[time-nuts] Fw: Optical transfer of time and frequency

[Bruce Griffiths]

 On Sunday, 1 May 2016 10:52 AM, Bruce Griffiths 
 wrote:
 

 White Rabbit is open hardware, you are free to build it yourself should you 
want to do so. All the relevant VHDL etc is available.There will also be 
suitable TDC designs available on the CERN site.You can also integrate these 
into your system if you want.
White Rabbit can handle thousands of nodes thus 3 or more won't be a problem.

Bruce 

On Sunday, 1 May 2016 10:35 AM, Ilia Platone  wrote:
 

  I found only preliminary data about these transceivers. I was meaning for a 
<2000€ overall solution, does a White Rabbit implementation fill this requisite 
( I couldn't find much information about its costs)? Also consider that nodes 
could be more than three also.
  Ilia.
  

  
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Re: [time-nuts] Rpair of an 8662 HP Generator

[KA2WEU--- via time-nuts]

The problem is solved, A German surplus dealer has/had bunch of these  
generator, calibrated and with guarantee for less then $ 3000. And in good  
shape. 
 
Who wants  the old one .. no cost , power supply in trouble , Ulrich 
 
 
In a message dated 4/15/2016 10:01:56 P.M. Eastern Daylight Time,  
time-nuts@febo.com writes:

Thanks,  I do not have a repair manual and I hate to abandon the signal   
generator after man years of positive use... Ulrich  


In a  message dated 4/15/2016 9:14:21 P.M. Eastern Daylight Time,   
paulsw...@gmail.com writes:


Ulrich
To  your first  question I am unaware of anyone that repairs them. Though 
there are   many places that might, typical cal and repair shops. I have a 
sick 
8662  also  (age) and need to dig in. At least I know the board and the 
most  
likely issue.  The yahoo user group has a lot of useful  details.
Regards
Paul
WB8TSL






On Fri, Apr  15, 2016 at 7:08 PM, Dr. Ulrich Rohde via  time-nuts  
<_time-nuts@febo.com_ (mailto:time-nuts@febo.com) >  wrote:

Thanks

Sent  from my iPhone


On Apr 15,  2016, at 6:38 PM, "John Miles" <_john@miles.io_ 
(mailto:j...@miles.io)  >  wrote:

>> My  signal generator has a poor,  intermittent  power  supply.  The RF
>> section is ok.  Who can please  tell me which company can and  will fix  
these
>>  older
>> but excellent   generators?
>>
>>  Thanks, Ulrich
>
> Have  a look at the capacitors in the voltage  divider that drives the  
bases of the switching transistors.  There's a  good chance  that's your 
problem, and they probably need to be replaced even  if  not.  75-TVA1607 
(Mouser 
p/n for Sprague TVA1607) works   well.
>
> It would be nice to use 105C parts if you can find   some, but the 85C 
TVA1607s have worked well for me in multiple 8662As  over  several years.
>
> The other likely suspect is one of  the large  screw-terminal 
electrolytics on the motherboard.  The  power supply can  
almost-but-not-quite start up 
when one of those is  completely open.   High ESR is very likely to cause 
intermittent  operation.
>
> --  john, KE5FX
> Miles Design  LLC
>
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Re: [time-nuts] Optical transfer of time and frequency

[Ilia Platone]

I found only preliminary data about these transceivers.

I was meaning for a <2000€ overall solution, does a White Rabbit 
implementation fill this requisite ( I couldn't find much information 
about its costs)?


Also consider that nodes could be more than three also.

Ilia.


Il 30/04/2016 12:27, Bruce Griffiths ha scritto:

There are synchronous free space optical gigabit ethernet links available, it 
shouldn't take too much to modify one for White Rabbit.
Bruce
  


 On Saturday, 30 April 2016 10:13 PM, Magnus Danielson 
 wrote:
  


  Hi,

On 04/29/2016 11:45 PM, Michael Wouters wrote:

On Sat, Apr 30, 2016 at 6:14 AM, Magnus Danielson
 wrote:

Well, giving the conditions mentioned, doing ranging codes such as those
used by GPS is very easy and cheap. Doing this in bidirectional isn't too
hard. Doing a suitably high chip-rate should cost very little.

I've done two-way time-transfer over optical fibre using exactly this
technique. The TDEV is about 1 ps for tau>1s. Not so cheap, about 25K
euro per node (20K signal processing - NI FPGA, 2K laser and power
supplies, 1K detector, 1K RF electronics) in my setup, but that cost
could be greatly reduced since a $100 OEM FPGA could do the signal
processing (I've already done work on this but currently looking for
motivation to finish it off) and a simple, intensity-modulated laser
would probably be fine. A 2K euro budget would be a challenge though.

FPGA-wise, you need a very little FPGA resources.
If you consider the RedPitaya (200 USD) for instance, it is way beyond
what is needed.


The two-way time-transfer is relatively easy, but you will need to do some
calibration to get the precision needed.


At first glance, I would think that you should be able to define the
optical RX/TX path to within 10 cm without any trouble and that gives
you 300 ps accuracy. Even on fibre links, I don't think anyone would
claim an accuracy of better than a few hundred ps.

With a bit of calibration you can remove each nodes systematic asymmetry.

For optical fibers many does not even bother to do a pseudorandom
rangning. A repeating pattern suffice, such as that of SDH frames.

Cheers,
Magnus
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--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999

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[time-nuts] Article on leapseconds

[Mark Sims]

Ars Technica just published a piece on leapseconds.  There is some interesting 
info on what makes the earth a poor clock and our abilities to measure it  
(want to smooth it out a bit... cut down all the trees).
http://arstechnica.com/science/2016/04/the-leap-second-because-our-clocks-are-more-accurate-than-the-earth/

  
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Re: [time-nuts] Kinemetrics/Truetime WWVB model 60-dc?

[Bob Darby]

Rob,

Take a look at http://www.maxmcarter.com/rubidium/2012_mod/#599

Might be a possible mod.

Bob darby

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Rob Seaman
Sent: Friday, April 29, 2016 7:13 PM
To: Discussion of precise time and frequency measurement 
Subject: [time-nuts] Kinemetrics/Truetime WWVB model 60-dc?

Howdy,

We’re in the process of upgrading our telescopes in various ways, including 
deploying spiffy new GNSS clocks. While rummaging around the shelves of old 
equipment, I came across the WWVB time code generators that had been retired 
themselves a dozen years ago or more (in favor of NTP and/or GPS equipment). 
These are Kinemetrics/Truetime model 60-dc. They appears to power up ok to the 
point of displaying the colons and flickering keep-alive LEDs (see p.51 of 
http://www.to-way.com/tf/60dc.pdf). It would be cool to bring them back to 
life, if only to serve as retro wall clocks.

It turns out the old 60 KHz antenna (same manufacturer, model A-60FS) was still 
mounted on the building, but I wasn’t able to get either of the two devices to 
lock when connected to it. The antenna had been repaired at some point, so I 
have no confidence that it's still in working condition after many years out in 
the weather after the case had been opened.

Now I’ve come across this notice from Spectracom:


http://spectracom.com/sites/default/files/document-files/Pending%20Changes%20in%20the%20WWVB%20Radio%20Signal%20Affects%20Precision%20Frequency%20and%20Timing%20Reference.pdf

which suggests that other vendors’ devices might also "no longer operate as 
intended as a result of the WWVB signal change” after July 2012.

If so, bummer!

If not, suggestions for acquiring a functioning antenna?

Many thanks for any information on these or similar devices. I should note that 
another telescope elsewhere on the mountain appears to still be using a Datum 
model 9100 (via Forth software!) nightly (though with WWV, not WWVB?)*  Does 
anybody have a manual for that unit?

Rob Seaman
University of Arizona
—
* there were even some IRIG wall clocks
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Re: [time-nuts] Optical transfer of time and frequency

[Bruce Griffiths]

There are synchronous free space optical gigabit ethernet links available, it 
shouldn't take too much to modify one for White Rabbit.
Bruce
 

On Saturday, 30 April 2016 10:13 PM, Magnus Danielson 
 wrote:
 

 Hi,

On 04/29/2016 11:45 PM, Michael Wouters wrote:
> On Sat, Apr 30, 2016 at 6:14 AM, Magnus Danielson
>  wrote:
>> Well, giving the conditions mentioned, doing ranging codes such as those
>> used by GPS is very easy and cheap. Doing this in bidirectional isn't too
>> hard. Doing a suitably high chip-rate should cost very little.
>
> I've done two-way time-transfer over optical fibre using exactly this
> technique. The TDEV is about 1 ps for tau>1s. Not so cheap, about 25K
> euro per node (20K signal processing - NI FPGA, 2K laser and power
> supplies, 1K detector, 1K RF electronics) in my setup, but that cost
> could be greatly reduced since a $100 OEM FPGA could do the signal
> processing (I've already done work on this but currently looking for
> motivation to finish it off) and a simple, intensity-modulated laser
> would probably be fine. A 2K euro budget would be a challenge though.

FPGA-wise, you need a very little FPGA resources.
If you consider the RedPitaya (200 USD) for instance, it is way beyond 
what is needed.

>> The two-way time-transfer is relatively easy, but you will need to do some
>> calibration to get the precision needed.
>>
>
> At first glance, I would think that you should be able to define the
> optical RX/TX path to within 10 cm without any trouble and that gives
> you 300 ps accuracy. Even on fibre links, I don't think anyone would
> claim an accuracy of better than a few hundred ps.

With a bit of calibration you can remove each nodes systematic asymmetry.

For optical fibers many does not even bother to do a pseudorandom 
rangning. A repeating pattern suffice, such as that of SDH frames.

Cheers,
Magnus
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Re: [time-nuts] Optical transfer of time and frequency

[Javier Serrano]

On Sat, Apr 30, 2016 at 8:06 AM, Bruce Griffiths
 wrote:
> So far I haven't found an existing free space optical implementation of White 
> Rabbit.

There are two groups working on that subject that I know of:

Jean-Pierre Aubry [1] and his colleagues in EPFL (Neuchâtel campus, in
Switzerland). They started around one year ago.

Javier Díaz [2] in the University of Granada (Spain). Javier just
visited Neuchâtel with a PhD student (Paco Girela) who is supposed to
start working on free space WR soon, if I understood correctly.

Tell me off list if you would like me to connect you.

Cheers,

Javier

[1] https://people.epfl.ch/242679
[2] http://www.ugr.es/~jda/
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Re: [time-nuts] Optical transfer of time and frequency

[Magnus Danielson]

The free-space implementation of White Rabbit remains to be done.
If you can modulate optical GE over your optical links, then it should 
work out fairly well.


Actually, if you get that working, I'm sure they would enjoy seeing a 
paper on that in EFTF.


Cheers,
Magnus

On 04/30/2016 08:06 AM, Bruce Griffiths wrote:

White Rabbit would be good in that a suitable TDC design with 1ns resolution 
already exists for White Rabbit. This TDC is used in the Tunka valley (near 
lake Baikal) Siberian Cherenkov telescope array. Note this TDC uses the SERDES 
receiver in the FPGA to implement a serial to parallel converter with a 1GHz 
clock synthesised from the 125MHz White Rabbit clock.
So far I haven't found an existing free space optical implementation of White 
Rabbit.
Bruce


 On Saturday, 30 April 2016 11:00 AM, Michael Wouters 
 wrote:


  So why not do White Rabbit free space ?

Cheers
Michael

On Sat, Apr 30, 2016 at 4:04 AM, Paul Boven  wrote:

Hi everyone,

On 04/29/2016 03:28 PM, Magnus Danielson wrote:


Phase/time transfer over fiber is shaping up, but White Rabbit is
starting to grow up and more reports for long distances is showing up.
ETFT is one of the placces to check for reports.



And the White Rabbit workshops, with the presentations online:
http://www.ohwr.org/projects/white-rabbit/wiki/Mar2016Meeting

I happen to be working on time transfer via White Rabbit. The White Rabbit
standard proscribes the use of 1000Base-Bx10 (10km reach bi-directional)
SFPs, but it turns out to work just fine with longer reach SFPs. However,
there are several effects that limit the accuracy that you can get on longer
links:

* Dispersion of the fiber (as the lasers change temperature, their
wavelength changes, and they experience a slightly different index of
refraction, hence propagation speed.

* Change in index of refraction in the fiber itself. The propagation speed
of both the uplink and downlink wavelength change, in absolute sense but
also their ratio changes. This is something the WR protocol can't
detect/correct for.

There are several people working on these issues, trying to improve both the
calibration and stability even further.

Regards, Paul Boven.


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Re: [time-nuts] Optical transfer of time and frequency

[Magnus Danielson]

Hi,

On 04/29/2016 11:45 PM, Michael Wouters wrote:

On Sat, Apr 30, 2016 at 6:14 AM, Magnus Danielson
 wrote:

Well, giving the conditions mentioned, doing ranging codes such as those
used by GPS is very easy and cheap. Doing this in bidirectional isn't too
hard. Doing a suitably high chip-rate should cost very little.


I've done two-way time-transfer over optical fibre using exactly this
technique. The TDEV is about 1 ps for tau>1s. Not so cheap, about 25K
euro per node (20K signal processing - NI FPGA, 2K laser and power
supplies, 1K detector, 1K RF electronics) in my setup, but that cost
could be greatly reduced since a $100 OEM FPGA could do the signal
processing (I've already done work on this but currently looking for
motivation to finish it off) and a simple, intensity-modulated laser
would probably be fine. A 2K euro budget would be a challenge though.


FPGA-wise, you need a very little FPGA resources.
If you consider the RedPitaya (200 USD) for instance, it is way beyond 
what is needed.



The two-way time-transfer is relatively easy, but you will need to do some
calibration to get the precision needed.



At first glance, I would think that you should be able to define the
optical RX/TX path to within 10 cm without any trouble and that gives
you 300 ps accuracy. Even on fibre links, I don't think anyone would
claim an accuracy of better than a few hundred ps.


With a bit of calibration you can remove each nodes systematic asymmetry.

For optical fibers many does not even bother to do a pseudorandom 
rangning. A repeating pattern suffice, such as that of SDH frames.


Cheers,
Magnus
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Re: [time-nuts] Optical transfer of time and frequency

[Michael Wouters]

On Sat, Apr 30, 2016 at 6:14 AM, Magnus Danielson
 wrote:
> Well, giving the conditions mentioned, doing ranging codes such as those
> used by GPS is very easy and cheap. Doing this in bidirectional isn't too
> hard. Doing a suitably high chip-rate should cost very little.

I've done two-way time-transfer over optical fibre using exactly this
technique. The TDEV is about 1 ps for tau>1s. Not so cheap, about 25K
euro per node (20K signal processing - NI FPGA, 2K laser and power
supplies, 1K detector, 1K RF electronics) in my setup, but that cost
could be greatly reduced since a $100 OEM FPGA could do the signal
processing (I've already done work on this but currently looking for
motivation to finish it off) and a simple, intensity-modulated laser
would probably be fine. A 2K euro budget would be a challenge though.

> The two-way time-transfer is relatively easy, but you will need to do some
> calibration to get the precision needed.
>

At first glance, I would think that you should be able to define the
optical RX/TX path to within 10 cm without any trouble and that gives
you 300 ps accuracy. Even on fibre links, I don't think anyone would
claim an accuracy of better than a few hundred ps.

Cheers
Michael
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Re: [time-nuts] Optical transfer of time and frequency

[Bruce Griffiths]

White Rabbit would be good in that a suitable TDC design with 1ns resolution 
already exists for White Rabbit. This TDC is used in the Tunka valley (near 
lake Baikal) Siberian Cherenkov telescope array. Note this TDC uses the SERDES 
receiver in the FPGA to implement a serial to parallel converter with a 1GHz 
clock synthesised from the 125MHz White Rabbit clock.
So far I haven't found an existing free space optical implementation of White 
Rabbit.
Bruce
 

On Saturday, 30 April 2016 11:00 AM, Michael Wouters 
 wrote:
 

 So why not do White Rabbit free space ?

Cheers
Michael

On Sat, Apr 30, 2016 at 4:04 AM, Paul Boven  wrote:
> Hi everyone,
>
> On 04/29/2016 03:28 PM, Magnus Danielson wrote:
>>
>> Phase/time transfer over fiber is shaping up, but White Rabbit is
>> starting to grow up and more reports for long distances is showing up.
>> ETFT is one of the placces to check for reports.
>
>
> And the White Rabbit workshops, with the presentations online:
> http://www.ohwr.org/projects/white-rabbit/wiki/Mar2016Meeting
>
> I happen to be working on time transfer via White Rabbit. The White Rabbit
> standard proscribes the use of 1000Base-Bx10 (10km reach bi-directional)
> SFPs, but it turns out to work just fine with longer reach SFPs. However,
> there are several effects that limit the accuracy that you can get on longer
> links:
>
> * Dispersion of the fiber (as the lasers change temperature, their
> wavelength changes, and they experience a slightly different index of
> refraction, hence propagation speed.
>
> * Change in index of refraction in the fiber itself. The propagation speed
> of both the uplink and downlink wavelength change, in absolute sense but
> also their ratio changes. This is something the WR protocol can't
> detect/correct for.
>
> There are several people working on these issues, trying to improve both the
> calibration and stability even further.
>
> Regards, Paul Boven.
>
>
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