Re: A puzzle with internet time and NIST time
It is instructive to look at the NIST website that discusses the time
standards and the broadcasting of the time.
http://tf.nist.gov/general/pdf/1383.pdf
There is a useful chart of available sources of time and the accuracy
available
on page 11, table 1.1.
Problems in reception are discussed, especially on page 24, from
which I quote:
WWVB clocks like those you might find in a home or office are shown in
Figure 2.10.
These clocks not only keep accurate time, but they automatically adjust
for Daylight
Saving Time, leap seconds, and leap years. They work by synchronizing an
inexpensive
quartz oscillator to the WWVB time code. The period of synchronization
varies from
model to model, but many units synchronize only once every 24 hours;
usually during the
evening when the signal is strongest. In between synchronizations, time
is kept using the
quartz oscillator. Typically, the quartz oscillator can maintain
frequency to within a few
parts per million, so it will take at least two or three days to gain or
lose a full second even
if WWVB has not been received. Therefore, synchronizing once per day is
usually enough
to keep a clock’s display on the right second. If you live within the
coverage area and
your WWVB clock is unable to synchronize, it usually means a source of
radio interference
is near the receiver. Some common culprits are computer monitors (some
have a
scan rate at or very close to 60 kHz), noisy AC wiring, fluorescent
lamps, or nearby power
lines, transformers, or radio transmitters.
--doug
--
Blessed are the peacekeepers...for they shall be shot at from both sides. --A.M. Greeley
Reply to: