atomic clocks

[dave]

On 06/26/2014 07:53 AM, jfeng@my-deja.com wrote:

On Thursday, June 26, 2014 7:08:09 AM UTC-7, dave wrote:
The Baud rate is like 1. I don't think decoding it takes very long.
My "synchronized" atomic clocks sometimes differ by a few seconds with the WWV audio tone.

You should reorient, you haven't had a lock recently.

 

[dave]

On 06/27/2014 06:42 AM, Michael A. Terrell wrote:

Arfa Daily wrote:

I'm sure they don't, but most of us on here are engineers of one kind or
another, and we *do* know better, so we ought not to be helping to
perpetuate this wrong description ...


Or the imaginary DB9 connectors?



9 pin d-sub

 

[Jeff Liebermann]

On Fri, 27 Jun 2014 08:02:28 -0700 (PDT), Tim R <timothy42b@aol.com>
wrote:

On Tuesday, June 24, 2014 2:02:04 PM UTC-4, Jeff Liebermann wrote:

Note that GPS time is 16 seconds ahead of UTC. There's also UT1 for
astronomers, which is where the leap second originates.

Is this always true? So GPS is precise to the nanosecond, but inaccurate by a quarter minute?

That's the difference between relative and absolute accuracy.

The way it works is that time originally had an astronomical
reference, which is based on the earth's rotation. The day was
divided into 24 equal hours, the calendar was divided into 365.25
days, etc. That worked fine as long as you didn't care about too many
decimal places. The problem was that the earth is slowing down 1.7
msec per day every century. There's also irregularities produced by
earthquakes, precession, and relativistic effects due to location and
altitude. In other words, the earth's rotation makes a lousy clock
for everyone except astronomers, who obviously need a clock that
points their instruments to the same place in the sky every time. So,
we have a divergence in time. The astronomy and navigation factions
follows the traditional earth's rotation model, where the length of a
second can vary somewhat. Those building timing instruments assume
that the length of a second is defined in absolute terms by the
vibration of various atoms, and do not change as the earth wobbles
it's way around the sun.

The problems begin when one tries to do celestial navigation with a
sextant using a GPS clock. 1 nautical mile = 1 minute of arc.
Therefore an error of 16 seconds would be 16/60 NM = 0.27 NM = 500
meter error. That's more than enough to miss a harbor entrance or hit
a navigation hazard. I occasionally give demonstrations on how to use
a sextant, and have to constantly remind people to use UTC, not GPS
time. Hint: Your cell phone uses GPS time.
<http://www.zdnet.com/blog/hardware/the-time-displayed-on-most-android-phones-is-wrong/19387>

The 16 seconds might not seem like much, but consider that it started
at zero 34 years ago. Left unchecked, we run the risk of repeating
the mess created by the harmonization of the Julian and Gregorian
calendars, which maintained an 11 day difference until 1752. There
were allegedly rioting in the streets demanding the return of the 11
lost days. Hopefully, that won't happen when UTC and GPS time are
eventually harmonized.

I hope this helps, but if you want a better explanation from the
experts, try the time nuts mailing list and archive:
<http://www.febo.com/pipermail/time-nuts/>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Michael A. Terrell]

dave wrote:

Michael A. Terrell wrote:

Or the imaginary DB9 connectors?

9 pin d-sub

It is a DE9

--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

 

[Jeff Liebermann]

On Fri, 27 Jun 2014 11:17:55 -0700 (PDT), Tim R <timothy42b@aol.com>
wrote:

According to Garmin, GPS time is off by the number of leap seconds
that UTC has added, since UTC adds these corrections and GPS does not.

Right.

However, a correction signal is sent with the transmission, and if
the GPS unit has the proper software it should match UTC to within
a second.

The problem is that many cell phones and a few GPS receivers don't
bother to include the compensation in sub-frame 4 of the "legacy" L1
C/A navigation message. No clue what happened to that in CNAV-2 or
the current L5-CNAV. I need to RTFM and am too busy/lazy/etc.

>So when I get home I'll fire up the eTrex and see if it matches UTC.

Here's my Droid X2 (Verizon) cell phone versus my Windoze XP clock:
<http://802.11junk.com/jeffl/crud/GPS-vs-UTC.jpg>
I ran a SNTP clock sync on the XP box just before I took the photo. It
shows 15 seconds difference instead of the real 16 seconds. I believe
that's due to latency or round off error in my XP box.

I would not be surprised if later cell phones compensated correctly. I
can dig out some other phones if you want something more current.

Of course, in science, nothing is permanent:
"UTC might be redefined without Leap Seconds"
<http://www.ucolick.org/~sla/leapsecs/>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Fri, 27 Jun 2014 15:18:17 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

However, a correction signal is sent with the transmission, and if
the GPS unit has the proper software it should match UTC to within
a second.

Looks like I haven't been paying attention. There's a mess of new GPS
to UPS conversion parameters available on the new L5 frequency that is
just now being turned on.
<http://www.insidegnss.com/node/3986>
It won't do anything for most existing devices because of the lack of
a suitable L5 (1176.45 MHz) receiver. Most smartphones and GPS
receivers only do L1 (1575.42 MHz) and L2 (1227.60 MHz). There are
only a few satellites that transmit on L5 at this time. Lots of other
changes coming:
<http://www.gps.gov/cgsic/meetings/2012/lawrence.pdf>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Michael A. Terrell]

Jeff Liebermann wrote:

On Fri, 27 Jun 2014 15:18:17 -0700, Jeff Liebermann <jeffl@cruzio.com
wrote:

However, a correction signal is sent with the transmission, and if
the GPS unit has the proper software it should match UTC to within
a second.

Looks like I haven't been paying attention. There's a mess of new GPS
to UPS conversion parameters available on the new L5 frequency that is
just now being turned on.
http://www.insidegnss.com/node/3986
It won't do anything for most existing devices because of the lack of
a suitable L5 (1176.45 MHz) receiver. Most smartphones and GPS
receivers only do L1 (1575.42 MHz) and L2 (1227.60 MHz). There are
only a few satellites that transmit on L5 at this time. Lots of other
changes coming:
http://www.gps.gov/cgsic/meetings/2012/lawrence.pdf

Some photos of the transmitters at WWV, WWVB, and WWVH in a recent
thread on Facebook:

<https://www.facebook.com/groups/transmittersites/permalink/713544682040515/>


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

 

[Jeff Liebermann]

On Sun, 29 Jun 2014 21:28:01 -0400, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

Some photos of the transmitters at WWV, WWVB, and WWVH in a recent
thread on Facebook:
https://www.facebook.com/groups/transmittersites/permalink/713544682040515/

Thanks. Very interesting. Note that there are no photos of WWVB on
that page. Only WWV(Ft Colins) and WWVH (Hawaii).

Tiny NIST WWVB pix:
<http://tf.nist.gov/stations/morevbpics.html>
<http://tf.nist.gov/stations/vbpicts.htm>

The big big big cage antenna used for 60 KHz (lowered):
<http://tf.nist.gov/images/radiostations/wwvb-large/art1.jpg>
Kinda difficult to see, so here's my enlarged and tweaked version:
<http://802.11junk.com/jeffl/WWVB%20test/WWVB-antenna-lowered.jpg>
<http://physics.nist.gov/TechAct.Archive/TechAct.99/Div847/Images/fig6.gif>
WWVB uses two transmitters in phase driving each antenna seperately.
Think big.

More photos:
<http://www.panoramio.com/photo/14672442>
<http://www.panoramio.com/photo/960723>



--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Brian Gregory]

On 21/06/2014 15:54, William Sommerwerck wrote:

The current crop of atomic clocks are inexpensive and largely
disposable. But the following might be of interest.

If the clock refuses to sync, check to see if the ferrite antenna is
loose and rattling. I've found that if it isn't sitting "vertical", it
doesn't pick up enough signal.

These clocks generally sync around midnight. But whoever wrote the
firmware didn't think to attempt a sync when the batteries were
installed. So if you don't want to wait forever, manually set the clock
to 11:55 PM (or thereabouts). You should have sync within a few minutes.

Ferrite aerials ALWAYS need to be horizontal with the side of the rod
roughly facing the transmitter.

The correct name for clocks like this is radio controlled.

In regions where the signal controls the change to and from summer time
the normal time these clocks sync themselves is at the time when changes
to and from summer time. 02:00 AM in Europe.
Some may also sync at other times of day in addition to 02:00 AM.

--

Brian Gregory (in the UK).
To email me please remove all the letter vee from my email address.

 

[Brian Gregory]

On 24/06/2014 15:46, dave wrote:

On 06/23/2014 12:04 PM, Ian Field wrote:




The waveceptor can be set up for use in a list of countries, but its a
fiddly process of pressing various buttons in the right order.

The clocks were bought in Lidl and AFAIK mostly German made - so they
probably sync to the 77kHz DCF in Frankfurt rather than the 60kHz MSF in
Anthorn, Cumbria (Formerly sited in Rugby).

Isn't GPS a lot less trouble? I'd worry about the elimination of the
leap second if I were you. FYI I have a dozen WWVB clocks of every
description (except 24hr analog).

GPS doesn't always work indoors.

--

Brian Gregory (in the UK).
To email me please remove all the letter vee from my email address.

 

[William Sommerwerck]

"Brian Gregory" wrote in message
news:wvednQ7Wd4GM8CzOnZ2dnUVZ7vydnZ2d@giganews.com...

Ferrite aerials ALWAYS need to be horizontal with the side
of the rod roughly facing the transmitter.

I agree in principal. But the antenna in my La Cross is vertical. And my
Oregon Scientific clocks work fine with their antennas vertical.

If you like, I can take a photo of the La Cross's internals, and you can see
which way the antenna is oriented.


Since my original post, I've discovered that the La Cross tries to sync at
midnight. The unit sits next to a large-screen TV, so this sync is often
blocked. Once the TV is shut off, the La Cross will almost immediately try to
sync again, regardless of the time.

 

[William Sommerwerck]

"William Sommerwerck" wrote in message news:lorrd6$mn1$1@dont-email.me...

> I agree in principal.

Sorry. Forty lashes with a WD-40 coated loopstick! Principle, of course.

 

[Geoffrey S. Mendelson]

Brian Gregory wrote:

GPS doesn't always work indoors.

Which is why I was looking into turning old Android phones into GPS based
NTP servers. You stick one in a window and it covers (via wifi) your entire
home.

Geoff.

--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379

 

[Jeff Liebermann]

On Mon, 30 Jun 2014 07:14:59 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net> wrote:

"Brian Gregory" wrote in message
news:wvednQ7Wd4GM8CzOnZ2dnUVZ7vydnZ2d@giganews.com...

Ferrite aerials ALWAYS need to be horizontal with the side
of the rod roughly facing the transmitter.

I agree in principal. But the antenna in my La Cross is vertical. And my
Oregon Scientific clocks work fine with their antennas vertical.

You still don't believe my crude test of antenna orientation?
<http://802.11junk.com/jeffl/WWVB%20test/>

If you like, I can take a photo of the La Cross's internals, and you can see
which way the antenna is oriented.

This I would like to see, especially since I can't find any photos
online. I'll trade you.... I'll build up my WWVB module to include a
flashing LED, that should demonstrate the quality of the signal by
flashing regularly at 1 second intervals when there's a good signal,
and flashing much faster and erratically when there's only noise.
<https://www.youtube.com/watch?v=bm5dC5vK0Os>
<https://www.youtube.com/watch?v=cBTsrkPFW2c> [1]
If you want, I'll mail something to you so that can convince yourself.
Now, here's someone that tried it with a vertically mounted loopstick
antenna:
<https://www.youtube.com/watch?v=qicOs6KaX5A>
Notice the rather erratic flashing light pattern. Hmmm...

What I guess(tm) is happening is that you are either in a good
location or have a particularly good loopstick, where the difference
in antenna orientation produces signal level changes from perhaps very
strong, to not so very strong. Therefore, it works in any
orientation. At my location, the signal is not so strong, so the
variation changes from usable, to totally gone.

Since my original post, I've discovered that the La Cross tries to sync at
midnight. The unit sits next to a large-screen TV, so this sync is often
blocked. Once the TV is shut off, the La Cross will almost immediately try to
sync again, regardless of the time.

I hot wired my Oregon Scientific to run all the time. It burns the
battery a bit more, but I can now see WHEN it will sync by simply
killing the power and waiting for the display to update. It takes
about 5 minutes with a strong signal. After about 9PM PDST, it will
erratically start to sync. After midnight, it's very consistently. I
haven't been up early enough to test when it stops.

WWVB loopstick winding and oscilloscope photos:
<http://www.prc68.com/I/Loop.shtml>


[1] At the very end of the video, notice that the flashing light
pattern changes. That's the 1 minute sync pattern.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[William Sommerwerck]

"Jeff Liebermann" wrote in message
news:nk03r9tu5pdlfodgb0e2ul0as4bm16jjsp@4ax.com...

I agree in principle. But the antenna in my La Cross is vertical. And
my Oregon Scientific clocks work fine with their antennas vertical.

You still don't believe my crude test of antenna orientation?
http://802.11junk.com/jeffl/WWVB%20test

Why should I disagree with your results?

The fact is that the La Cross antenna is positioned vertically. There's a
sort-of-slot for it, and as shipped, it's hot-glued in place.

If you like, I can take a photo of the La Cross's internals,
and you can see which way the antenna is oriented.

This I would like to see, especially since I can't find any photos
online. I'll trade you...

No trade is needed. Give me a day or two, and I'll send a photo.


> What I guess(tm)...

A man with my sense of humor...

...is happening is that you are either in a good location or have a
particularly good loopstick, where the difference in antenna
orientation produces signal level changes from perhaps very strong,
to not so very strong. Therefore, it works in any orientation. At my
location, the signal is not so strong, so the variation changes from
usable, to totally gone.

That's plausible. Some things are always true -- except then they're not.

 

[Michael A. Terrell]

Jeff Liebermann wrote:

On Sun, 29 Jun 2014 21:28:01 -0400, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

Some photos of the transmitters at WWV, WWVB, and WWVH in a recent
thread on Facebook:
https://www.facebook.com/groups/transmittersites/permalink/713544682040515/

Thanks. Very interesting. Note that there are no photos of WWVB on
that page. Only WWV(Ft Colins) and WWVH (Hawaii).

Most of the thread has expired. There were links to manuals for the
TMC transmitters that were designed & built for the Navy. There were
several other threads, but I couldn't find any of them.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

 

[Leif Neland]

Geoffrey S. Mendelson sendte dette med sin computer:

Brian Gregory wrote:

GPS doesn't always work indoors.


Which is why I was looking into turning old Android phones into GPS based
NTP servers. You stick one in a window and it covers (via wifi) your entire
home.

I do not see the point.

If you have wifi, in 99,9% you have internet, and then you can get time
by ntp.

A server or router on your network can most probably be set up to sync
to a server from eg pool.ntp.org and serve ntp for your network.

See http://www.pool.ntp.org for more info.

--
Husk křrelys bagpĺ, hvis din bilfabrikant har taget den idiotiske
beslutning at undlade det.

 

[Geoffrey S. Mendelson]

Leif Neland wrote:

I do not see the point.

If you have wifi, in 99,9% you have internet, and then you can get time
by ntp.

A server or router on your network can most probably be set up to sync
to a server from eg pool.ntp.org and serve ntp for your network.

See http://www.pool.ntp.org for more info.

Because NTP costs money to use. Not as in paying NTP servers, but in
eating up bandwidth (many places have very limited UPLOAD bandwith)
and it tends to overload the "atomic clock" (stratum 1) servers.

There is for example, only 1 stratum 1 server in Israel that is not
GPS based, and it is very heavily loaded. So loaded in fact, that
most connections are blocked.

There are no functioning pool servers in the country.

I'm sure Israel is not unqiue, once you get out of the EU, US and maybe
Canada, everyone has the same problem.

Geoff.


--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379

 

[Leif Neland]

Geoffrey S. Mendelson sendte dette med sin computer:

Leif Neland wrote:
I do not see the point.

If you have wifi, in 99,9% you have internet, and then you can get time
by ntp.

A server or router on your network can most probably be set up to sync
to a server from eg pool.ntp.org and serve ntp for your network.

See http://www.pool.ntp.org for more info.


Because NTP costs money to use. Not as in paying NTP servers, but in
eating up bandwidth (many places have very limited UPLOAD bandwith)
and it tends to overload the "atomic clock" (stratum 1) servers.

There is for example, only 1 stratum 1 server in Israel that is not
GPS based, and it is very heavily loaded. So loaded in fact, that
most connections are blocked.

You do not need a stratum 1 server

Every university and ISP ought to run a time server of stratum 2 or
more, and join the pool.ntp.org.

As the www.pool.ntp.org says:
"Note that it is not required that your server is a stratum 1 or 2
server - as this project is about load distribution mostly, there is no
reason why a stratum 3 or even stratum 4 server shouldn't join."

--
Husk křrelys bagpĺ, hvis din bilfabrikant har taget den idiotiske
beslutning at undlade det.

 

[dave]

On 06/27/2014 08:02 AM, Tim R wrote:

On Tuesday, June 24, 2014 2:02:04 PM UTC-4, Jeff Liebermann wrote:

Note that GPS time is 16 seconds ahead of UTC. There's also UT1 for

astronomers, which is where the leap second originates.



Is this always true? So GPS is precise to the nanosecond, but inaccurate by a quarter minute?

The earth is slowing down its RPM.