Daylight Saving Time – More Than You Wanted to Know Daylight Saving Time (not Daylight SavingS Time) What about DST computer system updates Check Correct Time on the Internet National Institute of Standards and Technology www.time.gov http://time.nist.gov Radio Controlled Clock Change to DST Automatically Primary Time and Frequency Standard for United States Email Question From Chrissy in Malaysia
The 60 kHz signal is located in a part of the radio spectrum called LF, which stands for low frequency.
The lowest frequency received by any of the other radios in your house is probably 530 kHz, the bottom of the AM broadcast band.
Even that frequency is nearly 10 times higher than the WWVB signal.
At 60 kHz, there isn’t enough room on the signal (bandwidth) to carry a voice or any type of audio information.
All that is sent is a code, which consists of a series of binary digits, or bits, which have only two possible values (0 or 1).
Bits are generated at WWVB by raising and lowering the power of the signal.
They are sent at a very slow rate of 1 bit per second, and it takes a full minute to send a complete time code
When you turn a radio controlled clock on, it will probably miss the first time code, so it usually takes more than one minute to set itself (sometimes 5 minutes or longer) depending on the signal quality and the receiver design.
Once your radio controlled clock has decoded the signal from WWVB, it will synchronize its own clock to the message received by radio.
Before it does so, it applies a time zone correction, based on the time zone setting that you supplied.
Primary Time and Frequency Standard for United States
Cesium Fountain Clock (NIST-F1)
Developed at the NIST laboratories in Boulder, Colorado.
The uncertainty of NIST-F1 is continually improving.
In 2000 the uncertainty was about 1 x 10-15
In Summer of 2005, the uncertainty had been reduced to about 5 x 10-16
Neither gain nor lose a second in more than 60 million years
NIST-F1 is referred to as a fountain clock because it uses a fountain-like movement of atoms to measure frequency and time interval.
First, a gas of cesium atoms is introduced into the clock’s vacuum chamber.
Six infrared laser beams then are directed at right angles to each other at the center of the chamber.
The lasers gently push the cesium atoms together into a ball.
In the process of creating this ball, the lasers slow down the movement of the atoms and cool them to temperatures near absolute zero.
Two vertical lasers are used to gently toss the ball upward (the "fountain" action), and then all of the lasers are turned off.
Under the influence of gravity, the ball then falls back down through the microwave cavity.
The round trip up and down through the microwave cavity lasts for about 1 second. During the trip, the atomic states of the atoms might or might not be altered as they interact with the microwave signal.
When their trip is finished, another laser is pointed at the atoms.
Those atoms whose atomic state were altered by the microwave signal emit light (a state known as fluorescence).
The photons, or the tiny packets of light that they emit, are measured by a detector.
This process is repeated many times while the microwave signal in the cavity is tuned to different frequencies.
Eventually, a microwave frequency is found that alters the states of most of the cesium atoms and maximizes their fluorescence.
This frequency is the natural resonance frequency of the cesium atom (9,192,631,770 Hz), or the frequency used to define the second.
Email Question From Chrissy in Malaysia
Spam Filters and Other Topics
90 billion spam per day (February 2007)
Easiest would be to use Outlook spam filters
Use filters to move “good” email into folders and leave spam in inbox
Corporate spam filters
Block open relays, known IP address
Block key word or phrases
Many good ones are available
Problem false positives
Don’t use your email address for contests or on discussion sites
Change or email address and start all over
Blocking Web-based Emails at Work
Your employer is probably blocking access to Yahoo
You can use a proxy server to bypass restrictions to blocked sites