Hi,

I read that the moving of NIST F1 1 floor indeed changed the frequency
quite a bit.
(The change in altitude was 11.5 feet)
That article also mentioned that the warming up of the building itself in
summer has an effect on some of the newest research clocks, because the
environment changes shape...
See
http://www.wired.com/science/discoveries/news/2007/12/time_nist?currentPage=all

(Not that those clocks are commercially available, though :-/ )

Greetings,
Pieter.

More importantly, does this impose an upper limit on data transport speed over
networks, in particular wireless networks?  If and when one produces the network
technology that would demand the accuracy and precision of these new
standards, if one object is moving relative to the other, there could be loss of
data as the moving clock goes out of sync with the stationary one.  We know this
was possible just from special relativity, but motion at "normal" speeds does
not contribute appreciably at the currently achievable accuracies and
precisions.  However, with the next generation, driving in a car or certainly
flying in a plane will limit bandwidth.  And, of course there's the gravitation
effect to contend with in the future as well, which could also limit bandwidth.

As I am thinking about this, does this impose a limit on GPS accuracy and
precision based on the next gen technology?

Jeff
 Jeffrey K. Okamitsu, PhD, MBA
+1-609-638-5402 US Mobile Phone
+1-240-421-0692 GSM Mobile Phone

From: Pieter ten Pierick time-nuts-mail@tenpierick.com
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Wed, September 29, 2010 12:55:59 PM
Subject: Re: [time-nuts] Next Generation Time/Frequency Standards May Require
Provisions Preventing Vertical Displacement

Hi,

I read that the moving of NIST F1 1 floor indeed changed the frequency
quite a bit.
(The change in altitude was 11.5 feet)
That article also mentioned that the warming up of the building itself in
summer has an effect on some of the newest research clocks, because the
environment changes shape...
See
http://www.wired.com/science/discoveries/news/2007/12/time_nist?currentPage=all

(Not that those clocks are commercially available, though :-/ )

Greetings,
Pieter.

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and follow the instructions there.

On 09/29/2010 06:56 PM, Jeffrey Okamitsu wrote:

You can compare two standards by levelling their gravitational centers
(similar to phase centers of GPS antennas) to the same level or within
same level to what degree they are comparable too.

Wither they need to be within 1 mm, 100 mm, 10 m or 1 km depends on the
quality of the oscillators.

Cheers,
Magnus

I was thinking more in terms of remotely located devices.  That is, not at
the same physical position where the sync signal is transmitted over some
reliable medium.   In that case, one will have to know the relative vertical
displacement.

Also, as I think further, in principle the local terrain at each location plays
a role as well.

Jeff
 Jeffrey K. Okamitsu, PhD, MBA
+1-609-638-5402 US Mobile Phone
+1-240-421-0692 GSM Mobile Phone

From: Magnus Danielson magnus@rubidium.dyndns.org
To: time-nuts@febo.com
Sent: Wed, September 29, 2010 1:51:30 PM
Subject: Re: [time-nuts] Next Generation Time/Frequency Standards May Require
Provisions Preventing Vertical Displacement

On 09/29/2010 06:56 PM, Jeffrey Okamitsu wrote:

You can compare two standards by levelling their gravitational centers (similar
to phase centers of GPS antennas) to the same level or within same level to what
degree they are comparable too.

Wither they need to be within 1 mm, 100 mm, 10 m or 1 km depends on the quality
of the oscillators.

Cheers,
Magnus

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and follow the instructions there.

On 09/29/2010 07:17 PM, Jeffrey Okamitsu wrote:

No, not really.

The imprecision of oscillators being used is so huge that gravitational
effects is swamped in normal everyday life. You need significant
elevation such as that of GPS satellites, but much of that effect can be
treated using frequency offset and the remaining effect involves movement.

No, gravitational effects is first degree compensated and only a minor
second degree effect needs compensation for some case. These effects is
very predictable.

You can always find cases where a particular effect forms a limit, but
relative theory doesn't form a practical limit for most of the day to
day life and use of technology.

For the case of telecommunication networks, the receiver will recover
the symbol rate of the signal in order to sample the symbols and later
those symbols is converted into bits. That the transmitter and receiver
has different gravitational potential causes a small offset in
frequency, but since the receiver PLL tracks the frequency then
frequency errors due to oscillator offsets, temperature changes, doppler
effects as one moves around etc.

Doppler effects is much more important, and it's effects is being
treated regularly, such as when talking in the GSM phone while driving
the car...

Cheers,
Magnus

Jeffrey Okamitsu wrote:

from the article:Holger Müller, a physicist at the University of
California, Berkeley, says that the study shows that relativity is no
longer confined to experiments working with huge speeds and distances.
"This is mainly a grand technological feat, but has an almost
philosophical component," he says. "It shows that relativity is
something tangible."

Hmm. I think that tvb's demo in the minivan was pretty impressive.....

Jeffrey Okamitsu wrote:

We already deal with relativistic corrections in GPS data, and also in
deep space navigation  (when you're measuring millimeter range
differences in the distance to Saturn and back, everything counts)..

A few years ago, I was working with some folks who were looking at time
transfer among different spacecraft for the Constellation program (e.g.
if you have relay satellites around the Moon or Mars or somewhere, and
you want precision timing to someone on the back side of either (i.e.
they can't see Earth directly).  The velocities are high enough that you
need to start contemplating relativistic effect:  e.g. at 7 km/s
sqrt(1-v^2/c^2) is about 1 part in 1E10.. If you need to synchronize
events to, say, 1 millisecond out of a day, that's 1 part in 1E11

Magnus Danielson wrote:

Unless you're also using the telecommunications signal as a measurement
tool (e.g. radio science).. To be honest, this is a curse for modern
deep space telecom designers.  Back in the day ( a couple decades ago or
so).. the data rates were very low (e.g. 7-10 bps) so at very low SNR,
one needs a pretty stable oscillator to be able to effectively use a
narrow filter.  Assuming you have that oscillator, it's not so hard to
also use it to do precision Doppler measurements (e.g. Transit and Argos
are examples of moderate precision nav using Doppler), so the
"requirement" to have an oscillator with good short term stability so
you can do nav also didn't drive cost.
Now, jump forward and we want to send and receive Megabits/second from
deep space.  With a multiMHz wide signal, it's not like we need to know
the carrier center frequency to a gnat's eyelash, so, in theory, as long
as the overall phase noise is OK, we don't need good Allan deviation
performance or even particularly good frequency accuracy.. 1 ppm out of
32 GHz is 32 kHz, which is pretty small compared to a 1 MHz wide data
signal.  So you'd think we could cheap out on the oscillator...  But,
no... the navigators and radio scientists are used to getting that
really rock solid signal for free...

But I digress...

Hmm.. I think crystal oscillator frequency variation in the phone is a
bigger factor.  Let's say you're zipping down the road at 200 km/hr
(55m/s), texting your friends.  That's about 0.2ppm Doppler or around
400 Hz (for a 2 GHz carrier).. as noted.. the XO probably has 1ppm (at
best.. more like 10ppm)

An even bigger problem in a mobile environment is multipath, which is
far worse than the Doppler.. The effective propagation path distance
could easily change 1000 meters in a fraction of a second.