Re: [time-nuts] A different way to think about time dilation?

[Bill Byrom]

I think you are on the wrong track with assuming that every object has a
velocity c. What you need to consider is relativity. Velocity is a local
measurement (local reference frame distance and local reference frame
time). Light (and other electromagnetic radiation) always travels at a
local velocity c (local distance divided by local time). Time dilation
is a way of describing the effect of the relativity of simultaneity.
Events which are not local (adjacent) to each other can't be
unambiguously described as simultaneous. There is no universal clock
which allows us to determine which of two separated events occurred
"before" the other.
 
There are two causes of time dilation:
(1) Relative uniform motion. If two spacecraft are passing each other
in uniform motion (not accelerating), from the point of view of
each spacecraft the clocks on the other vessel will be slow
compared to the local clocks. Due to the relativity of
simultaneity, the seeming contradiction of a lack of symmetry (each
of the remote clocks appears slow compared to the local clock)
isn't a problem if you consider the two spacecraft starting with no
motion at the same location, then moving relative to each other,
then coming together again.
(2) Gravitational fields (or - by the principle of equivalence -
acceleration). As the Pound-Rebka experiment verified, clocks at
different gravitational potentials appear to run at different rates
from each other. This also causes the gravitational redshift. This
is a symmetric effect, and observers at both gravitational fields
will agree that the clocks at one are slower than the other.
 
For an explanation of why relative motion causes time dilation, see:
 
https://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_time_dilation_due_to_relative_velocity
 
If you want to understand why the relativity of simultaneity is so
important, research the "ladder paradox" or the "train and platform
light flash" thought experiment:
 
https://en.wikipedia.org/wiki/Ladder_paradox
 
https://en.wikipedia.org/wiki/Relativity_of_simultaneity#The_train-and-platform_thought_experiment
 
Consider this last example as the velocity of the train approaches c.
Inside the train car, the observer at the center of the car will view
the experiment as very simple. If there are mirrors at each end of the
car, from the point of view of the observer at the center of the car the
light flash reaches the two end mirrors at exactly the same time, and
the reflected light pulses arrive back at the center simultaneously. But
from the point of view of the observer on the platform, the light
reaches the "back" mirror long before it reaches the "front" mirror, due
to the rapid motion of the train.
 
--
Bill Byrom N5BB
 
 
 
On Sun, Jul 10, 2016, at 11:01 AM, Chris Albertson wrote:
> Is this a valid TN subject?  It's about time but a little off of the
> usual
> subject of 10Mhz oscillators.
>
> I heard  of an alternate way to describe time dilation caused by
> velocity.
>   I think this makes it easier to understand but I've not been able to
> verify the math.  This alternate explanation also makes it easy to see
> why
> we can never go faster than light.   But I've not seen a mathematical
> derivation so it could be wrong or just an approximation.
>
> Here goes:
>
> 1) We assume a 4 dimensional universe with four orthogonal axis, x,
>y, z,
> and time (t)
> 2) assume that at all times EVERY object always has a velocity vector
> who's
> magnitude is "c", the speed of light.  The magnitude of this vector
> (speed)
> never changes and is the same for every particle in the universe.
>
> This at first seems a radical statement but how is moving at c much
> different from assuming every partial is at rest in t's own reference
> frame?  I've just said it is moving at c in it's own reference frame.
> Both
> c and zero are arbitrary speeds selected for connivance.
>
> How can this be?  I know I'm sitting in front of my computer and
> have not
> moved an inch in the last four hours.  c is faster than that.   Yes
> you
> are
> stationary in (x,y,z) but along the t axis you are moving one
> second per
> second and I define one second per second as c.  Now you get smart and
> try
> to move faster than c by pushing your chair backward in the Y
> direction
> at
> 4 inches per second.  So you THINK your velocity magnitude is
> the vector
> sum of c and 4 inch/sec which is greater than c.   BUT NO.  Your speed
> along Y axis causes time dilation such that your speed along T is now
> slower than 1 second/second.   In fact if you push your chair backward
> along Y real fast at exactly c your speed along t axis is zero, time
> stops.  Try pushing your chair at 0.7071 * c and you find
> yourself moving
> through t at 0.7071 sec/sec and the vector sum is c.  You can
> NOT change
> you speed from c all you can do to change the direction of the
> velocity
> vector and your speed through time is determined 

[time-nuts] GPS for Nixie Clock

[John Swenson]

I'm thinking about converting a Nixie clock I built years ago into using 
GPS for the time base. No real NEED, just for fun.


The clock uses an FPGA for formatting and display, using the 60Hz line 
frequency as the time base. The case is a single hollowed out block of 
walnut.


I'm looking into a TU36-D400-020 receiver. This seems to be optimized 
for timing purposes rather than navigation, it has 1PPS and 10KHz outputs.


I'd be getting it from RDR Electronics, which says it it uses the 
Motorola command set. This seems fine for me, it has the information I 
need, specifically UTC time so I don't have to worry about leap seconds.


I have a few questions about this receiver:
The data sheet lists two serial ports, but I don't see any information 
about which to use. Are they identical, do I have to use one for some 
functions and the other for other purposes?


What are the serial port parameters? 9600-8-N-1? Or something else?

Which is better to use, the 1PPS or the 10KHz? I can easily go either 
way. The clock display just goes down to seconds so 1PPS would work. I 
could also re-clock the 1PPS with the 10KHz.


What antenna to use? I would prefer something mounted inside the case. 
It is wood so an internal antenna will hopefully work. The board comes 
with a pigtail but it is not SMA.


Any other hints for using this?

I've never done a GPS interface before so I'm not sure about how I 
calibrate the time coming from the message over the serial port. Is it 
something like "the time is such and such at the rising edge of the next 
PPS, or the previous one? Or is there some other mechanism for 
calibrating when the second changes on the display to something close to 
reality?


I previously toyed with the idea of using an X72 rubidium oscillator 
just for the bragging rights, but I would still need the GPS to get the 
time, I decided the TU36 on its own is probably just fine.


Thanks,

John S.


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[time-nuts] GPS disciplined Mars clock

[Mark Sims]

For all those curious about all these weird and wonderful astronomical time 
scales this is a good start:
http://arxiv.org/pdf/1005.4415v3.pdf

  
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Re: [time-nuts] Good GPSDO on eBay?

[Chris Albertson]

My experience is different.  When I received a broken item from China, it
was damaged in shipment because it was poorly packed, the seller told be to
keep the broken part because he did not want to pay to ship something he
would just toss in the trash.

eBay's current policy is given here:
http://pages.ebay.com/help/policies/money-back-guarantee.html
It says that for items not as described the seller pays for return
shipping.   It seems that what you did was go through paypal who might had
a different policy they need to handle transactions outside of eBay

On Sun, Jul 10, 2016 at 2:23 AM, Clint Jay  wrote:

> No,  my experience with Chinese sellers,  even when you file a "not as
> described"  case,  is that eBay will require you to return the item at your
> own expense if the seller has stated they will not pay return shipping.
>
> Ebay's attitude was that the seller could just state in their item
> description that buyer is to cover return costs and that's it.  Game over.
>
> Which is why you occasionally still see items for peanuts and extortionate
> shipping costs, the seller then only has to refund you a couple of dollars
> on an item that may have cost you a hundred including shipping.
>
>   I ended up getting a total refund of £3 on a £28 item once I'd returned
> it and taken shipping into account. Also,  that was a PayPal refund, not a
> seller refund because they just refused shipment so eBay refused to refund
> as they had no proof of return.
>
> All the above are the reasons why I now rarely if ever buy anything costing
> more than a couple of pounds from China unless I know other people have had
> good experience with the item and seller.
> On 10 Jul 2016 05:46, "Chris Albertson"  wrote:
>
> > On Sat, Jul 9, 2016 at 5:51 PM, Richard W. Solomon 
> > wrote:
> >
> > > What a deal, if it arrives DOA, return shipment is on
> > > your nickel. I would look elsewhere.
> >
> >
> > That is not true.  If it were DOA and the seller would not take it back
> > post paid you could file a "not as described" on the seller and eBay
> would
> > refund the price.  eBay and Paypal offer pretty good buyer protection.
> >
> > Someone here said the seller uses multiple IDs.  It is more likely that
> one
> > person is making these and offering to multiple people who  then sell
> them
> > on eBay.   This is the way it works in China, a popular design gets made
> > and then is sold by many people.   It is all a cottage industry over
> there.
> >Pick any kind of electronic PCB level part, say a stepper motor driver
> > and you see the same exact part from 20 different sellers not one seller
> > with 20 IDs.(Well that is the general case, this specific one might
> be
> > different, who knows.)
> >
> > But so what even if the GPSDO is good only to 1xE10 that is still a very
> > useful device to own.  Yes some are literally 1,000 times better
> >
> > You could always build your own.  It is not hard nor is it expensive if
> you
> > have a reasonable goal and don't go for state of the art.
> > --
> >
> > Chris Albertson
> > Redondo Beach, California
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> >
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> and follow the instructions there.
>



-- 

Chris Albertson
Redondo Beach, California
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[time-nuts] GPS disciplined Mars clock

[Mark Sims]

I found some test data and tried those values with my code.   They agree to 
within a millisecond... and that difference is caused by my JD to Gregorian 
routine that adds a millisecond to the JD input to compensate for possible tiny 
double precision math errors...  All of Lady Heather's times are calculated in 
Julian to with fractional seconds, but the time displays are all truncated to 
seconds (since the screen is updated on one second intervals synced to the GPS 
receiver time message).  Without the millisecond fudge, those math errors can 
occasionally  cause what appears to be a duplicated/skipped time stamp.

I looked into adding BJD support but that requires some hairy calculations that 
depend upon externally supplied ephemeris, etc data... some of the equations 
can have thousands of coefficients.Also, BJD usage is generally applicable 
only when observing things way out in space.  Most BJD routines barf when the 
distance is within the solar system.   I'm now looking at adding HJD support... 
Heliocentric Julian Date, where instead of the solar system barycenter,  the 
reference location is the center of the sun.   That can be done without the 
need of external data. The time difference between BJD and HJD is around +/- 
the light travel time across the sun radius (the solar system barycenter 
generally stays within the sun).  Since Lady Heather is not observing some 
external event,  the HJD would basically be JD adjusted for the light travel 
time between you and the center of the sun... cool, but not all that useful 
(just like many of the things that Lady Heather can do). 

---
> Source code to do the conversion also on above site.  You should just use
their code as it is known correct .   
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[time-nuts] A different way to think about time dilation?

[Chris Albertson]

Is this a valid TN subject?  It's about time but a little off of the usual
subject of 10Mhz oscillators.

I heard  of an alternate way to describe time dilation caused by velocity.
  I think this makes it easier to understand but I've not been able to
verify the math.  This alternate explanation also makes it easy to see why
we can never go faster than light.   But I've not seen a mathematical
derivation so it could be wrong or just an approximation.

Here goes:

1) We assume a 4 dimensional universe with four orthogonal axis, x, y, z,
and time (t)
2) assume that at all times EVERY object always has a velocity vector who's
magnitude is "c", the speed of light.  The magnitude of this vector (speed)
never changes and is the same for every particle in the universe.

This at first seems a radical statement but how is moving at c much
different from assuming every partial is at rest in t's own reference
frame?  I've just said it is moving at c in it's own reference frame.  Both
c and zero are arbitrary speeds selected for connivance.

How can this be?  I know I'm sitting in front of my computer and have not
moved an inch in the last four hours.  c is faster than that.   Yes you are
stationary in (x,y,z) but along the t axis you are moving one second per
second and I define one second per second as c.  Now you get smart and try
to move faster than c by pushing your chair backward in the Y direction at
4 inches per second.  So you THINK your velocity magnitude is the vector
sum of c and 4 inch/sec which is greater than c.   BUT NO.  Your speed
along Y axis causes time dilation such that your speed along T is now
slower than 1 second/second.   In fact if you push your chair backward
along Y real fast at exactly c your speed along t axis is zero, time
stops.  Try pushing your chair at 0.7071 * c and you find yourself moving
through t at 0.7071 sec/sec and the vector sum is c.  You can NOT change
you speed from c all you can do to change the direction of the velocity
vector and your speed through time is determined by the angle between that
vector and the t axis.

It works ok to just use one of the three spacial axis because we can always
define them such that (say) the Y axis points in the direction of motion.
So a plot of your speed in the dy,t plane covers the general case and looks
like an arc of radius c.

If this works out then I have some work to do, like defining momentum as a
function of the area between the velocity vector and the t axis


-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] jovian and saturnian day length

[William H. Fite]

Here's some insight into measurement of jovian rotation back in the good
old days. A wee bit more sophisticated than looking at the Great Red Spot.

Gardner, FF & Shain, CA (1958). Further Observations of Radio Emission from
the Planet Jupiter. Australian Journal of Physics 11(1) 55-69.



On Saturday, July 9, 2016, jimlux  wrote:

> http://www.space.com/4314-length-saturn-day-revised.html
>
> They measure some presumed solid(ish) center.
>
> If the magnetic field axis and the rotation axis are displaced, you can
> measure when the magnetic field goes by.  Or by radio sources.
>
> Jupiter day length at the poles is slightly longer than day length at
> equator, but it's about 1% 9 hr 56 min vs 9 hr 50 min.
>
> I figure the Jupiter day length (which has been given as about 10 hours
> for a very long time, certainly before we sent spacecraft nearby) is
> probably from visual observation of the Great Red Spot.  You can easily see
> it move in a not very big telescope over the course of a night.
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>


-- 
I am Pulse. Unbreakable.
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Re: [time-nuts] Good GPSDO on eBay?

[Bob Camp]

Hi

The EEVB guys have been going around on these GPSDO’s for about a year
now. Lots of people have tried to get refunds on them. Pretty much every trick 
in the
book (replacement is in the mail …. need one more piece of information from you 
…
shipping clerk in the hospital with bubonic plague …) seems to have been used. 
If the
tricks work, they run you past the refund period stated and … poof … no refund.

We often jump on auction site sellers for some pretty minor things. That tends 
to 
turn this into a “they are all crooks” sort of discussion. A number of these 
guys do
indeed care about selling stuff. The do indeed honor their warranty. They stay 
in 
business under the same name for years and years. Those are the good guys. 
There *is* a difference. 

Bob

> On Jul 10, 2016, at 12:36 AM, Chris Albertson  
> wrote:
> 
> On Sat, Jul 9, 2016 at 5:51 PM, Richard W. Solomon 
> wrote:
> 
>> What a deal, if it arrives DOA, return shipment is on
>> your nickel. I would look elsewhere.
> 
> 
> That is not true.  If it were DOA and the seller would not take it back
> post paid you could file a "not as described" on the seller and eBay would
> refund the price.  eBay and Paypal offer pretty good buyer protection.
> 
> Someone here said the seller uses multiple IDs.  It is more likely that one
> person is making these and offering to multiple people who  then sell them
> on eBay.   This is the way it works in China, a popular design gets made
> and then is sold by many people.   It is all a cottage industry over there.
>   Pick any kind of electronic PCB level part, say a stepper motor driver
> and you see the same exact part from 20 different sellers not one seller
> with 20 IDs.(Well that is the general case, this specific one might be
> different, who knows.)
> 
> But so what even if the GPSDO is good only to 1xE10 that is still a very
> useful device to own.  Yes some are literally 1,000 times better
> 
> You could always build your own.  It is not hard nor is it expensive if you
> have a reasonable goal and don't go for state of the art.
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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Re: [time-nuts] Good GPSDO on eBay?

[Clint Jay]

No,  my experience with Chinese sellers,  even when you file a "not as
described"  case,  is that eBay will require you to return the item at your
own expense if the seller has stated they will not pay return shipping.

Ebay's attitude was that the seller could just state in their item
description that buyer is to cover return costs and that's it.  Game over.

Which is why you occasionally still see items for peanuts and extortionate
shipping costs, the seller then only has to refund you a couple of dollars
on an item that may have cost you a hundred including shipping.

  I ended up getting a total refund of £3 on a £28 item once I'd returned
it and taken shipping into account. Also,  that was a PayPal refund, not a
seller refund because they just refused shipment so eBay refused to refund
as they had no proof of return.

All the above are the reasons why I now rarely if ever buy anything costing
more than a couple of pounds from China unless I know other people have had
good experience with the item and seller.
On 10 Jul 2016 05:46, "Chris Albertson"  wrote:

> On Sat, Jul 9, 2016 at 5:51 PM, Richard W. Solomon 
> wrote:
>
> > What a deal, if it arrives DOA, return shipment is on
> > your nickel. I would look elsewhere.
>
>
> That is not true.  If it were DOA and the seller would not take it back
> post paid you could file a "not as described" on the seller and eBay would
> refund the price.  eBay and Paypal offer pretty good buyer protection.
>
> Someone here said the seller uses multiple IDs.  It is more likely that one
> person is making these and offering to multiple people who  then sell them
> on eBay.   This is the way it works in China, a popular design gets made
> and then is sold by many people.   It is all a cottage industry over there.
>Pick any kind of electronic PCB level part, say a stepper motor driver
> and you see the same exact part from 20 different sellers not one seller
> with 20 IDs.(Well that is the general case, this specific one might be
> different, who knows.)
>
> But so what even if the GPSDO is good only to 1xE10 that is still a very
> useful device to own.  Yes some are literally 1,000 times better
>
> You could always build your own.  It is not hard nor is it expensive if you
> have a reasonable goal and don't go for state of the art.
> --
>
> Chris Albertson
> Redondo Beach, California
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
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Re: [time-nuts] GPS disciplined Mars clock

[Chris Albertson]

Calculator here http://astroutils.astronomy.ohio-state.edu/time/hjd2bjd.html

Source code to do the conversion also on above site.  You should just use
their code as it is known correct .

BJD (date/time at the center of the solar system) is actually very commonly
used .  It is the best way to describe the time of an event outside the
solar system such as the timing of a variable star.  There is a huge amount
of published data in BJD.  But even within the solar system how do you
define when two events are simultaneous?   Obviously you need to pick a
vantage point where an assumed observer is.  The center of mass of the
solar system is not a bad choice of vantage point.

So when  you ask "what is the time on Mars?"  Is that what would you see if
you had a telescope good enough to read a Martian's wrist watch, or is it
what that watch would read if you brought it into your office.  Is either
of these of much practical use if you had friends living on Mars?   Yes, I
think the view of the clock through the telescope would be best that way
when your friend says he will call you at 8:00am your phone rings when you
see his watch reading 8:00am.   If you only had a clone of has watch then
you'd need a computer to make sense of it.Always when looking at a
planet you want to know the observed time (reading watch through telescope)
so you can interpret what you see, what is the longitude that is directly
facing you.

On Sat, Jul 9, 2016 at 3:35 PM, Mark Sims  wrote:

> I just added code to Lady Heather to calculate time in Terrestrial Time
> (TT) and Geocentric Terrestrial Time (TCG).   The difference is basically
> the time dilation effect of a time referenced to the center of the earth.
>  Now  I'm adding Barycentric Dynamic Time (TDB) which is TT referenced to
> the center of the solar system... basically another relativistic correction.
> Does anybody know of an online TT/TCG/TDB clock?  I can't seem to find one
> to check my math.
> I've also added Mercury/Venus/Pluto time/date... which I've arbitrarily
> defined as GPS seconds since the J1900 astronomical epoch divided by the
> orbital period.  I decided not to do times for those squishy gas-bag
> planets.
>
> ---
> > Hmm,  gravitational time dilation it might complicate things ...  I
> suppose it depends on whether your Mars clock is on the surface of Mars,
> Earth or somewhere else.
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>



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Does doubling a frequency alter the original ADEV of the frequency?

[timeok]

See also:

http://www.timeok.it/wp-content/uploads/2015/08/high-performance-frequency-doublerv1-31.pdf

Luciano
www.timeok.it


From: "time-nuts" time-nuts-boun...@febo.com
To: time-nuts@febo.com
Cc: 
Date: Sat, 9 Jul 2016 17:57:57 -0400
Subject: Re: [time-nuts] Does doubling a frequency alter the original ADEV of 
the frequency?


James wrote:
 
> Is there a preferred frequency doubler circuit which would do the least harm 
> to the ADEV of the oscillator?  The signal can be a square wave and does not 
> need to be a sine wave.  Thanks.  Jim Robbins
 
A quadrature-fed DBM produces the lowest jitter and noise.  My 
implementation can be found at:
 

 
A well-designed push-push frequency doubler is probably second (but note 
that many push-push designs you find on the web have various common 
design flaws).  My implementation can be found at:
 

 
Best regards,
 
Charles
 
 
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[time-nuts] Good GPSDO on eBay?

[Mark Sims]

I don't think there is a way to control the loop parameters except maybe some 
PFORTH commands.   The Trimble units can be put into holdover via software.  
The Symmetricom units require you to disconnect the antenna (or possibly use a 
SCPI command to manually set the DAC voltage...  Lady Heather does this with 
the Symmetricoms).

Trimble's save the survey in EEPROM,  Symmetricom's do not.  You can manually 
enter a position and stop the survey.

I got bare boards (one for $40!) since I bought them just to get Lady Heather 
working with them.  If you want to pay $30 - $60 extra to get one in a box is 
up to you and the bulgeosity of your wallet multiplied by your coefficient of 
lazy bastardness and divided by the Q factor of your box stash.  


I have not done any ADEV measurements on them,  but here a couple of links to 
EEVBLOG users that have.  It looks like they could use a little tuning.  One 
guy claims the Symmetricom oscillators have around 10 dB better phase noise  
(around 3dB worse than a HP-10811) than the Trimbles  YMMV in the 
oscillator phase noise sweepstakes.
http://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/?action=dlattach;attach=227310;image
http://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/?action=dlattach;attach=206950;image

-

> How good is the OCXO? Can you adjust the loop tuning parameters for best 
stability with the individual OCXO?  If not, does the loop cross over 
from the OCXO to the GPS at an appropriate tau, or does it exhibit the 
notorious "crossed over too early" hump in the xDEV plots?  Does it 
store its surveyed location or does it need to do a new survey every 
time it is powered up

  
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