Re: [time-nuts] Using lasers for data transmission

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 1 May 2016 15:02, "Bruce Griffiths"  wrote:
>
> The solution with high power is to use a beam expander so that the
unaided eye cannot collect a power greater than the safe limit. Using near
IR beams also helps.
> Bruce

It is a long time since I worked with lasers, so my knowledge is both out
of date and my memory not perfect. But I was a long while ago regularly
using and sometimes aligning a picosecond pulsed laser at about 800 nm. The
average output power was 1 W, so a very dangerous class IV laser. It
certainly hurt if one had the beam on ones skin, but it was not
sufficiently powerful to noticeably burn the skin if one did the obvious
thing and moves ones hand away.

But I believe people need to be particularly careful using IR lasers. The
lens in the eye will not focus Iinfra red on the retina,  so that is
probably why you say IR is safer. However one of the protective methods the
eye has is a "blink response". One blinks if one perceives a light source
as bright. Blinking offers some protection to the eye. But since one does
not see an IR laser source, one  does not blink, so IR lasers disable one
of the eyes protective mechanisms.

Hence there are various complications that arrive when discussing laser
safety issues.  I don't have the knowledge to advise on what is or not
safe,  but will warn there are several effects which are important,  and
many people don't realise this.

Laser safety is a nontrivial subject.

Dave.
___
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.

Re: [time-nuts] help

[Chris Albertson]

> But are you sure you want SMPTE... Do you have a source already?
>
>
You don't need GPS or SMPTE if you have an Internet connection.  The
computer can use a set of NTP servers from the "pool" to get time.  The
result is good enough that the seed of sound delay resulting from your
random distance to the bell will be the largest source of error.

If you convert timing errors to distance at the speed of sound.   You would
need the GPS only if you car about bell to ear distances of about one foot,
give or take

So for this use case the OP does not need a GPS or even a SMTPE connection
just a WiFi link to the internet would be more than enough for controlling
a horn blast from a light house


-- 

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.

Re: [time-nuts] help

[Chris Albertson]

On Sun, May 1, 2016 at 12:26 PM, Bill Baker via time-nuts <
time-nuts@febo.com> wrote:

> My problem:  I'd like some kind of off-the-shelf device that can take the
> time code and switch on or impulse another circuit-- specifically  I'd like
> to trigger a 180 year-old fog bell (I'm a lighthouse nut as well,
> www.henryisland.com) on the hour and maybe be able to impulse my minute
> school clocks.  I'm not at this group's technical level, so it's got to be
> pretty easy to program. So I need a box that I can program with SMPTE time
> in and a timed switch impulse out.  Any ideas?


I assume you only need to be accurate to within about 1/10th of a second or
so.  Any general purpose computer like and old PC can do this but today
you'd go with a Raspberry Pi 2 or some other single board computer.   The
first step is to keep the computer's internal clock in sync with your time
signal (NTP can do that and NTP will likely already be installed on the
computer)  then if the computer is running a Unix-like OS (such as Linux,
BSD or Mac OS X) there is a table you can set up that will run various apps
at certain scheduled times.   You'd simply set s cron tab entry to blow the
horn on every hour every hour.   Not much software to write as this kind of
stuff (syncing to an external clock and doing things on a schedule) is
built in to the OS.

OK if you need to be much more accurate it gets harder but really this is a
audio alarm and the speed of sound is very slow such that the delay you'd
experience from sending 100 feet from the fog bell is longer than the delay
introduced by the software

So yjr only thing you need is to write software that does just one thing,
ring the bell then quit and let "crond" call it based on entries from the
table.

I see suggestion to use an Arduino or the like and program it.  That could
work too but if the little computer is powerful enough to run a unix-lil OS
you save some effort because they already come with built-in utilities to
do things on a schulue and to stay sync'd with an external clock signal.
-- 

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.

[time-nuts] Original Oncores for free

[Joseph Gray]

Does anyone want two non-working 6-channel Oncores that I pulled from
Z3801A's? They may be repairable, but now that I have working VP's and
spares, I don't want to take the time to fool with them.

Just thought I'd ask before tossing them in the recycle bin.


Joe Gray
W5JG
___
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.

Re: [time-nuts] help

[jimlux]

On 5/1/16 1:26 PM, jimlux wrote:

On 5/1/16 12:26 PM, Bill Baker via time-nuts wrote:

My problem:  I'd like some kind of off-the-shelf device that can take
the time code and switch on or impulse another circuit-- specifically
I'd like to trigger a 180 year-old fog bell (I'm a lighthouse nut as
well, www.henryisland.com) on the hour and maybe be able to impulse my
minute school clocks.  I'm not at this group's technical level, so
it's got to be pretty easy to program. So I need a box that I can
program with SMPTE time in and a timed switch impulse out.  Any ideas?
Many thanks,
W1BKR


An Arduino or Teensy (http://www.pjrc.com) are both trivially easy to
program and have easy interfaces (With a large number of off the shelf
interface widgets like relays, optoisolators, etc.).  There's probably
off the shelf code and hardware interfaces for decoding your SMPTE or
other time codes.



In fact
http://forum.arduino.cc/index.php?topic=8237.0

https://hackaday.io/project/7694-arduino-timecode-smpte-ltc-reader-generator-shield/log/27289-stripped-down-ltc-reader-code-for-arduino

references someone decoding SMPTE from an audio signal.



But are you sure you want SMPTE... Do you have a source already?


Seems to me you'd want something like a GPS receiver.. equally easy. 
I've got code the reads a Garmin GPS-18 on a teensy somewhere around, 
and I'm sure others have stuff for basically any GPS receiver made.


Lately, i've just been logging 1pps from various sources using the teensy.

After all, don't you want your fog bell to be accurate to fractions of a 
microsecond, because otherwise you're not really a time-nut .







___
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.

Re: [time-nuts] synchronization for telescopes

[Michael Wouters]

Attila,

I don't think a cheap receiver like a LEAxxx will quite get you there.

On Mon, May 2, 2016 at 1:10 AM, Attila Kinali  wrote:
> Moin,
>
> Let's quickly recap what the requirements are and what has been discussed
> so far:
>

> What I think has the best chances of success is to use an Rb frequency
> standard at each site instead. This will give you a stable reference
> frequency which will allow you to average the data from the GPS module
> to find the precise time in the prostprocessing.
>
> As a GPS module, I would either use an LEA-M8F or a LTE-Lite. The LEA has
> an frequency/phase input which which an external reference can be measured.
> the LTE-Lite supports using an external oscillator. What you definitely
> need is to get the satellite phase data ouf of the module to relate
> the phase differences between the modules local oscillator to the satellites
> and from there to the other locations.
>

> This should bring you at least down to a 1ns uncertainty level
> (after calibration). Judging from Michael Wouters said, probably
> close to 200-300ps.
>

The number I quoted is for high quality geodetic receivers. There are
crucial differences between these and the cheap receivers in regard to
time-transfer. The first is how you relate your external clock's 1 pps
to GPS time.

 For a geodetic receiver, this is 'simple' - it takes a 1 pps and 10
MHz that it locks to and does a one-off pps sync to. The code and
phase measurements are then reported with respect to this clock. For
some receivers, there will be an internal delay that depends on the
phase relationship between the 10 MHz and 1 pps so you have to control
that.

For cheap receivers, with no external oscillator, the connection
between your clock and GPS time is more complicated. You normally set
the GPS receiver's reference time to be GPS. Code measurements are
then reported with respect to a software GPS clock, based on the
receiver's XO. It's a software clock because the XO isn't steered. The
receiver then outputs a 1 pps (which you can then measure with respect
to but with the limitation that the receiver can only place this pps
modulo the period of its internal clock, resulting in the usual
sawtooth. The receiver outputs a sawtooth correction which allows you
to reduce the sawtooth in post-processing, with varying degrees of
success. Of course you can average, but being confident that you have
eliminated bias at the level of a few hundred ps may be tricky.

Some aspects of this may eg the sawtooth be improved by using an
external oscillator but I don't have any experience of this.

The other important difference is the resolution of the receiver's
measurements. A cheap receiver reports the code measurements at
relatively coarse resolution, sometimes a few ns, whereas a geodetic
receiver reports at much higher resolution. If you had a cheap
receiver, the code measurement resolution is seldom specified so you
would have to test candidate receivers.

I have many years of raw code measurement data from many identical
receivers operating on baselines of a few km up to 20 km. I will try
to have a look later this week to confirm/deny/make ambiguous what I
said above.

Cheers
Michael
___
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.

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

[Magnus Danielson]

Javier,

On 05/01/2016 02:54 PM, Javier Serrano wrote:

On Sun, May 1, 2016 at 9:50 AM, Magnus Danielson
 wrote:

If I recall correctly, there where some White Rabbit stuff available from
vendors, was it only Ethernet switches or also cards?


Yes, the switch is available from two vendors that I know of. They are
referenced at [1]. For nodes, we have a page describing what hardware
support is needed [2]. Then there are various boards available
commercially which implement that hardware support, like [3].

For the particular case of WR-enabled TDCs, one could use the SPEC
PCIe carrier [3] with a TDC FMC [4] or a simple DIO FMC [5],
delegating then the TDC function to the FPGA on the carrier, using an
HDL core like [6]. Or roll your own, of course.


Thanks for this listing!


Has anybody experienced with free-space optical gigabit Ethernet
links? I am curious about whether the transceivers have a fixed
latency or at least a latency one can easily quantify online. This is
the trickiest part for adding WR support on top of a given physical
layer.


There exists optical links that is used to solve the "last mile" 
problems. I have not used any of those myself.


I also know that there is microwave links which essentially just 
converts the optical GE encoding onto a microwave carrier and back.

It could be an interesting option to consider.

Most of the microwave links that is in regular use however have modes 
that re-encode things and will break White Rabbit. It also breaks my 
stuff every once in a while, so I know more about these systems than I 
should know. My EFTF-2014 presentation and paper give some comments on it.


Cheers,
Magnus


Cheers,

Javier

[1] http://www.ohwr.org/projects/white-rabbit/wiki/Switch#Commercial-producers
[2] http://www.ohwr.org/projects/white-rabbit/wiki/WRReferenceDesign
[3] http://www.ohwr.org/projects/spec/wiki
[4] http://www.ohwr.org/projects/fmc-tdc/wiki
[5] http://www.ohwr.org/projects/fmc-dio-5chttla/wiki
[6] http://www.ohwr.org/projects/tdc-core/wiki


___
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.

Re: [time-nuts] help

[jimlux]

On 5/1/16 12:26 PM, Bill Baker via time-nuts wrote:

My problem:  I'd like some kind of off-the-shelf device that can take the time 
code and switch on or impulse another circuit-- specifically  I'd like to 
trigger a 180 year-old fog bell (I'm a lighthouse nut as well, 
www.henryisland.com) on the hour and maybe be able to impulse my minute school 
clocks.  I'm not at this group's technical level, so it's got to be pretty easy 
to program. So I need a box that I can program with SMPTE time in and a timed 
switch impulse out.  Any ideas?
Many thanks,
W1BKR


An Arduino or Teensy (http://www.pjrc.com) are both trivially easy to 
program and have easy interfaces (With a large number of off the shelf 
interface widgets like relays, optoisolators, etc.).  There's probably 
off the shelf code and hardware interfaces for decoding your SMPTE or 
other time codes.


The coding would be simple - the widget's not doing anything else, so 
there's nothing wrong with a structure like


void loop(){
if (msgavailable) {
get message
decode message
if right message{
digitalWrite(relaypin,HIGH)
sleep (10)
digitalWrite(relaypin,LOW)
}
}
}



___
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.

[time-nuts] help

[Bill Baker via time-nuts]

My problem:  I'd like some kind of off-the-shelf device that can take the time 
code and switch on or impulse another circuit-- specifically  I'd like to 
trigger a 180 year-old fog bell (I'm a lighthouse nut as well, 
www.henryisland.com) on the hour and maybe be able to impulse my minute school 
clocks.  I'm not at this group's technical level, so it's got to be pretty easy 
to program. So I need a box that I can program with SMPTE time in and a timed 
switch impulse out.  Any ideas?
Many thanks,
W1BKR
___
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.

Re: [time-nuts] Using lasers for data transmission

[Ilia Platone]

Thank you, I personally were talking about 1400nm 1mw lasers, however.

Supplying just above the threshold current is not a problem.

does the raising time can be reduced if using lower current/voltage 
raises or falls? I mean: how's calculated the raise time, full-scale 
pulse or for a mW/mA or so amount?


Ilia.


Il 01/05/2016 18:48, Mark Sims ha scritto:

There are "eye-safe" wavelengths that some laser diodes can operate at 
(generally greater than 1300 nm).  These are much less prone to damage eyes.  Basically 
your eyeball juice blocks the wavelength.  Still, there is some potential for cornea and 
lens damage at higher powers.
http://www.laserfocusworld.com/articles/2008/03/photonic-frontiers-eye-safe-lasers-retina-safe-wavelengths-benefit-open-air-applications.html


___
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.



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

___
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.

Re: [time-nuts] Using lasers for data transmission

[jimlux]

On 5/1/16 9:48 AM, Mark Sims wrote:

There are "eye-safe" wavelengths that some laser diodes can operate at 
(generally greater than 1300 nm).  These are much less prone to damage eyes.  Basically 
your eyeball juice blocks the wavelength.  Still, there is some potential for cornea and 
lens damage at higher powers.
http://www.laserfocusworld.com/articles/2008/03/photonic-frontiers-eye-safe-lasers-retina-safe-wavelengths-benefit-open-air-applications.html

If they eye blocks (as in absorbs) the power, fine, you don't get a 
retina burn, but you get cataracts or other damage instead (more like 
"looking into the waveguide with your remaining good eye").



It's all about energy deposition and there's copious literature on what 
safe levels are (on Wikipedia even)



This kind of thing is fairly easy to do safely, you just have to work 
through the scenarios and recognize that doing it outside isn't like 
doing it the relatively controlled environment of a lab.


With reference to my previous comment about binoculars and telescopes, I 
don't think you have to worry about someone at the intended receiver 
site looking back at the transmitter (any beam divergence at all will 
make the energy density so low at the receiver, it's probably not an issue).


It's someone who's a lot closer than you expected turning around and 
looking back at the transmitter or an unexpected specular reflection off 
something.



BTW those geophysics measurements with red visible lasers across 
California were mostly done with HeNe lasers, because that's what was 
available back then.  They also have a nice long cavity (The 1mW 
SpectraPhysics 155 that I had back in 1978 had a 30cm-ish cavity), so 
the spectral purity is quite good and the beam divergence is low.  The 
HeNe are also a lot brighter visually than the red diode laser pointers 
for the same optical power.


___
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.

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

[Javier Serrano]

On Sun, May 1, 2016 at 5:44 PM, Tom Van Baak  wrote:
> This particular issue -- how to synchronize (or, at least phase compare) 
> multiple oscillators by a two-way laser link over a few km to within 500 ps 
> -- is really quite interesting. It would, for example, allow me to do live 
> monitoring of 5071A Cs time dilation on my next mountain-valley relativity 
> experiment.

Maybe Koruza [1] could be a good starting point for such a
development. It does not meet the distance spec in its current state
but it is not too expensive and it's all open source hardware (and
software of course). I am pretty sure the Koruza team would be happy
to collaborate.

Cheers,

Javier

[1] http://koruza.net/
___
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.

[time-nuts] Using lasers for data transmission

[Mark Sims]

Also, a lot of laser diodes don't like to be "cold-started".  Your modulation 
scheme needs the laser to always be on at some minimum level above Ith.  Just 
crudely switching from off to on can quickly kill the diode.
  
___
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.

[time-nuts] Using lasers for data transmission

[Mark Sims]

There are "eye-safe" wavelengths that some laser diodes can operate at 
(generally greater than 1300 nm).  These are much less prone to damage eyes.  
Basically your eyeball juice blocks the wavelength.  Still, there is some 
potential for cornea and lens damage at higher powers.
http://www.laserfocusworld.com/articles/2008/03/photonic-frontiers-eye-safe-lasers-retina-safe-wavelengths-benefit-open-air-applications.html

  
___
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.

[time-nuts] My TS-2100 Started Working Today???

[Jason Rabel]

Hey Guys, sorry I've been MIA for a while. Things happened, moved 500+
miles, etc, etc...

I haven't had some of my time servers on in years, including my TS-2100.
Yesterday I was running some Ethernet cable in my house and also mounted a
GPS antenna up in the attic.

Fired up a few time servers, including my TS-2100 and of course like
everyone else it was showing like 1996... Saw the posts about the date &
leap second bug and updated GPS module and such. Okay, it was 11pm (CDT) and
I was too tired, I'll deal with it in the morning.

Came in this morning, time & date are correct! Checked NTP against other
servers and not even the leap second issue!

It was May 1st (UTC) last night when I fired it up, so I don't see how any
rollover could have fixed it.

My Endrun Praecis also decided to go nuts, but they have a firmware update
on their website (Yay lifetime support for Endrun). I believe it uses an old
Trimble module too.

Don't know how long it will last, but as long as it gives the correct time
I'll probably hold off purchasing that aftermarket GPS module unless the
price has come down from those posts I read last year.

I saw a few people were looking for the 4.1 firmware. I've always had it up
on my archives, along with PDF manuals and data sheet for the 2100...
There's also lots of other PDFs on old GPS stuff.

http://www.rabel.org/archives/Symmetricom/


Hope all is well with everyone,

Jason


___
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.

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

[Tom Van Baak]

> Has anybody experienced with free-space optical gigabit Ethernet
> links? I am curious about whether the transceivers have a fixed
> latency or at least a latency one can easily quantify online. This is
> the trickiest part for adding WR support on top of a given physical
> layer.

Hi Javier,

When searching this topic I ran across a commercial laser solution:

http://www.laseroptronics.com/products.cfm/product/27-0-0.htm
http://www.laseroptronics.com/index.cfm/id/57-66.htm
http://www.laseroptronics.com/index.cfm/id/57-69.htm
etc.

But, according to /57-67.htm it "starts" at $15k per node. Plus there's the 
cost of all the WR pieces, assuming the two are even compatible. So this is 
vastly above the ~$2k budget mentioned by OP. I also assume OP is not ready to 
embark on a one-off, multi-man-year R project.

This particular issue -- how to synchronize (or, at least phase compare) 
multiple oscillators by a two-way laser link over a few km to within 500 ps -- 
is really quite interesting. It would, for example, allow me to do live 
monitoring of 5071A Cs time dilation on my next mountain-valley relativity 
experiment.

/tvb
___
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.

[time-nuts] synchronization for telescopes

[Attila Kinali]

Moin,

Let's quickly recap what the requirements are and what has been discussed
so far:

1) Time sync system of two (multiple?) sites spaced around 2km to better
   than 1ns, preferably 100ps.

2) System has to be mobile, no fixed installation

3) No amateur radio license available

4) Total cost less than 2000€

5) FPGA skills available


I think the free space laser sync system is a neat idea, but designing and
building it takes quite a bit of skill and experience and it requires
line of sight.

The sync to radio signal would require quite some engineering as well
for anything but AM stations.

Setting up a transmitter doesn't work either because that requires and
amateur radio license.


What I think has the best chances of success is to use an Rb frequency
standard at each site instead. This will give you a stable reference
frequency which will allow you to average the data from the GPS module
to find the precise time in the prostprocessing.

As a GPS module, I would either use an LEA-M8F or a LTE-Lite. The LEA has
an frequency/phase input which which an external reference can be measured.
the LTE-Lite supports using an external oscillator. What you definitely
need is to get the satellite phase data ouf of the module to relate
the phase differences between the modules local oscillator to the satellites
and from there to the other locations.

As for the time stamping. Using a 400MHz clock is ok, but you need higher
resolution for the post processing, as you will need some bits to burn.
As you will be using an FPGA anyways, I recommend using the OHWR TDC Core [1].
This will give you something in the order of 100-200ps resolution.
The CERN people did an implementation on Spartan6, and our group ported it
to Cyclone4 (code not released yet, needs some serious clean-up). From the
problems we faced, i would recommend going for the Xilinx, as the Cyclone4
requires you to get the paid version of Quartus in order to place the circuit
where it works best. Good thing is though, that the FPGA TDC is very stable
over time, the drift we saw in our measurements is orders of magnitude below
the smallest cell size (we measure less than 1ps over 24h... if we can trust
the data)

This should bring you at least down to a 1ns uncertainty level
(after calibration). Judging from Michael Wouters said, probably
close to 200-300ps.


The hardware looks pretty simple: Feed the Rb's output to the GPS module.
Feed the PPS from the GPS and a PPS from the Rb to the FPGA and
time-stamp both (alternatively, use the Rb as frequency reference for the
FPGA). You need be carefull with the power supply of the FPGA and the
signal feeds as now the FPGA is a semi-analog device. Feed all timestamp
data from the FPGA over USB or Ethernet to a PC and store it there.

My guestimate for the cost of this system would be:

200.- for the Rb (from ebay)
200.- for the GPS module
500.- for the rest of the electronics including PCB

The rest is a software problem ;-)


Attila Kinali

[1] http://www.ohwr.org/projects/tdc-core

-- 
Reading can seriously damage your ignorance.
-- unknown
___
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.

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

[Javier Serrano]

On Sun, May 1, 2016 at 9:50 AM, Magnus Danielson
 wrote:
> If I recall correctly, there where some White Rabbit stuff available from
> vendors, was it only Ethernet switches or also cards?

Yes, the switch is available from two vendors that I know of. They are
referenced at [1]. For nodes, we have a page describing what hardware
support is needed [2]. Then there are various boards available
commercially which implement that hardware support, like [3].

For the particular case of WR-enabled TDCs, one could use the SPEC
PCIe carrier [3] with a TDC FMC [4] or a simple DIO FMC [5],
delegating then the TDC function to the FPGA on the carrier, using an
HDL core like [6]. Or roll your own, of course.

Has anybody experienced with free-space optical gigabit Ethernet
links? I am curious about whether the transceivers have a fixed
latency or at least a latency one can easily quantify online. This is
the trickiest part for adding WR support on top of a given physical
layer.

Cheers,

Javier

[1] http://www.ohwr.org/projects/white-rabbit/wiki/Switch#Commercial-producers
[2] http://www.ohwr.org/projects/white-rabbit/wiki/WRReferenceDesign
[3] http://www.ohwr.org/projects/spec/wiki
[4] http://www.ohwr.org/projects/fmc-tdc/wiki
[5] http://www.ohwr.org/projects/fmc-dio-5chttla/wiki
[6] http://www.ohwr.org/projects/tdc-core/wiki
___
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.

Re: [time-nuts] Using lasers for data transmission

[jimlux]

On 5/1/16 3:22 AM, Bruce Griffiths wrote:

The solution with high power is to use a beam expander so that the unaided eye 
cannot collect a power greater than the safe limit. Using near IR beams also 
helps.
Bruce



IR is a problem for eye safety, because IR doesn't trigger the blink 
reflex, so you can inadvertently "stare into the laser with the 
remaining good eye".



If you want to stay below, say, 1 mW/square cm, and you're running a 20 
mW laser, you'd want 20 square cm of aperture.  That's about 5cm diameter.


You should bear in mind that if you're doing "mountain top to mountain 
top" type applications there might be someone looking at you with 
binoculars or a telescope, which makes their "light gathering aperture" 
much larger, and increases the risk of injury.



___
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.

Re: [time-nuts] Using lasers for data transmission

[Michael Wouters]

Dear Ilia

On Sun, May 1, 2016 at 6:40 PM, Ilia Platone  wrote:
> The problem would be modulating a 10GBASE-T signals into a single laser
> beam, and demodulating it using (I think) an APD.
>

The White Rabbit cards use SFP (small form-factor pluggable) lasers
that plug into the card. These incorporate both the laser(s) (there
can be an uplink and downlink laser) and APD. Modulation in these
devices is simply by varying the current. This puts a frequency chirp
on the laser which exacerbates dispersive effects. You can do better
with an electro-optic device like a Mach-Zehnder intensity modulator -
but this isn't necessary.

> except the one depending on light travel, that shouldn't be a problem if
> using White Rabbit, there could be some problem with the modulating and
> transmitter/receiver delay response times.

I remember reading that the SFPs are a source of jitter but
nonetheless, sub-ns timing is achievable.

> I mean that lasers offer 100ps rise time, and the APDs I found offer 5ps
> rise time, these must be multiplied by all the wires that GigE needs, which
> should be 4 pairs if I remember correctly, and some are bi-directional, plus
> the modulation process.
>
> Ilia.
>

Cheers
Michael
___
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.

Re: [time-nuts] Misc topics

[KA2WEU--- via time-nuts]

I got a large reply to give the 8662 away, let the old/new one arrive and  
be ok, and the first one who contacted me will get mine. Good luck with the  
repair of the power supply. The 8662 works correct occasionally, starts up 
and  then not but is in specs.
 
I will be in San Francisco IMS /MTT giving papers in May, then I  will know 
more.
 
For those interested in advanced physics here is some work we are doing 
 
 
 Ulrich 
 
 
In a message dated 4/30/2016 6:40:27 P.M. Eastern Daylight Time,  
ka2...@aol.com writes:

https://en.wikipedia.org/wiki/Casimir_effect
 
 
 

___
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.

Re: [time-nuts] Using lasers for data transmission

[Bruce Griffiths]

The solution with high power is to use a beam expander so that the unaided eye 
cannot collect a power greater than the safe limit. Using near IR beams also 
helps.
Bruce
 

On Sunday, 1 May 2016 9:00 PM, Dr. David Kirkby (Kirkby Microwave Ltd) 
 wrote:
 

 > Hi,
> Several (many?) years ago National Geographic magazine show a picture
taken here in southern California of the state government sending red laser
signals between different mountain tops to keep track what was going on
near fault lines
> There were no technical details on what was taking place.  So it can be
done.
> At a hamfest a few years ago I bought both a red and green 35 mW laser
pen for about $15 each.  They do shine a long, long way.

35 mW is certainly unsafe to the eyes, so be very careful.  There maybe
legal issues about doing this.

> Whether these are powerful enough, or can be properly modulated for what
is needed, I have no idea.

You can pretty much modulate any laser diode. There are two important
currents to know about

* Threshold current I_th - below which it will not lase.
* Maximum operating current I_max - above which the device will be
destroyed.

You can AM modulate them by applying a DC current

I_th + (I_max - I_th)/2.

Then superimpose the modulation which has a peak value of (I_max - I_th)/2.

Those currents ensure that the laser is always lasing,  and gets you
theoretically 100% modulation.  For best lifetime,  run at lower levels of
peak modulation current.

Watch out for transient currents - lasers make transistors look like
antisurge fuses!

For point to point contact you want a beam which diverges as little as
possible.  IIRC the divergence is something like inversely proportion to
the cavity length.  For this reason a diode laser with its short cavity is
not optimal. But of course they are cheap.

A veey long time ago I used to know quite a lot about lasers,  but not
using them for years I realise that I have forgotten an awful lot!

FWIW, at university we had a 10 W argon ion laser. I think it took about 50
kW to produce those 10 W. When it was disposed of, it was sold to a company
that put on light shows.

Dave
___
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.


  
___
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.

Re: [time-nuts] Using lasers for data transmission

[Ilia Platone]

Threshold current should not be a problem because if there's no data the 
laser could go into "power saving mode".


As am modulation a simple buffer/r2r network DAC should do the job. The 
signals to transmit are three: Tx, and two bidirectional.


Ilia.


Il 01/05/2016 10:27, Dr. David Kirkby (Kirkby Microwave Ltd) ha scritto:

Hi,
Several (many?) years ago National Geographic magazine show a picture

taken here in southern California of the state government sending red laser
signals between different mountain tops to keep track what was going on
near fault lines

There were no technical details on what was taking place.  So it can be

done.

At a hamfest a few years ago I bought both a red and green 35 mW laser

pen for about $15 each.  They do shine a long, long way.

35 mW is certainly unsafe to the eyes, so be very careful.  There maybe
legal issues about doing this.


Whether these are powerful enough, or can be properly modulated for what

is needed, I have no idea.

You can pretty much modulate any laser diode. There are two important
currents to know about

* Threshold current I_th - below which it will not lase.
* Maximum operating current I_max - above which the device will be
destroyed.

You can AM modulate them by applying a DC current

I_th + (I_max - I_th)/2.

Then superimpose the modulation which has a peak value of (I_max - I_th)/2.

Those currents ensure that the laser is always lasing,  and gets you
theoretically 100% modulation.  For best lifetime,  run at lower levels of
peak modulation current.

Watch out for transient currents - lasers make transistors look like
antisurge fuses!

For point to point contact you want a beam which diverges as little as
possible.  IIRC the divergence is something like inversely proportion to
the cavity length.  For this reason a diode laser with its short cavity is
not optimal. But of course they are cheap.

A veey long time ago I used to know quite a lot about lasers,  but not
using them for years I realise that I have forgotten an awful lot!

FWIW, at university we had a 10 W argon ion laser. I think it took about 50
kW to produce those 10 W. When it was disposed of, it was sold to a company
that put on light shows.

Dave
___
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.



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

___
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.

Re: [time-nuts] Using lasers for data transmission

[Dr. David Kirkby (Kirkby Microwave Ltd)]

> Hi,
> Several (many?) years ago National Geographic magazine show a picture
taken here in southern California of the state government sending red laser
signals between different mountain tops to keep track what was going on
near fault lines
> There were no technical details on what was taking place.  So it can be
done.
> At a hamfest a few years ago I bought both a red and green 35 mW laser
pen for about $15 each.  They do shine a long, long way.

35 mW is certainly unsafe to the eyes, so be very careful.  There maybe
legal issues about doing this.

> Whether these are powerful enough, or can be properly modulated for what
is needed, I have no idea.

You can pretty much modulate any laser diode. There are two important
currents to know about

* Threshold current I_th - below which it will not lase.
* Maximum operating current I_max - above which the device will be
destroyed.

You can AM modulate them by applying a DC current

I_th + (I_max - I_th)/2.

Then superimpose the modulation which has a peak value of (I_max - I_th)/2.

Those currents ensure that the laser is always lasing,  and gets you
theoretically 100% modulation.  For best lifetime,  run at lower levels of
peak modulation current.

Watch out for transient currents - lasers make transistors look like
antisurge fuses!

For point to point contact you want a beam which diverges as little as
possible.  IIRC the divergence is something like inversely proportion to
the cavity length.  For this reason a diode laser with its short cavity is
not optimal. But of course they are cheap.

A veey long time ago I used to know quite a lot about lasers,  but not
using them for years I realise that I have forgotten an awful lot!

FWIW, at university we had a 10 W argon ion laser. I think it took about 50
kW to produce those 10 W. When it was disposed of, it was sold to a company
that put on light shows.

Dave
___
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.

Re: [time-nuts] Using lasers for data transmission

[Ilia Platone]

The problem would be modulating a 10GBASE-T signals into a single laser 
beam, and demodulating it using (I think) an APD.


except the one depending on light travel, that shouldn't be a problem if 
using White Rabbit, there could be some problem with the modulating and 
transmitter/receiver delay response times.


I mean that lasers offer 100ps rise time, and the APDs I found offer 5ps 
rise time, these must be multiplied by all the wires that GigE needs, 
which should be 4 pairs if I remember correctly, and some are 
bi-directional, plus the modulation process.


Ilia.


Il 01/05/2016 07:13, Perry Sandeen via time-nuts ha scritto:

Hi,
Several (many?) years ago National Geographic magazine show a picture taken 
here in southern California of the state government sending red laser signals 
between different mountain tops to keep track what was going on near fault 
lines.
There were no technical details on what was taking place.  So it can be done.
At a hamfest a few years ago I bought both a red and green 35 mW laser pen for 
about $15 each.  They do shine a long, long way.  Whether these are powerful 
enough, or can be properly modulated for what is needed, I have no idea.
On line I saw at least one China site that had much larger outputs available.  
The prices were modest. FWIW.
Regards,
Perrier
___
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.



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

___
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.

Re: [time-nuts] Z3801A recovering

[Joseph Gray]

After about three hours:
https://dl.dropboxusercontent.com/u/19599147/Z3801A%203hr.png

Ignore the graph discontinuity at the beginning. I had to power cycle
to change to UTC.


Joe Gray
W5JG


On Sun, May 1, 2016 at 1:30 AM, Joseph Gray  wrote:
> In past discussions about replacing a 6-channel Oncore in a Z3801A
> with an 8-channel VP Oncore, some claimed that the VP had to first be
> put into 6-channel mode, others indicated this was not necessary.
> Earlier tonight, I put a VP (still in 8-channel mode) into my
> malfunctioning Z3801A. Monitoring with Z38xx, I see no signs that this
> is a problem. Even the logs look clean.
>
> In reading the VP documentation, I saw that there were several
> 6-channel commands, along with similar 8-channel commands. That is why
> I thought I'd try using the VP without setting it to 6-channel mode.
> It was an experiment that seems to have succeeded.
>
> I don't want to jinx things, but so far, my formerly flaky Z3801A is
> working normally, after replacing the GPS module. The self survey
> finished in two hours (about 25 minutes ago). The EFC and PPS TI/s
> graphs are no longer going wild.
>
> I'm going to monitor this for quite a while before I call it fixed.
> Then it's on to repairing the Z3801A that I traded for.
>
> In addition to replacing the GPS module, I also replaced three caps on
> the power supply board. On initial inspection, C108 and C110 had a
> faint white ring around them, on the PCB, as though they had out
> gassed. There was also some corrosion on pin TP104, which sits between
> C108 and C110. The caps checked fine with my LCR meter, but I thought
> I'd replace them while I had things apart. I also replaced C111, which
> is nearby. When I removed the caps, there was no corrosion on the PCB.
>
> When I inspected the other Z3801A which is awaiting repair, I saw the
> same faint white rings around C108 and C110. There was no corrosion on
> TP104, however. I will replace those caps as well, when I get to it.
>
>
> Joe Gray
> W5JG
___
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.

Re: [time-nuts] Z3801A recovering

[Joseph Gray]

In past discussions about replacing a 6-channel Oncore in a Z3801A
with an 8-channel VP Oncore, some claimed that the VP had to first be
put into 6-channel mode, others indicated this was not necessary.
Earlier tonight, I put a VP (still in 8-channel mode) into my
malfunctioning Z3801A. Monitoring with Z38xx, I see no signs that this
is a problem. Even the logs look clean.

In reading the VP documentation, I saw that there were several
6-channel commands, along with similar 8-channel commands. That is why
I thought I'd try using the VP without setting it to 6-channel mode.
It was an experiment that seems to have succeeded.

I don't want to jinx things, but so far, my formerly flaky Z3801A is
working normally, after replacing the GPS module. The self survey
finished in two hours (about 25 minutes ago). The EFC and PPS TI/s
graphs are no longer going wild.

I'm going to monitor this for quite a while before I call it fixed.
Then it's on to repairing the Z3801A that I traded for.

In addition to replacing the GPS module, I also replaced three caps on
the power supply board. On initial inspection, C108 and C110 had a
faint white ring around them, on the PCB, as though they had out
gassed. There was also some corrosion on pin TP104, which sits between
C108 and C110. The caps checked fine with my LCR meter, but I thought
I'd replace them while I had things apart. I also replaced C111, which
is nearby. When I removed the caps, there was no corrosion on the PCB.

When I inspected the other Z3801A which is awaiting repair, I saw the
same faint white rings around C108 and C110. There was no corrosion on
TP104, however. I will replace those caps as well, when I get to it.


Joe Gray
W5JG
___
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.

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

[Magnus Danielson]

Javier,

If I recall correctly, there where some White Rabbit stuff available 
from vendors, was it only Ethernet switches or also cards?


Cheers,
Magnus

On 05/01/2016 01:14 AM, Bruce Griffiths wrote:



  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.



___
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.


___
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.

[time-nuts] Using lasers for data transmission

[Perry Sandeen via time-nuts]

Hi,
Several (many?) years ago National Geographic magazine show a picture taken 
here in southern California of the state government sending red laser signals 
between different mountain tops to keep track what was going on near fault 
lines.
There were no technical details on what was taking place.  So it can be done.
At a hamfest a few years ago I bought both a red and green 35 mW laser pen for 
about $15 each.  They do shine a long, long way.  Whether these are powerful 
enough, or can be properly modulated for what is needed, I have no idea.
On line I saw at least one China site that had much larger outputs available.  
The prices were modest. FWIW.
Regards,
Perrier
___
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.