Re: [time-nuts] Using lasers for data transmission
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 Bruce It is a long time since I worked with lasers, so my knowledge is both out of date and my memory not perfect.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
> 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
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
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
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
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
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
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
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
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
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
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
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
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???
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
> 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&D 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
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
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
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
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
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
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
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
> 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
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
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
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
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.