Re: [time-nuts] GPS DO Alternatives
On 12/8/12 9:30 AM, johncr...@aol.com wrote: Instead the discussion has centered on what microprocessor (of a hundred that would work) and how to eliminate glue logic and and a few analog parts to save money. This is silly - silicon is CHEAP. Silicon is cheap, but for one-off fabrication by a hobbyist that isn't always the case. As was mentioned in a couple of the mails in the long discussion, for a single person to build something like this requires a combination of skills and materials. Someone may be fine at software, but doesn't want to fabricate circuitry, or vice versa. So, there was discussion of what could you do that would literally be plug and play with minimal hardware design and assembly required (so the playing would be with software). This isn't an unusual scenario.. The AMSAT folks have run into it vis a vis ground stations. So have others (APRS). A colleague of mine (N5BF) comments that what you really need is something where someone can impulse buy enough to do something useful fairly quickly. The kit idea: buying $100 worth of parts and then having to spend 6 weeks assembling and testing means that lots of people will have $100 parts bags sitting on a shelf, unused. You'd be better off selling a $200 assembled and tested widget. Yes, you won't sell quite as many, but a LOT more of them will be actually used than those bags o'parts. A particularly attractive model is where you have a hardware component that is delivered pretty much ready to go, with basic software, and the fooling around is with changes in the software or parameters. For the GPSDO world, this might be experimenting with different filters and holdover strategies, or maybe tuning it to work with your particular OCXO. This is why the Arduino is so popular. No or minimal soldering required, a wealth of simple software that almost does what you need it to, be it monitoring the temperature of your beer fermentation, turning on and off sprinklers or whatever. Anything where the software is quite complex, that will inhibit experimentation, unless there's a lot of documentation of the theory of operation and software design, and the software has to be written to facilitate modification. For the Arduino, the limited amount of storage sort of self limits the complexity of applications. Once you move into the PC world it gets a lot harder. And realistically, a lot of hobby written software doesn't have a good architecture or underlying design. It sort of just growed in place with successive modifications to add features, etc. And it works, but it's not very easy to figure out how to modify it. ___ 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] GPSDO Alternatives
On 12/6/12 1:56 PM, Bob Camp wrote: Hi The single best thing about a TBolt is Lady Heather. Consider how many years it's taken to get it to where it is today. Consider how many people have worked extensively on it. It's a wonderful thing to have available. Could you make a homebrew gizmo look just like a TBolt? Sure you could. It might well take you forever to do all the reverse engineering, validation, and testing, but it can be done. I'd guess it would take less time to re-write a version of LH from scratch Of course, the process of experimenting and trying to duplicate the Tbolt is fairly educational. It touches a lot of interesting areas in RF design and metrology, as well as software algorithms. One might do it for the same reason that someone builds a fusor in their garage. There are easier ways to get neutrons, but building a fusor is a nice combination of learning about high vacuum, high voltage, nuclear physics and metrology, etc. Both are a heck of a lot cheaper than building and flying a CubeSat, for instance. ___ 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] GPSDO Alternatives
On 12/6/12 11:12 PM, Hal Murray wrote: Suppose you just implement a simple bang-bang control. Suppose the EFC is 1 volt and the frequency is correct but the GPSDO phase is a bit early relative to the GPS PPS. So the FF says early and the software says go-faster. That keeps happening for a while, the frequency keeps getting faster and faster. Finally, the GPSDO PPS catches up with the GPS PPS, but now it's frequency is way fast. The FF says go slower, so the control software starts dropping the EFC. But the frequency is still way too high so the error is still increasing. After a while the frequency gets low enough so the PPS/phase error starts catching up. Eventually the PPS error crosses over, but by then the frequency offset is way way low. ... Isn't that cyclic pattern stable? Is there a simple tweak to break that loop? Do you first have to recognize that you are in that mode? If so, how? ... yes.. what you've described is essentially a first order control loop. You can add higher order terms (e.g. integral or derivative) so that you don't get overshoot. I might be able to do fix that in software by looking at the times when things change state. Suppose it's 193 seconds between the first early and the last early and that the EFC went from X to Y. I think that's enough info to work out the crossover point and work back to the desired EFC. Yes.. that's another approach.. you figure out what the model is, and solve backwards. But that all sounds too complicated. What would hardware-only guys do with a 1 bit A/D? ___ 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] GPSDO Alternatives (GLUE)
On 12/6/12 5:01 PM, Bob Camp wrote: Hi The solution to the problem is well known in several forms. Cost is below $5 for pretty much all of them. No need to re-invent the wheel. The gotcha is that you can't do it 100% with internal CPU peripherals. You will need *some* glue. I think that's the interesting aspect of this discussion (because it mirrors many similar such discussions I've had over the years).. The challenge is not in building a GPSDO.. there's tons of ways to do that at minimal hardware cost.. The challenge is how do you do it without using any additional glue logic or hardware That is, given things you can buy off the shelf, and no hardware work other than fabricating cables or soldering a wire or two, what can you do inexpensively. ___ 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] GPSDO Alternatives
On 12/6/12 11:20 PM, Don Latham wrote: Good thought, Bob. AD9548 $27, eval board a whopping $250, get a thunderbolt :-). The eval board has a lot of SMA's on it... This is a general problem with eval boards these days.. They provide a lot of functionality on the board to make it easy to evaluate the chip (USB interfaces, buffer memories, etc.) but that makes it hard to use the eval board as a sort of glorified chip carrier. For instance, all those nice serial interface ADC and DAC parts.. it would be nice to have a little board with the converter, power supply filtering and maybe an opamp buffer, and bring the serial interface pins to the edge where you could just wire it to something like a PIC eval board or Arduino or parallel printer port. But no.. they have a weird connector that goes to a mother board with a fancy preprogrammed micro and dual port memory and stuff.. all so you can just hook up a signal generator and capture samples to run FFTs to duplicate the databook graphs. ___ 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] GPSDO Alternatives
On 12/6/12 1:06 AM, Chris Albertson wrote: Yes. The idea was the simplest GPSDO that can be build with no PCB around an Arduino. We already know how to build compllelx and expensive GPSDO. That is too easy. I think you can use the PWM DAC on the Aruino to drive the OCXO. The bandwidth of this signal is way low so you can filter the PWM output with a (say) 1Hz low pass filter. I would worry about how you'd build that filter to be low noise AND suitably filter the PWM output so that there's no leakage of the PWM modulation. Seems it would be easier to hook up a serial interface DAC with lots of bits than fool with filters.. ___ 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] Power Grid Time and Frequency
On 12/6/12 4:42 AM, Bob Smither wrote: On 12/05/2012 02:32 PM, M. Simon wrote: Do you have a link for the nifty site? This one is not just for the west coast, but has good reporting of grid conditions: http://fnetpublic.utk.edu/index.html They have several real time graphic and table displays of grid frequency. The Sample Events tab has links to movies of the grid frequency during major storms and an east coast earthquake. I think there's another one that is similar somewhere on the west coast (Washington state?) .. I'm hunting for the URL (it was on this list, I think).. ___ 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] GPSDO Alternatives
On 12/6/12 9:45 AM, Dale J. Robertson wrote: Arduino is Dirt Cheap! And available over the counter retail at hundreds of Radio Shacks.. You get an idea during the day, and you can run out and buy one right then.. (yes, you can mail order, but the fastest turnaround is a few days, unless you pay an enormous next day shipping premium) This is one reason why Arduino is by far and away the most common uProc in, e.g., high school science projects. ___ 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] GPSDO Alternatives
On 12/5/12 12:06 AM, Bruce Griffiths wrote: Hal Murray wrote: albertson.ch...@gmail.com said: What is the simplest phase detecter that could work? I think only that, and then a duouble oven crystal from eBay, a GPS and and Arduido. You also need a good D2A to drive the EFC on the osc. A synchronous filter of a suitably level translated (CMOS analog switch plus low noise reference) PWM output should work well. True.. but I think the OP was wanting something that doesn't require designing a circuit and building it. So what you really want is a high performance DAC on a Arduino shield, or, alternately, a high performance DAC on a cheap eval board that you can easily hook up to an Ardino type processor. This is a bit trickier.. Lots of ADC stuff out there, not so much DAC stuff. http://embeddednewbie.blogspot.com/2011/02/review-of-arduino-dac-solutions.html seems to have a number of approaches. Adafruit has a shield with a Microchip MCP4921 12 bit serial dac here's a 16 bit solution http://www.shaduzlabs.com/article-12.html but it's a build it yourself solution. If you're not size/mass/power constrained, you might be able to find an inexpensive used programmable power supply. I do this using a Prologix controller driving Agilent E3646 power supplies.. Big, Expensive, etc. but it does work. Yes the Aruino is expensive compared to a bare uP chip but using one, I thin you could build a GPSDO without a PCB and the Arduino's USB connection could be usful for power and logging/control. I wouldn't want to power a GPSDO from USB. It will get power cycled every time I need to work on the logging PC. Besides, you only get 2.5 watts. The oven will probably take more than that during warm-up. Bruce ___ 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] Very challenging phase noise measurement, does anyone have an idea??
On 12/5/12 2:45 PM, Marek Peca wrote: This last idea is interesting... could be simulated by Matlab or similar. It is known to work in ordinary non-linear transistor-based mixers. It will produce more messy spectrum than double-balanced mixer, however, for this purpose and completely within digital domain, it makes absolutely no harm, in my oppinion. On the other hand, simplicity of two resistors ADC may help. for that matter, fit two sinusoids to the two inputs (which will inevitably be at different frequencies, eh?) ___ 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] Time security musing - attacking the clock itself
On 12/3/12 9:59 PM, gary wrote: I was a bit concerned about clicking the fob for no good reason. I assume each click is a different number. I only use it for ebay and paypal. [Incidentally, they jacked the price from $5 to $30.] The RSA fob doesn't have a button. It just displays a 6 digit number that changes once a minute or so. The number is generated by a pseudo random number generator which is seeded in a way that is tied to the serial number. The compromise last year at RSA involved someone getting access to the serial number-seed list. (This is obviously not a public key system). Now a phone has accurate network time, so they could get really tricky with the time as part of the code. I was meditating a bit on the power grid synchronization. If all the sites but one are in sync, then the generator whose sync is being hacked will have a hard time trying to feed the grid while being out of phase. This should be detectable electronically in the generator interface. If the timing is moved slowly, the the conflict would build slowly as well. The problem is that how would you distinguish this from normal load dispatch for the generator. That's how you set the power flow: you adjust the phase of your generator to slightly leading the grid, and power flows from generator to grid. In the dark ages, I TAs an electronics class set up for non electrical engineers. I considered it kind of brutal since they tried to cover just about everything in one class. Well it included what we used to call motors and rotors. [I suspect this isn't even taught anymore.] One of the lab experiments was to sync a generator to the mains. Now the generator was driven by a motor from the mains, so this wasn't particularly difficult. You would put a meter between your generator and the mains and drag on the shaft a bit until the phase error was zero, then turn the switch to connect them. Things were going OK but then I heard a nasty sound and the lights flickered a bit. It turns out some curious students wanted to see what happened if the generator and mains were out of phase. Well, the mains wins. Yes.. there are stories of *big* drive shafts shearing or enormous turbomachinery ripping off the floor bolts. It is apparently hard to move the grid. The interconnection problem is complicated by the fact that there are long transmission lines in the system which have all the usual transmission line issues like reflections, etc. Your simple lab exercise would be substantially more complicated if there were a 1000 km long transmission line between the grid and generator. What you have in the real system is dozens of coupled oscillators, all with their own stiffness coupled by a complex network of transmission lines with propagation delays and mismatch. On 12/3/2012 8:12 PM, Jim Lux wrote: On 12/3/12 6:34 PM, Hal Murray wrote: li...@lazygranch.com said: I have one of those key fobs. Does the code somehow inform the power the be about the drift in the built in clock? Or is the time element of the code so sloppy that the drift is acceptable? The magic number changes every second or so. Every 30 seconds or every minute.. I've seen both. My fob is once a minute, the iPhone soft fob is 30 seconds. You only have to scan a few seconds either side of the correct time to find a valid match. Every time the server gets a match it can update its memory of the fob time to reduce its searching in the future. Exactly, the maximum time difference is a settable parameter. You could measure/compute the drift too. I don't know if that's worth the effort. It would probably change with temperature so seasonal or lifestyle changes could throw the prediction way off. I don't think they do that.. I think it's a reset when validated... [I have no inside knowledge. I could be totally wrong, but that seems reasonable to me. They may have a better approach.] It's all described on the RSA website.. Hmm.. I suspect I could time my fob once a day, and see how many seconds a day it drifts.. without a timed camera it would be hard to get tighter than 1 second resolution.. the iPhone one almost certainly uses the internal clock in the phone. ___ 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 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] Time security musing - attacking the clock itself
On 12/4/12 4:28 PM, Bill Hawkins wrote: Sorry about this, Tom, but there's some misinformation here. I wasn't reading this until I saw your posting. -Original Message- From: Jim Lux Sent: Tuesday, December 04, 2012 7:58 AM On 12/3/12 9:59 PM, gary wrote: I was meditating a bit on the power grid synchronization. If all the sites but one are in sync, then the generator whose sync is being hacked will have a hard time trying to feed the grid while being out of phase. This should be detectable electronically in the generator interface. If the timing is moved slowly, the the conflict would build slowly as well. The problem is that how would you distinguish this from normal load dispatch for the generator. That's how you set the power flow: you adjust the phase of your generator to slightly leading the grid, and power flows from generator to grid. - End Original Message A. You cannot have one generator feeding the grid while being out of phase. See any text on coupled (bussed) rotating synchronous machines. Yes, if the buss is infinitely stiff and infinitesimally short. If the transmission line is 1000 km long with significant inductance and capacitance, then the phase of a generator at one end and the phase of a generator at the other end (or somewhere in between) will be quite different. The AC intertie in California that runs up the central valley, for instance, has transients (e.g. instantaneous phase variations) that take hours to die out. One of the big advantages of DC links is that they don't have this problem.. one end acts as a constant current source/sink, the other as a constant voltage source/sink.(DC links have other problems, but they're still easier than stabilizing a 1500 km long ac transmission line with sources and loads all along it) It's fascinating to look at the phase/frequency plots during the northeast blackout a few years ago. There's even an IEEE Standard (1344) on timing for power lines. IEEE 1344 gives GPS timing as 200ns. that standard calls out a signal at 1pps with 1E-7 stability and 1us max variation from UTC. Appendix B of that doc says that you need to be able to measure phase to 0.1 degree for state estimation, stability monitoring, control, and relaying. B. There is no phase adjustment for the generator. Phase angle with respect to the grid is determined by whether you are giving or taking power with respect to the grid. To increase your phase lead on the grid, you apply more steam to the turbine. yes.. I was sloppy.. but the point is that the phase of the power coming out of the generator slightly leads that of the sink (e.g. current flows FROM generator to grid). Time has nothing to do with it, except at the central dispatching office for a generating region. If time on the grid, measured in generated cycles, lags the number of 60 (or 50) Hz cycles since midnight (or some reference) then the dispatcher calls for or remotely commands more power to be generated at some stations until the lost cycles are made up. The entire distribution network stays in synch, as it must. The way they measure relative phase (and frequency) is by comparison with a good clock. There's a nifty website out there that shows the instantaneous and integrated phase difference between various places on the pacific coast, so you can see power flow changing. Hope that clears things up. Now, if you are talking about the huge power inverter at the junction of a DC transmission tie line and an AC network, then yes, you can adjust the phase angle to control power flow - but this is not controlled by a clock. Bill Hawkins ___ 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] Time security musing - attacking the clock itself
On 12/3/12 9:32 AM, dlewis6767 wrote: I agree, Bob. Like the billboard on the side of the highway says: - Does Advertising Work? JUST DID - The bad guys can read this list same as the good guys. Security through obscurity never works in the long run. Much better to discuss vulnerabilities in the open, and discuss countermeasures that are robust. Clock synchronization is of great interest in a variety of crypto systems where keys are changed on a predetermined schedule (the RSA two factor authentication key fob is an interesting instance). It's even trickier when you have to distribute time in a secure way (in the sense that not only is the at the tone, the time is message is reliable, but also that the timing of the tone is reliable). The various redundancy and reasonableness checks (e.g. for GPS) are in this area as well. The question is: Can I distribute timing information through a network reliably ___ 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] Time security musing - attacking the clock itself
On 12/3/12 6:34 PM, Hal Murray wrote: li...@lazygranch.com said: I have one of those key fobs. Does the code somehow inform the power the be about the drift in the built in clock? Or is the time element of the code so sloppy that the drift is acceptable? The magic number changes every second or so. Every 30 seconds or every minute.. I've seen both. My fob is once a minute, the iPhone soft fob is 30 seconds. You only have to scan a few seconds either side of the correct time to find a valid match. Every time the server gets a match it can update its memory of the fob time to reduce its searching in the future. Exactly, the maximum time difference is a settable parameter. You could measure/compute the drift too. I don't know if that's worth the effort. It would probably change with temperature so seasonal or lifestyle changes could throw the prediction way off. I don't think they do that.. I think it's a reset when validated... [I have no inside knowledge. I could be totally wrong, but that seems reasonable to me. They may have a better approach.] It's all described on the RSA website.. Hmm.. I suspect I could time my fob once a day, and see how many seconds a day it drifts.. without a timed camera it would be hard to get tighter than 1 second resolution.. the iPhone one almost certainly uses the internal clock in the phone. ___ 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 a frequency synthesizer replacement for motherboard oscillator
On 11/30/12 4:58 PM, John Ackermann N8UR wrote: On Nov 30, 2012, at 7:42 PM, John Ackermann N8UR j...@febo.com wrote: In this case, you're not looking for the RTC but rather the clock that drives the COU Read CPU. Stupid iPad keyboard. I was wondering.. Clock Oscillator Unit? Cryptic Obfuscated 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] Best phase detector / mixer for 100MHz?
On 11/26/12 10:11 AM, Demian Martin wrote: I asked Wenzel about mixers for phase noise measurement and they directed me to Marki Microwave as what they use: http://www.markimicrowave.com/2770/Mixers.aspx I have not obtained or tested any myself but it's a pretty solid recommendation I think. Isn't Marki making the old WJ mixers? That seems to be what someone told me a few years ago: they basically have all the tooling and designs, etc. ___ 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] DDS - higher frequecies
On 11/25/12 4:30 PM, Hal Murray wrote: Suppose I have an A/D running at 1 MHz. The standard simple minded approach is that it will work for any input signal with a bandwidth up to 1/2 MHz. We usually think of that in the baseband, but it also works for, say 1.25 to 1.5 MHz. The input signal gets aliased down into the baseband. (and if you are unlucky, which is easy, some of the aliasing reflects back and overlaps so you can't tell X-y from X+y) There is similar math for D/A, the reverse direction. I think this applies for a DDS making higher frequencies than simple arithmetic would allow it to generate. Yes.. you generate all the aliases.. Fx, Fs-Fx, Fs+Fx, 2Fs-Fx, 2Fs+Fx, etc. Does anybody have a good web page for how that works? My simple expectations are that it would have to generate lots of harmonics and then go through a filter to get rid of all the wrong stuff. I'm missing the step where all the harmonics come from. Not exactly harmonics, but aliases. What you are doing is convolving the sampling function (a series of ideal impulses, either in frequency or time domain) with the other signal. It's basically the opposite of an undersampling IF ANd, because the typical output has a sample/hold, it's not a series of impulses, but a staircase, so the frequency domain has a sin x/x shape to it. Are they just really tiny and I have to do a lot of good filtering and amplification? Yes.. And all the usual things about timing jitter aggravating the higher order outputs more than the first order, etc. Do I need something other than a traditional DDS for this sort of stuff? ___ 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] DDS - higher frequecies
On 11/25/12 5:19 PM, Said Jackson wrote: Hal, Check out the Analog Devices website. Good info on DDS Dacs there. You want to stay a bit away from the 1/2fs Nyquist limit in your DA. The reason is the image coming down from your 1MHz clock. If you output say 0.45MHz, you have an image at 0.55 MHz already (1MHz - 0.45MHz) so your filter has to be extremely steep to make that work and remove the spur at 0.55 MHz.. Check out the Mini Circuits LFCN low pass filters, they work at higher frequencies, and are very steep.. Your filter quality is going to determine how close you can get to Nyquist. There's also a variety of intermod type products that show up, particularly when you talk about spurs from phase truncation and the like. So you get not only the phase truncation spurs, but also all the aliases of those spurs. There's a fair amount of literature around about this, especially from about 10-20 years ago, when 1GHz ADCs and the logic to drive them weren't easy to come by. People wanted to generate signals in the hundreds of MHz range, but with logic and DACs that were slower. There's a reason that people do dithering in these sorts of applications: it degrades the peak performance, but at least it keeps you from having a big spur in the wrong place. There's a nice PhD dissertation out there (which name escapes me right now) that has a whole matlab code to simulate/analyze it. ___ 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] 12.8 MHz OCXO
On 11/24/12 8:28 AM, Alan Melia wrote: Joe the reason why its not so uncommon may not be obvious in the US :-)) 12.8MHz is used as a reference for commercial and amateur PLLs in Europe where the common channel spacing is 12.5kHz (/1024) or 6.25kHz (/2048). This may mean that 12.8MHz oscillators may be more easily found in Europe ?? A TCXO should be capable of 0.1ppm. I have seem a lot in mobile/cellular product from a UK firm called Golledge but I dont know what the specs were. since it's for a low cost one-off project, what about a inexpensive 1ppm TCXO with some form of temperature stabilization (something as simple as a appropriate coefficient thermistor/resistor combination might hold temperature within a degree, while room temp fluctuates 10 degrees). Or do you need it to be stable over wild, rapid swings in temperature (e.g. it's outdoors or something). Or do you need good phase noise too (the run of the mill OCXO is quieter than the run of the mill TCXO) ___ 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] WWVB new modulation
On 11/22/12 12:12 PM, Larry McDavid wrote: I realize this modulation scheme change is perceived as a sensitive subject. But, really, since the full scheme is fully disclosed no company has a monopoly on its use. Actually, I think the developing company does have patents on some of the receiver implementations. You can probably design around them. My question is, will this new scheme offer enough advantages to merit the production of commercial equipment to use it, and ultimately whether low-cost equipment will be sufficiently advantageous to merit its design and production in volume like the typical WWVB digital clocks prevalent today. ___ 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] Inexpensive modular gps with 1pps
On 11/15/12 4:30 AM, David J Taylor wrote: i just used this to with a raspberry pi with good success. https://www.adafruit.com/products/746 james === It looks idea, James, but ... with the 15 mm square patch antenna it seems deaf compared to similar devices with 25 mm antennas. Perhaps understandable, but I just bought one and it's been sitting for well over an hour and not yet acquired lock. The device I bought from China, sitting next to it, has been happily locked for that whole period. (As I'm running a test I don't want to unlock the other device). Just a caveat for someone considering using these devices indoors - size matters! 25 mm antenna device: http://www.satsignal.eu/ntp/NEO-6M-under-initial-test.jpg http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html Cheers, David ALl good ideas.. but I was looking more for something a bit more packaged.. like a hockey puck with wires coming out. ___ 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] Inexpensive modular gps with 1pps
On 11/15/12 5:33 AM, David wrote: On Thu, 15 Nov 2012 05:02:54 -0800, Jim Lux jim...@earthlink.net wrote: On 11/15/12 4:30 AM, David J Taylor wrote: i just used this to with a raspberry pi with good success. https://www.adafruit.com/products/746 james === It looks idea, James, but ... with the 15 mm square patch antenna it seems deaf compared to similar devices with 25 mm antennas. Perhaps understandable, but I just bought one and it's been sitting for well over an hour and not yet acquired lock. The device I bought from China, sitting next to it, has been happily locked for that whole period. (As I'm running a test I don't want to unlock the other device). Just a caveat for someone considering using these devices indoors - size matters! 25 mm antenna device: http://www.satsignal.eu/ntp/NEO-6M-under-initial-test.jpg http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html Cheers, David ALl good ideas.. but I was looking more for something a bit more packaged.. like a hockey puck with wires coming out. I picked up a used Garmin GPS18-5Hz hockey puck to play with and after updating the firmware, have gotten good results with the cable going out a window and the unit sitting on the lower edge of the roof. Its 5 pulse per second output has 60ns of resolution according to the Racal Dana 1992 I repaired implying about a 16.6 MHz timing clock. That's the kind of thing I'm looking for.. or the Synergy TrakPuck ... or one of those pods that came with mapping software 5-10 years ago. I wonder if there's a new version of the GPS18, since I need something that is available off the shelf (and likely to remain so for at least 2-3 years).. Is there a timing output on the GPS16x? (or are the serial messages synchronized in some way) ___ 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] Inexpensive modular gps with 1pps
On 11/15/12 4:10 PM, Bob Camp wrote: Hi Not much of a market for that sort of stuff. Bob Big enough that Synergy Garmin have pricing for anywhere from 1 to 1000 units ___ 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] Inexpensive modular gps with 1pps
Looking for a non-surplus ( e.g. A current catalog item) gps module, with serial ( ttl or rs232) and 1 pps. Doesn't need high performance(100ns is fine), but should be $100 ish. Something with an integrated antenna would be great. ___ 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] Is it sensible to update every few seconds from NTP server?
On 11/7/12 5:42 PM, shali...@gmail.com wrote: That sounds odd, as most radios take tens of millisecond, if not hundreds to switch from transmit to receive and back in any mode other than break-in CW. Further JT65 is used with propagation modes that typically do not have a stable or predictable propagation time like moonbounce or meteor scatter, so I don't understand why mS timing would be necessary? I must be missing something. maybe some form of Coherent or very low speed CW or equivalent, where you use an external reference to get symbol timing. Say you were sending at 1 bit per second, using a 1 PPS as your symbol clock. You send a sync pattern at the beginning, then free run for the message. Don't forget that the implementation may be very unsophisticated or adopted/modified from some hardware design where the timing was counted down from a good clock, and now it's just a slavish copy in software. ___ 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] For my whole life timezones have been weird
On 11/3/12 8:50 AM, Chris Albertson wrote: On Fri, Nov 2, 2012 at 10:32 PM, Sarah White kuze...@gmail.com wrote: So, at or around 1981 (the year I was born) there was a cool concept. IBM was selling personal computers (IBM-PC compatible later became a thing) and by the time I was old enough to operate a modem, I had one myself. Life was good. Wonder if there is any sensible way to petition microsoft to fix this stupid mistake dating back to the DOS era. Windows 8 / metro is out now, and I can't bloody stand the changes. I always wonder why people continue to use MS Windows. Perhaps thheir employers force them to. But other than that why? I don't know that it's force... At JPL we have an enormous variety of desktop OSes, and for the most part, nobody much cares which one you use as long as you can get your job done. Perhaps because you have a (expensive to replace) tool that requires IE for access? Perhaps because the large installed base means that design tools are written for Windows first and others later? Perhaps because of the large installed base it's easier to find folks to write software for Windows than for other products. Perhaps because for all its ills, Windows isn't that bad a desktop environment. The kind of timekeeping thing we're discussing here is, when it gets right down to it, not going to affect the vast majority (99.99%?) of users. That is the root cause of all Window's problems. The company was run be a chief software architect who technically very ignorant and lacked any formal education in the subject. Windows still suffers because it tries to maintain backwards compatabilty Hardly the root of all problems.. Yes, the conflation of kernel and UI (most of Windows is really all about UI capabilities: heck it's the very name of the product). The kernel of NT was based on the architecture of VAX/VMS, which was fairly nice. Real multitasking, real pre-emption, real process isolation, real dynamic run time binding. (none of which DOS had) You can say it suffers from needing backward compatibility.. overall, they've done a half way decent implementation of this these days (there were some real clunkers along the way). But it's also important to allow people to use their significant investment in old software. You may have the best idea in the world and a very cool OS that implements it, but who's going to pay for recoding all those billions of lines of software for your new OS? And assuming that money falls from the sky to pay for it, where are you going to find all those software people to do the work, at any price? Sure, I've seen lots of people just dying for the opportunity to decipher some 20 year old enterprise application and convert it to a new OS. You have to remember that in 1980 we have computers that would allow 100 people to simultainiously log in and do work from 100 different termmiansl. Well before that actually. More like late 60s. TymShare corp, for instance. Dartmouth BASIC for another. ANd note that those timesharing systems provided an environment that essentially hid the OS (kernel wise) from the user. You fired up your ASR33 and were in the BASIC environment from the get go. This also is the environment that BillG started doing computing work in. He didn't start sitting at a keypunch cranking out JCL cards to compile his COBOL or FORTRAN jobs and allocating DASD for the temporary files. We have the Internet (called arpanet back then. We had email and UNIX was alive and well. We even had mice and track balls This was not the dark ages the only real difference was the price of hardware. And in this age gates did NOT know the difference between an OS and a command shell and he was running Microsoft. Don't make the mistake of confusing public statements with background and knowledge. For all you know, Gates wanted to deliberately confuse the two for marketing reasons. 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 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] GPS receiver testing
Hello Said, I'm familiar with your postings on the Time Nuts list, so I thought I'd ask your advice. I searched the Time Nuts archive, but didn't come up with what I was looking for (reference to a good GPS tutotial). We have a GPS project in-house that requires us to characterize receiver module performance. We have a Litepoint IQ-Nav box with several stored scenarios, but no other signal generators with GPS personalities in them. We need to measure position accuracy and time accuracy. We may also need to get some characterization of the 1 PPS output. There's folks at JPL who do this kind of thing all the time.. I'll ask who you should contact.. It kind of matters on what you're testing for, but I'm sure there's someone who can point you in the right direction. Jim ___ 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] GPS receiver testing
On 10/31/12 6:17 PM, Tom Van Baak wrote: Please read John Plumb's paper: http://tycho.usno.navy.mil/ptti/ptti2002/paper29.pdf and Rick Hambly's paper: http://tycho.usno.navy.mil/ptti/ptti2002/paper9.pdf At JPL, most of the calibration and performance testing and such is done using an antenna outside with actual signals, rather than a test set (although we do have some fancy signal simulators). Depending on what data you can get out of your receiver, working with the GIPSY offline processing system might be useful. IN a post processing sense, you can determine what your receiver *should* have been returning. This morning, I was in a meeting where the JPL GPS folks were talking about improving the terrestrial reference frame accuracy from cm scale to mm scale over the next few years (and tieing it to celestial references as well). This has to account for all the things like solid earth tides, plate movement, etc. ___ 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] Timing performance of servers
On 10/25/12 11:02 AM, li...@lazygranch.com wrote: The GPS seeing the horizon isn't required. Those satellites are filtered out by software. The timing GPSs are designed to be less sensitive to the horizon. when tracking a satellite above the cutoff, you still want the antenna to not respond down to the horizon, because that might be where the multipath is coming from. ___ 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] : L1 GPS timing signal(s) into local time on computer(s)
On 8/21/12 9:53 AM, Sarah White wrote: Wow. Okay. The user manual actual considers this cable delay to be worth mention? I can see why the trimble thunderbolt is a favorite among time nuts 3 I'm sold. Cable time offset is in basically all GPSes. An awful lot of GPS receivers (for timing) are installed where there's a long run of coax to the antenna. 100 ft wouldn't be unusual, and that's 120-150 ns in typical coax. Since even the lamest GPS receivers put out a 1 pps that's good to tens of ns, you might as well offer the correction. If all you're interested in is frequency, then you may not care about the correction. If all you're interested is time to, say, microseconds, likewise (until you get up into the 1000 ft of cable range). But, since it's a basic parameter in the GPS engine's calculations, and some applications need it, you might as well always have it. I always thought it was weird to have that feature available in a handheld GPS with a fixed antenna, but I was at a tradeshow asking a Trimble guy about it some 20 years ago.. Here is a paraphrase of the reasons: 1) Our competitor has a removable antenna and they need the cable correction, so we need the cable correction so that in a comparison chart we both have a check mark in that Cable Length Correction. 2) We use the same chip set and software in multiple receivers, and it's easier to just keep it the same. 3) We have a reradiator thing that lets you use an external antenna a cable, and a coupler to the handheld, and for that, the length correction is useful. ___ 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] Controlling FEI 5680A
On 1/14/12 9:18 PM, Chris Albertson wrote: Not over kill at all. It is worth paying a few $$ not to have to design a PCB. Worse then that is that most will take shortcuts and design it so that you need a sppepcial IC programmer to program the PIC. Thee $20 development boards allow you to download the firmware over USB so users can do it themselves. I'm looking at this pair of boards: http://arduino.cc/en/Main/ArduinoEthernetShield http://arduino.cc/en/Main/ArduinoBoardUno Ethernet and and SD card slot might seem overkill too. But I want to track performance, read out the phase difference over time and so one. So I want to be able to connect a desktop computer and a USB cable is to short. Ethernet will let me check from work or with my phone. the SD card can be used to log data. Likely hold a two years of data on a 8GB card. I've got just that pair.. several of them. It's great..what's nice about Arduino is that you can just go buy one at Radio Shack. For a lot of applications, it's a nice simple solution with minimal hassles and fooling around. Examples get you started with things like simple webservers, etc. The Arduino language is a sort of C, and for some reason Arduino land uses non standard jargon (sketches, shields), but it's not too bad. I had a summer intern who had never programmed before in his life turn one into a controller to cycle three solenoid valves in a couple weeks. If you like PICs, that works too. There are off the shelf boards, etc. that work fairly well. What all of these don't do well is complex stuff. If your program gets over, say, 1000 lines, you're probably trying to do too much for that little machine. It's not a multitasking operating system with disk drives, etc. Even if there ARE a lot of libraries that make it seem like a full-up environment (e.g. BSD sockets, file systems on SD) it really isn't. it's still a little embedded microcontroller. ___ 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] HP8720C manuals?
I just found an old 8720C at work, and I was thinking of pressing it into service to do some experiments with measuring changes in receiver filters and antenna match over temperature. (Since I don't have to pay rental on it, it can just sit in the corner with the temp chamber and I can slap those GPS and S-band filters in there and fool with it, sort of in the background. ANswer all those questions about just how much timing uncertainty is due to the filters with some empirical data) I'm not looking for a big project, and I don't know how hard or easy it is to pull data out of the beast via GPIB. The problem is that I don't have the programming manual, and Agilent doesn't have it on their site. Nor is it on BAMA, etc. I'm sure someone here at JPL has a copy, but being somewhat lazy, I thought I'd probe the timenut hivemind. I do have all the docs for an 8510 I had in the lab until last year (the owner project asked for it back) so if you happen to know that the 8510 and 8720 work pretty much the same, that helps.. ___ 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] HP8720C manuals?
On 10/17/12 12:59 PM, gandal...@aol.com wrote: Not exactly the programming manual but would it help?. _http://na.tm.agilent.com/8720/programm/xrefhpib.htm_ (http://na.tm.agilent.com/8720/programm/xrefhpib.htm) Ah, wait.try this:-) _http://na.tm.agilent.com/8720/manuals/872XC_PG_REF.pdf_ (http://na.tm.agilent.com/8720/manuals/872XC_PG_REF.pdf) Regards Nigel GM8PZR OK.. what google or other fu did you have to find that. I hunted through that site for quite a while.. I am impressed! Jim ___ 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] HP8720C manuals?
On 10/17/12 3:35 PM, David Kirkby wrote: On 17 October 2012 20:35, Jim Lux jim...@earthlink.net wrote: Someone found the manual I needed (see the other posts).. it was on that general website but not linked from anywhere... Another place to get information, is asking on the Agilent VNA forums. http://www.home.agilent.com/owc_discussions/category.jspa?categoryID=32 There are several, one of which is devoted to programming. http://www.home.agilent.com/owc_discussions/forum.jspa?forumID=73 useful. I'm just in the process of writing some code to drag data off the 8720D. It's written for the National Instruments GP-IB board, and Ive only compiled it under Solaris, though I expect it would compile under Linux with no problem. It uses the standard Mine is in Python using the Prologix Ethernet/GPIB widget. But same general objective.. drag down data and dump it in a standard file format that can be ingested by other programs. There's several QB4.5 examples out there too.. It should be straightforward to cobble something up.. ___ 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] Followup (still want a GPS-type NTP refclock)
On 10/17/12 4:48 PM, Sarah White wrote: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 10/17/2012 6:04 PM, Chris Albertson wrote: ((...snip...)) -- 1 Indoor antennas can work. It depands on the details. Hopefully the skylight looks to the south. BTW that thin sheet of plastic that makes the skylight window will not protect from lightening. It makes little difference. ((...snip...)) -- 2 It means those plug-in power suply boxes that plug into a wall outlet and have a coaxial power plug. They are use to power cell phone charges and notebook computers and you name it. Most people have many of those around the hose. The output voltage will be printed in the cube (part 1) This is a glass skylight window, not plastic. Also, the skylight window in question is not the highest point on the roof, there is a domed metal cover on an exhaust fan vent thingy... Regardless though, landlord won't allow things to go on roof or in the yard so I'm stuck with using the window. Skylights work fairly well.. just stick the antenna on the bottom of the window and hope for the best. If you have a handheld GPS (or phone which does GPS), you can hold it up there and see if it works. The worst case is that they've put some sort of metallic film on the window to reduce thermal losses.. There are ways to fix that, but non-trivial. ... Basically, this way I won't have to consider any waterproofing for the antenna, and just hope that if lightning strikes it goes for the exhaust vent dome thingy instead... Ah well whatever. My plan remains unchanged in this regard --- it is going to be in one of the south-facing (roof is angled) skylight windows. And that's with a $6 navigation GPS thingy (USB puck-type NMEA-only) That's navigation... Timing mode only needs 1 satellite lock after all, and I suspect I will at minimum be able to get needed 1 satellite lock with nearly any active GPS antenna. Ah, but this is Time-Nuts.. are you sure you don't need 1E-13 performance? You may not think you do today, but inevitably, the horrible uncertainty in your time stamps will gnaw at your innermost soul, and pretty soon, you'll be building choke rings, wrapping your $6 receiver in an oven, cobbling together some weird combination of surplus parts. ___ 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] To use or not to use transmission line, splitters for GPS receivers
On 10/10/12 8:10 AM, bro...@pacific.net wrote: Hi: The reason for the GPS orbits is so that the ground track repeats. Have Fun, Brooke and that makes it easy to predict visibility. Tomorrow will be the same as today, shifted by 4 minutes. ___ 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] multi time zone display for wall mounting?
I'm looking for an off the shelf commercial time display (or combination of displays).. Needs to display at least 3 zones, in 24 hr form (UTC, Pacific, Eastern), and should display Day of Year, as well. I can feed timecode to it, or even better, if it can ingest NTP. 1 second precision is more than enough. Needs to be readable from 20 feet away, but not huge... 2-3 high digits are probably in the ballpark. ___ 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] multi time zone display for wall mounting?
On 10/9/12 9:20 AM, Robert Darlington wrote: I like the Symmetricom ND-4, however I don't know if you can have it alternate between TZs. You can buy more than one and label them like I did. That's fine.. multiple displays are no problem.. http://www.symmetricom.com/products/gps-solutions/time-code-displays/Network-Time-Displays/ They can get NTP server and timezone through DHCP options, so if you have that infrastructure in place it's just a matter of plugging them into your network and they come right up. They even do Power over Ethernet so you only need to run one Ethernet cable to each clock -no separate power. -Bob On Tue, Oct 9, 2012 at 9:02 AM, Jim Lux jim...@earthlink.net wrote: I'm looking for an off the shelf commercial time display (or combination of displays).. ___ 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] multi time zone display for wall mounting?
On 10/9/12 10:09 AM, Chris Albertson wrote: For wall displays, I've noticed more and more people simply mounting a large HD TVs to the wall and driving it with a computer. Even the menu board in back of Starbucks and the directory near the elevator that lists who is in what room on that floor. I've seen the 9:16 TVs mounted vertically too. Interestingly, I have two 42 inch monitors already up on the walls.. but I wanted to avoid getting them too cluttered with other displays. Also, the TV draws many watts compared to some small LED display. Is a TV set turn key? Maybe not if you lack the staff to create the display graphics. But from a hardware point of view it is Oh.. it's trivial to throw up a time display in a window on the big display.. We've even got a cool little java ap that does Mars time so you can tell if your co-worker who's doing MSL ops is likely to be in their office, or asleep at home. For this application we are totally earth based, though. That said, any high quality wall clock will work. Actually, most high quality wall clocks don't do things like DOY. But I know they exist, which is what I'm looking for.. ___ 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] RFX GPSDO - Anybody played with one of these?
On 10/2/12 10:35 PM, b...@lysator.liu.se wrote: On 10/2/12 2:36 PM, saidj...@aol.com wrote: Hello Paul, thanks much for the feedback! Yes, we think we have identified a nice combination of oscillators, GPS, and firmware that seems to work pretty well. The GPSTCXO units cannot be compared to a lower cost $150 Thunderbolt in terms of phase noise or stability of course, and they have CMOS 10MHz outputs, but then the TB's cost around $1500 new I guess. We think the GPSTCXO's and LC_XO type units will work quite well wherever standard OCXO's are used today, and power/size/weight are an issue. Intriguing.. Can it handle the Doppler, etc., for a cubesat in LEO? (7km/s) The total Doppler isn't usually the issue (the GPS satellites are moving faster, after all), but the receiver may not work for high velocities, high altitudes? GPS SVs moves at around 4km/s, but nevertheless there are still COCOM limits implemented in nearly all receivers (never break both 504m/s and 18km height) Doh. of course. higher is slower In any case, though, nothing stops Jackson Labs from selling one that is export controlled and has no restrictions. ___ 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] RFX GPSDO - Anybody played with one of these?
On 10/2/12 5:08 AM, Azelio Boriani wrote: Yes, I agree. On Tue, Oct 2, 2012 at 1:29 PM, Bob Camp li...@rtty.us wrote: Hi The OCXO probably isn't going to do very well with the outdoor temperature swings… Bob Why not.. granted it's easier with large mass and large insulation, but ultimately, it's all about the closed loop gain of the temperature control loop. With small mass, the time lag effects will be small, at least. ___ 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] GPS Modulation and 10 MHz Delay Lock
On 10/2/12 3:39 PM, johncr...@aol.com wrote: Hello All - Here is a link that describes the GPS modulation. You do not need the 1 pps to lock the 10 MHz oscillator to the atomic clock in the satellites. http://www.kowoma.de/en/gps/signals.htm If you look at the block diagram you see PN code modulates the carrier at the 1.023 MHz chip rate. This is done by BPSK modulation of the carrier with the PN code. It can be done simply with a double balanced mixer. This spreads the signal with PSK at the chip( i.e. code clock) rate. Note also the modulo - 2 addition of the data to the code sequence. This called code inversion modulation. After de-spread of the code in the receiver - the signal is then simple BPSK and may be demodulated by a Costas or Squaring Loop to get at the data message. The obtain precision frequency needed I believe the T bolt simply locks to the chipping rate using some form of Delay Lock Loop. It is NOT at PLL. There is no need what ever to deal with the 1 pps using this method. The internal 10 MHz oscillator is controlled by this locking circuit and is part of the code correlation loop. That's not quite how it works.. It would work for terrestrial links where there is no Doppler, but in the GPS case, there is significant Doppler shift on all the signals. Since the carrier and the chips are generated from a common source on the spacecraft (the carrier frequency is a multiple of the chip rate, in fact), you can recover carrier and chips at the same time. But.. most receivers these days don't actually have an analog tracking loop at all. They digitize the input signal (1 bit quantizer) at a rate that makes the carrier alias down to something convenient (a few hundred kHz is typical.. you want it far enough away from zero that Doppler never makes it go negative). In the experimental receiver in SCaN Testbed flying on ISS it's about 39 MHz sample rate. Once you've got your one bit samples, you do some sort of combined Doppler/Code phase acquisition (these days, often using an FFT), then track both together digitally using some form of NCO. The tracking loops for all the satellite signals aren't necessarily independent and might be part of a Kalman filter that estimates all the observables together. Finally, from all that, you have an estimate of your local clock offset and timing offset, and from that you can generate your 1pps, typically with another NCO (with granularity of your clock rate). Since it's unlikely that your clock is EXACTLY an even number of cycles per second, at each second, a bit of error accumulates, until you have an whole cycle's worth leading to the familiar sawtooth error. That sawtooth error is predictable, of course, so you can generate a time error estimate for each 1pps pulse (or, even, control a variable delay to line it up). The important thing is that in modern receivers, nowhere is there a signal at the GPS carrier frequency, nor is there a signal at the chip rate. There *is* probably a signal (with low precision) at the code epoch (every millisecond), but it's different for each satellite signal, of course. ___ 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] GPS Jammer
On 10/2/12 4:48 PM, Charles P. Steinmetz wrote: The Power Output is 0.5 Watts and it claims a jamming range of 1-10 Meters. Anybody think there is something wrong? I'd expect a much greater range with a 0.5 W jammer. But note that 0.5 W is the total output power -- the transmit power is only 10 dBm (0.01 W). Whatever those terms mean. (Does total output power include far IR and heat?) maybe it has some real bright LEDs to indicate it's on? ___ 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] Best counter setting for ADEV?
On 10/2/12 7:00 PM, shali...@gmail.com wrote: The Thunderbolt is a special case that does not provide sawtooth correction because it does not need it. It uses the OCXO as the clock for the processor while disciplining it to GPS so there is no nominal timing error between where the 1PPS is versus where it should be. The processor is able to bring the PPS edge exactly where it wants it, instead of the typical 25 to 40 ns granularity of most other GPS receivers that operate on a separate clock. Pretty simple and elegant solution. But it does depend on having a good oscillator that can be shoved around. That costs money and 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] GPS Jammer
On 10/2/12 7:33 PM, johncr...@aol.com wrote: In considering the effect of a simple jammer on a GPS receiver, a simple link analysis is insufficient. What must also be considered is the anti-jam capability of the receiver which due to spread spectrum processing gain will reject any simple jamming signal even though is it 10's of dB stronger than the desired signal. not most simple GPS receivers which have very little AJ capability. They have a single bit quantizer (or maybe a 1.5 or 2 bit) after the LNA. If the LNA doesn't saturate, then the quantizer is captured by the strong CW carrier. This is a classic problem with DSSS receivers and led to a lot of research in the 80s on things like adaptive excisers to remove CW carriers. If you built a linear receiver with a lot of dynamic range, then, yes, the process gain will suppress the CW tone, but you still have to acquire the code, and as Dixon says (paraphrasing) acquisition is the secret sauce in spread spectrum systems. Back when I was doing this kind of thing seriously (mid to late 80s), acquisition, particularly robust techniques, were literally SECRET (in the DoD sense). There have been a nice series of articles in GPS World over the past few months about the variety of inexpensive GPS jammers out there. (and the problems they cause). ___ 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] RFX GPSDO - Anybody played with one of these?
On 9/30/12 10:51 PM, Thomas Valerio wrote: Actually, it was in Nuts Volts as well, and I was thinking about posting a similar query to the list, but my incentive and my interest pretty much went negative when my cursory investigation revealed that price information appeared to be non-existent. IMHO for pretty much *everything* that is for sale, if you have to ask for the price it is a scam. The message that I get from non-existent pricing information is that this product's price/value proposition can't stand on it's own, the only way you will be convinced to purchase, at a usually inflated price point, is after the snake oil sales people have had a chance to get their spiel out. I don't find that to be the case for connectorized RF components. Virtually all manufacturers have a listing of most of their parts and data sheets, but very few have a price list online. MiniCircuits is a notable exception. Yes, well established piece parts might have pricing from a distributor, as well. But for a lot of new components, the final price might not be set yet, and may also depend on your specific requirements. A mfr might not want to commit to a 10,000 piece production run and hope that their eventual customer didn't want a particular inspection or test that they decided not to do. It's also the case that for some of these components, they're not available in small quantities. I've called many a mfr up for some product aimed at the wireless industry and asked about pricing, and their question is how many thousand a month will you be using.. ___ 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] Best GPSDO
On 9/28/12 8:31 PM, Chris Albertson wrote: On Fri, Sep 28, 2012 at 5:29 PM, Bob Camp li...@rtty.us wrote: HI Sort of an open ended question, but there is a fairly simple couple answers: SInce it's close in phase noise and not far removed, things like PLL's are going to transfer it directly from the reference to the output. It will of course scale by 20 log N where N is the amount you multiplied or divided the reference frequency by. Double the frequency and the phase noise goes up by 6 db. So in my example case of scaling the 10Mhz t-bolt to 14.5Mhz Assuming a perfect DDS chip the T-Bolt's phase noise would be scaled up by 20 Log(1.45) I'm assuming this works, that I can go from 10MHz to 120Mhz and then to 14.5MHZ and the total effect is the same as going directly from 10 to 14.5, except for the noise the equipment introduces as added. You can guess the real question here: how good does the 10MHz reference need to be to test real-world receivers? It has to be quieter than the oscillator in the real world receiver. If your real-wold receiver is a cryogenic ruby maser with a downconveter driven by a hydrogen maser reference, then the answer is really, really good.. If the real world receiver uses a run of the mill TCXO, then not nearly as good. The 20log10(N) thing does work pretty well. In a PLL synthesizer, you'll pick up a little extra noise from the phase detector and other circuitry, but for back of the envelope to see if your idea is going to work, the 20log10(N) is just fine. This gets into a whole interesting area of microwave source design, because inside the loop the phase noise is the reference oscillator multiplied up (20log10(N) noise), and outside the loop, it's the microwave oscillator. So you have an interesting optimization problem, particularly if you want tuning over a wide range. Wide range VCOs implies that the MHz/volt gain is quite high, so noise on the tuning signal shows up on the output. The resonator is often lower Q, so that it can be moved around by the control signal (usually some sort of varactor scheme), and that means the medium distance away phase noise suffers. High performance DROs for instance, have a tough time tuning the entire 50 MHz deep space comm bands at 7 or 8 GHz ___ 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] frequency and time from cell
On 9/27/12 10:41 PM, Majdi S. Abbas wrote: On Fri, Sep 28, 2012 at 07:38:03AM +0200, b...@lysator.liu.se wrote: Dont you have GPS/Cs locked cell networks anymore in the US? http://www.endruntechnologies.com/cdma.htm Björn, Past experience with CDMA TOD references here is that they fare much worse than WWVB TOD references. Haven't tried using them for frequency, but I wouldn't be surprised at similar results there. the cell site might be locked to a good reference, but that doesn't mean the propagated signal you can receive is. As I understand it, one of the uses of good timing is/was to do Time Difference of Arrival (TDOA) to meet E-911 location accuracy requirements. These days, with A-GPS in most phones, I wonder if that's still the case. ___ 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] WWVB PM Receiver
On 9/26/12 10:15 PM, Peter Monta wrote: I'm not sure about residual carrier aiding the tracking process. A Costas loop recovers the carrier pretty well, and a symbol aided loop (where the I channel has a hard limiter, for instance) does even better. Yes, these work (and a soft tanh() limiter improves on the hard limiter a little bit), but I think they don't work as well as a PLL with a pure carrier, where performance is measured as the variance of the phase estimate at a given SNR. After all, the energy is still the same. True, but information has been lost as a result of introducing these unknown phase transitions. Now if the phase transitions are known, one can certainly wipe them off by multiplying by a noiseless replica of the known phase modulation, and then you're back to pure carrier. But if you don't know the transitions ahead of time, you need the Costas loop to find them for you, and that costs SNR. In WWVB's case, many of these phase transitions probably can be predicted. But the point is not so much that good timing receivers for the new signal are problematic. On the contrary, they're no problem at all with a little DSP. But for the sake of backward compatibility, putting 5 or 10 percent of the signal power into a carrier seems a small price to pay. Or, you can use an acausal processing scheme.. demodulate the bits, then go back and remove them from the input signal. If what you're doing is recovering timing to a gnat's eyelash, that would probably work. Using a Costas-loop preprocessor to a legacy phase receiver is almost to the point where you're better off tossing the legacy receiver and just using the preprocessor. I don't want to sound too negative here. I'm glad WWVB is getting these improvements, and the clarification from John Lowe earlier today about the openness of the signal is helpful. But backward compatibility would have been so easy to put in. Cheers, Peter ___ 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] WWVB PM Receiver
On 9/27/12 7:23 AM, J. Forster wrote: Jim, What you are suggesting is essentially a spread spectrum system where the chip pattern is time varient. IMO, this is an incredible kludge. And, there is no gurantee that the algorythm for generating the chip pattern will not change down the road. I think I poorly explained what I was thinking. Store the raw samples Run the samples through a demodulator to recover the bits using whatever technique works best: for instance, you can make your symbol transition decisions based on many bits at once, as opposed to only those you have already seen. Then, take those decoded bits and use them in a second pass through the data to remove the bits (sort of like the inphase arm in a Costas loop) so you can get a carrier only version of the input signal (with some noise at the symbol boundaries, most likely). Excise the transitions where the SNR is lower. Then, do your carrier frequency and phase recovery on what's left over. There's probably some elegant approach to deciding what to excise and what not to. But, in any case, no a priori knowledge of the bits is needed. (We did something like this at JPL to recover telemetry bits from Phoenix coming out of the plasma on EDL. Recover the carrier and symbol timing when you're farther down and then run the demodulator backwards in time). It's always easier to track than to acquire, after all, so why not acquire later when the signal is strong, and track backwards to where the signal is weak. ___ 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] WWVB / Xtendwave patents
On 9/27/12 2:58 PM, Bob Camp wrote: Hi It would be interesting to hear what the patent lawyers on the list think about the patents. Given a quick read, they appear to cover any use of the specific transmitted format for receiving time information. IANAL, but.. reading Claim 1.. a key aspects are the combination of PSK and ASK, with different data. This is somewhat unusual, and may not have been done exactly like that. said phase modulation *is independent* of the information represented by said pulse width modulation/amplitude shift keyed modulation is a phrase that occurs in ALL of the independent claims. (my emphasis added) QAM is, of course, simultaneous PSK and ASK, but it's a single data stream that is being encoded. Is there prior art for transmitting one kind of data using ASK and something else PSK? For instance, is WWV (which is primarily ASK) has a subcarrier, but the subcarrier is also AM. Another possible source of prior art might be a PSK encoded digital squelch on a AM or FM modulated signal (if such a system exists). Bob On Sep 27, 2012, at 2:54 PM, Scott Newell newell+timen...@n5tnl.com wrote: Looks like one has issued (8,270,465). Application 20120082008 appears to be relevant as well. http://www.google.com/patents/US8270465 http://www.google.com/patents/US20120082008 ___ 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 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] Why the fuss?
On 9/27/12 10:02 AM, Bob Camp wrote: Hi Right here in PA for one. You essentially can not buy a new house without there being various conditions written into the title. One universal one is no antennas. The only exception is for one 19 sat dish for TV, since that's a federal mandate. Actually, 1 meter for microwave signals and any size for VHF/UHF signals. But it has to be designed for reception of TV and FM broadcast signals. (No lawyering around claiming that you've got a multi element, multiband Yagi that is designed for 7 MHz and 70 MHz simultaneously) ___ 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] WWVB Now a Monopoly
On 9/26/12 7:11 PM, J. Forster wrote: But if someone here designed and built a $100 receiver and offered it to the group, that could well violate some of their IP. As to building a home brew receiver and certifying a onsie so your lab's cal is traceable, I'd certainly not trust a cal done that way. Doing spacecraft communications is hardly the same thing. Well..if you're trying to do NIST traceable cals in a legally acceptable way, then it's very unlikely that any homebuilt receiver that infringed the patent would be acceptable, from a patent standpoint. The general exemption to practice the invention is for development of a new invention, not to make use of it for other reasons (otherwise, the patent wouldn't be particularly useful in terms of exclusivity). OTOH, if you cobble up a (non-infringing) receiver and validate its performance analytically, why wouldn't that be acceptable for a traceable calibration. It's no different than using a homebuilt quartz oscillator as a transfer standard, is it? Now, if you're selling calibration services, it would be a tougher sell to your customers: they'd have to believe in your analysis or oscillator building. This is in the sense that if I use a HP 105, the long history and tradition of HP is essentially standing behind the design and the published performance standards; a homebuilt standard has a higher bar for the great unwashed public. If you want traceability for, say, a journal article, then I think the bar is set differently. For state of the art stuff, the article usually describes the calibration approach, and it's up to the reader to decide if you did it adequately. ___ 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] Lady Heather on a Laptop
On 9/27/12 3:10 PM, Charles P. Steinmetz wrote: Chris wrote: In another post you mentioned $0.21/kWH (you must be in California?), so adjust all of these by a factor of 2.625 for your location -- but I think the service rates in most of the US are closer to ours than to yours). A lot of areas have tiered rates. The base tier might be $0.10/kWh, and the average might be in the $0.10-0.15 range (most of the US is in that range). However, in this application, you should be looking at the marginal rate.. what does the next kWh cost, and in a tiered environment that can be pretty pricey (0.34/kWh for me in Southern California, last month, because it was hot). Throw in time of use metering and it gets more complex. (and worth it to charge a battery at night and disconnect from the line during the day). ___ 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] BPSK Receiver GPS Antenna siting
On 9/27/12 4:34 PM, Bob Camp wrote: Hi A PLL locks to phase. If the phase switches by 180 degrees, the phase tracking switches signs. There's no way to track that. You either need to double the frequency (and thus eliminate the modulation) or demodulate the signal and lock to the result. If you simply put up a real narrow filter and hit it with continuous 180 degree phase shifts, the output will be nothing at all… that's the whole thing about the inphase arm on a Costas loop.. that gets multiplied by the phase error signal from the quadrature arm and fixes the sign flip from the modulation. ___ 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] WWVB Now a Monopoly
On 9/26/12 9:46 AM, J. Forster wrote: I just received this in reply to a query ablot the availability of receiver designs for the new WWVB format: No sir, the government does not have a receiver design. The design has been created by Xtendwave under an SBIR grant. Their design is proprietary. To me this reads... If you want to use the publicly financed WWVB service, you MUST buy the Xtendwave hardware. Not exactly... you could design your own receiver and use it. (hopefully not infringing any patents from Xtendwave) ___ 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] WWVB Now a Monopoly
What would annoy me is less-than-full disclosure of the transmitted signal and its properties. For example, there's a claim in the paper that the (31 26) Hamming code used can detect double-bit errors in the encoded time. You are right. The standard Hamming code: detect and correct 1 (3,1) (7,4) (15,11) (31,26) Add a parity bit and you can detect 2 errors. There's also an (11,8) code that can detect 2, correct 1 And a (72,64) which works and uses the same number of bits as a (9,8) parity check, with the advantage of detecting 2 and correcting 1. Maybe there's another parity bit in the system somewhere, too. I think detecting double-bit errors would require an additional parity bit, and that the assertion in the paper is just a boo-boo, but I also keep wondering if the claim might in fact be true, that there might be a really clever way to use that with something else in the signal to detect double-bit errors, and the paper just isn't pointing that out. That would be annoying. Dennis Ferguson ___ 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] WWVB Now a Monopoly
On 9/26/12 4:26 PM, J. Forster wrote: And would anybody accept the results as accurate? why not.. the transmit signal specification is published, you could analytically prove what the receiver performance should be and verify your implementation against it We do this all the time with BPSK and QPSK receivers by running BER curves vs Eb/No. On 9/26/12 9:46 AM, J. Forster wrote: I just received this in reply to a query ablot the availability of receiver designs for the new WWVB format: No sir, the government does not have a receiver design. The design has been created by Xtendwave under an SBIR grant. Their design is proprietary. To me this reads... If you want to use the publicly financed WWVB service, you MUST buy the Xtendwave hardware. Not exactly... you could design your own receiver and use it. (hopefully not infringing any patents from Xtendwave) ___ 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] WWVB Now a Monopoly
On 9/26/12 5:15 PM, Bob Camp wrote: Hi Last time I checked, you can build one for your own use and are allowed to use what ever you want, regardless of it's patent status. not precisely true..there's some restrictions on that process (e.g. you can practise an invention in the course of making another invention that uses it) But if you build it and don't tell anyone you built it, it would be hard for you to be sued for infringement. ___ 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] WWVB PM Receiver
On 9/26/12 9:11 PM, Peter Monta wrote: Have you actually tried it and gotten it working, except possibly in a very strong signal area? This is precisely the issue. Squaring the WWVB signal results in a significant SNR penalty. At high SNR it doesn't matter that much; at low SNR you are in a world of hurt. I had suggested to John Lowe that they consider retaining some carrier in the signal, which would be trivial to do---instead of a modulation index of 180 degrees for BPSK, make it 120 degrees or 150 degrees, so that there remains a little bit of pure carrier at 60 kHz that's trackable with PLL receivers. He said something about being receptive to the idea, but apparently it was not adopted, since the latest document still says antipodal BPSK. Ironically, GPS is heading in the opposite direction. The legacy C/A and P(Y) signals have no unmodulated pilot spreading codes, while the newer ones at L2 and L5 have strong pilots that allow much better tracking. I'm not sure about residual carrier aiding the tracking process. A Costas loop recovers the carrier pretty well, and a symbol aided loop (where the I channel has a hard limiter, for instance) does even better. After all, the energy is still the same. ___ 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] PLL behavior
On 9/19/12 1:08 AM, Azelio Boriani wrote: In my opinion you fall in the case of disciplining with holdover... this is more like a disciplined oscillator (like a GPSDO) problem than a PLL. Good point... it's like what happens when we come out of holdover. ___ 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] PLL behavior
On 9/19/12 4:38 AM, Bob Camp wrote: Hi Commonly this sort of thing is done with a sample and hold in the loop. No reference in / put the loop voltage in hold. You still have a phase drift and need to cope with the phase offset when the reference comes back. or, in our case, we run the loop, but don't have any error signal input (if you have a second or third order loop, you might as well essentially predict what is going on) ___ 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] PLL behavior
I'm looking for info on behavior of a PLL (with VCXO) when the reference comes and goes periodically. When the reference is gone, the PLL will flywheel according to whatever the loop filter does. (we can turn off the input to the filter, so we're not trying to track noise).. What I'm particularly interested in is the behavior in the PLL when the reference returns. The overall situation is where we are trying to make a frequency/phase measurement over 10-100 seconds, where the reference has a 50% duty cycle, and is on for a second, off for a second. I can fairly simply model this, or just try it, but I'm looking for some references to an analytical approach. ___ 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] PLL behavior
On 9/18/12 8:39 AM, Don Latham wrote: won't it depend almost entirely on the charge pump filter? Classic PLL with a mixer, not with a Phase Frequency Detector and charge pump.. But yes, it depends in large part on the loop filter, but also on the behavior of the oscillator.. (i.e. where does it go with fixed tune input) ___ 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] Hi Power LED Light power supply...
On 9/18/12 6:54 AM, Bob Camp wrote: Hi The shutter on a conventional movie projector is very much an on / off device. They run well below 120Hz. Actually, the typical movie projector uses a rotary shutter which runs at twice the frame rate (e.g. 48 flashes/second) and is hardly a fast transition. The actual waveform is more like a trapezoid (imagine a narrow beam of light going through a rotating disk with two sectors in it..) There's also noticeable movement of the film as the shutter is opening and closing, however, your eye/brain is pretty immune to overall image shifts, particularly when it fills the field of view: it's not much different than handling the saccades of your normal eye movements. 24 fps is quite visible to most people (hence interlace on TVs to get 50 or 60 fields/second) The phosphors in a white LED are at least as long persistence as those in a TV set. There are a *lot* of TV's out there that refresh at 60 Hz or less. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Poul-Henning Kamp Sent: Tuesday, September 18, 2012 9:05 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Hi Power LED Light power supply... In message ac9e4c92327746d4a521facd35d9d...@vectron.com, Bob Camp writes: I suspect those same 120Hz sensitive people would not be able to watch TV or a movie :) I suggest you either carry out a couple of experiments yourself, or go a little easy on the irony. CRTs, and LCDs go out of their way to avoid flickering using physical or electronic persistence, whereas a naked LED wil happily flash up to several hundred kHz if you ask it to. ___ 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] PLL behavior
On 9/18/12 1:49 PM, Magnus Danielson wrote: On 09/18/2012 05:28 PM, Jim Lux wrote: I'm looking for info on behavior of a PLL (with VCXO) when the reference comes and goes periodically. When the reference is gone, the PLL will flywheel according to whatever the loop filter does. (we can turn off the input to the filter, so we're not trying to track noise).. What I'm particularly interested in is the behavior in the PLL when the reference returns. The overall situation is where we are trying to make a frequency/phase measurement over 10-100 seconds, where the reference has a 50% duty cycle, and is on for a second, off for a second. I can fairly simply model this, or just try it, but I'm looking for some references to an analytical approach. The leakage of your filter will cause the frequency to have drifted a little during the off period, so one way of modelling it would be that you would treat it like a frequency step. However, if you think a little about it, the drift will most likely not be that great so you would only shifted a somewhat in phase, and what you get is a phase step response. It's really trivial to analyze and it has already been done to great extent. It helps if you realize that a dirac delta has the LaPlace form of I(s) = 1, and then that a phase step has the formula I(s) = /|phi / s and that a phase ramp/frequency step has the formula I(s) = /|omega / s^2. Applying these I(s) to you PLLs H(s) gives you the O(s) for your response to these stress-tests. Apply inverse LaPlace transform for impulse responces. That is basically what I have now.. I guess the next question that leads to is how big is the phase step, and that depends on what the oscillator did (in a statistical sense) during the flywheel time, which in turn, I should be able to figure out from the Allan Deviation data. A lot of classical loop analyses (in terms of the statistics) makes the assumption that the phase detector response is linear (that is, that the error signal is linearly proportional to phase error), which is reasonable for small delta phase. But in the phase step case, that might not be. I suppose then, it's more like looking at the acquisition behavior analysis. ___ 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] Hi Power LED Light power supply...
On 9/18/12 10:57 AM, Tom Knox wrote: I remember reading that Hollywood played with faster frame rates and found a substantial number of people experience motion sickness. Not so much the frame rate, but generating imagery that isn't realistic.. your eye expects motion blur (particularly in projected images), and if you project a series of very sharp frames with lots of depth of field, it confuses your brain, because it's trying to process out the motion, but the cues are a little bit off. One cause of motion sickness, for that matter, is where the image your eye sees doesn't match the signals from the vestibular canals. The original Star Tours at Disneyland was quite noticeable for this, because it used a lot of rotation movements (which shift the local G vector) to simulate acceleration since it had limited travel on the motion base. i.e. if you keep the forward view constant and showing an acceleration, and tilt your chair back, the force pushing you back into the chair matches what you'd expect from the visual cue, except for the rotation. Some people didn't get affected much, others did (it made me quite nauseous, while a standard roller coaster doesn't). And images that move with a lag relative to your head motion are notorious (early 3 D graphics goggle displays with a Polhemus head position sensor..) ___ 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] PLL behavior
On 9/18/12 9:48 AM, Raj wrote: If you break the DC control chain of the PLL with a A2D and a controller and back with a D2A .. you would program the control with any kind of behavior you want. Just a thought! That is exactly what we do... the PLL is actually implemented digitally (DAC driving the VCO).. But what I'm looking for is a theoretical treatment of the output statistics (Allan Dev, mostly) in terms of the interrupted reference input. For context.. we do precision ranging of spacecraft in deep space by sending a hydrogen maser derived signal TO the spacecraft which locks a local VCXO to that signal, and then uses the VCXO to generate a return signal with a constant ratio (e.g. 880/741) to the input. By measuring the time it takes for the round trip (essentially counting phase cycles on the return signal (against our hydrogen maser, again), we measure Range and Doppler, which is then used to determine the position of the spacecraft. Typical performance is sub-meter and sub cm/sec. (A very high performance would be that the transponder adds 4E-15 Allan Dev over 1000 sec... 1E-11 or 1E-12 over 10-100 secs is more usual) What we want to know is what happens if the receiver and transmitter can't run at the same time? Obviously, we have less information coming into the system (we see the uplink half the time, so right there, we have a 2:1 hit) and the ground end only sees the transmit signal half the time (another 2:1 hit), so, from an information theory standpoint we've already put ourselves in a hole, but, what does the statistics really look like for the turnaround loop.. Full Duplex full power turnaround is expensive in power, mass, etc. (for instance, you have to have good filters to make sure that your receiver isn't corrupted by the transmitter) ___ 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] Z3801 Replacement GPS Receiver Card
On 9/17/12 3:00 PM, Azelio Boriani wrote: OK, you can test a VP Oncore GPS receiver alone if you have a mean to translate the TTL serial port to a regular RS232 for the PC. This can be done with a MAX232 chip (or equivalent). There are a ton of these (serial TTL ports) available inexpensively for use with Arduinos. In the under $20 range, usually. Try Sparkfun.com for instance.. ___ 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] Z3801 Replacement GPS Receiver Card
On 9/17/12 3:34 PM, Chris Albertson wrote: $20 is to much. I pay about $4 shipping included for the DB9 with the Max chip attached. So you basically just attach 5V TTL to the back of the connector. That works. if you have 5V handy.. The USB to ttl serial is handy when you don't necessarily have 5V on a convenient pin. Lots of people sell these. See ebay #180688345029 for an example. These work well for the Oncore GPS because both use 0.1 inch male headers, use 0.1 female jumpers to connect. Buy a handful as they are generally useful. Indeed... those might be useful. What I'd also like to find is a cheap current loop interface (for running low speed serial connections long distances using cat 5 wire) On Mon, Sep 17, 2012 at 3:22 PM, Jim Lux jim...@earthlink.net wrote: On 9/17/12 3:00 PM, Azelio Boriani wrote: OK, you can test a VP Oncore GPS receiver alone if you have a mean to translate the TTL serial port to a regular RS232 for the PC. This can be done with a MAX232 chip (or equivalent). There are a ton of these (serial TTL ports) available inexpensively for use with Arduinos. In the under $20 range, usually. Try Sparkfun.com for instance.. ___ 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] GPSDO control loops and correcting quantizationerror
On 9/16/12 10:20 AM, Magnus Danielson wrote: On 09/16/2012 05:47 PM, Poul-Henning Kamp wrote: Dave Mills coined the term allan intercept as the cross over of the two sources allan variances and it's a good google search for his relevant papers. I'm not entirely sure his rule of thumb for regulating to that point is mathematically sound precise, but the concept itself is certainly valid, even if you have to compensate for the timeconstant of the PLL you use to regulate to that point. Well, what is being used is phase-noise intercept. Conceptually a similar intercept point will be available in Allan variance. However, as you shift between noise-variants, the Allan (and Modified Allan) variance has different scaling factor to the underlying phase noise amplitudes. The danger of using the Allan variance variant is that you get a bias in position compared to the phase-noise plots cross-overs. However, the concept is essentially the same, and the relative slopes is the same. You get in the right neighbourhood thought. The concept has been in use in the phasenoise world of things, so you would need to search the phase-noise articles to find the real source. It's been used to generate stable high-frequency signals. The analysis of PLL based splicing of ADEV curves is tricky, and I have not seen any good comprehensive analysis even if the general concept is roughly understood. The equivalent on phase-noise is however well understood and leaves no magic too it. I'm not sure that the theory of phase noise intercepts, in practical systems, is actually used. It seems that everyone I've talked to uses the theory to get in the ballpark and then does simulations at the design review, and ultimately, builds it and tests, and then tweaks the implementation to optimize (especially if the loop closure is implemented digitally in software/FPGA) When talking real high performance, there's so many confounding error factors that it's not like you can build what theory says and hit the mark. The *actual* noise distributions follow the Leeson model in general, but have lumps and bumps, and there's always narrow band oddities (power supply filtering, noise from switching power converters, etc.) Let's face it, real high performance source design has a lot of art and craft in it. You can't get to that point without sound engineering, but that last order of magnitude is all about suck it and see. I spent a lot of time with the code in NTPns, to try to get that PLL to converge on the optimum, and while generally good, it's not perfect. The basic problem is that the data you have available for autotuning, is the allan variance between your input and your steered source. It's a complex field, and things like temperature dependencies helps to confuse you. Ain't that the truth.. And then, there's proving that what you built is actually doing what you claim. State of the art sources require beyond state of the art verification methods... It's easy to write a spec for, say, incremental Allan Dev of 1E-16 at some tau. A bit harder to test at a constant frequency. Now throw in a varying frequency (say, because of temperature variation or Doppler).. ___ 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] Be aware of test equipment seller orzel-enterprises on eBay
On 9/10/12 11:03 PM, Chris Albertson wrote: On Mon, Sep 10, 2012 at 4:11 PM, David Kirkby david.kir...@onetel.netwrote: I've also had to pay inport duties and VAT on this, which comes to a US equivalent of around $220. I doubt I will be able to recover that. Talk to your customs people. Almost always oin most con tries if you re-export an item you can apply for a refund. I don't know the rules in the UK but it works like that in the US and Canada. One amusing case was when I worked at Hughes Aircraft. The company imported a rather large (close to $1M) diamond from Amsterdam and paid a large duty on it. They sawed a section out of it to make an optical window for a probe to be sent to Venus. Then after launch they applied for and got a refund of the duty because the diamond was exported out of the US to another planet where to this day it remains. My point is that re-export is common and they should have a procedure for it. We ship test equipment (and spacecraft) to other countries fairly regularly. Generally, one acquires what is known as a carnet de passage (or simply a carnet) for the dutiable goods. Such a carnet requires posting a bond or letter of credit or government memorandum of understanding that provides for payment in the event that the goods are not taken out. It's not an after the fact thing, although I suppose, anything is negotiable, given sufficient time and money. It gets even more complicated if you send something into space and it might come back (e.g. to ISS) (same thing applies to taking an automobile through some places in Africa or South America..where the duty is very high on cars) ___ 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] SC Cut
On 9/11/12 3:58 PM, Magnus Danielson wrote: On 09/12/2012 12:00 AM, Richard (Rick) Karlquist wrote: There is plenty of documentation at the IEEE web site in the UFFC society's section. EerNisse gave a paper at the Frequency Control Symposium on it at the time. Kusters followed up a year later with experimental data. I am not aware of any controversy about these two guys being the inventors, and I have attended many FCS's. I don't know how you prove to the Wiki police that there is no paper predating EerNisse's paper. Maybe there is a patent on it. UFFC has some excellent resources on the web which does not require you to be a member to use: http://www.ieee-uffc.org/frequency_control/teaching.asp Kusters died this March.. in his in memoriam thing, they mention this 1981 Ultransonics Symposium John A. Kusters, The SC CUT CRYSTAL - AN OVERVIEW, pp 402-409 Has a bunch of references.. TS theory in 74, TTC experimental confirmation in 75, SC (stress compensated) theory in 75, actual experimental evidence in 78 ___ 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] OT: Packing and shipping of test equipment
On 9/11/12 6:45 PM, Geoffrey Smith wrote: Folks, Following the Peter Gottlieb post, it seems that a number of list members have been victims of carriers that mishandled badly packed gear. I now too often the heart ache of a broken handles and the handle through the box wall, not to mention that rattling sound as a something rolls around in the cabinet. May I suggest that we pool our ideas on minimum packing requirements to be posted as an article on say ebay.Simple thing like no loose beans, bubble wrap size for instrument weight, box wall thickness, preparedness to pay for better packing ( there is no free lunch) etc. Forget insurance, bad packing voids most policies and who can value the loss anyway. There may be appropriate MIL standards? May be even a feedback score on ebay if we all ask for it? I notice that the experienced sellers can still pack test equipment with recycled packaging and get the items from Europe, USA and Asia in the condition it was advertised. Conversely I also note that the newer ebay list-ers are more likely to have packing problems. Packaging is a very complex science... We had an incident a couple years ago where a piece of not-quite-flight prototype hardware was packed in a standard foam filled shipping case; hand carried on the plane with a second seat, etc. It slipped when getting it out of the minivan at the destination and he caught it between his knees and the bumper and it slid to the ground. Some of the shock sensors on the package tripped. Since this is a) a million dollar piece of gear b) essentially a rehearsal of the delivery of the real deal a few months later There was a LOT of official attention. Here's what I learned: 1) we put shock sensors that were WAY too sensitive on the package (if your device can take a 50g shock, and you put 10g shock sensors on, all you get is aggravation, not useful information) given the actual fragility of the part. 2) Nobody actually knows how much packaging is right, without a lot of research. It is CERTAINLY not a simple use X inches of foam or something like that. You need to know the spring constant of the packing material and then calculate the forces when it's dropped (from some specified height) and figure out what the peak acceleration is. there's a whole science to this. As you can imagine, it turns out that foam can be too stiff or too soft, and that the appropriate foam density and thickness is dependent on both the mass of the thing being supported and the expected loading. the previous guidelines we had of ensure 4 of foam and stuff like that were basically worthless, and we'd just been lucky in the past. People who design shipping packaging for things like computers actually build test packages and instrument them,because, basically, it's an empirical design problem. (there was a an interesting case of someone shipping an iPhone recording accelerations via various shippers a couple years ago).. The iPhone maxes out way too low, but you could easily build a suitable tester with an Arduino and some off the shelf accelerometer shields.. Or, if you're being paid to do this, you spend $600 and buy the calibrated recording accelerometer and do some tests. Take home message: packaging is non trivial. A simple: pack it in two boxes with X inches of crumpled paper or peanuts isn't going to work. Historically, at work, we've had reasonably good luck with the foam in place scheme where they squirt a expanding foam into plastic bags around your stuff (if you've rented test equipment, you know what I'm talking about).But I suspect there's a whole art to picking a foam density and box size that this works for, most of the time. In general, this will wind up with a box that is MUCH larger than you think. When you're shipping a 50k network analyzer, a few hundred bucks extra in shipping for dimensional size penalties isn't a big deal. When you're shipping a $100 surplus widget, perhaps it is. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Re; New Wrist watch
On 9/10/12 6:57 AM, David McGaw wrote: He's making a joke - If you are traveling across time zones, why not just set it to UTC and be done with it? :-) David This is a bigger deal than one might think. Especially since calendaring software tries to be helpful and adjust things. So while you might want your alarm clock on your iPhone to ring at, say, 730AM LOCAL time, if you set an appointment in pacific time zone, it helpfully changes it to 3 hours earlier when you land in EDT land. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] New wrist Watch
On 9/9/12 7:05 AM, Stan, W1LE wrote: Hello The Net: I need to consider getting a new wrist watch, but I need a second hand and a digital display is unacceptable. What would you consider in the 150$ price range ? Thunderbolt driving a stepper motor? Would be nice to have state of the art accuracy with a lifetime battery and high reliability. Oh.. the battery will weigh a huge amount, but it will last a lifetime, because yours will be very short carrying it It won't be state of the art (I think tvb's cesium wrist watch does that.. but it doesn't have the non-digital display you want) grin couldn't resist... ___ 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] HP10514B Mixer Terminations
On 9/9/12 9:37 PM, li...@lazygranch.com wrote: What am I missing here? Vce = Vbe, so the diode connected transistor isn't saturated. I think it's where the diode is fully conducting, and into the linear part of the V/I curve, not in the square law part any more. In normal use the LO port is driven hard enough that the mixer is (hopefully) acting as a switch (and RF port is -10dB relative to the LO) ___ 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] crystal (or MEMS) oscillators with low hysteresis
Consulting the hive-mind here on the list.. If one were looking for small/cheap/mass produced oscillators which have decent phase noise.. what kind has the most repeatable frequency vs temperature curve. The usual 1ppm TCXO has about 0.1 ppm hysteresis, while other less stable oscillators may have bigger variation with temperature (1ppm/degree C isn't a problem) but be more repeatable (perhaps the kind that they use as a thermometer?) And, then, are those available in an inexpensive mass produced form (e.g. the precision quartz thermometer is NOT inexpensive or mass produced) Phase noise need (not a hard requirement) is not a big driver -45 @ 1 Hz -75 @ 10 Hz -105 @ 100 Hz -130 @ 1 kHz -145 floor out to 15 MHz The parts I use now are actually about 10 dB better than that (-58 at 1 Hz, -90 @ 10 Hz, -117 at 100 Hz, and floor of -153) Ideally, I'd like to find something that has zero hysteresis.. BUT, if there is an equation that can predict the hysteresis by knowing the temperature history, that would probably work (although that has a bunch of problems... what about temperature changes when power is off) This isn't a spec that typically shows up in the mass produced XO catalog: they focus more on bounding the frequency error over some range of environments .. good to within 50 ppm from 10-55 C or something like that. So I'm looking for practical experience. ___ 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] crystal (or MEMS) oscillators with low hysteresis
On 9/7/12 12:20 PM, Bob Camp wrote: Hi I'm guessing that power is also an issue, so cheap OCXO's are out. If that's true, I believe you are already at the cheap vs good inflection point with the cell phone TCXO. At $2 they are pretty tough to beat. Just the fancy crystal in something better is going to give you a big boost in the price. power and size.. Yes.. the cellphone tcxo is probably it.. but I was wondering if something else that's not TC might not have better hysteresis properties. Short of buying a batch and trying them... which I'll do, but before just randomly picking things out of the Digikey catalog, it's possible someone has more insight into the inner workings of cheap clock oscillators. For instance, they make inexpensive fairly high performance low power oscillators for COSPAS (emergency locator beacon) and wildlife tracker use. But you'd never know that they have the higher performance unless you asked. AT the high, expensive end, I've got all the data I need.. ___ 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] coupled oscillator book available online
A retired coworker of mine (Pogo) just published a book through JPL's DESCANSO series Coupled-Oscillator Based Active-Array Antennas: Ronald J. Pogorzelski and Apostolos Georgiadis http://descanso.jpl.nasa.gov/Monograph/series11_chapter.cfm?force_external=0 Why is this interesting to time-nuts? There's a whole raft of stuff in there about coupled oscillators, phase noise of injection locked and coupled oscillators, modeling and analysis of them.. And, it's free to download. (although I'm sure you could buy a hardcopy from Wiley.. Don't know who gets the royalties. Or a copy translated into Chinese, for that matter..) Jim ___ 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] 60 Hz line quirks, anybody recognize this stuff?
On 8/31/12 11:35 PM, Hal Murray wrote: The context is using the 60 Hz line for timing. I'm feeding 60 Hz from a wall wart transformer into a modem control signal that the kernel PPS stuff watches. Mostly, it works as expected, but occasionally, it picks or drops a cycle. In order to understand what was going on, I fed the same signal into the audio input and setup a job to capture the audio. Here is an example of a pick: http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a-pick.png http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a0.png http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a1.png OK, that somewhat makes sense. Something happened several days ago. I used to get picks/drops rarely, say ballpark of 1 a month. Now I'm getting 10 or 20 per day. So I started looking closer. I'm now seeing stuff like this. I've got lots and lots of examples. I added a second PC with different hardware. It sees the same stuff. Does anybody recognize this? http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-a0.png http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-b0.png http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-c0.png http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-d0.png http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-e0.png Interesting.. a 2-5 millisecond cutout. And very sharp edged. That's what's weird.. if it were something in the electrical distribution/transmission system, I don't know that it would be that clean (after all, the power line is a moderately effective low pass filter) And it also doesn't look like switching from one source to another. That is, the signal looks phase continuous. Are the gaps 1/6 or 1/12th cycle long? (thinking here of an 3phase inverter with an intermittent switching device) I wonder if the line goes open or to zero? ___ 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] 60 Hz line quirks, anybody recognize this stuff?
On 9/1/12 6:56 AM, Arthur Dent wrote: IMO, you have an instrumentation issue. I don't think the power grid can do anything like that. YMMV, -John I agree. If this was happening on the grid by the time this blip had traveled down the line to you it would have been so filtered through transformers and other devices and you wouldn't see sharp edges on the waveform but see a slightly rounded distorted waveform, not the sharp transitions you are seeing. If it isn't your test equipment then it is still something local to you like a loose electrical connection in your house momentarily causing your voltage to drop and then it arcs to reconnect the power. If you use an AM radio (not use a radio in the A.M. ;-) ), you could hear this as static or clicks as you observe this waveform on the screen. Do you have a triac/scr switch somewhere upstream? Like an X-10 module or something? Or a remote power controller with a solid state relay? That sharp edged, it's probably not coming from the utility. I don't know.. do the new fancy electric meters have a remote control disconnect feature in them? I could see that being some sort of SSR. Or an automatic transfer switch or grid-tied inverter that periodically interrupts the line, to detect backfeeding from the load? Or a solar power installation with a grid-tie that's doing something weird.On your neighbor's house? With a bug that shorts the line to neutral for a millisecond, and it pulls your voltage down too. ___ 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] oscillators
On 9/1/12 8:32 AM, Bob Camp wrote: Hi Observing a curve and being able to compensate it are often two different things. Hysteresis is one very obvious example. Another is simple sensor lag. A some what less obvious one is that the temperature performance is also influenced by the rate of change in temperature. Here's another thing to consider: If your crystal is running 3 ppm / C, and you are after 3.0 x 10^-11 stability at one second - You will need to either have a rate of change at ~ 1x10^-5 C/sec (0.6 mC / min) or you will need to compensate for some pretty small changes. That of course makes a bunch of assumptions …. In this application, the requirement for frequency accuracy has to do with initial acquisition.. that is, you want the signal (or receiver tuning) to be within some few hundred Hz of where it's expected to be (because the receiver is narrow band). The ground station typically has a Doppler predict based on orbit knowledge, that predict has some uncertainty. Added to the radio frequency uncertainty. (SNUG - Space Network User Guide, has more info) Once you've acquired, the receiver and ground station will track (i.e. the ground station puts in the estimated Doppler, so all you're really tracking is the variation in the local oscillator). (for a LEO satellite at 2.3 GHz, the 7km/s orbital velocity already puts tens of kHz variation on it) (and this completely neglects that a modern radio could use something like an FFT for acquisition) Temperature changes are pretty slow.. I'm seeing 5-10 degree cyclical variation over 90-100 minutes. Actually, the bigger change is during the warm up transient, going from off and cold to on and warm over 10 minutes or so. In other applications, where you're not going in and out of the sun every revolution (i.e. deep space, rather than LEO) and you were interested in Allan deviation type measurements for gravity science (where we're looking for 1E-13 over 100 sec sort of performance), what we'd probably do is warm up early.. Turn it on, compensate based on the measured temperature, and then hold the compensation fixed during the measurement, letting the ground worry about the apparent frequency change due to Doppler. We'd have a high quality narrow band signal, just at an unknown (but reasonably stable) frequency. What the science team is usually interested in is small relative changes in phase amplitude(occultations) or in small changes in frequency (Doppler, for gravity science). (we regularly measure velocity to cm/sec precision for outer planet orbiters like Cassini, Juno, etc.) ___ 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] oscillators
On 9/1/12 11:00 AM, Bob Camp wrote: Hi I suspect that a good IT cut would probably do better than an SC in either application. In the deep space situation, a copper slug in a dewar sounds like a reasonable addition to the design. If you're going to do dewars, then you're talking USOs for which the technology is quite well developed with ovens, etc. But that's a kilo, several watts, and a liter. What you want is something that is better than, say, 0.1 ppm, that is comparable in mass/power/volume/cost to an existing 1-5 ppm TCXO (about 1x2x0.5 cm) ___ 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] oscillators
On 8/31/12 7:06 AM, Bob Camp wrote: Hi An SC is going to have it's temperature curve centered up around 95C or so. If it's been cut as an OCXO crystal the turns will be up there as well. By the time it gets to room temp, the delta F / delta T is moving mighty fast. Think in terms of multiple ppm/C. A typical cell phone TCXO crystal is in the sub 0.1 ppm/C range in the vicinity of room temp. In addition, SC's are pretty hard to pull. For a normal TCXO (no DDS) something 40 ppm of range would be needed. By the time you get the wide tune stuff in the circuit, the phase noise isn't going to be anything special. Bob We're not pulling the crystal.. we just let it sit. What we do is change an NCO in the software radio implementation. Typically, you have a coarse tune with a PLL in steps of 500kHz-1MHz, and then you do the fine tune in software with a digital mixer/downconverter and an NCO (which also is part of the carrier tracking loop). ___ 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] oscillators
On 8/31/12 7:16 PM, Bob Camp wrote: Hi Ok, that gets you back to the basics of really major delta F / delta T slopes. Bob yeah.. but as long as you know what the curve is.. the NCO has a huge range (after all, we already have to tune over 500 kHz...a few hundred Hz isn't a big deal. A more complex problem is doing insitu calibration from, e.g., GPS signals or from some externally received frequency reference. (since the radio in question can also work as a GPS receiver, eventually). ___ 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] oscillators
On 8/29/12 8:45 PM, Richard (Rick) Karlquist wrote: On 8/27/2012 11:45 PM, WB6BNQ wrote: A microprocessor controlled XO is a non oven crystal oscillator system that has additional computational control providing a bit more than just mere passive temperature compensation. The additional computational capability deals with having coefficients of that particular oscillator's behavior pre coded to compensate for the nonlinear behavior over a given temperature rang It doesn't use coefficients. It has a look up table of frequency vs temperature. A microprocessor controlled XO system allows for using cheap crystals with minimum processing time and costs. Because of limited storage space there is no No it doesn't use a cheap crystal. It uses a *special* SC cut crystal. This crystal could very easily cost more than an OCXO crystal. Isn't the crystal cut (and the circuit designed) in such a way that it supports both the fundamental and the third overtone simultaneously, and comparing the frequencies of the two (or, more accurately, fF- fthird/3) is how they measure the temperature, which is then used to look up the correction factor in a PROM. ___ 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] oscillators
On 8/29/12 9:22 PM, Hal Murray wrote: rich...@karlquist.com said: No it doesn't use a cheap crystal. It uses a *special* SC cut crystal. This crystal could very easily cost more than an OCXO crystal. http://www.q-tech.com/mcxo.html What's special about it? Has to support the overtones properly. Not only does it have to be a good oscillator crystal, it also has to be a good thermometer I assume the cost-more aspect would be to allow an overall goodness factor competitive with an OCXO in the low power corner of the marketplace. It might be cheaper overall to use a good crystal and a uP to correct for temperature than provide the power to run the oven. Power consumption, size, etc. Also, faster startup time (no waiting for an oven to stabilize) The other area where a uP is useful is in an environment with high vibration. It can correct for acceleration as well as temperature. There were several good URLs mention on this list in the past year or two. The context was radar on helicopters. Helicopters are full of vibrations/accelerations. The numbers work out such that the frequency broadening due to vibration is interesting if your radar is looking for slowly moving things like people. -- Crazy question dept: What do low cost rubidium oscillators do when vibrating? Is it dominated by the cleanup crystal? ___ 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] oscillators
On 8/30/12 9:33 AM, Bob Camp wrote: Hi The fundamental / third approach is one of several possible ways to go. You can also run an SC on the B and C modes to get thermometer data. Early implementations used a pair of independent blanks, one cut to be a good thermometer. Some have even gone as far as to mount a thermistor on the crystal. I've used the sensor on oscillator can technique very recently on a software defined radio. Over the next year, I'll get some data on how well it works in use. The idea is to use a low power TCXO and a sensor, rather than an OCXO, to meet a fairly tight frequency requirement (a few hundred Hz out of 2 GHz) The TCXO can get you do a few ppm or better. The sensor should let me get about an order of magnitude better, and I need to measure the temperature anyway, and it's easy to integrate with the software waveform code. ___ 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] oscillators
On 8/30/12 12:37 PM, Bob Camp wrote: Hi The original patents on the MCXO are government property. One of the Ft. Monmouth guys came up with the fundamental / third overtone idea back in the 80's. Several (at least three) companies were licensed by the government to make the part. Gotta be careful there.. A lot of times these days, the government doesn't own the patent, they get a government use license. If it was a civil servant doing the work, then, yes, government owns it, and anyone can use it. However, if it was a contractor at a government facility, or developed under a contract (particularly a university), then it might be much stickier. If you wanted to build something to sell to the government, then getting a license is easy. But for the general public, perhaps not. Working at JPL, which is part of Cal Tech, on NASA's nickle, we're made VERY aware of exactly who owns the fruits of our brains, and who gets to use it. The Bayh Dole act has many unexpected consequences. These days, a lot of the people working at government labs are not civil servants, but are Technical Support and Engineering Personnel. This allows them to report a lower headcount of government employees. ___ 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] oscillators
On 8/30/12 6:12 PM, Bob Camp wrote: Hi If the temperature is varying slowly *and* there are no gradients you may get your order of magnitude over some range. You might be surprised at your TCXO. A lot of them are pretty darn good in the vicinity of room temp. You may already be an order of magnitude past your ppm or two for fairly normal temperature changes. Temp does vary slowly (the radio weighs on the order of 6kg).. Need to hold spec (in theory) from -20 to +40C. The oscillator runs about 10 degrees hotter inside. About 0.2 ppm from 5C to 40C. +/- 1ppm worst case over the whole temperature range. What I'm also interested in is whether I can compensate a non TCXO 66MHz CPU clock oscillator (even cheaper, potentially better phase noise with a higher Q crystal, etc.) ___ 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] oscillators
On 8/30/12 6:29 PM, Magnus Danielson wrote: On 08/31/2012 03:12 AM, Bob Camp wrote: Hi If the temperature is varying slowly *and* there are no gradients you may get your order of magnitude over some range. You might be surprised at your TCXO. A lot of them are pretty darn good in the vicinity of room temp. You may already be an order of magnitude past your ppm or two for fairly normal temperature changes. I haven't seen that any of the TCXOs compensates for the temperature hysteresis. It would be cool if they did. That is the dominant error source for changes over the 5-40C.. about 0.2 ppm difference when going up from -55 to +85 and going down over the same range. The ability to handle temperature gradients can be troublesome for both TCXOs and OCXOs. TCXOs have become quite good these days. Cheers, Magnus ___ 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] oscillators
On 8/30/12 9:04 PM, Bob Camp wrote: Hi A standard clock crystal is pretty much junk. as far as temperature performance is concerned. Even a cheap TCXO is likely to be pretty good over 25 C +/- 10C. yes.. but, say, one had a decent SC cut with good phase noise properties, but large (but repeatable) temperature characteristics. Can I get good accuracy AND good phase noise, for less hassle/power/size than an OCXO? My radio has a TCXO and a clock oscillator, so the clock oscillator is my test article for the temperature compensation scheme.. Bob On Aug 30, 2012, at 11:35 PM, Jim Lux jim...@earthlink.net wrote: On 8/30/12 6:12 PM, Bob Camp wrote: Hi If the temperature is varying slowly *and* there are no gradients you may get your order of magnitude over some range. You might be surprised at your TCXO. A lot of them are pretty darn good in the vicinity of room temp. You may already be an order of magnitude past your ppm or two for fairly normal temperature changes. Temp does vary slowly (the radio weighs on the order of 6kg).. Need to hold spec (in theory) from -20 to +40C. The oscillator runs about 10 degrees hotter inside. About 0.2 ppm from 5C to 40C. +/- 1ppm worst case over the whole temperature range. What I'm also interested in is whether I can compensate a non TCXO 66MHz CPU clock oscillator (even cheaper, potentially better phase noise with a higher Q crystal, etc.) ___ 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 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] oscillators
On 8/27/12 10:45 PM, Chris Albertson wrote: On Mon, Aug 27, 2012 at 7:33 PM, Jim Lux jim...@earthlink.net wrote: On 8/27/12 4:15 PM, Rick Karlquist wrote: Several decades ago, the concept of the smart clock arose at what was then HP. The idea was as discussed here to characterize past aging, predict future aging, and then correct the aging. We know what a OCXO is and a TCXO is. I was at a presentation at work a whike back and they called what you describe a MPCXO or MicroProcessor Compensated XO.They said the characteristics were between the OCXO and TCXO Doesn't the thunderbolt do this. I think it watches the aging rate of the OCXO and adjusts during hold over. Not really. The MCXO has a one time calibration for frequency vs temperature that's programmed into it (and some use *very* clever ways to measure the temperature). The disciplining algorithms in a GPSDO are a bit smarter; some explicitly develop a model for the f vs T and apply it, in others it's essentially embedded in a higher order filter which takes the measured T, along with other parameters, into the filter. I don't know if the GPSDOs try to do a time series fit/model (at least for low order terms) to deal with things like diurnal variation. They could. I should note that the MCXO approach, popularized as a better TCXO in a small low power package, is also used in some software defined radios, except that there's no separate microcontroller. The frequency vs temperature characteristic is just embedded in the other algorithms in the radio's host processor. ___ 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] oscillators
On 8/27/12 4:15 PM, Rick Karlquist wrote: Several decades ago, the concept of the smart clock arose at what was then HP. The idea was as discussed here to characterize past aging, predict future aging, and then correct the aging. The goal wasn't to turn a quartz oscillator into an atomic clock replacement, but simply to get the oscillator through a 1 hour or so holdover time during GPS outages. It sort of worked for that very limited purpose, but in general, past performance of HP crystals wasn't a very good predictor of future results. Crystals would age in one direction for a while and possibly slow down as time when on, but then then might start aging in the other direction. There were also frequency jumps that were substantial and totally random. The reason why the HP crystals were unpredictable was that all the deterministic processes such as mass preferentially depositing on the crystal, so as to make the frequency age lower, had been eliminated by years of manufacturing improvements. The remaining processes were of the nature of quartz stress relaxation that were very random. Rick Karlquist We see similar things in USOs (and other components as well) for spaceflight.. Things that people worried about 60 or more years ago just don't occur anymore. People used to obsessively try to match diodes in HV strings, for instance, because the process variability was high enough to make a difference. These days, you get a reel of diodes and they're all pretty much the same, and even reel to reel from month to month they don't change much.That's what all that 6-sigma stuff is all about, after all. All the low hanging, and even middle hanging, fruit has been picked.. (one big exception.. ICs which are not designed for radiation tolerance seem to have large variability in radiation tolerance..it's just not something that's controlled for in the process) ___ 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] Modern motherboard with RS232 port
On 8/19/12 7:26 PM, Chuck Harris wrote: Residential power is traditionally measured in watts, not V-A. Commercial power is typically measured in V-A, with an additional fee for power factor problems. residential meters measure watts (active power) not VA... What you want is the Kill-A-Watt.. a $30 widget that measures all the parameters.. A great little deviec. -Chuck Harris Ed Palmer wrote: It's important to remember that on a computer, the wattage shown has no relationship to the wattage pulled from the socket. The numbers shown are maximum values. You have to measure the power draw and you have to measure it in volt-amps, not watts because that's how residential power is measured (at least in North America). Buy an energy meter that shows volt-amps. They're relatively cheap - typically less than $50. Ed ___ 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] new member with questions NTP, PRS, GPS, ocxo
On 8/17/12 10:41 PM, Mark Spencer wrote: Regarding the NTP server another option is to buy a stand alone NTP server that can accept a 1pps and or 10 Mhz input, and feed it the GPS or other reference of your chosing. I picked up a Datum unit from ebay which is currently fed 1pps from a Jackson Labs Fury. It also accepts 10 Mhz as well which it will use in lieu of it's built in VCXO. I agree with the comments about the Fury being a nice plug and play GPSDO solution. I thought long and hard about going the ebay route and acquring a used HP GPSDO to supplement my Thunderbolt and ended up buying the Fury. That being said the price differnce between the Fury and a typical used Thunderbolt is signficant. I would steer clear of the typical combined NTP, GPS units with TCXO's or VCXO's if you are interested in a using them as a source of a highly accurate 10 Mhz reference signal. The VCXO in my datum NTP server is orders of magnitude less stable than a typical OCXO. Depends on the options.. The Symmetricom/TrueTime XL-DC had a low phase noise option that's pretty good, for instance, so if you found one that had the NTP option too, you're in good shape. Installing a GPS antenna in a location with a clear view of the sky is also helpfull. ___ 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] ideas so far for first GPS, NTP project
On 8/18/12 6:23 PM, J. L. Trantham wrote: I use one like this (theBay item 270881742870) and it works well in NW Florida under some trees. I could get better performance if I had it up higher but it serves my purposes. There are also ones with higher gain out there as well, up to about 40 dB IIRC. Yeah, but gain isn't a big deal. It's designed to overcome the loss of the transmission line to the receiver. What's important is the noise figure of the LNA, more than the gain. Most receivers have a 1 bit quantizer, so all you really care is that the signal from the antenna is big enough that the antenna noise dominates over the receiver noise. If I had to guess, I'd say that as long as the antenna/preamp gain is more than the loss in the cable (and power dividers, etc.) by some few dB, you're fine. ___ 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] Early WWV Oscillator
On 8/14/12 1:42 PM, Ron Ward wrote: HI Robert: WOW! Thanks. I need to build a double oven for my thunderbolt and set it to about 50 Degrees C. I am really just trying to reduce the 24 hour temperature range. I am looking at an application note from National Semiconductor, AN 266, for a precision oven. It claims .001 degree C! The internal oven for the Trimble Oscillator is most likely not as good as the one featured in the application note. There's a book called Building Scientific Apparatus http://www.amazon.com/Building-Scientific-Apparatus-John-Moore/dp/0813340063 that has a whole chapter on precision temperature control (to millidegrees, if not finer) ___ 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] What size graphs do people like? (How big is yourscreen?)
On 8/8/12 5:19 AM, Sylvain Munaut wrote: Hi, SVG is uncompressed text. PNG compresses well, at least for simple cases. Decently configured web servers will compress SVG on the fly during transport, wich yields a 9k transfer size. (and your server is definitely not properly configured for SVG, it doesn't compress and serves it as text/plain ...) decently configured probably excludes my application, where I have a very limited function server (an Arduino) Web services are a convenient, nearly universal, scheme to communicate between boxes. It's not always in the context of a traditional fat server/thin client sort of model. In fact, I'd say that the client end (the web browser) typically has more computing and display horsepower (on a per connection basis) than the server in most cases. Even a fairly big server serving 100s of pages per second to iPhone type clients has a more horsepower on the receiving end than the sending end. ___ 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.
