[time-nuts] The ultraAtomic clock for home

Tom Van Baak tvb at LeapSecond.com
Wed Apr 5 00:57:54 EDT 2017

Paul, et al,

The La Crosse 1235UA does indeed receive the new WWVB PSK format. It was first brought to our attention by Brooke Clarke some months ago:


Prices vary from affordable to lets-see-how-much-we-can-charge, depending on the month and source. I bought a couple to measure and tear apart.

As advertised and predicted they set themselves within minutes, at all times of day, even under adverse reception conditions. Those of you new to the "enhanced" (and mostly backwards-compatible) WWVB format can look at hundreds of postings in the time-nuts archives in the past 5 years (google for site:febo.com wwvb psk) where we discussed this topic.

The La Crosse movement is made by U.T.S. -- the same German OEM (www.u-t-s.de/) that makes the guts of lots of MSF / DCF77 / WWVB / JJY wall clocks. This new WWVB-PSK version is quite a bit more complex than the traditional WWVB-AM version. Two orthogonal antenna tilted at 45 degrees is one clue; a few more CoB (chip on board) is another. It has two steppers; one for hours/minutes and one for seconds. Also the usual optical feedback sensor for alignment of gears & hands. It uses one or two C-cells and also has an "ECO-mode" switch. Given that most WWVB receivers use AA or AAA or even tiny watch-batteries, the need for two large C-cells and an optional ECO mode suggests maybe there's a power issue.

User manual: http://www.lacrossetechnology.com/media/catalog/product/4/0/404-1235ua-ss_1.pdf

I'll upload the tear down photos to: http://leapsecond.com/pages/ultratomic/

Note also these WWVB/PSK clocks are among the first WWVB clocks I have that handle a positive leap second correctly. During the most recent leap second (2016-12-31) they paused at :59 for an extra second. See the IMG_3126 video in the above directory. The audio track is a Heathkit WWV s/w receiver.


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