La Crosse Technology WT5721
Digital Radio Controlled Atomic Projection Alarm
with Wireless Indoor Outdoor Thermometer

Please click for a larger picture.

Features:

• Accurate to 1 second per million years
• Atomic clock sets automatically to WWVB radio signal (manual setting is also possible)
• 12/24 hour time display (hour, minute, second)
• Calendar display (day, month, date)
• Three projection modes: time only, outdoor temperature only, or alternating between the two
• Projection is continuous with ac powering
• Projection is initiated via pushbutton and 3 seconds in duration with battery powering (pushbutton projection is also available with ac powering)
• Projection auto-focusing for display from 3 to 6 feet away (maximum projection distance is 10 feet)
• Projected display can be rotated 360° in 90° increments for proper viewing
• Projector case rotates 180° to further orient the projected display
• Three different intensity settings for projected display, plus an "off" setting. With battery powering, "off" is the only option; the intensity is not adjustable and the projection is via pushbutton (not continuous).
• Dual alarm settings with adjustable snooze function
• Time zone setting (13 available) with map display for U.S. time zones
• Daylight saving time ON/OFF option
• Indoor temperature display in either °F or °C
• Outdoor temperature display (via 433 MHz transmission) in either °F or °C
• Electro-luminescent backlight for LCD display (2-second duration)
• Integral base for table/shelf/desktop placement
• Atomic clock powered by ac adapter (included) or by two AA alkaline batteries, with normal life of about 1 year
• Remote wall-mount transmitter powered by two AAA alkaline batteries, with normal life of about 1 year

Specifications:

• Indoor temperature measuring range:
  41° to 140°F with 0.2°F resolution
  (5° to 60°C with 0.1°C resolution)
• Outdoor temperature measuring range:
  -21.8° to 157.8°F with 0.2°F resolution
  (-29.9° to 69.9°C with 0.1°C resolution)
• Temperature checking intervals:
  Indoor: every 10 seconds
  Outdoor: every 5 minutes
• Transmission distance:
  maximum 82 feet (25 meters)
• Clock dimensions:
  5.25 inches (13.3cm) wide
  3.5 inches (8.9cm) high
  1.5 inches (3.8cm) deep (including base)
• LCD display dimensions:
  2.5 inches (6.35cm) wide
  1.5 inches (3.8cm) high
  Time number height: 0.75 inch (1.9cm)
• Remote transmitter dimensions:
  5.19 inches (13.2cm) wide
  3.58 inches (9.1cm) high
  1.45 inches (3.7cm) deep
• Power source:
  AC adapter (included):
  120Vac, 60Hz input
  3.4Vdc, 100mA output
  Optional: two AA alkaline batteries

The La Crosse Technology WT5721 Radio Controlled Projection Atomic Alarm Clock with Temperature Display:

The La Crosse Technology Radio Controlled Atomic Projection Alarm Clock with Temperature Display maintains its incredible accuracy by automatically tuning into the WWVB radio signal. The built-in antenna ensures reliable signal reception up to 2000 miles (3200km) from the WWVB transmitter. As a result, the La Crosse Technology atomic clock will calibrate to the atomic clock not only throughout the mainland U.S. but also in much of Canada. You need only insert the batteries, wait until the signal is received, and program the desired additional settings. In locations outside of WWVB range, the LaCrosse clock can be manually set and will provide the high degree of accuracy of any quality quartz clock.

In a nutshell, here's how the the La Crosse clock works: The atomic clock's antenna is specifically tuned for optimal reception of the 60 kHz time signal. The time signal received on the antenna is demodulated by an onboard receiver, which sends the information to the clock's CMOS microprocessor for decoding. Once your clock has automatically set its time for the first time, it ensures continuing accuracy by automatically tuning into the WWVB radio signal once per day at midnight. As long as your clock is kept within transmitter range, it will continue to display the absolutely precise time, automatically adjusting for summer time/winter time changeovers if the daylight savings time option is ON. Should you move your atomic clock out of transmitter range for an extended period of time, the clock will continue to operate as a highly accurate quartz-controlled clock. Upon re-entering the transmitter range, your atomic clock will correct itself again to the precise WWVB time signal.

Radio-controlled Time:

The NIST (National Institute of Standards and Technology, Time and Frequency Division) maintains a radio station, WWVB, in Ft. Collins, Colorado. The WWVB radio station derives its signal from the NIST atomic clock in Boulder, Colorado. A team of atomic physicists is continually measuring every second of every day, to an accuracy of ten billionths of a second per day. These physicists have created an international standard, measuring a second as 9,192,631,770 vibrations of a Cesium-133 atom in a vacuum.

WWVB (the station’s identification just like any other radio station) continuously broadcasts time and frequency signals at 60 kHz. The carrier frequency provides a stable frequency reference traceable to the national standard. There are no voice announcements on the station, but a time code is synchronized with the 60 kHz carrier and is broadcast continuously at a rate of 1 bit per second using pulse width modulation. The time code contains the year, day of year, hour, minute, second, and flags that indicate the status of Daylight Saving Time, leap years, and leap seconds.