/m over most of the continental United States
and Southern Canada during some portion of the day. Although this value is
well above the thermal noise floor, man-made noise and local interference
from a wide range of electronic equipment can easily mask the signal.
Positioning receiving antennas away from electronic equipment helps to
reduce the effects of local interference.
> I posted a question about this on the CentOS email list and
> received more responses than those postings about problems
> with the new Firefox release. I must have really struck a
> very sensitive system time nerve.
>
> This large response was a bit of a surprise and included a
> bunch of time related horror stories. It became clear why
> using an RCC chip on motherboards would NOT be a good idea.
> GPS network time servers seemed to be a preferred choice.
>
> All of our bedrooms have Radio-Controlled Clocks. At 5:30
> this morning, half of the clocks displayed the correct time.
> The other half of the clocks were incorrectly showing a time
> one hour ahead. Maybe this is one more piece of evidence to
> reject using an RCC time base for computers, at lease in thestate of
> Arizona.
>
>
>
>
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--
Stephen J Smoogen.
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