Author Topic: GPS vs WWV data stream  (Read 451 times)

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Offline WA4AOS

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GPS vs WWV data stream
« on: June 10, 2021, 07:03:00 pm »
I understand WWV will shut down operations soon and there are groups trying to get the feds to continue to fund this viable service.
Does anyone know if the data stream used on GPS is the same as used with WWV? I'm considering a very low 1mv DDS transmitter for 5 or 10 MHz and feed the GPS data into the xmitter. My need is to keep my old Heathkit GC 1000H clocks going wo retrofitting each unit with a GPS rx.

Any thoughts?

Glenn WA4AOS
 

Offline fourfathom

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Re: GPS vs WWV data stream
« Reply #1 on: June 10, 2021, 08:32:53 pm »
I think this WWV shutdown story is old news, and never came to pass.  There was a 2019 federal budget proposal that would have shut down WWV transmitters, but that wasn't approved, and as of 2020 WWV funding seems to be adequate.  I even see that there was a 2021 WWVB upgrade, supposedly completed a few months ago.
 

Offline james_s

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Re: GPS vs WWV data stream
« Reply #2 on: June 11, 2021, 04:56:44 am »
I hope that's the case. I also have a GC-1000, it's one of my prized possessions. I also have about half a dozen devices that rely on the 60kHz WWVB signal. Most people probably don't know what WWVB is, but there are hundreds of millions of "atomic" clocks that rely on it to work.
 

Offline evb149

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Re: GPS vs WWV data stream
« Reply #3 on: June 11, 2021, 05:03:42 pm »
I don't know about the shut-down plans, but to answer one question there's probably no direct relationship between WWV and GPS.  In fact even WWV's various services have different protocols and specifications depending on the transmitter frequency (as I recall).

And what GPS actually sends out to the receivers is actually typically something that is not directly related to what a GPS receiver puts out.

GPS receivers often support two or more output data formats, and there are probably over a dozen "common" formats.
NMEA-0183 is (as I recall) the designation of a common "plain text over a serial / communications port" type format that many or most receivers support generating at least some subset of (it isn't mandatory to support anything among the optional content elements).  Then there are various manufacturer specific "binary" and "text" output protocols.  Then there are variants used for different applications -- IIRC maritime or other kinds of receivers may have some different output variants vs. land mobile ones though they may be variants of NMEA-0183, I forget.

So to convert one to the other would need a moderate amount of transcoding and also resynchronization in time.

 

Offline james_s

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Re: GPS vs WWV data stream
« Reply #4 on: June 11, 2021, 09:51:21 pm »
They are indeed unrelated, WWV, WWVH and the GPS satellites each have their own independent array of atomic clocks. The clocks themselves should be comparably accurate but in practice GPS is likely to be more accurate due to propagation characteristics of the shortwave and LF broadcasts that WWV uses. 
 

Offline jpanhalt

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Re: GPS vs WWV data stream
« Reply #5 on: June 11, 2021, 11:12:21 pm »
As one might say, it depends on what you mean by "more accurate."

Quote
The difference is that GPS time is not corrected to match the rotation of the Earth, so it does not contain leap seconds or other corrections that are periodically added to UTC.  As of January 2017, GPS time is 18 seconds ahead of UTC because of the leap second added to UTC December 31, 2016.
Google: Difference between UTC and GPS time

In terms of UTC, WWVB is more accurate.
 

Online MIS42N

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Re: GPS vs WWV data stream
« Reply #6 on: June 12, 2021, 09:50:05 am »
There is a relationship between the time provided by GPS receivers and the various WWx broadcasts. The GPS time does not have leap seconds because it complicates the navigation calculations. However the GPS transmissions give the offset between GPS time and UTC so a GPS receiver reports time in UTC. The GPS and WWx broadcasts are related back to NIST. See https://www.nist.gov/pml/time-and-frequency-division/time-distribution. The conversion of GPS data to WWVB format has been tackled, see https://www.anishathalye.com/2016/12/26/micro-wwvb/

Deriving time from GPS is probably better than using the WWx broadcasts because the propagation delay correction has already been worked out by the receiver, the time should be within 100ns. Unless you know the distance between the WWx transmitter and your receiver to better than 30 meters, the GPS should win.
 


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