WWVB Celebrates 50 Years of Broadcasting Time 97
First time accepted submitter doublebackslash writes "On July 5th, WWVB, NIST's timekeeping radio station transmitting near Fort Collins, will celebrate 50 years of continuous operation. Operating at 60kHz, the signal actually follows the curvature of the Earth via a trick of electromagnetics, allowing nearly the entire globe to receive an accurate time signal, which has in recent years reached an accuracy of 1 part in 70 trillion. Recent upgrades, which came in $15.9 million under budget will allow the station to be better received even in large buildings, giving it an edge on timekeeping that not even GPS can touch, with its need for open skies to receive a signal."
And (Score:4, Informative)
It also operates at 5MHz, 10MHz, 15MHz, and 20MHz.
Re:And (Score:5, Informative)
No, that's WWV on those frequencies.
Re: And (Score:5, Informative)
WWVH also operates on those frequencies. It is possible to hear both at the same time with good conditions and a good antenna. As a user of HF spectrum this is a valuable resource.
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WWVH doesn't operate on 20 MHz. WWV and WWVH also broadcast on 2.5 MHz, though.
Although the exact set of frequencies used has changed over the years.
TFA completely ignored that CHU Canada also broadcasts time signals. It's not a US monopoly, even if the NIST clocks are probably the world's most accurate. CHU broadcasts on 7.333 MHz, and I think on 14.666.
WWVB is unique, however, in that it is tailored for reception and decoding by automated time-tracking equipment. The WWV and CHU stations provide voice data.
TFA is also spouting nonsense about WWVB being something only good for toys.
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I'm fairly certain that CHU [wikipedia.org] has moved from 7333 kHz to 7850 kHz. It also transmits on 3330 kHz and 14670 kHz.
WWV and WWVH also have digital-compatible subcarrier signal formats [wikipedia.org], BTW.
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I'm fairly certain that CHU [wikipedia.org] has moved from 7333 kHz to 7850 kHz. It also transmits on 3330 kHz and 14670 kHz.
WWV and WWVH also have digital-compatible subcarrier signal formats [wikipedia.org], BTW.
As you might have guessed, I don't switch on the shortwave that often these days.
I think Japan also broadcasts time signals. Not sure what other countries do, though.
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Then this discussion might be the impetus for you to switch on and have a listen! There's still an awful lot of interesting-tending-to-weird stuff on HF these days. If you have an SSB-compatible receiver, you can listen in on amateur radio folks working the world. The US version of the bands we use are listed here [arrl.org] in several formats - they're mostly representative of ham usage worldwide.
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Then this discussion might be the impetus for you to switch on and have a listen! There's still an awful lot of interesting-tending-to-weird stuff on HF these days. If you have an SSB-compatible receiver, you can listen in on amateur radio folks working the world. The US version of the bands we use are listed here [arrl.org] in several formats - they're mostly representative of ham usage worldwide.
I've got my own impetus. It's Hurricane season! WX4NHC 14.325Mhz.
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Excellent! Those guys do good work. Are you a ham?
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.. and the programming seems way too predictable.
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National Institute of Standards and Technology time: this is Radio Station WWV, Fort Collins Colorado, broadcasting on internationally allocated standard carrier frequencies of two-point-five, five, ten, fifteen, and twenty megahertz, providing time of day, standard time interval, and other related information. Inquiries regarding these transmissions may be directed to the National Institute of Standards and Technology, Radio Station WWV, 2000 East County Road 58, Fort Collins, Colorado, 80524.
Sometimes I tune my shortwave radio to 5 or 10 MHz just to listen to WWV click away. It's kind of relaxing, and makes me think about things. The electronic clock ticking. It just goes on forever and ever like the heartbeat of civilization.
I actually have kind of an obsession with WVV. I was at the transmitter site a couple years ago, nerding the fuck out and taking pictures like a giddy school girl.
You'd (Score:5, Funny)
You'd think they'd be a bit more accurate than just "On July 5th"
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If they tried being more accurate they'd have to explain what time scale [ucolick.org] they were broadcasting way back then.
My God, it's full of words!
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Speaking of accuracy their claims are somewhat misleading. Their reference atomic clock is that good but if you receive the signal you aren't going to get 1 part in 70 trillion.
It's a very useful service, don't get me wrong, but for accuracy GNS is the best option at the moment.
I implemented a teensy WWCB transmitter once (Score:5, Interesting)
Some 15 years ago, when they were at their original low power, my area was so fringe that my fancy new WWVB wristwatch just wouldn't pick it up.
The protocol is really quite straightforward and well documented at their site. The 60kHz signal sends binary by sending either full power or a bit less (I forget how many dB). I used a computer synced with NTP and a plain old soundcard generating 60kHz from a sound card into an audio amp, and I just did either full on or full off. The output ran into a big coil that I had wound to be roughly resonant around 60kHz.
Much to my amazement, it worked. So I just kept the watch near that coil overnight and it synced perfectly, until WWVB cranked up their power at which point I retired the mess.
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Perhaps it was a 192khz sound card.
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192KHz sampling rate. Maybe the DAC is capable of outputting a 60KHz signal? Although the I/V converter stages usually do some low pass filtering.
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Re:I implemented a teensy WWCB transmitter once (Score:4, Interesting)
This one could, and I don't claim to know why. But I saw it clearly on my oscilloscope: 60kHz.
Actually it wasn't exactly 60kHz, it was 59 point something because of quantization according to a frequency counter, but apparently it was close enough to keep the watch happy.
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It's simple. People who say they did things that are demonstrably false, never did that thing, they just imagined they could, after some time has passed, they retell it as if they had.
Anyway it is possible with something like an M-Audio 192, which has a 192kHz sampling rate, but it would be much less expensive to drive an oscillator like a 555 from your parallel port. Not that I've tried.
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Nearly the entire globe- except not really (Score:5, Informative)
>"Operating at 60kHz, the signal actually follows the curvature of the Earth via a trick of electromagnetics, allowing nearly the entire globe to receive an accurate time signal"
Except it doesn't. It depends on time of day, weather, season, exact location, how much local interference, building construction, elevation, and many other factors.
I really WISH it were as strong and wonderful as implied in the summary, but it is not. I have used radio controlled, WWVB clocks for many years and one thing they are NOT is "reliable", at least not where I live. Of the dozens of clocks I have used over 20+ years, NONE of them could get a reliable signal anywhere I have lived in the Mid Atlantic coast of the USA.
I am lucky to have it sync several nights in a row and then go weeks without a signal (sometimes even a month). Unfortunately, none of the clocks I have seen will store a step adjustment, so they drift just like any other quartz clock- some are even worse than just a cheap $15 non-radio-controlled clock.
Having to constantly set and sync clocks on everything (except my computer equipment and SOME of the radio clocks) is really annoying in 2013. With all that freed up VHF TV, why couldn't the government have set aside just a tiny blip that could be used for another time sync that could penetrate buildings and work in the daytime and regardless of weather?
Oh well. WHEN it works, it is nice.
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The problem I have is there's no error correction/checksum -- the signal is binary-digit encoded, so it's possible to get a clock that think it's synced but is off by X hours or X minutes or X seconds while otherwise thinking that all is well. This isn't a big problem on smarter systems that continuously monitor the signal but most wall clocks/etc. only check from time to time so they can spend 12 hours thinking it's another time entirely. This isn't incredibly common because the signal is 1 bit per second,
There is error checking now. (Score:1)
Nist revised the WWVB format, it now carries two time signals on the same carrier. The enhanced time signal encodes the date/time as a 26 bit number with 5 parity bits. Absolutely foolproof, no, but there is now error checking for clocks that support this new format.
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Let's see... 60kHz is Low Frequency: approximately a wavelength of 5km.
Very High Frequency: 30-300MHz: a wavelength between 10m and 1m.
NIST would have to set up transmitters for your VHF time source all over the freaking place.
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Yes, I know. There would have to be a presence at nearly every TV station. Or they could use a tiny bit of UHF and get the TV stations to do it for them. At lest it would then get "everywhere" in each market.
Either that, or add an a single 60Hz east coast transmitter and alternate transmissions every minute between the two.
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I like this idea. Sort of the RF counterpart to round-robin DNS.
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They do. They're called GPS satellites.
Re:Nearly the entire globe- except not really (Score:5, Informative)
Indeed they don't even claim anything close to worldwide coverage themselves. Here are their estimated coverage maps [nist.gov].
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I'm pretty sure, that outside of the US, Joe Public doesn't even know WWVB exists, which is a shame as a single standard global time signal (back in the day) would have been kinda cool.
Here in the UK we have something similar (even runs on the same frequency):
http://www.npl.co.uk/science-technology/time-frequency/products-and-services/time/msf-radio-time-signal [npl.co.uk]
http://en.wikipedia.org/wiki/Time_from_NPL [wikipedia.org]
It's referred to as the 'Rugby clock'.
-Jar
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I see, "world" as in "World Series".
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I have used radio controlled, WWVB clocks for many years and one thing they are NOT is "reliable", at least not where I live.
It occurs to me that if the signals have almost no chance of reaching China according to the coverage maps, the factory making these things is probably just guessing if it works or not.
Even if they have some sort of signal generator mockup, it would seem to be difficult to replicate exact local conditions in the USA.
Re:Nearly the entire globe- except not really (Score:5, Informative)
> It occurs to me that if the signals have almost no chance of reaching China
As you say it would be trivial for the manufacturer to build a WWVB test generator,
however there are multiple alternatives to WWVB around the world.
Many clock chips can switch to an alternative signal if WWVB isn't audible.
http://www.cl.cam.ac.uk/~mgk25/time/lf-clocks/ [cam.ac.uk]
FWIW, I can hear WWVB in Australia, although I do need an outside antenna.
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Thank you for that wonderfully informative post! I thought I was crazy when one of my clocks syncs and it is exact 20 minutes TO THE SECOND off. It is probably a flipped bit and without any checksum, there you have it.
I agree with you also on the last part- it is not like it would be difficult to build a little smarts into a clock so it will reject something that seems wrong and try again. Also, if it would just store a step adjustment, it could, theoretically, "learn" to tell correct time to within one
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What freed up VHF TV? My area has more VHF channels post-digital than it did before. Locally, channels 6, 13, 23 and 51 are all on VHF (RF channels 6, 12, 7 and 13, respectively).
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Most stations in most areas of the USA moved to UHF during digital conversion. Even in your area, you have only 4 stations on 13 VHF channels, leaving 9 free.
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There are 12, actually (there is no channel 1) but you are right. There are 8 vacant. I suppose something could be done there, provided some care was taken to ensure that it also didn't interfere in adjoining markets.
One thought that I've been playing with lately is the idea of putting very narrowbanded signals into channel boundaries. WWVB's signal is extremely narrow banded, having a theoretical nyquist frequency of 0.5 Hz (though the reality is probably a bit broader due to modulating square waves ont
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If you saw my other post, I think another suitable idea would be to have a second, east coast transmitter and then have it alternate transmission with the west coast transmitter every minute or so. That way we could retain compatibility with all existing equipment and yet have MUCH better coverage.
About TV- yeah, I know what you mean.
Accuracy... (Score:5, Informative)
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The broadcast signal is that accurate. And even the received signal is that precise, given a stationary receiver. So baring multi-path issues (which are detectable) you can do a one-time calibration for your local propagation delay to make your local accuracy match your precision.
Moreover, they also provide a frequency reference, in addition to the time signal, so you can do your time timekeeping just by counting peaks. Such references are immune to propagation delay (though not to Doppler effects, if your
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Re:Accuracy... (Score:4, Interesting)
You do have a point.
Given that light travels about 0.3 m in one nanosecond, a variation in the signal path-length of about 300 m would induce a smudge on the arrival-times of about a microsecond. Realistic path-length variations could no doubt be larger, and could vary over a time-period of minutes or hours, depending on ionospheric conditions. This would of course be much larger than the inferred time-accuracy of 1.14e-14 s in the single second between each broadcast 'tick'.
However, GPS [wikipedia.org] is subject to the same vagaries of ionospheric conditions, as well as error in signal-interpretation. It has a theoretical accuracy of 14 ns, but more typically it is 100 ns.
No doubt the received accuracy of both WWVB and GPS could be improved by frequently collecting and applying the appropriate ephemera corrections for a given geographical location.
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Whoops, sorry for responding to my own post, but I forgot to add that light travels only about 4 micrometres in 1.4e-14 s, and it's not hard to imagine that the signal-path varies by much more than that in a single second, even for a relatively quiet ionosphere. So yes, you can't get the full benefit of WWVB's accurate clock on a second-by-second basis.
Re:Accuracy... (Score:5, Informative)
Even with no path length variation, good luck determining the path length to any specific location to micrometers in order to correct for the delay. Good luck doing so even within 15 meters (50 ns).
Using long term averaging, one might get frequency accuracy close to the claim, but not time (unless you have a hydrogen maser, I suppose). GPS is the best global time time distribution system available. If you look at BIPM Circular T [bipm.org], even national time labs have a hard time tracking UTC within 100 ns over a month. So, if you get GPS time accurate to 50 ns, (which is base off UTC(USNO), you're doing well.
The other factor is that the time isn't actually known until after the fact - UTC is a weighted average. UTC(NIST) [bipm.org], which is what's being broadcast, can differ by ~4e-8/s (~40 ns) from the actual time, a billion times worse than the claim.
Re:Accuracy... (Score:4, Interesting)
For some time I plotted the jitter of reception of DCF-77 (a similar transmitter in Germany) and I found there was a clear cycle of increase and
decrease of the jitter of the pulses output by my receiver (measured over one minute) over the day.
At daytime the jitter is around 20us, at nighttime it is more like 200us.
This is most likely explained by path length variations that apparently are depending on propagation.
(although texts about such transmitters often boast that there is no propagation effect like the one seen at shortware at those frequencies)
The claimed accuracy is of course at the source, and maybe when you started receiving WWVB years ago and perform some kind of averaging
over a long interval, you could eventually get an accuracy like that, but there is no way it can be achieved over short intervals, let alone for
individual second pulses.
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But the only way to do that is to have a better time source to begin with. And if you have that, why do you need WWVB?
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Ah, no, it's the muppets at Telstra who clearly don't come from Queensland, Western Australia, or the Northern Territory.
Software Defined Radio & WWVB? (Score:2, Interesting)
So anyone here tried using a software defined radio setup to receive and decode the WWVB signal?
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Exactly what I was wondering. I think you'd need a special devices or add-on module capable of receiving such low frequency signals.
Quotation in summary come from.... (?) (Score:1)
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Besides the new format breaking existing receivers that use a phase locked loop to decode the signal, Xtendwave, who may have had prior inside information, has patents covering the new format.
accuracy (Score:2)
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Quite the understatement (Score:4, Insightful)
" $15.9 million under budget"
Sure that'd be be a nice change for some billion dollar government project - to run a little under instead of doubling the budget,
But this was a budget of $16 million...
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Using less than the grant is what "under budget" means.
They were given X dollars and told to do Y. Thus X is the "budget" for Y. In this case they did Y but spent less than X. That's what we call "under budget".
But yes, hopefully no one actually proposed what they did would cost $16 million. Or if they did, hopefully that person now has a job in which they do not do budget estimates.
How Accurate? ... Right (Score:2)
An accuracy of 1 part in 70 trillion. Yeah. Maybe right at the clock they use. But people setting their clocks by it live a distance from the station. And the speed of the radio waves is finite. So the further from the station the less effectively accurate the signal is (people don'
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You kn
Re:How Accurate? ... Right (Score:5, Insightful)
No, it can't. The Earth's circumference is about 25,000 miles, which means that nothing can be more than 12,500 miles away by the shortest route. Considering that the speed of light is roughly 186,000 miles/second, the maximum propagation delay is about 67.2 ms.
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If you want a frequency standard, instead of knowing what UTC is "now", you can use the chroma signal from broadcast TV. The big stations use atomic clocks as a reference.
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You don't even need that, you can just use an appropriate ferrite rod and decoder board with a handful of discrete components and hook it up to a serial port.
http://www.buzzard.me.uk/jonathan/radioclock.html [buzzard.me.uk]
It uses what I call the Woz method, aka minimal hardware, do it in software. You will actually get a better result using that method as well because the computer is capturing the timestamps of the signal edges directly without it going through some intermediate process.
One day I will get around to doing
WWV and NSA crypto (Score:3)
We had several KWR-37 devices that needed time sync to under one second worldside with the transmitting station when changing daily key cards. WWW()x was great until you where some where past SE asia, then we used the Russia time sync RWM to lock devices,
http://en.wikipedia.org/wiki/RWM [wikipedia.org]
http://en.wikipedia.org/wiki/KW-37 [wikipedia.org]
http://www.nsa.gov/public_info/_files/uss_pueblo/Section_V_Cryptographic_Damage_Assessment.pdf [nsa.gov]
Syncing Seismographs (Score:2)