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Author Topic: WWVB broadcast format changed  (Read 1180 times)
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Langley
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« on: October 31, 2012, 12:55:03 00:55 »

Those of us in the Americas who still have ancient WWVB referenced frequency standards just became proud boat anchor owners. On 29 Oct the NIST changed the 60KHz time code broadcasts to include phase modulated data in addition to the AM PWM encoded data, rendering carrier phase-locked receivers useless (other than a 30min "transition" period at midnight until 31Jan2013 when the PM is turned off).

The NIST very reasonably claims consumer clocks using only the AM component of the signal should be unaffected, but I'll still be checking all my radio-controlled clocks tonight.

Excerpt below from NIST announcement:
Beginning Monday, October 29, 2012 at 1500 UTC, NIST Radio Station WWVB will begin broadcasting a phase modulation (PM) time code protocol. The new PM signal, which has been tested over the past several months, will provide significantly improved performance in new products that are designed to receive it.  Existing radio-controlled clocks and watches will not be affected by the new broadcast protocol, and will continue to work as before. A detailed technical description of the new format can be found here.   
Disciplined oscillator products that track and lock to the 60 kHz WWVB carrier and were designed to work as frequency standards, will not work with the PM signal and will now become obsolete.

http://www.nist.gov/pml/div688/grp40/upload/NIST-Enhanced-WWVB-Broadcast-Format-2012-09-26-2.pdf
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bigtoy
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« Reply #1 on: November 02, 2012, 01:41:45 01:41 »

And there I was thinking about making a little project to receive / decode this signal. It's nice because it works indoors, where GPS does not. Hmmm.
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Langley
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« Reply #2 on: November 02, 2012, 03:14:52 03:14 »

Actually, it appears clocks using the AM/PWM part of the signal continue to work just fine as predicted (mine do, anyway), so any design you might be contemplating based on amplitude detection should still work as before.

Demodulating the new PM phase inversion data should greatly improve interference rejection, though, and might make an interesting project. My CMMR-6P-60 module receives virtually nothing but noise during daylight hours, even after upgrading to the 100mm ferrite rod, so it'd be really interesting to see if it's now feasible to decode the PM signal in SW during the day without resorting to heroic measures like this outdoor antenna.(!)
http://www.ka7oei.com/wwvb_antenna.html

Example of carrier tracking receiver mod to accommodate the new format:
http://www.maxmcarter.com/rubidium/2012_mod/index.html


With $21 SiRFStar IV GPS modules like the Maestro A1035-H available, though, it's hardly worth worrying about. I just got one of these and it typically sees at least a couple of sats and outputs NMEA time even in my basement using just the integrated patch antenna.
http://www.mouser.com/maestrowireless/
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