On Feb 20, 9:09*am, BillGill wrote:
---MIKE--- wrote:
I just bought a cheap electric alarm clock - made in China naturally.
When I plugged it in it displayed the correct time. *How does it do
this? *Does it pick up a radio signal? *The clock works perfectly. *I am
just curious.

* * * * * * * * * ---MIKE---
In the White Mountains of New Hampshire
* (44° 15' *N - Elevation 1580')

Does it have a little picture of a dish antenna on it? *When you
plugged it in did it go crazy and start spinning rapidly? *If so
it receives the time code from the NIST time transmitter in Boulder, CO.
However, there are some that have been set at the factory and they
have a battery back up time chip in them so that the time is correct
from the start. *Supposedly you never have to set these, but they
are standard quartz movements that won't keep the correct time forever.
I prefer the ones that set themselves to the NIST transmissions.

Bill

Are some of the more modern ones made using quartz crystals for their
regular timekeeping functions (as opposed to being synchronized with
the AC mains?) reason I ask is that I have never had a plug-in alarm
clock that has kept anything resembling accurate time when running on
battery backup - an outage lasting more than an hour or two will
result in the clock being wildly off. The way that this was explained
to me was that they generally got their timekeeping signal from the
60Hz AC power and only used the quartz oscillator when the power went
out, and that plug-in alarm clocks generally used the cheapest
oscillators (possibly ones that were rejected for use in wris****ches
or other battery operated devices?)

nate