Re: [time-nuts] Phase modulation detection/NIST plan
HI A died in the wool Time Nut who doesn't care what time it is - what's the world coming to Bob Hi Bob, I think you mean dyed in the wool. A *died* in the wool time nut could be used to describe a frozen 19th century sextant and sidereal pendulum clock carrying Antarctic explorer. ;-) /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Phase modulation detection/NIST plan
More importantly, how many things don't really need a clock to begin with! :) Every piece of equipment in our house shows a different time. I wouldn't complain if they all automatically adjusted. My current solution is to just stop looking at the clocks, and it's amazing how much easier life gets if you just stop worrying about things! :) Dan On 7/14/2012 10:50 AM, time-nuts-requ...@febo.com wrote: Hi I think the answer to how many places would it be used is to simply count the number of things that have the wrong time on them each time the power burps. There are maybe a dozen gizmos like that in this room (yes I'm in the kitchen). Bob ___ 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] Phase modulation detection/NIST plan
More importantly, how many things don't really need a clock to begin with! :) ABSOLUTELY! If you turn on the coffee maker when you walk int the kitchen, it'll be done by the time you fix breakfast. And so on... A clock on almost everything is totally superfluous, IMO. Things that do need to be externally synchronized, like video recorder, can bette4r use the program time. Every piece of equipment in our house shows a different time. I wouldn't complain if they all automatically adjusted. My current solution is to just stop looking at the clocks, and it's amazing how much easier life gets if you just stop worrying about things! :) Finally, a voice of common sense! Dan -John = On 7/14/2012 10:50 AM, time-nuts-requ...@febo.com wrote: Hi I think the answer to how many places would it be used is to simply count the number of things that have the wrong time on them each time the power burps. There are maybe a dozen gizmos like that in this room (yes I'm in the kitchen). Bob ___ 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] Phase modulation detection/NIST plan
Confucius say: Man with two clocks never know what time it is. Al Every piece of equipment in our house shows a different time. I wouldn't complain if they all automatically adjusted. My current solution is to just stop looking at the clocks, and it's amazing how much easier life gets if you just stop worrying about things! :) ___ 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] Phase modulation detection/NIST plan
HI A died in the wool Time Nut who doesn't care what time it is - what's the world coming to Bob On Jul 16, 2012, at 9:34 AM, J. Forster wrote: More importantly, how many things don't really need a clock to begin with! :) ABSOLUTELY! If you turn on the coffee maker when you walk int the kitchen, it'll be done by the time you fix breakfast. And so on... A clock on almost everything is totally superfluous, IMO. Things that do need to be externally synchronized, like video recorder, can bette4r use the program time. Every piece of equipment in our house shows a different time. I wouldn't complain if they all automatically adjusted. My current solution is to just stop looking at the clocks, and it's amazing how much easier life gets if you just stop worrying about things! :) Finally, a voice of common sense! Dan -John = On 7/14/2012 10:50 AM, time-nuts-requ...@febo.com wrote: Hi I think the answer to how many places would it be used is to simply count the number of things that have the wrong time on them each time the power burps. There are maybe a dozen gizmos like that in this room (yes I'm in the kitchen). Bob ___ 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] Phase modulation detection/NIST plan
Just because I like Brie, doesn't mean I like French Bread or wine. I am interested in Standards of Time Interval for engineering purposes. I havn't looked at my oven clock in probably 25 years. I presume it's accurate twice a day or somewhere on earth, but I couldn't care less. IMO, adding a clock to an oven, dishwasher, refrigerator, toaster oven, coffee maker, etc. is simply another useless feature. Bling to catch the eye of the clueless shopper. I'd much rather the maker spent the $0.50 a digital clock costs on meaningful quality improvements in those features that actually matter. YMMV, -John HI A died in the wool Time Nut who doesn't care what time it is - what's the world coming to Bob On Jul 16, 2012, at 9:34 AM, J. Forster wrote: More importantly, how many things don't really need a clock to begin with! :) ABSOLUTELY! If you turn on the coffee maker when you walk int the kitchen, it'll be done by the time you fix breakfast. And so on... A clock on almost everything is totally superfluous, IMO. Things that do need to be externally synchronized, like video recorder, can bette4r use the program time. Every piece of equipment in our house shows a different time. I wouldn't complain if they all automatically adjusted. My current solution is to just stop looking at the clocks, and it's amazing how much easier life gets if you just stop worrying about things! :) Finally, a voice of common sense! Dan -John = On 7/14/2012 10:50 AM, time-nuts-requ...@febo.com wrote: Hi I think the answer to how many places would it be used is to simply count the number of things that have the wrong time on them each time the power burps. There are maybe a dozen gizmos like that in this room (yes I'm in the kitchen). Bob ___ 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. ___ 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] Phase modulation detection/NIST plan.. PS
PS: 30 odd years ago, I bought a toaster for about $20 that worked fine and made good toast until recently. It only failed because a piece of bread got jammed and was impossible to clean. So, I bought a new toaster, for about the same price. It didn't last 30 weeks. In my view, this is NOT progress. I detest having to resolve supposedly solved problems. YMMV, -John Just because I like Brie, doesn't mean I like French Bread or wine. I am interested in Standards of Time Interval for engineering purposes. I havn't looked at my oven clock in probably 25 years. I presume it's accurate twice a day or somewhere on earth, but I couldn't care less. IMO, adding a clock to an oven, dishwasher, refrigerator, toaster oven, coffee maker, etc. is simply another useless feature. Bling to catch the eye of the clueless shopper. I'd much rather the maker spent the $0.50 a digital clock costs on meaningful quality improvements in those features that actually matter. YMMV, -John HI A died in the wool Time Nut who doesn't care what time it is - what's the world coming to Bob On Jul 16, 2012, at 9:34 AM, J. Forster wrote: More importantly, how many things don't really need a clock to begin with! :) ABSOLUTELY! If you turn on the coffee maker when you walk int the kitchen, it'll be done by the time you fix breakfast. And so on... A clock on almost everything is totally superfluous, IMO. Things that do need to be externally synchronized, like video recorder, can bette4r use the program time. Every piece of equipment in our house shows a different time. I wouldn't complain if they all automatically adjusted. My current solution is to just stop looking at the clocks, and it's amazing how much easier life gets if you just stop worrying about things! :) Finally, a voice of common sense! Dan -John = On 7/14/2012 10:50 AM, time-nuts-requ...@febo.com wrote: Hi I think the answer to how many places would it be used is to simply count the number of things that have the wrong time on them each time the power burps. There are maybe a dozen gizmos like that in this room (yes I'm in the kitchen). Bob ___ 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. ___ 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] Phase modulation detection/NIST plan.. PS
I just hope it didn't died on the last leapsecond...? On 16/07/2012 22:50, J. Forster wrote: PS: 30 odd years ago, I bought a toaster for about $20 that worked fine and made good toast until recently. It only failed because a piece of bread got jammed and was impossible to clean. So, I bought a new toaster, for about the same price. It didn't last 30 weeks. In my view, this is NOT progress. I detest having to resolve supposedly solved problems. YMMV, -John Just because I like Brie, doesn't mean I like French Bread or wine. I am interested in Standards of Time Interval for engineering purposes. I havn't looked at my oven clock in probably 25 years. I presume it's accurate twice a day or somewhere on earth, but I couldn't care less. IMO, adding a clock to an oven, dishwasher, refrigerator, toaster oven, coffee maker, etc. is simply another useless feature. Bling to catch the eye of the clueless shopper. I'd much rather the maker spent the $0.50 a digital clock costs on meaningful quality improvements in those features that actually matter. YMMV, -John HI A died in the wool Time Nut who doesn't care what time it is - what's the world coming to Bob On Jul 16, 2012, at 9:34 AM, J. Forster wrote: More importantly, how many things don't really need a clock to begin with! :) ABSOLUTELY! If you turn on the coffee maker when you walk int the kitchen, it'll be done by the time you fix breakfast. And so on... A clock on almost everything is totally superfluous, IMO. Things that do need to be externally synchronized, like video recorder, can bette4r use the program time. Every piece of equipment in our house shows a different time. I wouldn't complain if they all automatically adjusted. My current solution is to just stop looking at the clocks, and it's amazing how much easier life gets if you just stop worrying about things! :) Finally, a voice of common sense! Dan -John = On 7/14/2012 10:50 AM, time-nuts-requ...@febo.com wrote: Hi I think the answer to how many places would it be used is to simply count the number of things that have the wrong time on them each time the power burps. There are maybe a dozen gizmos like that in this room (yes I'm in the kitchen). Bob ___ 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. ___ 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. -- Jean-Louis Oneto OCA GeoAzur - Avenue Nicolas Copernic 06130 Grasse - France e-mail: jean-louis.on...@obs-azur.fr ___ 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] Phase modulation detection/NIST plan
On 07/14/2012 06:47 AM, Brooke Clarke wrote: Hi: The key thing GPS is lacking is Daylight Savings Time. WWV WWVB have the DST bits that allow a clock to show the local time. One reason GPS doesn't have it is that it is not coordinated globally. For instance, US is not shifting DST at the same time as Europe. There is no obvious right here. Keeping track of the time-zones and their changes keeps the time-zone folks alert and requires a constant maintenance. Keeping it in the GPS signal would require mapping of position to time-zone area, and only then it could be keyed down. These mappings does not stay stable, so any downlink format would need to describe them and would take considerable time. This is why it is best managed by the user himself. 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.
Re: [time-nuts] Phase modulation detection/NIST plan
Hi I think the answer to how many places would it be used is to simply count the number of things that have the wrong time on them each time the power burps. There are maybe a dozen gizmos like that in this room (yes I'm in the kitchen). Bob On Jul 14, 2012, at 12:41 AM, Hal Murray wrote: d...@dieconsulting.com said: There are innumerable applications for low cost low power human level 1 second accurate time of day in modern electronic systems - examples are traffic lights and school crossing signs and water sprinklers and street lights and other outdoor lighting and many others... these systems are not normally network connected and there is no current wide area technology short of power hungry GPS with its weak signals and relatively high cost and difficult reception from many locations to do this. How many of those are really interested in low power? The only one I see on your list that might run off batteries is water sprinklers. All the rest use enough power that a GPS unit would be in the noise. I think the main argument for WWVB receivers vs GPS receivers would be cost. In either case, you have to get the antenna outside the metal enclosure and that may be the major cost. (I suppose a sprinkler controller could be mounted in a plastic enclosure.) school crossing signs is another possibility. In the last year or two, I've seen several setups around here that have solar powered LEDs mounted at street level at pedestrian crossings. They are great at night but not so great during the day. (But during the day the pedestrians are easier to see.) -- These are my opinions. I hate spam. ___ 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] Phase modulation detection/NIST plan
I don't see why school crossing signs, water sprinklers, street or outdoor lighting need 1 second timing. Ten minutes, or a photocell, would be more than adequate. Synchronized traffic lights, perhaps. But there are other cheaper, ways of doing that like a simple radio link. -John === d...@dieconsulting.com said: There are innumerable applications for low cost low power human level 1 second accurate time of day in modern electronic systems - examples are traffic lights and school crossing signs and water sprinklers and street lights and other outdoor lighting and many others... these systems are not normally network connected and there is no current wide area technology short of power hungry GPS with its weak signals and relatively high cost and difficult reception from many locations to do this. How many of those are really interested in low power? The only one I see on your list that might run off batteries is water sprinklers. All the rest use enough power that a GPS unit would be in the noise. I think the main argument for WWVB receivers vs GPS receivers would be cost. In either case, you have to get the antenna outside the metal enclosure and that may be the major cost. (I suppose a sprinkler controller could be mounted in a plastic enclosure.) school crossing signs is another possibility. In the last year or two, I've seen several setups around here that have solar powered LEDs mounted at street level at pedestrian crossings. They are great at night but not so great during the day. (But during the day the pedestrians are easier to see.) -- These are my opinions. I hate spam. ___ 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] Phase modulation detection/NIST plan
On Sat, Jul 14, 2012 at 06:15:14AM -0700, J. Forster wrote: I don't see why school crossing signs, water sprinklers, street or outdoor lighting need 1 second timing. Ten minutes, or a photocell, would be more than adequate. While there are many many other applications, the issue for most of these devices is not 1 second accuracy, but automagic setting of the time without operator intervention or manual procedure required. For many ordinary folks the always slightly different push button gyrations required to set the time on a device with limited buttons and display are all too often a complete barrier to getting the time set right (this is the VCR blinking 12:00AM phenomenon). And in outside environments clock oscillator thermal behavior will ensure something preset to the correct will wander pretty far out quite quickly (plus of course DST needs to be set too). And working with only approximate time is another source of terrible confusion for users... if they set it to go off at exactly 11 PM and it goes off at 11:08 PM they are likely going to be confused and frustrated... especially if difficult or even impossible steps are required to correct the time. Photocells don't work for situations where the desired on or off times are civil times (not turning on the water sprinklers until 11 PM for example or turning off the tennis court lights at 10 PM)... at best it takes lots of software to convert light and dark from them to anything approximating a 10 minute accurate estimate of the time of day and shadows and sun angles and so forth ensure that this is never going to be particularly accurate. Synchronized traffic lights, perhaps. But there are other cheaper, ways of doing that like a simple radio link. I refuse to believe that a reliable mile or more range RF link would be cheaper than a loopstick and maybe a couple of passives tied to pins on a SOC chip... and there are all those situations where even a mile isn't enough or obstacles or RFI block ISM band links. -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ 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] Phase modulation detection/NIST plan
On Wed, Jul 11, 2012 at 03:48:52PM -0400, paul swed wrote: David Read your comments and have been traveling. So finally a chance to email. I read the document also and walked away with what I shared. In your reading would you believe the following. Its an absolute phase and that when it switches to 0 there is 1 transition at the beginning of the second to 180 degrees staying that way to the next bit or flipping again to 0 degrees if its a 1 at the 1 sec tic??? What I mean by absolute phase is that a 1 is always 180 degrees and a zero always 0 degrees. In your example this would imply that the two ones in a row would result in two seconds of 180 degree phase without a flip after the first 1. The document is confusing, but the best I can do with its language is to conclude they are talking about absolute phase. Normally when one talks about baseband waveforms one is referring to absolute I and Q components relative to an unchanging carrier phase, not relative I and Q with respect to the last bit phase. So I take their language to mean a zero is 0 degrees and a 1 180 degrees relative to an unchanging carrier. Differential encoding is the opposite, a 1 is always the opposite phase from the last bit, a zero always the same phase as the last bit (or sometimes the inverse where a zero is the transition and a one is not). Is there a way to sense from the document that there is a bias towards 0 lets say. Differential encoding tends to have little DC component or bias toward either one or zero or one phase or the other, absolute encoding does if the data it encodes does. -- An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ 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] Phase modulation detection/NIST plan
On 07/14/2012 01:49 AM, David I. Emery wrote: On Wed, Jul 11, 2012 at 03:48:52PM -0400, paul swed wrote: David Read your comments and have been traveling. So finally a chance to email. I read the document also and walked away with what I shared. In your reading would you believe the following. Its an absolute phase and that when it switches to 0 there is 1 transition at the beginning of the second to 180 degrees staying that way to the next bit or flipping again to 0 degrees if its a 1 at the 1 sec tic??? What I mean by absolute phase is that a 1 is always 180 degrees and a zero always 0 degrees. In your example this would imply that the two ones in a row would result in two seconds of 180 degree phase without a flip after the first 1. The document is confusing, but the best I can do with its language is to conclude they are talking about absolute phase. Normally when one talks about baseband waveforms one is referring to absolute I and Q components relative to an unchanging carrier phase, not relative I and Q with respect to the last bit phase. So I take their language to mean a zero is 0 degrees and a 1 180 degrees relative to an unchanging carrier. I think the PTTI article isn't as much documentation as presentation of general principle, showing details more as to present how it can be done, but not necessarily guarantee it will be done that way. Knowing the synchronisation sequence, polarity should not be ambiguous. Also note that other data such as hours would be known from the AM signal, so we can reverse engineer it. A receiver knowing this sequence will either bootstrap from the AM or attempt straight lock. It's not too hard to build a maximum likelihood receiver for it. 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.
Re: [time-nuts] Phase modulation detection/NIST plan
On Sat, Jul 14, 2012 at 02:38:34AM +0200, Magnus Danielson wrote: I think the PTTI article isn't as much documentation as presentation of general principle, showing details more as to present how it can be done, but not necessarily guarantee it will be done that way. Knowing the synchronisation sequence, polarity should not be ambiguous. Also note that other data such as hours would be known from the AM signal, so we can reverse engineer it. A receiver knowing this sequence will either bootstrap from the AM or attempt straight lock. It's not too hard to build a maximum likelihood receiver for it. I read the article as not a definitive specification frozen in stone, but as a complete and relatively fully specified proposed design with perhaps some details subject to adjustment or revision. The question of absolute versus differential phase shift keying is, of course, rather fundamental to being able to decode the signal at one level but at another not terribly central to the core of the design for a coding and modulation scheme that works at much lower C/N levels than the AM version did while preserving the legacy AM and its coding for existing hardware. SOME place in the design of a differentially coded signal there has to be a decision whether or not to structure the data encoding so some specific bit (or more properly symbol) in each frame (or at least some known frames relative to the time of day) (in this case I mean 1 minute long TOD frame) is of a known absolute reference phase. If this is done than it becomes possible in a reasonable time to determine an absolute 60 KHz carrier phase after a fade, if it is not done and every single bit of data is not absolutely predictable (the current TOD coding would be absolutely predictable given knowledge of the time and date and of leap seconds and DST settings, but they make clear future extensions would probably not have this property as additional messages are added including emergency messages and the like which are never predictable) there is no way to reliably decide after a fade which phase is which as this depends on knowing the number of ones and zeros in all the frames transmitted since one last saw the signal, something that is in the general case impossible if the signal has faded and the bits were not observed. An absolute encoding has no ambiguity - if one knows the time of day within a second one knows the transmitted phase except for during bits that might vary with unknown data (eg emergency messages, extensions to the standard and newly changed DST and leap second settings and FEC bits based on them) and MOST bits are always known phases, especially of course the sync code words. So even with terribly poor C/N one should be able to relatively quickly resolve the phase ambiguity after a period of signal loss... and in many cases if one still has a good idea of the time, within a couple of seconds (symbols) of signal reacquisition. On another point, I am not of the school that providing much better weak signal performance for simple, low power, and cheap LF time of day clocks using WWVB is somehow a minor improvement that primarily benefits China because they make most cheap self setting atomic clocks. There are innumerable applications for low cost low power human level 1 second accurate time of day in modern electronic systems - examples are traffic lights and school crossing signs and water sprinklers and street lights and other outdoor lighting and many others... these systems are not normally network connected and there is no current wide area technology short of power hungry GPS with its weak signals and relatively high cost and difficult reception from many locations to do this. And with minimal effort to ensure compatibility, there should be no conflict with use of the same carrier signal as a frequency reference too... the problem of several decades old antique time and frequency gear being incompatible seems very minor, and of course we have already discussed ways to handle this if needed. And as long as the existing frequency reference use of the carrier continues to work as a backup to GPS with modern updated gear that capability hasn't been lost - except maybe if your particular variety of tin foil hat requires vacuum tube VLF reference gear because of EMP fears or something similar. I think the new WWVB proposal seems sensible and a reasonable design...that should serve the public well. -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
Re: [time-nuts] Phase modulation detection/NIST plan
d...@dieconsulting.com said: There are innumerable applications for low cost low power human level 1 second accurate time of day in modern electronic systems - examples are traffic lights and school crossing signs and water sprinklers and street lights and other outdoor lighting and many others... these systems are not normally network connected and there is no current wide area technology short of power hungry GPS with its weak signals and relatively high cost and difficult reception from many locations to do this. How many of those are really interested in low power? The only one I see on your list that might run off batteries is water sprinklers. All the rest use enough power that a GPS unit would be in the noise. I think the main argument for WWVB receivers vs GPS receivers would be cost. In either case, you have to get the antenna outside the metal enclosure and that may be the major cost. (I suppose a sprinkler controller could be mounted in a plastic enclosure.) school crossing signs is another possibility. In the last year or two, I've seen several setups around here that have solar powered LEDs mounted at street level at pedestrian crossings. They are great at night but not so great during the day. (But during the day the pedestrians are easier to see.) -- These are my opinions. I hate spam. ___ 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] Phase modulation detection/NIST plan
Hi: The key thing GPS is lacking is Daylight Savings Time. WWV WWVB have the DST bits that allow a clock to show the local time. Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Phase modulation detection/NIST plan
On Fri, Jul 13, 2012 at 09:47:12PM -0700, Brooke Clarke wrote: Hi: The key thing GPS is lacking is Daylight Savings Time. WWV WWVB have the DST bits that allow a clock to show the local time. And that is important for most routine civil human use. Nor something that could somehow be added to GPS which is worldwide in scope without adding lots of message information and dealing with all the crazyness of international time zones and political jurisdictions. WWVB serves the US (and maybe Canada) where DST start and end is pretty much global. Besides the costs greatly favor WWVB receivers... as the authors of the paper point out their whole decoder would fit neatly in a tiny corner of the silicon of a typical SOC chip these days... and AFAIK there is no practical current way to do this with GPS. And while it is true that good Faraday cages like metal enclosures with tight seals kill the LF, a good sized bush might take out GPS and won't impact LF reception, which also works pretty well inside many buildings and in particular common wood frame houses unlike GPS. Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ 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] Phase modulation detection/NIST plan
I received the following message from John Lowe at NIST. I thought it might be of interest to you. -Original Message- From: John Lowe [mailto:l...@boulder.nist.gov] Sent: Monday, July 09, 2012 12:55 PM To: Ron Ward Subject: Re: Phase-locking 60 kHz timing and frequency standard receivers We are changing the format to improve our reception capability. Frequency standard comparisons will still be possible with new or modified equipment. On 7/5/2012 9:39 AM, Ron Ward wrote: Hi John: Why is WWVB changing to BPSK? For cheaper clocks? What about frequency standard comparisons with WWVB? How am I going to monitor GPS and ensure that it's working correctly and not being played with by DOD? What am I going to do with our phase-locking 60 kHz timing and frequency standard receivers? Why did you not make the new data format backward compatible with existing phase-locking 60 kHz timing and frequency standard receivers, like they did with black and white to color TV transition in the 1950's? What about +- 45 degree modulation? We use to have LORAN, OMEGA, and WWVB. Thanks, Ron -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of David I. Emery Sent: Friday, July 13, 2012 8:35 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Phase modulation detection/NIST plan On Sat, Jul 14, 2012 at 02:38:34AM +0200, Magnus Danielson wrote: I think the PTTI article isn't as much documentation as presentation of general principle, showing details more as to present how it can be done, but not necessarily guarantee it will be done that way. Knowing the synchronisation sequence, polarity should not be ambiguous. Also note that other data such as hours would be known from the AM signal, so we can reverse engineer it. A receiver knowing this sequence will either bootstrap from the AM or attempt straight lock. It's not too hard to build a maximum likelihood receiver for it. I read the article as not a definitive specification frozen in stone, but as a complete and relatively fully specified proposed design with perhaps some details subject to adjustment or revision. The question of absolute versus differential phase shift keying is, of course, rather fundamental to being able to decode the signal at one level but at another not terribly central to the core of the design for a coding and modulation scheme that works at much lower C/N levels than the AM version did while preserving the legacy AM and its coding for existing hardware. SOME place in the design of a differentially coded signal there has to be a decision whether or not to structure the data encoding so some specific bit (or more properly symbol) in each frame (or at least some known frames relative to the time of day) (in this case I mean 1 minute long TOD frame) is of a known absolute reference phase. If this is done than it becomes possible in a reasonable time to determine an absolute 60 KHz carrier phase after a fade, if it is not done and every single bit of data is not absolutely predictable (the current TOD coding would be absolutely predictable given knowledge of the time and date and of leap seconds and DST settings, but they make clear future extensions would probably not have this property as additional messages are added including emergency messages and the like which are never predictable) there is no way to reliably decide after a fade which phase is which as this depends on knowing the number of ones and zeros in all the frames transmitted since one last saw the signal, something that is in the general case impossible if the signal has faded and the bits were not observed. An absolute encoding has no ambiguity - if one knows the time of day within a second one knows the transmitted phase except for during bits that might vary with unknown data (eg emergency messages, extensions to the standard and newly changed DST and leap second settings and FEC bits based on them) and MOST bits are always known phases, especially of course the sync code words. So even with terribly poor C/N one should be able to relatively quickly resolve the phase ambiguity after a period of signal loss... and in many cases if one still has a good idea of the time, within a couple of seconds (symbols) of signal reacquisition. On another point, I am not of the school that providing much better weak signal performance for simple, low power, and cheap LF time of day clocks using WWVB is somehow a minor improvement that primarily benefits China because they make most cheap self setting atomic clocks. There are innumerable applications for low cost low power human level 1 second accurate time of day in modern electronic systems - examples are traffic lights and school crossing signs and water sprinklers and street lights and other outdoor lighting and many others
Re: [time-nuts] Phase modulation detection/NIST plan
David Read your comments and have been traveling. So finally a chance to email. I read the document also and walked away with what I shared. In your reading would you believe the following. Its an absolute phase and that when it switches to 0 there is 1 transition at the beginning of the second to 180 degrees staying that way to the next bit or flipping again to 0 degrees if its a 1 at the 1 sec tic??? Is there a way to sense from the document that there is a bias towards 0 lets say. I could not figure that out. What I have seen on the scope is that I believe a 0 could be multiple flips during the 0 bit and thats perplexing. Regards Paul. On 7/9/2012 1:53 AM, David I. Emery wrote: On Sun, Jul 08, 2012 at 09:02:53PM -0400, Bob Camp wrote: Hi The gotcha is that they may change the sync word based on test data. They may also tweak other vague points in the spec based on the troubles they run into in their tests or with their silicon. I finally read the wwvb.pdf paper (yes, do so before opening mouth)... I think I read the Binary Phase Shift Keying Modulation paragraph on page 10 to indicate they are using ABSOLUTE, not differential BPSK. They refer to the baseband waveforms s0(t) and s1(t). To me this is the absolute I vector... and this clearly says that a 0 is always upward (or by convention in phase), and a one is always downward (180 out)... They clearly say the phase shift is 180 degrees... I would think this clearly could be phrased better... It appears the data format they propose is quite well defined in the paper, though they clearly indicate that a proposed extension is changing the barker code sync word for frames every so often so as to indicate a different frame type that might contain highly entropic (eg volatile and unpredictable) information of undefined character including a possible mechanism for sending arbitrary and completely apriori unpredictable bitstreams, though doubtless constrained by the hamming codes used for FEC/error detection and the barker code sync word. On a quick read it appears the complete 60 second time frame format is defined unambiguously. There are somewhat unpredictable DST bits and leap second bits in there... but in practice those change VERY infrequently from 60 second frame to frame or even from week to week or year to year. (Yes Congress likes to muck with DST every decade or so...). I am still reading more carefully, but I think this means that the entire phase and amplitude sequence of the signal is defined for the current initial version if you know the time of day and date and the current leap second and DST settings (which change VERY infrequently). And I *THINK* I understand this means the absolute phase sequence relative to the 60 KHz going into the modulator at the transmitter Thus the initial signal phase modulation could be removed by some comparatively simple itty bitty microp software driving a balanced modulator BUT future signal extensions might not have that property. As for acquiring bit sync with the signal, both the amplitude and phase information should allow a micro to do this easily and relatively quickly if the I vector were provided to the micro somehow. This would presumably be possible by either sampling the 60 KHz directly with an A/D (at 240 Ksample/sec) or by using an external balanced mixer driven by local synthesized 60 KHz. Even just an envelope detector would work with strong signals because of the AM component, and this might be enough to acquire adequate bit sync for some purposes. Software PLLs at 1 second rate are duck soup for even a SLOW micro... and frequency errors are tiny so tracking can be tight. And acquisition for these is also very fast given reasonable SNR. Only takes forever if SNR is so low it takes that many seconds correlation to see a reliable tick. I admit as I think about this that if one synthesized the clock for a itty bitty simple micro from say a local DUT 10 MHz whose phase relative to WWVB one is monitoring one could do much of the entire job by using programmable timers on the micro and its internal A/D. This includes phase error versus WWVB output and of course TOD output. One would almost certainly want to either use external balanced mixers (FET switches ?) and produce an analog I and Q (low pass filtered) for processing by a really slow micro or use a fast enough one to take a stream of actual real 60 KHz input samples at 240 KHz and compute filtered I and Q) (and LP filter/decimate it) (yes, with accurate A/D clocking from suitable microp output pin interval timers you might well be able to subsample by a lot and not actually ever deal with even any close to a 240 KHz sample stream with the micro). This would of course allow computation of the vector positions of the WWVB signal modulation in I and Q space relative to the 10 MHz clock from the
Re: [time-nuts] Phase modulation detection/NIST plan
David Read your comments and have been traveling. So finally a chance to email. I read the document also and walked away with what I shared. In your reading would you believe the following. Its an absolute phase and that when it switches to 0 there is 1 transition at the beginning of the second to 180 degrees staying that way to the next bit or flipping again to 0 degrees if its a 1 at the 1 sec tic??? Is there a way to sense from the document that there is a bias towards 0 lets say. I could not figure that out. Regards Paul. On 7/9/2012 1:53 AM, David I. Emery wrote: On Sun, Jul 08, 2012 at 09:02:53PM -0400, Bob Camp wrote: Hi The gotcha is that they may change the sync word based on test data. They may also tweak other vague points in the spec based on the troubles they run into in their tests or with their silicon. I finally read the wwvb.pdf paper (yes, do so before opening mouth)... I think I read the Binary Phase Shift Keying Modulation paragraph on page 10 to indicate they are using ABSOLUTE, not differential BPSK. They refer to the baseband waveforms s0(t) and s1(t). To me this is the absolute I vector... and this clearly says that a 0 is always upward (or by convention in phase), and a one is always downward (180 out)... They clearly say the phase shift is 180 degrees... I would think this clearly could be phrased better... It appears the data format they propose is quite well defined in the paper, though they clearly indicate that a proposed extension is changing the barker code sync word for frames every so often so as to indicate a different frame type that might contain highly entropic (eg volatile and unpredictable) information of undefined character including a possible mechanism for sending arbitrary and completely apriori unpredictable bitstreams, though doubtless constrained by the hamming codes used for FEC/error detection and the barker code sync word. On a quick read it appears the complete 60 second time frame format is defined unambiguously. There are somewhat unpredictable DST bits and leap second bits in there... but in practice those change VERY infrequently from 60 second frame to frame or even from week to week or year to year. (Yes Congress likes to muck with DST every decade or so...). I am still reading more carefully, but I think this means that the entire phase and amplitude sequence of the signal is defined for the current initial version if you know the time of day and date and the current leap second and DST settings (which change VERY infrequently). And I *THINK* I understand this means the absolute phase sequence relative to the 60 KHz going into the modulator at the transmitter Thus the initial signal phase modulation could be removed by some comparatively simple itty bitty microp software driving a balanced modulator BUT future signal extensions might not have that property. As for acquiring bit sync with the signal, both the amplitude and phase information should allow a micro to do this easily and relatively quickly if the I vector were provided to the micro somehow. This would presumably be possible by either sampling the 60 KHz directly with an A/D (at 240 Ksample/sec) or by using an external balanced mixer driven by local synthesized 60 KHz. Even just an envelope detector would work with strong signals because of the AM component, and this might be enough to acquire adequate bit sync for some purposes. Software PLLs at 1 second rate are duck soup for even a SLOW micro... and frequency errors are tiny so tracking can be tight. And acquisition for these is also very fast given reasonable SNR. Only takes forever if SNR is so low it takes that many seconds correlation to see a reliable tick. I admit as I think about this that if one synthesized the clock for a itty bitty simple micro from say a local DUT 10 MHz whose phase relative to WWVB one is monitoring one could do much of the entire job by using programmable timers on the micro and its internal A/D. This includes phase error versus WWVB output and of course TOD output. One would almost certainly want to either use external balanced mixers (FET switches ?) and produce an analog I and Q (low pass filtered) for processing by a really slow micro or use a fast enough one to take a stream of actual real 60 KHz input samples at 240 KHz and compute filtered I and Q) (and LP filter/decimate it) (yes, with accurate A/D clocking from suitable microp output pin interval timers you might well be able to subsample by a lot and not actually ever deal with even any close to a 240 KHz sample stream with the micro). This would of course allow computation of the vector positions of the WWVB signal modulation in I and Q space relative to the 10 MHz clock from the DUT. And from that one should be able to compute the various moments of 10 MHz DUT clock drift and do a decent job of
Re: [time-nuts] Phase modulation detection/NIST plan
There is an advantage to BPSK switching at the zero crossings in that the spectrum is significantly narrowed. -John == Could not the phase modulation be made +/-90 degrees, with the appropriate number of stuff bits being added so that the average phase remains constant? Would the older receivers simply average out the phase variation over a longer period? David GM8ARV -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] Phase modulation detection/NIST plan
HI My assumption is that for what we would be doing, one lock is all it's going to take. The local clock will be good enough to allow you to never need to re-aquire. You will indeed steer to maintain phase, but you already have and know what's coming in on the modulation. Bob On Jul 8, 2012, at 9:16 PM, J. Forster wrote: If you have a deep fade every few hours or minutes, as is common, relock time becomes an issue. -John == Hi The clocks we would be using are *much* better than what most military systems use…. I also *assume* that an initial lock up that takes a hour is perfectly acceptable in this application. You will still need a lot of hours / days / what ever of data to get useful stability off of WWVB, spending an hour or more to acquire from a cold start will have little net impact. Bob On Jul 8, 2012, at 7:29 PM, J. Forster wrote: A risky assumption, and a cold start could be tricky. Equatorial took many minutes to lock up, with a much higher data rate, and it did it by slowly sweeping the local clock. Aside: That's why military spread spectrum systems like good local clocks. They lock up a whole lot faster that way. -John Hi In this case the data format and it's contents are highly computable. If you have a good local clock *and* an initial lock, the rest of what follows is predictable. That of course assumes we know the real format …. Bob On Jul 8, 2012, at 6:58 PM, J. Forster wrote: Hi Peter, That's be the hard way, but yes, if the message BPSK coded is computable and of a known format. If the message contained more than time, like solar flux, it gets more complicated very rapidly. A similar thing was done with the Equatorial system 30+ years ago. In that case, each data bit was broken into something like 32 or 64 chips (I don't remember). There were two maximally distant, orthogonal chip patterns, representing 1 and 0. The incoming BPSK message went through a 0 or 180 degree switch, then the IF stages. The switch was driven from a local (known pattern) chip generator, so that if everything was synced up the narrow band IF would put out the 0 or 1 that had been encoded. BTW, this trick vastly improved the system S/N becaust it narrowed the receiver IF bandwidth many times. If the chip pattern is not known (fixed) or computable (like a correct TOD) things go to pot quickly. Rather than building such a kludge, it would be easier to use the locked clock in a newly designed receiver and phase compare that to your local standard directly. -John == Any possibility of using the decoded signal to un-do the modulation and feed the reconstituted signal to the older receiver? On 7/8/2012 12:56 PM, paul wrote: Ei Sorry if I have your name reversed. By taking this approach it eliminates the ability to use wwvb as a frequency reference because it destroys that traceability. Thats what we are trying to preserve. Or at least re-establish for the older phase measuring receivers. Regards Paul On 7/8/2012 12:10 PM, Tofurk Ei wrote: If the changeover you are talking about is this one: http://www.nist.gov/pml/newsletter/radio.cfm as a proof of concept a DVB-T dongle/upconverter combo could almost certainly handle PM easily to output whatever it encodes, when paired with gnuradio.. The RTL2832U chip might also be able to handle some low band signals directly, using direct sampling. No upconverter. Regardless, then the data would be fed into gnuradio - the gnuradio developers GUI is called gnuradio companion It has a nifty way of doing this kind of thing, one builds a flow graph where the actual demodulation is simply laid out graphically and tested. When everything works to one's satisfaction the file is saved and it gets compiled - then it can run - its basically a python script. If the modulation scheme is public, I think you can be almost certain that gnuradio might be quite useful to rapidly design a tool to demodulate it. Perhaps very quickly. For the money, one really couldn't hope to beat the flexibility of this combination in any other manner. If I were interested in trying this I would join the gnuradio mailing list and ask there. Perhaps the answer is surprisingly simple. ___ 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
Re: [time-nuts] Phase modulation detection/NIST plan
On 07/09/2012 03:32 AM, Bob Camp wrote: HI My assumption is that for what we would be doing, one lock is all it's going to take. The local clock will be good enough to allow you to never need to re-aquire. You will indeed steer to maintain phase, but you already have and know what's coming in on the modulation. Except for leap second announcements. Another thing is to monitor for cycle-slips. 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.
Re: [time-nuts] Phase modulation detection/NIST plan
Hi Leap seconds may never happen if PHK gets things organized … :)… Cycle slips are the main thing you would be watching for. The slow steer to maintain synch is to catch or correct cycle slips. Bob On Jul 9, 2012, at 6:15 PM, Magnus Danielson wrote: On 07/09/2012 03:32 AM, Bob Camp wrote: HI My assumption is that for what we would be doing, one lock is all it's going to take. The local clock will be good enough to allow you to never need to re-aquire. You will indeed steer to maintain phase, but you already have and know what's coming in on the modulation. Except for leap second announcements. Another thing is to monitor for cycle-slips. 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] Phase modulation detection/NIST plan
Ei Sorry if I have your name reversed. By taking this approach it eliminates the ability to use wwvb as a frequency reference because it destroys that traceability. Thats what we are trying to preserve. Or at least re-establish for the older phase measuring receivers. Regards Paul On 7/8/2012 12:10 PM, Tofurk Ei wrote: If the changeover you are talking about is this one: http://www.nist.gov/pml/newsletter/radio.cfm as a proof of concept a DVB-T dongle/upconverter combo could almost certainly handle PM easily to output whatever it encodes, when paired with gnuradio.. The RTL2832U chip might also be able to handle some low band signals directly, using direct sampling. No upconverter. Regardless, then the data would be fed into gnuradio - the gnuradio developers GUI is called gnuradio companion It has a nifty way of doing this kind of thing, one builds a flow graph where the actual demodulation is simply laid out graphically and tested. When everything works to one's satisfaction the file is saved and it gets compiled - then it can run - its basically a python script. If the modulation scheme is public, I think you can be almost certain that gnuradio might be quite useful to rapidly design a tool to demodulate it. Perhaps very quickly. For the money, one really couldn't hope to beat the flexibility of this combination in any other manner. If I were interested in trying this I would join the gnuradio mailing list and ask there. Perhaps the answer is surprisingly simple. ___ 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] Phase modulation detection/NIST plan
Any possibility of using the decoded signal to un-do the modulation and feed the reconstituted signal to the older receiver? On 7/8/2012 12:56 PM, paul wrote: Ei Sorry if I have your name reversed. By taking this approach it eliminates the ability to use wwvb as a frequency reference because it destroys that traceability. Thats what we are trying to preserve. Or at least re-establish for the older phase measuring receivers. Regards Paul On 7/8/2012 12:10 PM, Tofurk Ei wrote: If the changeover you are talking about is this one: http://www.nist.gov/pml/newsletter/radio.cfm as a proof of concept a DVB-T dongle/upconverter combo could almost certainly handle PM easily to output whatever it encodes, when paired with gnuradio.. The RTL2832U chip might also be able to handle some low band signals directly, using direct sampling. No upconverter. Regardless, then the data would be fed into gnuradio - the gnuradio developers GUI is called gnuradio companion It has a nifty way of doing this kind of thing, one builds a flow graph where the actual demodulation is simply laid out graphically and tested. When everything works to one's satisfaction the file is saved and it gets compiled - then it can run - its basically a python script. If the modulation scheme is public, I think you can be almost certain that gnuradio might be quite useful to rapidly design a tool to demodulate it. Perhaps very quickly. For the money, one really couldn't hope to beat the flexibility of this combination in any other manner. If I were interested in trying this I would join the gnuradio mailing list and ask there. Perhaps the answer is surprisingly simple. ___ 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] Phase modulation detection/NIST plan
Peter indeed there could be But it should not need to be decoded to undo the psk. Plus documentation lacks some of the details I think to actually do it. But that would be a significant project since the formats not been settled completely yet. Regards Paul. On 7/8/2012 6:40 PM, Peter Gottlieb wrote: Any possibility of using the decoded signal to un-do the modulation and feed the reconstituted signal to the older receiver? On 7/8/2012 12:56 PM, paul wrote: Ei Sorry if I have your name reversed. By taking this approach it eliminates the ability to use wwvb as a frequency reference because it destroys that traceability. Thats what we are trying to preserve. Or at least re-establish for the older phase measuring receivers. Regards Paul On 7/8/2012 12:10 PM, Tofurk Ei wrote: If the changeover you are talking about is this one: http://www.nist.gov/pml/newsletter/radio.cfm as a proof of concept a DVB-T dongle/upconverter combo could almost certainly handle PM easily to output whatever it encodes, when paired with gnuradio.. The RTL2832U chip might also be able to handle some low band signals directly, using direct sampling. No upconverter. Regardless, then the data would be fed into gnuradio - the gnuradio developers GUI is called gnuradio companion It has a nifty way of doing this kind of thing, one builds a flow graph where the actual demodulation is simply laid out graphically and tested. When everything works to one's satisfaction the file is saved and it gets compiled - then it can run - its basically a python script. If the modulation scheme is public, I think you can be almost certain that gnuradio might be quite useful to rapidly design a tool to demodulate it. Perhaps very quickly. For the money, one really couldn't hope to beat the flexibility of this combination in any other manner. If I were interested in trying this I would join the gnuradio mailing list and ask there. Perhaps the answer is surprisingly simple. ___ 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. ___ 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] Phase modulation detection/NIST plan
Hi Peter, That's be the hard way, but yes, if the message BPSK coded is computable and of a known format. If the message contained more than time, like solar flux, it gets more complicated very rapidly. A similar thing was done with the Equatorial system 30+ years ago. In that case, each data bit was broken into something like 32 or 64 chips (I don't remember). There were two maximally distant, orthogonal chip patterns, representing 1 and 0. The incoming BPSK message went through a 0 or 180 degree switch, then the IF stages. The switch was driven from a local (known pattern) chip generator, so that if everything was synced up the narrow band IF would put out the 0 or 1 that had been encoded. BTW, this trick vastly improved the system S/N becaust it narrowed the receiver IF bandwidth many times. If the chip pattern is not known (fixed) or computable (like a correct TOD) things go to pot quickly. Rather than building such a kludge, it would be easier to use the locked clock in a newly designed receiver and phase compare that to your local standard directly. -John == Any possibility of using the decoded signal to un-do the modulation and feed the reconstituted signal to the older receiver? On 7/8/2012 12:56 PM, paul wrote: Ei Sorry if I have your name reversed. By taking this approach it eliminates the ability to use wwvb as a frequency reference because it destroys that traceability. Thats what we are trying to preserve. Or at least re-establish for the older phase measuring receivers. Regards Paul On 7/8/2012 12:10 PM, Tofurk Ei wrote: If the changeover you are talking about is this one: http://www.nist.gov/pml/newsletter/radio.cfm as a proof of concept a DVB-T dongle/upconverter combo could almost certainly handle PM easily to output whatever it encodes, when paired with gnuradio.. The RTL2832U chip might also be able to handle some low band signals directly, using direct sampling. No upconverter. Regardless, then the data would be fed into gnuradio - the gnuradio developers GUI is called gnuradio companion It has a nifty way of doing this kind of thing, one builds a flow graph where the actual demodulation is simply laid out graphically and tested. When everything works to one's satisfaction the file is saved and it gets compiled - then it can run - its basically a python script. If the modulation scheme is public, I think you can be almost certain that gnuradio might be quite useful to rapidly design a tool to demodulate it. Perhaps very quickly. For the money, one really couldn't hope to beat the flexibility of this combination in any other manner. If I were interested in trying this I would join the gnuradio mailing list and ask there. Perhaps the answer is surprisingly simple. ___ 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. ___ 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] Phase modulation detection/NIST plan
Hi In this case the data format and it's contents are highly computable. If you have a good local clock *and* an initial lock, the rest of what follows is predictable. That of course assumes we know the real format …. Bob On Jul 8, 2012, at 6:58 PM, J. Forster wrote: Hi Peter, That's be the hard way, but yes, if the message BPSK coded is computable and of a known format. If the message contained more than time, like solar flux, it gets more complicated very rapidly. A similar thing was done with the Equatorial system 30+ years ago. In that case, each data bit was broken into something like 32 or 64 chips (I don't remember). There were two maximally distant, orthogonal chip patterns, representing 1 and 0. The incoming BPSK message went through a 0 or 180 degree switch, then the IF stages. The switch was driven from a local (known pattern) chip generator, so that if everything was synced up the narrow band IF would put out the 0 or 1 that had been encoded. BTW, this trick vastly improved the system S/N becaust it narrowed the receiver IF bandwidth many times. If the chip pattern is not known (fixed) or computable (like a correct TOD) things go to pot quickly. Rather than building such a kludge, it would be easier to use the locked clock in a newly designed receiver and phase compare that to your local standard directly. -John == Any possibility of using the decoded signal to un-do the modulation and feed the reconstituted signal to the older receiver? On 7/8/2012 12:56 PM, paul wrote: Ei Sorry if I have your name reversed. By taking this approach it eliminates the ability to use wwvb as a frequency reference because it destroys that traceability. Thats what we are trying to preserve. Or at least re-establish for the older phase measuring receivers. Regards Paul On 7/8/2012 12:10 PM, Tofurk Ei wrote: If the changeover you are talking about is this one: http://www.nist.gov/pml/newsletter/radio.cfm as a proof of concept a DVB-T dongle/upconverter combo could almost certainly handle PM easily to output whatever it encodes, when paired with gnuradio.. The RTL2832U chip might also be able to handle some low band signals directly, using direct sampling. No upconverter. Regardless, then the data would be fed into gnuradio - the gnuradio developers GUI is called gnuradio companion It has a nifty way of doing this kind of thing, one builds a flow graph where the actual demodulation is simply laid out graphically and tested. When everything works to one's satisfaction the file is saved and it gets compiled - then it can run - its basically a python script. If the modulation scheme is public, I think you can be almost certain that gnuradio might be quite useful to rapidly design a tool to demodulate it. Perhaps very quickly. For the money, one really couldn't hope to beat the flexibility of this combination in any other manner. If I were interested in trying this I would join the gnuradio mailing list and ask there. Perhaps the answer is surprisingly simple. ___ 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. ___ 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] Phase modulation detection/NIST plan
A risky assumption, and a cold start could be tricky. Equatorial took many minutes to lock up, with a much higher data rate, and it did it by slowly sweeping the local clock. Aside: That's why military spread spectrum systems like good local clocks. They lock up a whole lot faster that way. -John Hi In this case the data format and it's contents are highly computable. If you have a good local clock *and* an initial lock, the rest of what follows is predictable. That of course assumes we know the real format . Bob On Jul 8, 2012, at 6:58 PM, J. Forster wrote: Hi Peter, That's be the hard way, but yes, if the message BPSK coded is computable and of a known format. If the message contained more than time, like solar flux, it gets more complicated very rapidly. A similar thing was done with the Equatorial system 30+ years ago. In that case, each data bit was broken into something like 32 or 64 chips (I don't remember). There were two maximally distant, orthogonal chip patterns, representing 1 and 0. The incoming BPSK message went through a 0 or 180 degree switch, then the IF stages. The switch was driven from a local (known pattern) chip generator, so that if everything was synced up the narrow band IF would put out the 0 or 1 that had been encoded. BTW, this trick vastly improved the system S/N becaust it narrowed the receiver IF bandwidth many times. If the chip pattern is not known (fixed) or computable (like a correct TOD) things go to pot quickly. Rather than building such a kludge, it would be easier to use the locked clock in a newly designed receiver and phase compare that to your local standard directly. -John == Any possibility of using the decoded signal to un-do the modulation and feed the reconstituted signal to the older receiver? On 7/8/2012 12:56 PM, paul wrote: Ei Sorry if I have your name reversed. By taking this approach it eliminates the ability to use wwvb as a frequency reference because it destroys that traceability. Thats what we are trying to preserve. Or at least re-establish for the older phase measuring receivers. Regards Paul On 7/8/2012 12:10 PM, Tofurk Ei wrote: If the changeover you are talking about is this one: http://www.nist.gov/pml/newsletter/radio.cfm as a proof of concept a DVB-T dongle/upconverter combo could almost certainly handle PM easily to output whatever it encodes, when paired with gnuradio.. The RTL2832U chip might also be able to handle some low band signals directly, using direct sampling. No upconverter. Regardless, then the data would be fed into gnuradio - the gnuradio developers GUI is called gnuradio companion It has a nifty way of doing this kind of thing, one builds a flow graph where the actual demodulation is simply laid out graphically and tested. When everything works to one's satisfaction the file is saved and it gets compiled - then it can run - its basically a python script. If the modulation scheme is public, I think you can be almost certain that gnuradio might be quite useful to rapidly design a tool to demodulate it. Perhaps very quickly. For the money, one really couldn't hope to beat the flexibility of this combination in any other manner. If I were interested in trying this I would join the gnuradio mailing list and ask there. Perhaps the answer is surprisingly simple. ___ 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. ___ 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] Phase modulation detection/NIST plan
On 07/09/2012 12:46 AM, paul wrote: Peter indeed there could be But it should not need to be decoded to undo the psk. Plus documentation lacks some of the details I think to actually do it. But that would be a significant project since the formats not been settled completely yet. I have looked at the PTTI 2011 paper (wwvb.pdf) and much of a format is being shown. Has anyone established the 14 bit sync-word and verified the format? It seems that aligning up with the normal AM broadcast should be possible. Can someone record it as it has been reduced to say 2 kHz and analyze the produced audio file? Recoding with 48 kHz sampling rate should allow almost trivial 2 kHz I-Q demodulation to illustrate phase swaps. 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.
Re: [time-nuts] Phase modulation detection/NIST plan
Ei Sorry if I have your name reversed. By taking this approach it eliminates the ability to use wwvb as a frequency reference because it destroys that traceability. Thats what we are trying to preserve. Or at least re-establish for the older phase measuring receivers. Regards Paul Are you getting at something along the lines of everything about the old system is a known quantity, and any error is just going to creep in at one point..the accuracy is easy to maintain using that system? The accuracy of the crystals on these cheap SDRs is terrible because temperature variations are severe in those little dongles as they warm up. Once their temps stabilize, most people use their drivers to enter in a ppm value that cancels the error out somewhat. Uncorrected the inaccuracy typically ranges from a few khz at 60 MHz to 40 or 50 KHz or more at 2200 Mhz. Also the dongles vary in the range of frequencies they can tune. Some of them will go, as I said, as high as 2207-2210 MHz. They don't cover the HF bands out of the box, but a few months back some adventurous people discovered that by feeding a HF signal directly into the RTL2832, bypassing the tuner chip, they can be made to tune the HF bands - at what is described as enough sensitivity to listen to shortwave, hams using SSB and CW. They can also be made to tune below the AM band, somehow. Its possible they could be modified with off the shelf parts to have quite respectable sensitivity and selectivity, even though they were not made to tune those bands.. Nobody with any decent test equipment has characterized this direct sampling mode's performance because most of the people who are playing with them simply don't have the equipment to aspire to such things.. but the fact seems striking to me that here is a device which until quite recently could be found for under $20 in retail environments that with quite minimal modifications could quite possibly function as both a multimode communications receiver over a very large chunk of the spectrum, sucking down up approximately a 2.6 to 3.2 MHz slice of spectrum at a time, or alternatively could function as a sort of poor mans spectrum analyzer.. Throw in the ability to use gnuradio which is a very sophisticated set of tools for communications engineering, and you have a situation where, since the cost of entry is so low, its not so unreasonable to devote some time to trying to grok some radio scheme and work with it to see what can be done. Digital radios are no less capable than analog radios, nor are the results achieved with them any less capable of being accurate. All the sources of error are quantifiable and probably those dongles are a situation where a small investment in replacing the crystal with a TCXO, air cooling or basic thermal management, calibration, etc, might pay off big in results very quickly. Already people are doing the kind of things that people do with expensive equipment with them, not $20 toys. So, there are just a load of possibilities with them. A way to see if this NIST format could be worked with would be to save a capture file of the broadcast signal to disk and then it would be possible to work with that offline later in gnuradio even when the transmitter was not broadcasting that kind of modulation. Its surprising that this broadcasting format has not been published as an open spec. Thats a whole other (important) issue right there. Anyway, I saw the discussion about this changeover and I thought the idea might seem like a crazy one but I think it could potentially work and keep the cost low. If these other issues could be dealt with. But I think they might be straightforward to deal with for you guys as its your area of expertise. When you have one of these finger-sized little things in your hand and you are fooling around with it, its pretty amazing. I say that as somebody who has been into radio ever since I was a very little kid. I am hard to impress with technology.. and this was pretty awesome. The misgivings were expressed in one of the earlier posts that this changeover was proceeding too rapidly and fears that technically it could create a captive market - Just like with the breakup of Ma Bell, competition is good.. and having some other options close at hand would keep everything more honest. (Unrelated, Just curious, did any of you guys ever live in Tarrytown NY?) Tofurk ___ 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] Phase modulation detection/NIST plan
Hi The clocks we would be using are *much* better than what most military systems use…. I also *assume* that an initial lock up that takes a hour is perfectly acceptable in this application. You will still need a lot of hours / days / what ever of data to get useful stability off of WWVB, spending an hour or more to acquire from a cold start will have little net impact. Bob On Jul 8, 2012, at 7:29 PM, J. Forster wrote: A risky assumption, and a cold start could be tricky. Equatorial took many minutes to lock up, with a much higher data rate, and it did it by slowly sweeping the local clock. Aside: That's why military spread spectrum systems like good local clocks. They lock up a whole lot faster that way. -John Hi In this case the data format and it's contents are highly computable. If you have a good local clock *and* an initial lock, the rest of what follows is predictable. That of course assumes we know the real format …. Bob On Jul 8, 2012, at 6:58 PM, J. Forster wrote: Hi Peter, That's be the hard way, but yes, if the message BPSK coded is computable and of a known format. If the message contained more than time, like solar flux, it gets more complicated very rapidly. A similar thing was done with the Equatorial system 30+ years ago. In that case, each data bit was broken into something like 32 or 64 chips (I don't remember). There were two maximally distant, orthogonal chip patterns, representing 1 and 0. The incoming BPSK message went through a 0 or 180 degree switch, then the IF stages. The switch was driven from a local (known pattern) chip generator, so that if everything was synced up the narrow band IF would put out the 0 or 1 that had been encoded. BTW, this trick vastly improved the system S/N becaust it narrowed the receiver IF bandwidth many times. If the chip pattern is not known (fixed) or computable (like a correct TOD) things go to pot quickly. Rather than building such a kludge, it would be easier to use the locked clock in a newly designed receiver and phase compare that to your local standard directly. -John == Any possibility of using the decoded signal to un-do the modulation and feed the reconstituted signal to the older receiver? On 7/8/2012 12:56 PM, paul wrote: Ei Sorry if I have your name reversed. By taking this approach it eliminates the ability to use wwvb as a frequency reference because it destroys that traceability. Thats what we are trying to preserve. Or at least re-establish for the older phase measuring receivers. Regards Paul On 7/8/2012 12:10 PM, Tofurk Ei wrote: If the changeover you are talking about is this one: http://www.nist.gov/pml/newsletter/radio.cfm as a proof of concept a DVB-T dongle/upconverter combo could almost certainly handle PM easily to output whatever it encodes, when paired with gnuradio.. The RTL2832U chip might also be able to handle some low band signals directly, using direct sampling. No upconverter. Regardless, then the data would be fed into gnuradio - the gnuradio developers GUI is called gnuradio companion It has a nifty way of doing this kind of thing, one builds a flow graph where the actual demodulation is simply laid out graphically and tested. When everything works to one's satisfaction the file is saved and it gets compiled - then it can run - its basically a python script. If the modulation scheme is public, I think you can be almost certain that gnuradio might be quite useful to rapidly design a tool to demodulate it. Perhaps very quickly. For the money, one really couldn't hope to beat the flexibility of this combination in any other manner. If I were interested in trying this I would join the gnuradio mailing list and ask there. Perhaps the answer is surprisingly simple. ___ 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. ___ 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] Phase modulation detection/NIST plan
Hi The gotcha is that they may change the sync word based on test data. They may also tweak other vague points in the spec based on the troubles they run into in their tests or with their silicon. Bob On Jul 8, 2012, at 8:07 PM, Magnus Danielson wrote: On 07/09/2012 12:46 AM, paul wrote: Peter indeed there could be But it should not need to be decoded to undo the psk. Plus documentation lacks some of the details I think to actually do it. But that would be a significant project since the formats not been settled completely yet. I have looked at the PTTI 2011 paper (wwvb.pdf) and much of a format is being shown. Has anyone established the 14 bit sync-word and verified the format? It seems that aligning up with the normal AM broadcast should be possible. Can someone record it as it has been reduced to say 2 kHz and analyze the produced audio file? Recoding with 48 kHz sampling rate should allow almost trivial 2 kHz I-Q demodulation to illustrate phase swaps. 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] Phase modulation detection/NIST plan
If you have a deep fade every few hours or minutes, as is common, relock time becomes an issue. -John == Hi The clocks we would be using are *much* better than what most military systems use . I also *assume* that an initial lock up that takes a hour is perfectly acceptable in this application. You will still need a lot of hours / days / what ever of data to get useful stability off of WWVB, spending an hour or more to acquire from a cold start will have little net impact. Bob On Jul 8, 2012, at 7:29 PM, J. Forster wrote: A risky assumption, and a cold start could be tricky. Equatorial took many minutes to lock up, with a much higher data rate, and it did it by slowly sweeping the local clock. Aside: That's why military spread spectrum systems like good local clocks. They lock up a whole lot faster that way. -John Hi In this case the data format and it's contents are highly computable. If you have a good local clock *and* an initial lock, the rest of what follows is predictable. That of course assumes we know the real format . Bob On Jul 8, 2012, at 6:58 PM, J. Forster wrote: Hi Peter, That's be the hard way, but yes, if the message BPSK coded is computable and of a known format. If the message contained more than time, like solar flux, it gets more complicated very rapidly. A similar thing was done with the Equatorial system 30+ years ago. In that case, each data bit was broken into something like 32 or 64 chips (I don't remember). There were two maximally distant, orthogonal chip patterns, representing 1 and 0. The incoming BPSK message went through a 0 or 180 degree switch, then the IF stages. The switch was driven from a local (known pattern) chip generator, so that if everything was synced up the narrow band IF would put out the 0 or 1 that had been encoded. BTW, this trick vastly improved the system S/N becaust it narrowed the receiver IF bandwidth many times. If the chip pattern is not known (fixed) or computable (like a correct TOD) things go to pot quickly. Rather than building such a kludge, it would be easier to use the locked clock in a newly designed receiver and phase compare that to your local standard directly. -John == Any possibility of using the decoded signal to un-do the modulation and feed the reconstituted signal to the older receiver? On 7/8/2012 12:56 PM, paul wrote: Ei Sorry if I have your name reversed. By taking this approach it eliminates the ability to use wwvb as a frequency reference because it destroys that traceability. Thats what we are trying to preserve. Or at least re-establish for the older phase measuring receivers. Regards Paul On 7/8/2012 12:10 PM, Tofurk Ei wrote: If the changeover you are talking about is this one: http://www.nist.gov/pml/newsletter/radio.cfm as a proof of concept a DVB-T dongle/upconverter combo could almost certainly handle PM easily to output whatever it encodes, when paired with gnuradio.. The RTL2832U chip might also be able to handle some low band signals directly, using direct sampling. No upconverter. Regardless, then the data would be fed into gnuradio - the gnuradio developers GUI is called gnuradio companion It has a nifty way of doing this kind of thing, one builds a flow graph where the actual demodulation is simply laid out graphically and tested. When everything works to one's satisfaction the file is saved and it gets compiled - then it can run - its basically a python script. If the modulation scheme is public, I think you can be almost certain that gnuradio might be quite useful to rapidly design a tool to demodulate it. Perhaps very quickly. For the money, one really couldn't hope to beat the flexibility of this combination in any other manner. If I were interested in trying this I would join the gnuradio mailing list and ask there. Perhaps the answer is surprisingly simple. ___ 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. ___ 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
Re: [time-nuts] Phase modulation detection/NIST plan
There is not an infinity of good sync words. A typical good sync word has a high positive autocorrelation when synced, sloping downwards monotonically. Thus the cross-correlation of the received word with a locally stored reference can be used to steer the loop using a small dither and a lock-in technique. -John Hi The gotcha is that they may change the sync word based on test data. They may also tweak other vague points in the spec based on the troubles they run into in their tests or with their silicon. Bob On Jul 8, 2012, at 8:07 PM, Magnus Danielson wrote: On 07/09/2012 12:46 AM, paul wrote: Peter indeed there could be But it should not need to be decoded to undo the psk. Plus documentation lacks some of the details I think to actually do it. But that would be a significant project since the formats not been settled completely yet. I have looked at the PTTI 2011 paper (wwvb.pdf) and much of a format is being shown. Has anyone established the 14 bit sync-word and verified the format? It seems that aligning up with the normal AM broadcast should be possible. Can someone record it as it has been reduced to say 2 kHz and analyze the produced audio file? Recoding with 48 kHz sampling rate should allow almost trivial 2 kHz I-Q demodulation to illustrate phase swaps. 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. ___ 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] Phase modulation detection/NIST plan
Could not the phase modulation be made +/-90 degrees, with the appropriate number of stuff bits being added so that the average phase remains constant? Would the older receivers simply average out the phase variation over a longer period? David GM8ARV -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] Phase modulation detection/NIST plan
On Sun, Jul 08, 2012 at 09:02:53PM -0400, Bob Camp wrote: Hi The gotcha is that they may change the sync word based on test data. They may also tweak other vague points in the spec based on the troubles they run into in their tests or with their silicon. I finally read the wwvb.pdf paper (yes, do so before opening mouth)... I think I read the Binary Phase Shift Keying Modulation paragraph on page 10 to indicate they are using ABSOLUTE, not differential BPSK. They refer to the baseband waveforms s0(t) and s1(t). To me this is the absolute I vector... and this clearly says that a 0 is always upward (or by convention in phase), and a one is always downward (180 out)... They clearly say the phase shift is 180 degrees... I would think this clearly could be phrased better... It appears the data format they propose is quite well defined in the paper, though they clearly indicate that a proposed extension is changing the barker code sync word for frames every so often so as to indicate a different frame type that might contain highly entropic (eg volatile and unpredictable) information of undefined character including a possible mechanism for sending arbitrary and completely apriori unpredictable bitstreams, though doubtless constrained by the hamming codes used for FEC/error detection and the barker code sync word. On a quick read it appears the complete 60 second time frame format is defined unambiguously. There are somewhat unpredictable DST bits and leap second bits in there... but in practice those change VERY infrequently from 60 second frame to frame or even from week to week or year to year. (Yes Congress likes to muck with DST every decade or so...). I am still reading more carefully, but I think this means that the entire phase and amplitude sequence of the signal is defined for the current initial version if you know the time of day and date and the current leap second and DST settings (which change VERY infrequently). And I *THINK* I understand this means the absolute phase sequence relative to the 60 KHz going into the modulator at the transmitter Thus the initial signal phase modulation could be removed by some comparatively simple itty bitty microp software driving a balanced modulator BUT future signal extensions might not have that property. As for acquiring bit sync with the signal, both the amplitude and phase information should allow a micro to do this easily and relatively quickly if the I vector were provided to the micro somehow. This would presumably be possible by either sampling the 60 KHz directly with an A/D (at 240 Ksample/sec) or by using an external balanced mixer driven by local synthesized 60 KHz. Even just an envelope detector would work with strong signals because of the AM component, and this might be enough to acquire adequate bit sync for some purposes. Software PLLs at 1 second rate are duck soup for even a SLOW micro... and frequency errors are tiny so tracking can be tight. And acquisition for these is also very fast given reasonable SNR. Only takes forever if SNR is so low it takes that many seconds correlation to see a reliable tick. I admit as I think about this that if one synthesized the clock for a itty bitty simple micro from say a local DUT 10 MHz whose phase relative to WWVB one is monitoring one could do much of the entire job by using programmable timers on the micro and its internal A/D. This includes phase error versus WWVB output and of course TOD output. One would almost certainly want to either use external balanced mixers (FET switches ?) and produce an analog I and Q (low pass filtered) for processing by a really slow micro or use a fast enough one to take a stream of actual real 60 KHz input samples at 240 KHz and compute filtered I and Q) (and LP filter/decimate it) (yes, with accurate A/D clocking from suitable microp output pin interval timers you might well be able to subsample by a lot and not actually ever deal with even any close to a 240 KHz sample stream with the micro). This would of course allow computation of the vector positions of the WWVB signal modulation in I and Q space relative to the 10 MHz clock from the DUT. And from that one should be able to compute the various moments of 10 MHz DUT clock drift and do a decent job of compensating for it (better and better as the DUT clock gets more stable/predictable) and ride out fairly long fades and outages without losing a pretty good idea of the expected WWVB phase. Presumably most standards whose phase one is tracking with such setups are very stable, thus the holdover should be considerable if one uses a good error and drift estimate to adjust ones local idea of WWVB phase relative to local clock derived from the standard to compensate. And guess what, determining a local error and drift estimate is precisely what such a system
