The time and frequency station that synchronizes radio-controlled clocks and wristwatches across the U.S. is WWVB, 60 kHz, near Fort Collins, Colorado.  The station broadcasts with two antennas and two transmitters for reliability but still drops off the air on occasion.  That was the case on December 11, 2008 from 11:36 AM to 12:17 PM PST and we asked what happened.

It turns out that winds of about 50 MPH or more physically move WWVB's wire antennas enough to upset the impedance match to the transmitters.  Even though an automated tuning system is in place, it can't keep up with rapid reactance shifts caused by big winds according to the facility manager.

The best solution for WWVB in the presence of high winds is to assign an operator (when possible) to manually correct the antenna reactance, just the way a board operator "rides gain" on audio from a live stage production.  An operator can react faster than the present automated impedance controller.

During normal operation, WWVB transmits 24 hours per day, seven days a week, providing the nation with reliable time and frequency information.  CGC uses WWVB to synchronize its master oscillator which is then used in CGC's frequency measuring service.  (GPS is not authorized for this purpose, see FCC Rule 73.1540(c).)

To learn much more about WWVB, visit: http://tf.nist.gov/stations/wwvb.htm

Written by Robert Gonsett, W6VR, December 15, 2008
and referenced in The CGC Communicator newsletter #872

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