WWVB Celebrates 50 Years of Broadcasting Time

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."

Comments

Re:And

[Telecommando]

No, that's WWV on those frequencies.

You'd

[JustOK]

You'd think they'd be a bit more accurate than just "On July 5th"

I implemented a teensy WWCB transmitter once

[Clueless Moron]

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.

Nearly the entire globe- except not really

[markdavis]

>"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.

Re:Nearly the entire globe- except not really

[Trepidity]

Indeed they don't even claim anything close to worldwide coverage themselves. Here are their estimated coverage maps.

Re:Nearly the entire globe- except not really

[Ozoner]

> 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/

FWIW, I can hear WWVB in Australia, although I do need an outside antenna.

Accuracy...

[msauve]

WWVB time propagation isn't accurate to 1.4 e-14, as stated. The souce might be, but propagation delays and variability make it so you can get nowhere close to that upon reception. GPS is better in all respects, other than perhaps reception in some particular locations.

Re:Accuracy...

[msauve]

The claim was "allowing nearly the entire globe to receive an accurate time signal..."

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, 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), 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: And

[jrmcferren]

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.

Re:How Accurate? ... Right

[techno-vampire]

The time to receive could be a second or two behind the real time for someone receiving on the far side of the earth.

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.