[time-nuts] Timelab question

[Mark Sims]

Yes, it should.  Heather can input from a serial/USB connection or TCP/IP.   
Your GPIB interface needs to stream data in a "talk-only" mode.

Currently my TIC reader can handle either time interval (period) data or time 
stamps.   It knows about TICC data with channel identifiers on the values and 
HP 5313x format (commas in the numbers, embedded statistics, and us / d flags), 
 or generic (untagged)  data.  I'm not currently handling data from more than 
one input device at a time or frequency data as input. 

 I need to add some code to handle potential phase wraps for time intervals / 
time stamps.  Also maybe support frequency input.

 Heather can process up to 4 channels of data and simultaneously calculates 
ADEV/HDEV/MDEV/TDEV for each channel.  You can switch the display / plots 
between the 4 adevs for a selected channel or a selected adev type for all four 
channels.

--

> Any chance that Lady Heather would support the HP5370A/B ? Does she support
HPIB in some way (or using the BeagleBone brain transplant and tcp).
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Re: [time-nuts] advice

[Bruce Griffiths]

Perhaps one could use a laser stabilised to an atomic absorption line to 
interrogate an atomic absorption cell or equivalent in the other location via 
optical fiber using the absorption cell as a frequency discriminator. Trapped 
ion or Bose-Einstein condensates could be used in the absorption "cells".
Bruce  

On Thursday, 23 February 2017 3:09 PM, Bruce Griffiths 
 wrote:
 

 It would be better to lock the laser to a suitable optical absorption line or 
other optical transition.Long term stability can be better than an optical 
cavity provided the absorption cell parameters are stabilised. Other techniques 
such as using  a Bose Einstein condensate can be helpful.
Bruce  

On Thursday, 23 February 2017 3:02 PM, Attila Kinali  
wrote:
 

 On Wed, 22 Feb 2017 00:54:34 -0800
Hal Murray  wrote:

> How stable is a good laser and/or how hard do I have to work (or how much do 
> I have to pay) to get one stable enough for this experiment?  What's the line 
> width on a typical laser?  How much does it wander with temperature and 
> supply voltage and phase of the moon?

A normal ECDL system gets a line width sub 1MHz pretty easily, the better
ones are in the order of 10-100kHz. With the right stabilization system
sub 1Hz linewidths can be achieved [1,2]. Stability is in the order
of 10^-14 to 10^-16 (ADEV/MDEV) from 1s to a few 100s. Long term seems
to be limited by temperature stability, creep of spacer material and
mirror aging (no particular order).
I haven't had a look at this topic in a while so I cannot tell you
what the current state of the art is.


            Attila Kinali

[1] "Sub-hertz-linewidth diode laser stabilized to an ultralow-drift
high-finesse optical cavity", by Hirata, Akatsuka, Ohtake, Morinaga,
2014
http://dx.doi.org/10.7567/APEX.7.022705

[2] "A sub-40-mHz-linewidth laser based on a silicon single-crystal
optical cavity", Kessler, Hagemann, Grebing, Legero, Sterr, Riehle,
Martin, Chen, Ye, 2012
http://dx.doi.org/10.1038/nphoton.2012.217


-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                -- Miss Matheson, The Diamond Age, Neil Stephenson
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[time-nuts] (fwd) Re: ``direct'' RS-232 vs. RS-232 via USB vs. PPSdecoding cards

[qb4]

>
>I think that's enough to synchronize the counter on the Ethernet card with 
>the CPU counter.  You need either something like a PPS connected to both the 
>Ethernet and some pin on the CPU, or you need some pin the CPU can control 
>connected over to the Ethernet.

It seems like it would be pretty easy synchronize the frequencies on
the card and processor if the processor has an Always Running APIC
timer (this is apparently a different thing than the Skylake Always
Running Timer...) because In the case of the i250/i350 ethernet
controller and post-core2 intel chipsets they both run off a 25MHz XO.
For time transfer you'd still be relying on latency of running code
rather than hardware-synchronized register capture.

>Do you have any info on the Linux support?  What magic term to I search for?  
>(I'm guessing it's a magic ioctl.)

You're right, the ioctl is named PTP_SYS_OFFSET_PRECISE  -- there is a
capability bit that can be checked, but it looks like up to kernel 4.9
it's supported only on Skylake onboard ethernet.  
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Re: [time-nuts] TTimelab question

[Bob Bownes]

We have a local metalworking place that will laser cut steel and Al to 3/8". 
For small runs (like 1), they are very competitive to simply buying the 
materials alone. I had them make me 3 1U panels from 3/16" steel with 12 D 
holes to build N patch panels. $15 ea. Powder coated in my color of choice. 
Blanks were about 6 iirc. Well worth not punching all those holes!

Take a look in your search engine of choice. If you can't find one, our guy 
will ship. ;)

> On Feb 22, 2017, at 16:44, Bob Stewart  wrote:
> 
> Hi John,
> 
> I have to agree with you about enclosures.  They make the difference between 
> a DIY unit and a nice commercial unit, but they are very expensive.  The 
> enclosures I use are about $20 each from Mouser.  But the end panels are 
> another $20 each: milled front and back.  So, that's $60 per unit.  One 
> suggestion I might make is to check into what it would cost to make the end 
> panels from circuit board.  At volume, it might be significantly cheaper that 
> $20 per panel.  Learning KICAD well enough to make an end panel isn't that 
> difficult.
> 
> OSHPark has better prices on larger volume orders.  Off the cuff without 
> looking, I think I pay about $19 per mainboard for an order of 10, so that 
> would probably work out to $15 for a pair of PCB end panels.  That's still 
> $35 per enclosure, though.  You'd probably need to order 15 of each to meet 
> their minimums.  There are other suppliers that have better prices, but I 
> have no experience with them or their costs.  It wouldn't be as nice as 
> milled aluminum, but it should work just as well.
> Bob 
> -
> AE6RV.com
> 
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
> 
>  From: John Ackermann N8UR 
> To: Discussion of precise time and frequency measurement  
> Sent: Wednesday, February 22, 2017 8:13 AM
> Subject: Re: [time-nuts] TTimelab question
> 
> I really like the setup that Mark is describing.  As to TAPR's plans, 
> we've found that enclosures are a challenge -- metalwork is pretty 
> expensive unless you get significant volume, and in our niche market, 
> that's hard to do.
> 
> But I am hoping to find an inexpensive clamshell-type enclosure with 
> flat front and rear panels, and then do up designs (perhaps with Front 
> Panel Express) for those panels.  That can be done at a reasonable cost, 
> and at a minimum we can make design files available so people can order 
> their own panels.
> 
> For my own use, I'm also going to do a couple of 2U rack enclosures -- 
> one to hold two TICCs operating independently, and another for the 
> "megaTICC" -- four units slaved together to make an 8 channel counter, 
> with a Raspberry Pi controller along the line of what Mark described. 
> (In multi-board mode, each TICC outputs on its own USB line, so the 
> RPi's main purpose is to deal with the 8 channels of data from 4 USB 
> connections.)
> 
> I'll make the design files for those enclosures available as well, but 
> it may be a while as my entire lab is now packed up as we are in the 
> final stages of moving from Atlanta back to Dayton.
> 
> Also, in a day or three I'll be announcing a simple project that sprung 
> out of the TICC assembly and testing process that some of you might find 
> useful.  We're still finalizing details on that.
> 
> John
> 
> 
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Re: [time-nuts] advice

[Attila Kinali]

On Wed, 22 Feb 2017 00:54:34 -0800
Hal Murray  wrote:

> How stable is a good laser and/or how hard do I have to work (or how much do 
> I have to pay) to get one stable enough for this experiment?  What's the line 
> width on a typical laser?  How much does it wander with temperature and 
> supply voltage and phase of the moon?

A normal ECDL system gets a line width sub 1MHz pretty easily, the better
ones are in the order of 10-100kHz. With the right stabilization system
sub 1Hz linewidths can be achieved [1,2]. Stability is in the order
of 10^-14 to 10^-16 (ADEV/MDEV) from 1s to a few 100s. Long term seems
to be limited by temperature stability, creep of spacer material and
mirror aging (no particular order).
I haven't had a look at this topic in a while so I cannot tell you
what the current state of the art is.


Attila Kinali

[1] "Sub-hertz-linewidth diode laser stabilized to an ultralow-drift
high-finesse optical cavity", by Hirata, Akatsuka, Ohtake, Morinaga,
2014
http://dx.doi.org/10.7567/APEX.7.022705

[2] "A sub-40-mHz-linewidth laser based on a silicon single-crystal
optical cavity", Kessler, Hagemann, Grebing, Legero, Sterr, Riehle,
Martin, Chen, Ye, 2012
http://dx.doi.org/10.1038/nphoton.2012.217


-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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[time-nuts] Timelab question

[Mark Sims]

There are apparently companies out there that specialize in low volume 
semi-custom enclosures.  They are a lot like the cheap PCB manufacturers that 
we are now blessed with in their economies of scale.   I think the guy 
mentioned the price for this power supply enclosure was around $35 (BTW, it's a 
really nifty power supply.  There is a long thread on EEVBLOG covering its 
development.  It uses and Arduino Due for the processor.)

https://www.crowdsupply.com/envox/eez-h24005
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs.PPSdecoding cards

[jimlux]

On 2/22/17 3:37 AM, Hal Murray wrote:





We could get a USB logic analyzer.  That would give us some more data on the
USB timings.  (There are probably some limits in the specs, but I won't be
surprised if somebody doesn't get it right..)



USB has a basic timing interval of 125 microseconds (8 kHz) and most 
devices follow that in some way (e.g. they'll burp out a buffer every 
125 microseconds, or do a bulk transfer, etc.)


The stuff I've done with microcontrollers with USB onboard (mostly 
Teensy devices, which is the Freescale micro) seem to have this sort of 
125 microsecond granularity in timing.



I just ran across this, which has lots of useful timing info
http://www.usbmadesimple.co.uk/ums_6.htm#frames_and_microframes

There's a whole lot of complexity in how the bus switches directions 
(since there's only two wires), how it detects the speed, etc.


(and let's not even get started on hub and device power management, 
which was my particular bete noir a few years ago...)



I make no claims about USB 3.0..

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Re: [time-nuts] advice

[Tim Shoppa]

So this is the Pound-Rebka experiment with lasers instead of the original Fe57 
gamma rays and Mossbauer effect?

Tim N3QE

Sent from my VAX-11/780

> On Feb 21, 2017, at 9:33 PM, Bill Byrom  wrote:
> 
> Review the theory and results in this paper:
> 
> http://science.sciencemag.org/content/329/5999/1630?variant=full-text&sso[1]
> 
> 
> For small height changes on the surface of Earth, a clock that is higher
> by a distance ∆h runs faster by ...
> The gravitational shift corresponds to a clock shift of about 1.1 ×
> 10−16 per meter of change in height.
> --
> 
> Bill Byrom N5BB
> 
> 
> 
> 
> 
> 
> 
>> On Tue, Feb 21, 2017, at 11:13 AM, Rhoderick Beery wrote:
>> 
>> Greetings Time-Nuts!
> 
>> 
> 
>> I'm a physics theorist interested in performing an experiment
>> to measure
>> the gravitational time dilation beneath the surface of the
>> Earth. Boulby
>> Labs in the UK is 1.1 km down which would generate a time differential
>> from
> 
>> the surface on the order of 1 part in 10^15 -- not much to work with!
>> 
> 
> 
> 
> 
> Links:
> 
>  1. 
> http://science.sciencemag.org/content/329/5999/1630?variant=full-text&sso=1&sso_redirect_count=1&oauth-code=251c50aa-4576-4ddf-aa31-b39ac90299c2
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Re: [time-nuts] advice

[Bruce Griffiths]

For a spherical body of uniform density the value of g below the surface is 
proportional to  the radial distance of the location from the centre of the 
sphere.  For a spherically symmetric body only the mass contained within the 
sphere  below the point has any effect on the measured value of g.
The record for optical clocks is detecting the effect on frequency of a change 
in elevation of 1cm or so.
Bruce 

On Thursday, 23 February 2017 1:02 PM, Hal Murray  
wrote:
 

 > Δf/fo = g Δh/c2

Does that work when going down below the surface as well as when up above it?

(My last physics class was a long time ago.  I remember doing the integrals 
for computing the gravity inside a sphere, but don't remember the answer.  I 
wouldn't be surprised if a factor of 2 or pi was involved below the surface..)


-- 
These are my opinions.  I hate spam.




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Re: [time-nuts] advice

[Chris Albertson]

I'm curious about what you are trying to find out with this
experiment.   Certainly it is not to prove that time does in fact
dilate.Are you planning on using time to measure relative
differences in gravity?   That seems reasonable because as it turns
out times is the physical quantity that can be measured to the highest
precision.   It might be interesting to see how the rate of time
changes as a result of Earthquakes, magma circulating deep underground
or as the moon orbits the earth and the tides change.

I think the record for detecting time dilation using clocks in a 1
meter difference in elevation.   I'm sure someone here knows where
this was published.

On Tue, Feb 21, 2017 at 9:13 AM, Rhoderick Beery  wrote:
> Greetings Time-Nuts!
>
> I'm a physics theorist interested in performing an experiment to measure
> the gravitational time dilation beneath the surface of the Earth. Boulby
> Labs in the UK is 1.1 km down which would generate a time differential from
> the surface on the order of 1 part in 10^15 -- not much to work with!
>
> I've investigated measuring redshift/blueshift from lasers but our
> wavemeter technology is no where near accurate enough. I've concluded that
> my best solution is to use atomic clocks, of which I know very little
> about. I thought a clock-enthusiast mail group would be a fantastic way for
> me to learn about the subject as well as possibly spur ideas on the lab
> test design itself.
>
> Thanks in advance!!
> ---
> Rhoderick Beery
> direct: 402-817-9363
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-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] advice

[Azelio Boriani]

Does gravity work differently under the surface? Maybe the redshift is
different going below the surface.



On Wed, Feb 22, 2017 at 3:22 AM, Bill Hawkins  wrote:
> In the confusion, I forgot that we are concerned with gravitational time
> dilation, not time of flight.
>
> The University of Minnesota has a lab about 2500 feet down in the Soudan
> mine. The following is their brief description:
>
> "The Soudan Underground Laboratory is a general-purpose science
> facility, which provides the deep underground environment required by a
> variety of sensitive experiments."
>
> Here's a link to the Soudan page:
>  https://www.physics.umn.edu/outreach/soudan/tour/
>
> Why is it named Soudan? The original miners found northern Minnesota to
> be extremely cold at times, so they named the town for someplace warm.
>
> Let me know if you are seriously considering this, and I will find a
> contact for you.
>
> Bill Hawkins
>
> -Original Message-
> From: Bill Hawkins [mailto:bill.i...@pobox.com]
> Sent: Tuesday, February 21, 2017 8:08 PM
>
> Neutrinos? Look up the OPERA experiment that measured neutrinos going
> faster than light. Turned out to be a loose optical fiber connector to a
> timing instrument.
>
> Fermi Lab has/had the MINOS experiment going 500 miles from Chicago to a
> mine in northern Minnesota. The generated neutrinos go through Wisconsin
> but are not noticed there, AFAIK.
>
> Bill Hawkins (Resident of Minnesota, but not a physicist, just a BSME)
>
>
> -Original Message-
> From: Bob Stewart
> Sent: Tuesday, February 21, 2017 1:48 PM
>
> Hi,
> Have you been in touch with Fermi-Lab?  They run a neutrino experiment
> with a receiver somewhere underground in Wisconsin.  At least that's
> what I recall.  I used to live next to a Physics professor who has a
> minor part in the experiment.  I'm not even sure what sort of data they
> collect there; whether it's time or something else.
>
> Bob Stewart (Not a physicist)
>
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Re: [time-nuts] advice

[Hal Murray]

> Δf/fo = g Δh/c2

Does that work when going down below the surface as well as when up above it?

(My last physics class was a long time ago.  I remember doing the integrals 
for computing the gravity inside a sphere, but don't remember the answer.  I 
wouldn't be surprised if a factor of 2 or pi was involved below the surface.)


-- 
These are my opinions.  I hate spam.



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[time-nuts] Timelab question

[Mark Sims]

A nasty bug crawled into my ear last night and muttered something like:

"Put the TICC counter circuit, a 1/5/10/15 Mhz PICDIV divider, input squarer, 
terminator relay, etc on a module.Make a motherboard that 4-8 of those 
modules can plug into along with an ATMEGA processor.  Output the data via good 
ole RS-232 ... everybody can probably find a USB-Serial converter that works 
with their system... they may not be able to find a driver for a specific / 
custom USB device like an Ardunio USB port".  Oh, and put some footprints for a 
quality reference OCXO and some power regulators on the motherboard.

That damn little critter in my ear keeps burrowing deeper and closer to my 
frontal builditbellum...  I'm off to the store to see if I can find some bug 
spray before it gets there.

---

> For my own use, I'm also going to do a couple of 2U rack enclosures -- 
one to hold two TICCs operating independently, and another for the 
"megaTICC" -- four units slaved together to make an 8 channel counter
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Re: [time-nuts] TTimelab question

[Bob Stewart]

Hi John,

I have to agree with you about enclosures.  They make the difference between a 
DIY unit and a nice commercial unit, but they are very expensive.  The 
enclosures I use are about $20 each from Mouser.  But the end panels are 
another $20 each: milled front and back.  So, that's $60 per unit.  One 
suggestion I might make is to check into what it would cost to make the end 
panels from circuit board.  At volume, it might be significantly cheaper that 
$20 per panel.  Learning KICAD well enough to make an end panel isn't that 
difficult.

OSHPark has better prices on larger volume orders.  Off the cuff without 
looking, I think I pay about $19 per mainboard for an order of 10, so that 
would probably work out to $15 for a pair of PCB end panels.  That's still $35 
per enclosure, though.  You'd probably need to order 15 of each to meet their 
minimums.  There are other suppliers that have better prices, but I have no 
experience with them or their costs.  It wouldn't be as nice as milled 
aluminum, but it should work just as well.
Bob 
-
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: John Ackermann N8UR 
 To: Discussion of precise time and frequency measurement  
 Sent: Wednesday, February 22, 2017 8:13 AM
 Subject: Re: [time-nuts] TTimelab question
   
I really like the setup that Mark is describing.  As to TAPR's plans, 
we've found that enclosures are a challenge -- metalwork is pretty 
expensive unless you get significant volume, and in our niche market, 
that's hard to do.

But I am hoping to find an inexpensive clamshell-type enclosure with 
flat front and rear panels, and then do up designs (perhaps with Front 
Panel Express) for those panels.  That can be done at a reasonable cost, 
and at a minimum we can make design files available so people can order 
their own panels.

For my own use, I'm also going to do a couple of 2U rack enclosures -- 
one to hold two TICCs operating independently, and another for the 
"megaTICC" -- four units slaved together to make an 8 channel counter, 
with a Raspberry Pi controller along the line of what Mark described. 
(In multi-board mode, each TICC outputs on its own USB line, so the 
RPi's main purpose is to deal with the 8 channels of data from 4 USB 
connections.)

I'll make the design files for those enclosures available as well, but 
it may be a while as my entire lab is now packed up as we are in the 
final stages of moving from Atlanta back to Dayton.

Also, in a day or three I'll be announcing a simple project that sprung 
out of the TICC assembly and testing process that some of you might find 
useful.  We're still finalizing details on that.

John

   
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Re: [time-nuts] Timelab question

[Paul Alfille]

Any chance that Lady Heather would support the HP5370A/B ? Does she support
HPIB in some way (or using the BeagleBone brain transplant and tcp).

Paul Alfille K1PHA

On Tue, Feb 21, 2017 at 6:35 PM, Mark Sims  wrote:

> At one time Timelab worked well for me under Wine.  It's been years since
> I tried it.
>
> I recently got in a TAPR TICC and am in the process of adding time
> interval counter support to Lady Heather.   It's not even remotely as nifty
> as Timelab (and never will be),  but it does run under Windows / Linux /
> macOS and FreeBSD.  It can calculate and plot ADEV/HDEV/MDEV/TDEV.  The
> code supports up to 4 simultaneous channels of TICC data (but the TICC is
> currently a 2 channel device).
>
> Besides the TICC it should work (single channel) with HP53xxx counters and
> counters that output time stamps or time intervals in "talk only" mode.
> There is the possibility of supporting more than one counter device...
> Heather can now handle up to 10 com devices and TCP/IP links.
>
> I plan to package up my TICC and a couple of TADD-2 Mini dividers with a
> RPI-3 and the 7" touchscreen display and an Osciiloquartz 8663 DOXCO to
> make a small ADEV analyzer box.
>
> --
>
> > Wine is just a mess as far as Timelab is concerned.  Most of the time it
> doesn't display the plot area.  I've pretty much given up on it.
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Re: [time-nuts] TTimelab question

[Bob Camp]

Hi


> On Feb 21, 2017, at 11:45 PM, Mark Sims  wrote:
> 
> I doubt that it is something TAPR would do.   Building complete systems gets 
> into all sorts of issues (mainly regulatory).

There’s also the issue of cost. If you need to sell maybe 200 gizmos at $100 to 
make things work, The same process is a bit more 
exciting when it’s 200 gizmos at $800. In the first case, somebody needs to 
front the money for a $20,000 project. In the second 
case they may need to take out a second mortgage. If 20 of the $100 devices 
don’t sell, they have $2K in inventory to write off.
In the second case they have $16K. As you can quickly see on their web site, 
some of their projects hang around in inventory 
for a *long* time.  Yes, that’s all in sales dollars to make the math easy. 
Somehow I doubt that TAPR is a high margin / high profit
organization :)

Bob

>   But it is easy enough to build.   They sell a nice case that the RPI3 and 
> touchscreen mounts in.  The PI+touchscreen+case sells for around $110.   The 
> TICC(s) connect to it via USB.  
> 
> There are also some Win10 tablets with 1024x600 touch screens that sell for 
> around $60 (apparently Microsoft doesn't charge manufacturers for Win10 on 
> tablets with small/low res screens).
> 
> I  am thinking about laying out a front-end board for the TICC.  It would 
> have some switchable (relay?) 50 ohm input terminators,  switchable PICDIV 
> dividers for PPS/1MHz/5MHz/10MHz/15MHz (or 2.5 MHz)  inputs,  footprints for 
> a decent reference oscillator (MV89/8663/DIP/etc), and a 12V to 5V (3A?) 
> power converter for the  TICC and PI... most of the better surplus 
> oscillators run off of 12V.  Also maybe add a data multiplexer for combining 
> the outputs of two TICC boards into one data stream (but Heather could do 
> that in software).  John has some ideas for a similar board.  
> 
> -
> 
>> Wow!  If you can persuade John and TAPR to produce that, I would be there
> with my chequebook before the ink had dried on the web-page! :-)
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs.PPSdecoding cards

[Hal Murray]

t...@leapsecond.com said:
> It seems to me that if the read path and the write path are different it
> breaks down. Given how USB works, not to mention all the layers of software
> involved I can't imagine the paths are equal. There's no doubt you can get
> great consistency from your method. But turning that into precise time
> requires some kind of calibration of the actual code path delays.

There are 3 clocks: PC, USB, and Gizmo on the end of the USB.

We could get a USB logic analyzer.  That would give us some more data on the 
USB timings.  (There are probably some limits in the specs, but I won't be 
surprised if somebody doesn't get it right..)

I think the problem is how to get accurate timing on a write from PC.  With 
that, we could collect some data, wave our hands, and make an estimate on the 
error bars.

The USB firmware has a schedule with slots for the Gizmo.  (I don't know the 
USB details, so this is a bit handwavy.)  You can get synced with the USB 
schedule by doing a read.  Then pause a bit, do a write, then a read.  The 
Gizmo returns time stamps (its clock) for the write and read.  Now adjust the 
length of the pause to minimize the PC time between start of write and finish 
of the read.  That gives you an upper bound on the time error between the 
Gizmo clock and the PC clock.

We could subtract off the USB data transfer times, and maybe some of the idle 
times.  With some kernel hacking, we could get some PC time stamps for when the 
read and writes finish.  On the read side, that just saves a bit of CPU time - 
interrupt to running user code.  I don't know how to wait for a buffer to get 
sent.  There may be an ioctl for that.

I'm not sure it would ever be good enough for serious time-nuts work, but it 
would be an interesting experiment.


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Re: [time-nuts] advice

[Hal Murray]

bruce.griffi...@xtra.co.nz said:
> If you have a dark fiber or 2 between the surface and the lab and a pair of
> sufficiently stable lasers (one at the surface and one in the underground
> lab) you could look at the change in beat frequency between the lasers
> (around 50Hz for a pair of red lasers). 

Interesting idea.  Thanks.

How stable is a good laser and/or how hard do I have to work (or how much do 
I have to pay) to get one stable enough for this experiment?  What's the line 
width on a typical laser?  How much does it wander with temperature and 
supply voltage and phase of the moon?


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Re: [time-nuts] advice

[Bill Byrom]

Review the theory and results in this paper:

http://science.sciencemag.org/content/329/5999/1630?variant=full-text&sso[1]


For small height changes on the surface of Earth, a clock that is higher
by a distance ∆h runs faster by ...
The gravitational shift corresponds to a clock shift of about 1.1 ×
10−16 per meter of change in height.
--

Bill Byrom N5BB







On Tue, Feb 21, 2017, at 11:13 AM, Rhoderick Beery wrote:

> Greetings Time-Nuts!

> 

> I'm a physics theorist interested in performing an experiment
> to measure
> the gravitational time dilation beneath the surface of the
> Earth. Boulby
> Labs in the UK is 1.1 km down which would generate a time differential
> from

> the surface on the order of 1 part in 10^15 -- not much to work with!
>  




Links:

  1. 
http://science.sciencemag.org/content/329/5999/1630?variant=full-text&sso=1&sso_redirect_count=1&oauth-code=251c50aa-4576-4ddf-aa31-b39ac90299c2
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Re: [time-nuts] TTimelab question

[John Ackermann N8UR]

I really like the setup that Mark is describing.  As to TAPR's plans, 
we've found that enclosures are a challenge -- metalwork is pretty 
expensive unless you get significant volume, and in our niche market, 
that's hard to do.


But I am hoping to find an inexpensive clamshell-type enclosure with 
flat front and rear panels, and then do up designs (perhaps with Front 
Panel Express) for those panels.  That can be done at a reasonable cost, 
and at a minimum we can make design files available so people can order 
their own panels.


For my own use, I'm also going to do a couple of 2U rack enclosures -- 
one to hold two TICCs operating independently, and another for the 
"megaTICC" -- four units slaved together to make an 8 channel counter, 
with a Raspberry Pi controller along the line of what Mark described. 
(In multi-board mode, each TICC outputs on its own USB line, so the 
RPi's main purpose is to deal with the 8 channels of data from 4 USB 
connections.)


I'll make the design files for those enclosures available as well, but 
it may be a while as my entire lab is now packed up as we are in the 
final stages of moving from Atlanta back to Dayton.


Also, in a day or three I'll be announcing a simple project that sprung 
out of the TICC assembly and testing process that some of you might find 
useful.  We're still finalizing details on that.


John

On 02/21/2017 11:45 PM, Mark Sims wrote:

I doubt that it is something TAPR would do.   Building complete systems gets 
into all sorts of issues (mainly regulatory).   But it is easy enough to build. 
  They sell a nice case that the RPI3 and touchscreen mounts in.  The 
PI+touchscreen+case sells for around $110.   The TICC(s) connect to it via USB.

There are also some Win10 tablets with 1024x600 touch screens that sell for 
around $60 (apparently Microsoft doesn't charge manufacturers for Win10 on 
tablets with small/low res screens).

I  am thinking about laying out a front-end board for the TICC.  It would have 
some switchable (relay?) 50 ohm input terminators,  switchable PICDIV dividers 
for PPS/1MHz/5MHz/10MHz/15MHz (or 2.5 MHz)  inputs,  footprints for a decent 
reference oscillator (MV89/8663/DIP/etc), and a 12V to 5V (3A?) power converter 
for the  TICC and PI... most of the better surplus oscillators run off of 12V.  
Also maybe add a data multiplexer for combining the outputs of two TICC boards 
into one data stream (but Heather could do that in software).  John has some 
ideas for a similar board.

-


  Wow!  If you can persuade John and TAPR to produce that, I would be there

with my chequebook before the ink had dried on the web-page! :-)
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Re: [time-nuts] advice

[Bill Byrom]

This short paper was issued by NIST researchers in 2010, and it
discusses making accurate gravitational time dilation / redshift
measurements using lasers:
http://tf.boulder.nist.gov/general/pdf/2447.pdf



Quoting that paper:

> Differences in gravitational potential can be detected by comparing
> the tick rate of two clocks. For small height changes on the surface
> of Earth, a clock that is higher by a distance Δh runs faster by
> 

> Δf/fo = g Δh/c2

>
> where g ≈ 9.80 m/s2 is the local acceleration due to gravity. The
> gravitational shift corresponds to a clock shift of about 1.1 × 10−16
> per meter of change in height.


So at your laboratory depth of 1.1 km, the fractional frequency change
should be about:
1.2 x 10-13 (1.2 parts in 10^13)

--

Bill Byrom N5BB



On Tue, Feb 21, 2017, at 11:13 AM, Rhoderick Beery wrote:

> I'm a physics theorist interested in performing an experiment
> to measure
> the gravitational time dilation beneath the surface of the
> Earth. Boulby
> Labs in the UK is 1.1 km down which would generate a time differential
> fromthe surface on the order of 1 part in 10^15 -- not much to
> work with!

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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPSdecoding cards

[Bob Camp]

Hi


> On Feb 21, 2017, at 9:50 PM, Trevor N.  wrote:
> 
> On Tue, 21 Feb 2017 07:37:34 -0500, BC wrote:
>> 
>> Some 1588 chip sets have (or had, I haven’t looked recently) external sync 
>> pins. 
>> This does get into the whole, what’s a motherboard / what’s a peripheral 
>> debate. Plugging in a 1588 card to get that pin probably no longer counts
>> as a simple solution. If plugging in a card *does* count then that opens up 
>> a lot of possible options. 
>> 
>> Bob
> 
> I found while looking at the datasheets for newer Intel server
> ethernet cards that they have the ability to timestamp GPIO pin
> transitions, but none of them have their internal timebase
> synchronized to a counter in the CPU. It looks like they are clocked
> from a separate XO on the card.

Everything on a motherboard traces back to this or that XO. None of the time 
sources are anything that would get you excited as a frequency standard. Linking
them together can be exciting. Replacing this or that one with a better 
frequency
source *is* possible in some cases. If you are going to replace one, why not
replace several :)

Bob

>  Maybe if it was synchronized to the
> PCIe clock / BCLK  they could take advantage of that new Always
> Running Timer in Skylake processors.  I'm surprised that Intel hasn't
> made a big deal about it. Support for it was added in the Linux e1000e
> driver early last year.
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Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPSdecoding cards

[Hal Murray]

q...@comcast.net said:
> I found while looking at the datasheets for newer Intel server ethernet
> cards that they have the ability to timestamp GPIO pin transitions, but none
> of them have their internal timebase synchronized to a counter in the CPU.
> It looks like they are clocked from a separate XO on the card.  Maybe if it
> was synchronized to the PCIe clock / BCLK  they could take advantage of that
> new Always Running Timer in Skylake processors.  I'm surprised that Intel
> hasn't made a big deal about it. Support for it was added in the Linux
> e1000e driver early last year.

Thanks.

I think that's enough to synchronize the counter on the Ethernet card with 
the CPU counter.  You need either something like a PPS connected to both the 
Ethernet and some pin on the CPU, or you need some pin the CPU can control 
connected over to the Ethernet.

Do you have any info on the Linux support?  What magic term to I search for?  
(I'm guessing it's a magic ioctl.)

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