Recent Change at WWVB (60kHz) Could Affect Your Digital Clock/Wristwatch

March 26, 2012

Probably the most popular radio station in the United

States is WWVB on 60 kHz.  Almost all atomic clocks and self-

setting wristwatches are tuned to that station to obtain

the correct time of day.

     On paper at least, WWVB could improve its signal penetration
by 14 dB if it added phase modulation (PM) to its existing
amplitude modulated (AM) carrier.  Because AM would be
maintained when PM is added, almost all existing clocks and
wristwatches should continue to work well.  However, new
receivers designed to decode the PM signal should work much
better – as if WWVB had increased its power by 14 dB.
WWVB has already conducted about five experiments where PM
has been added for brief periods of time.  The first PM injection
was in about March of this year.  The latest PM injection began at
11AM PDST on Thursday, June 7, 2012 and concluded 24 hours later.
The next experiment is planned to start on June 14 and will run
for 15 consecutive days, ending June 29 prior to the June 30 Leap
Second addition.  Field data will be gathered on the east coast
to better determine how much of the calculated 14 dB improvement
is realized in practice.
Again, almost all existing WWVB receivers should operate
properly regardless of whether PM is turned on or off.  However,
certain old fashioned time and frequency receivers using phase-
locked-loops (PLLs) will be confused by the PM signal and will not
operate properly, notably old PLL-equipped Spectracom and Tracor
receivers.  Fortunately, WWVB plans to shut off PM for one hour
on each of the work week days during the 14 day test window in
order to allow those old receivers to resync.
Assuming the 14 day test is successful, WWVB plans to
permanently add PM in August or September.  So, if you happen to
have one of the old fashioned affected receivers, you should have
plenty of time to replace or upgrade it, or switch to a GPS
reference standard.
Questions or comments should be directed to WWVB broadcast
manager John Lowe at 303-497-5453, or by writing to john.lowe
(at)  Watch the following Website for updated

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