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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#41
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LED alarm clocks all lose accuracy over time
Jim Yanik wrote in message
4... "Ian Field" wrote in : "gregz" wrote in message -september .org... "N_Cook" wrote: Bill Proms wrote in message ... I have 3 Intelli-Time LED alarm clocks around the house, just like the one he -- Jim Yanik jyanik at localnet dot com OT: Have you seen the recent thread on rec.antiques.radio+phono ? |
#42
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LED alarm clocks all lose accuracy over time
Heath had an FM tuner with direct frequency entry.
I never saw another for home use, but there may have been another for commercial use. Not quite correct. AFAIK, Heath made the world's first digitally tuned stereo FM tuner. The kit was appallingly expensive -- around $550 35+ years ago. It used little cards you notched for a particular station. I saw it at a hi-fi show, with the Heath rep explaining how you could use it to monitor the station's broadcast frequency. (In my best Menckenesque manner, I set him straight.) Tuners with direct frequency entry were and are uncommon, because it requires a keypad, plus a decoder to output the digital value needed to set the local oscillator. As the tuner would have a station memory anyway, which most people would use to store their favorite stations, direct entry has little advantage (except during initial setup). GE made at least two clock radios with direct entry. (Yes, I have one.) Because there's no overlap between AM and FM frequencies (in kHz and MHz), you didn't need to specify the band. Component tuners with direct entry are virtually unheard-of. Toshiba had one, I believe, and my Parasound T3 permits direct entry from the remote control. Does anyone know of any others? |
#43
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LED alarm clocks all lose accuracy over time
On Sun, 20 May 2012 00:41:44 -0700, isw wrote:
The 1pps output can be used to run a digital clock, but I would hate to see the final cost. Why use the 1 pps? Any cheap GPS you get on eBay will output NMEA "sentences" in ASCII that tell you the precise time. Just use those. The NEMA sentences are not synchronized to GPS time and add delays in the decoding process. The time might be off a fraction of a secod. However, using the NEMA sentence is probably adequate for a consumer alarm clock. $GPZDA give the time as: $--ZDA,hhmmss.ss,xx,xx,xxxx,xx,xx hhmmss.ss = UTC xx = Day, 01 to 31 xx = Month, 01 to 12 xxxx = Year xx = Local zone description, 00 to +/- 13 hours xx = Local zone minutes description (same sign as hours) The 1pps output has the advantage of simplicity and easy of integration with existing digital clock designs. Say, $15 for the GPS, another $15 for an Arduino, $5 for an LCD, and whatever crystal you have on hand, stuck in a home-made oven. Maybe another $20 for all the "glue", and the rest, as they say, is just software. The cheapest GPS board or module that I could find is about $40. http://www.sparkfun.com/categories/4?sort_by=price_asc&per_page=50 Chips seem to run about $8/1000. Using your prices, a commercial digital alarm clock product would retail about $175-$200. Meanwhile, WWVB controlled "atomic" alarm clocks are selling for $15. This one decodes NEMA sentences, and has some compromises due to running on battery power: http://www.siliconchip.com.au/cms/A_111192/article.html To conserve the battery, the GPS module is only used to synchronise the clock every 44 hours and following synchronisation, the clock will either skip seconds or double-step to reach the correct time. After synchronisation the microcontroller is also able to calculate the inherent inaccuracy of its crystal oscillator and will compensate by occasionally skipping or double-stepping a second. This process can also compensate for aging of the crystal and will keep the clock accurate between synchronisations. http://geoffg.net/GPS_Synchronised_Clock.html http://www.siliconchip.com.au/cms/gallery/article.html?a=111709 -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#44
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LED alarm clocks all lose accuracy over time
On Sun, 20 May 2012 00:32:56 -0700, isw wrote:
Incidentally, I'm building my own 10MHz GPSDO for running my test eqipment and ham junk. It's NOT a trivial or inexpensive exercise: http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm You can get short-term performance equal to a good crystal and long-term accuracy pert' near equal to the cesium beam clocks on the satellites for a whole lot less than that. Start with a 10 MHz rock in a home-brew oven, and divide it down to make a "regular clock". Compare the time given by that clock to GPS time, and twiddle the crystal oscillator to make it track, using a very long time constant filter in the loop. The longer it runs, the more accurate it gets. Good idea. However, if I'm going to go through the trouble of dividing down to 1pps (1Hz), I might as well add a FLL (frequency lock loop) and sync the oscillator a 1pps GPS reference. The regular clock idea also has a potential problem. One missed pulse and the clock is off by 1 full second. Since there's no way to detect a missing pulse, or recover gracefully from such a clock slip, it has the potential for going awry. After it's run for a while, you can do without GPS updates for fairly long periods (depending on how good your oscillator/oven is) with very little loss in accuracy. Maybe true, but I would have no easy way to determine if it needed to be resynced with the GPS clock. If it drifted off frequency for some reason, all my measurements would be off. Setting the frequency to 1*10^-11 takes days to set, and the same time to reset. Might as well leave it on all the time. In order to produce usable synchronization of simulcast data transmitters, the frequency accuracy and stability has to be 0.05ppm or (5*10^-8) for wide area coverage. That's not going to require a GPSDO but it would be nice. I've considered building that sort of rig where the oscillator's frequency is controlled by altering the temperature of the oven. Groan. Low noise oscillators use SC cut quartz crystals. That produces a rather steep frequency/temp curve at room temperature, but flattens out at about 80-100C. Vary the temperature around this flat part of the curve, and you'll see almost no change in frequency. Worse, it might go the wrong direction if it shows a peak or dip in the curve. http://www.conwin.com/pdfs/at_or_sc_for_ocxo.pdf Nice idea, but it will only work if you use an AT cut crystal and then only if you can deal with the dip in the curve. The big advantage of doing things that way is that there are no extra paths for noise to get into the oscillator, as there would be if you used some sort of variable capacitor. Good idea, but glass piston trimmers and varactor electronic tuning are usually good enough. Microphonics are the major danger of using trimmers. If the trimmer is solidly built, and the components are buried in RTV for shock proofing, it should be adequate. The 1/f phase noise of an oscillator is directly related to the power density of the device. That means using a moderately high current device at about 10% of its rated current. That's also why nobody uses low noise RF front end transistor for low noise oscillators. That leaves flicker noise, which reduced with lots of negative feedback. This should give you an idea of what commercial GPSDO oscillators are doing: http://www.leapsecond.com/pages/fury/phase.htm Check the Flexradio forum for what the SDR users are running. A GPSDO is preferred, but there are plenty of less accurate devices being used. The stock radio has a TCXO. The GPSDO upgrade costs $700. Little wonder users are looking at alternatives. http://cart.flexradio.com/FLEX-6000-GPSDO-Upgrade_p_899.html Incidentally, some data on the accuracy of the 60Hz power line frequency: http://www.leapsecond.com/pages/mains/ -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#45
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LED alarm clocks all lose accuracy over time
On Sun, 20 May 2012 00:13:49 -0700, isw wrote:
ALmost certainly a crystal; ceramic resonators have way too much drift with temperature. 32 KHz crystals are very difficult to trim because they don't like to have any extraneous capacitance hung on them. 32.768KHz crystals are somewhat of a special case when it comes to trimming. The problem is that the crystals are tuning forks, not bulk quartz devices like higher frequency devices. What's inside: http://en.wikipedia.org/wiki/File:Inside_QuartzCrystal-Tuningfork.jpg Typical specs are something like 7-12pF shunt capacitance. It is possible to trim the frequency with a variable capacitor that is centered around this capacitance. It's done all the time in electronic wrist watches. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#46
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LED alarm clocks all lose accuracy over time
gregz wrote:
"William Sommerwerck" wrote: Many years ago I reviewed Heath's "Most-Accurate Clock" for one of Ed Dell's magazines. It used the Bureau of Standards' shortwave time signals. Sync was a bit touchy (I eventually replaced the carbon calibration pots with ceramic), but it otherwise worked very well. It even had an interface that allowed your computer to reset its clock each time the machine restarted. When I needed money a few years back, I sold it on eBay for something like $400, without anyone questioning the price. If Heath wants to come back as a kit company, it needs to design products that have no commercial equivalents. Heath had an fm tuner with direct frequency entry push button. I never saw another for home use, but there may have been another or commercial use. I think it was GE that had an alarm clock like that in the late 70s. It was actually pretty cool. It had a little keypad on it. |
#47
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LED alarm clocks all lose accuracy over time
Jeff Liebermann wrote:
dark if the US pulls the plug on WWVH and WWVB. That's not going to happen. Quite the contrary, there are plans to add a US east coast transmitter. See: http://en.wikipedia.org/wiki/WWVB under "Service Improvement Plans". That's dead. What's left as of March 2012 is a plan to move from AM to BPSK, which is supposed to make it possible to receive the signal farther away and in areas with more noise and multipath distortion. There was a trial in early March, any see any results yet? How will this affect any old devices that use the AM signal method? Will someone be selling, as I proposed (and shouldda patented) devices that get the correct time via NTP and broadcast microwatt signals for local area time sync? Geoff. -- Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379 In 1969 the US could put a man on the moon, now teenagers just howl at it. :-( |
#48
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LED alarm clocks all lose accuracy over time
"Cydrome Leader" wrote in message ... gregz wrote: "William Sommerwerck" wrote: Many years ago I reviewed Heath's "Most-Accurate Clock" for one of Ed Dell's magazines. It used the Bureau of Standards' shortwave time signals. Sync was a bit touchy (I eventually replaced the carbon calibration pots with ceramic), but it otherwise worked very well. It even had an interface that allowed your computer to reset its clock each time the machine restarted. When I needed money a few years back, I sold it on eBay for something like $400, without anyone questioning the price. If Heath wants to come back as a kit company, it needs to design products that have no commercial equivalents. Heath had an fm tuner with direct frequency entry push button. I never saw another for home use, but there may have been another or commercial use. I think it was GE that had an alarm clock like that in the late 70s. It was actually pretty cool. It had a little keypad on it. About that era, Henry's radio had a batch of project pages in their catalogue - one of which was a digital clock. I started building it but never got around to finishing it. Usual excuses; can't afford the next lot of parts, by the time I got around to it the parts had become obsolete etc. The project was ongoing for many years and the parts added to it depended where I was working at the time! Pretty sure I still have the board in a tea chest at the back of the garage somewhere. |
#49
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LED alarm clocks all lose accuracy over time
I think it was GE that had an alarm clock like that
in the late 70s. It was actually pretty cool. It had a little keypad on it. I mentioned that in a preceding post. It was the 7-4760, I believe. I still have it. The keypad needed cleaning every couple of years. |
#50
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LED alarm clocks all lose accuracy over time
On Sun, 20 May 2012 18:34:03 +0000 (UTC), "Geoffrey S. Mendelson"
wrote: Jeff Liebermann wrote: dark if the US pulls the plug on WWVH and WWVB. That's not going to happen. Quite the contrary, there are plans to add a US east coast transmitter. See: http://en.wikipedia.org/wiki/WWVB under "Service Improvement Plans". That's dead. What's left as of March 2012 is a plan to move from AM to BPSK, which is supposed to make it possible to receive the signal farther away and in areas with more noise and multipath distortion. There was a trial in early March, any see any results yet? How will this affect any old devices that use the AM signal method? No. AM transmissions were to continue, alternating with phase shift modulation. http://www.jks.com/wwvb.pdf In an attempt to cost-effectively address the reception challenges, NIST is introducing a new protocol for the WWVB broadcast, which will preserve its amplitude modulation properties, in order to maintain backwards compatibility and not impact existing devices, while adding phase-modulation that would allow for the greatly improved performance. Some details on the test. I couldn't find any conclusions or official results: http://www.jks.com/wwvb/wwvb.html Will someone be selling, as I proposed (and shouldda patented) devices that get the correct time via NTP and broadcast microwatt signals for local area time sync? Good idea. I haven't seen any such device. Instead of broadcasting, this might be a good use for power line communications (HomePlug, X10, etc.) or RF (Z-wave). Incidentally, while broadcasters seem to be killing off their OTA time signals (used to set VCR clocks), the cable providers are using OOB (out of band) signaling to set the clock in their cable set top boxes. You could probably retransmit that data to a wall clock. If all else fails, you can call the NIST at 303-499-7111 for WWV and just play the time over a speaker. Yep, it works. Web clock: http://nist.time.gov It says accurate to 0.3 seconds. More on such clocks: http://www.precisionclock.com -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#51
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LED alarm clocks all lose accuracy over time
On 5/20/2012 9:45 AM, William Sommerwerck wrote:
Heath had an FM tuner with direct frequency entry. I never saw another for home use, but there may have been another for commercial use. Not quite correct. AFAIK, Heath made the world's first digitally tuned stereo FM tuner. The kit was appallingly expensive -- around $550 35+ years ago. It used little cards you notched for a particular station. I saw it at a hi-fi show, with the Heath rep explaining how you could use it to monitor the station's broadcast frequency. (In my best Menckenesque manner, I set him straight.) Tuners with direct frequency entry were and are uncommon, because it requires a keypad, plus a decoder to output the digital value needed to set the local oscillator. As the tuner would have a station memory anyway, which most people would use to store their favorite stations, direct entry has little advantage (except during initial setup). GE made at least two clock radios with direct entry. (Yes, I have one.) Because there's no overlap between AM and FM frequencies (in kHz and MHz), you didn't need to specify the band. Component tuners with direct entry are virtually unheard-of. Toshiba had one, I believe, and my Parasound T3 permits direct entry from the remote control. Does anyone know of any others? Dick Sequerra made one as I recall, and the RACAL, Rhode and Schwartz, and other surveillance receiver makers also had direct synthesis / tuning as well. |
#52
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LED alarm clocks all lose accuracy over time
William Sommerwerck wrote:
I think it was GE that had an alarm clock like that in the late 70s. It was actually pretty cool. It had a little keypad on it. I mentioned that in a preceding post. It was the 7-4760, I believe. I still have it. The keypad needed cleaning every couple of years. I once had the older vacuum flourescent version. They changed to LEDs at one some point. I forgot how/why mine broke. |
#53
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LED alarm clocks all lose accuracy over time
In article ,
Jeff Liebermann wrote: On Sun, 20 May 2012 00:41:44 -0700, isw wrote: The 1pps output can be used to run a digital clock, but I would hate to see the final cost. Why use the 1 pps? Any cheap GPS you get on eBay will output NMEA "sentences" in ASCII that tell you the precise time. Just use those. The NEMA sentences are not synchronized to GPS time and add delays in the decoding process. The time might be off a fraction of a secod. However, using the NEMA sentence is probably adequate for a consumer alarm clock. Much better, in the long run -- the time they report has a bit of sample-to-sample jitter, true, but the long-term drift is close enough to zero to not matter. You don't correct your local oscillator on the basis of its time difference compared to a particular sample -- you correct it to force the long-term drift to zero. The longer it runs, the more accurate it becomes. The notion of using irregular or not-continuous data samples to create accurate clocks even over jittery channels has been around for a while. Both MPEG 2 and Cable Modems use versions of it. Isaac |
#54
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LED alarm clocks all lose accuracy over time
In article ,
Jeff Liebermann wrote: On Sun, 20 May 2012 00:32:56 -0700, isw wrote: Incidentally, I'm building my own 10MHz GPSDO for running my test eqipment and ham junk. It's NOT a trivial or inexpensive exercise: http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm You can get short-term performance equal to a good crystal and long-term accuracy pert' near equal to the cesium beam clocks on the satellites for a whole lot less than that. Start with a 10 MHz rock in a home-brew oven, and divide it down to make a "regular clock". Compare the time given by that clock to GPS time, and twiddle the crystal oscillator to make it track, using a very long time constant filter in the loop. The longer it runs, the more accurate it gets. Good idea. However, if I'm going to go through the trouble of dividing down to 1pps (1Hz), I might as well add a FLL (frequency lock loop) and sync the oscillator a 1pps GPS reference. The regular clock idea also has a potential problem. One missed pulse and the clock is off by 1 full second. Since there's no way to detect a missing pulse, or recover gracefully from such a clock slip, it has the potential for going awry. By "regular clock" I meant anything you like that reads out in "time of day"; not necessarily something you bought. I don't understand why there would ever be a missed once-per-second pulse (assuming you know how to design digital stuff), but even so, the next time a NMEA sentence comes along (or whenever you decide to read the next one), you'd know you were off, and which way. After it's run for a while, you can do without GPS updates for fairly long periods (depending on how good your oscillator/oven is) with very little loss in accuracy. Maybe true, but I would have no easy way to determine if it needed to be resynced with the GPS clock. If it drifted off frequency for some reason, all my measurements would be off. But if it ran at the same rate as the GPS clock, then it wouldn't be drifting ... Setting the frequency to 1*10^-11 takes days to set, and the same time to reset. Might as well leave it on all the time. Well, of course it's on all the time; there's no other way to keep the oscillator stable. But if your local notion of time (what the NTP folks call "epoch") tracks the data coming from the GPS, then it will eventually be within that error band. And if it stays on longer, it'll become ever more accurate (long-term). In order to produce usable synchronization of simulcast data transmitters, the frequency accuracy and stability has to be 0.05ppm or (5*10^-8) for wide area coverage. That's not going to require a GPSDO but it would be nice. I've considered building that sort of rig where the oscillator's frequency is controlled by altering the temperature of the oven. Groan. Low noise oscillators use SC cut quartz crystals. That produces a rather steep frequency/temp curve at room temperature, but flattens out at about 80-100C. Vary the temperature around this flat part of the curve, and you'll see almost no change in frequency. Worse, it might go the wrong direction if it shows a peak or dip in the curve. http://www.conwin.com/pdfs/at_or_sc_for_ocxo.pdf Nice idea, but it will only work if you use an AT cut crystal and then only if you can deal with the dip in the curve. Use whatever crystal you want/need to get the temperature/frequency curve you need. Pick an oven temperature range that gives the slope you need. I don't see what's so hard about it. It's not even clear to me why you even need a low-noise oscillator for a clock, assuming it's being disciplined by a more accurate "master" (the GPS time system). The big advantage of doing things that way is that there are no extra paths for noise to get into the oscillator, as there would be if you used some sort of variable capacitor. Good idea, but glass piston trimmers and varactor electronic tuning are usually good enough. Microphonics are the major danger of using trimmers. If the trimmer is solidly built, and the components are buried in RTV for shock proofing, it should be adequate. Yes, but if they're not even there to begin with, then they're pretty noiseless even without special measures ... The 1/f phase noise of an oscillator is directly related to the power density of the device. That means using a moderately high current device at about 10% of its rated current. That's also why nobody uses low noise RF front end transistor for low noise oscillators. That leaves flicker noise, which reduced with lots of negative feedback. The short-term noise and the long-term stability are different. That's why super-precision sources use rubidium oscillators (low noise, poor drift), stabilized by cesium devices (higher noise, essentially zero long-term drift). If you're building a clock, the noise and jitter aren't very important; long-term drift is. Isaac |
#55
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LED alarm clocks all lose accuracy over time
In article , "N_Cook"
wrote: Klaatu wrote in message ... "Bill Proms" wrote in message ... I have 3 Intelli-Time LED alarm clocks around the house, just like the one he http://www.acurite.com/clock/alarm-c...alarm-clock-13 027a2.html I initially bought these due to them keeping time when the power goes off and auto resetting for DST. There is a problem, however. Each of the clocks becomes inaccurate over time. If I set them all manually to the same time, within a few months, each one will be off by 3-5 minutes. So I ask, what is the problem and is there any way to repair it? Thanks in advance, Bill http://www.ebay.com/itm/Westclox-700...rm-Clock-/2610 19821915?pt=LH_DefaultDomain_0&hash=item3cc5fe675b or, if you want to see the display at night http://www.ebay.com/itm/Atomic-Proje...61330?pt=US_Cl ocks&hash=item484513a7b2 I've used one of the projection alarm clocks for 4 years now, with the projector light on 24/7. No problems. Its has battery back-up, but no projection if the power fails. All the alarm and wall clocks in the house are now atomic. So is my wris****ch. IMHO, If a clock doesn't show the correct time, its not a clock...its a timer. Confucius , he say, but even a stopped clock tells the right time twice a day And his smarter cousin says "Quite true, but can you tell me when I should look at it to set my watch?" Isaac |
#56
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LED alarm clocks all lose accuracy over time
On May 19, 7:13*pm, Jim Yanik wrote:
"Ian Field" wrote : "gregz" wrote in message -september .org... "N_Cook" wrote: Bill Proms wrote in message ... I have 3 Intelli-Time LED alarm clocks around the house, just like the one he http://www.acurite.com/clock/alarm-c...igital-alarm-c lock-13 027a2.html I initially bought these due to them keeping time when the power goes off and auto resetting for DST. *There is a problem, however. *Each of the clocks becomes inaccurate over time. *If I set them all manually to the same time, within a few months, each one will be off by 3-5 minutes. So I ask, what is the problem and is there any way to repair it? Thanks in advance, Bill I've always put this down to hash on the mains being interpreted as extra cycles by the clock monitoring input. The supply companies contractually have to correct the mains frequency so an exact number of cycles per day (50/60)x60x60x24, but at any instant can be above or below the nominal frequency. I doubt if any use power line for sync. Most have battery backup. Crystals jump frequency from time to time. Even one I bought recently uses mains sync, but it has a battery & crystal divider backup to cover outages. The mains frequency varies depending on peak demand/off peak, but long term its average has less drift than the cheap crystal oscillator they're going to put in a radio alarm clock. radio alarm clock probably won't even use an xtal;like Jeff L. says,they may use a cheap RC osc. I note my MW oven clock that derives it's clock from line freq. has better stability than other "digital" clocks.(like my PC clock....) (of course,I use an internet program to keep the PC clock fairly close. I used to use a program(Atomic Clock) that direct-dialed the Naval Observatory,but the long distance calls cost too much.) -- Jim Yanik jyanik at localnet dot com Try PC Atomic Sync. You select your time server and the PC can sync every hour or day or manual. I turn machines off at night and have the sync program run once at boot AND set the PC 15 seconds fast. When they start recording TV they never clip the head. The OP referenced a clock that sets itself. How can it be wrong? WWVB clocks usually have problems receiving the data during the day - too much noise but work well at night. This implies you need a decent time base between successful data reads. My 'goofy clock' uses the power line as the time base but switches to the uProc clock during power failures. The uProc clock can be 'calibrated' for reasonable accuracy. What happens is the crystal frequency is divided down to make a fake 60Hz reference pulse when the power line is absent and the divisor is 'tweaked'. I have the WWVB receivers and the code is mostly written for goofy. G² |
#57
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LED alarm clocks all lose accuracy over time
isw wrote:
If you're building a clock, the noise and jitter aren't very important; long-term drift is. It's also part of the modern perception that precision is much greater than it is. A clock that reads hours and minutes is accurate to around 30 seconds. A clock that reads hours minutes and seconds is accurate to 1/2 second. Neither are accurate to a millisecond. I it started with airlines who would write 12:30 for "sometime before 1 o'clock" for departure and 2:00 for "around 1:30" for arrival. People expect exact numbers where they are approximate, and it is easy to arrive on time if you allow enough "slop" to commenpensate for anything. Mousillini (pardon the spelling) "made the trains run on time" by adjusting the schedules to reality. I've also seen it in ham radio where the frequency really is around 14.200, but someone logs it as 14.203154 because that's what their (inacurate) receiver reads it as and in computers where someone thinks floating point numbers are integers. :-( For most people a clock that reads in minutes is ok, and for almost everyone who needs more accuracy seconds is ok. Just about every clock made stays within a second for a few minutes, and auto correcting via GPS, NTP or WWV would do well enough. I would expect that an HF receiver clock where you set the minutes and it autocorrects to the minute pips on WWV or CHU would do fairly well, and in most of the US and Canada do it without the interference problems the VLF radios have. Note that I don't have access to any of those sources, or the EU equivalents. The best that I can do is to run real NTP clients on all my computers, which sync to a main NTP server on my network. The main NTP server syncs to a variety of sources, which confuses it because they are all within a millisecond of each other except for two Apple EU ones which are 5 seconds off. I put them in a long time ago and probably should remove them. The irony of all of this is the only thing that needs accurate timing is catching a bus, which never comes at any exact time anyway and recording programs off of the DBS system I susbscibe to. Since we have their PVR, it gets its time and programing information from the feed, but is set to start recording early and end late. They don't even trust themselves. :-) Geoff -- Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379 In 1969 the US could put a man on the moon, now teenagers just howl at it. :-( |
#58
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LED alarm clocks all lose accuracy over time
"Cydrome Leader" wrote in message
... William Sommerwerck wrote: I think it was GE that had an alarm clock like that in the late 70s. It was actually pretty cool. It had a little keypad on it. I mentioned that in a preceding post. It was the 7-4760, I believe. I still have it. The keypad needed cleaning every couple of years. I once had the older vacuum flourescent version. They changed to LEDs at one some point. I forgot how/why mine broke. The vacuum-fluorescent version did 'not have a digital tuner. (I have that one, too. It works, but it could stand a bit of fixing-up.) |
#59
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LED alarm clocks all lose accuracy over time
It's also part of the modern perception that precision
is much greater than it is. A clock that reads hours and minutes is accurate to around 30 seconds. A clock that reads hours minutes and seconds is accurate to 1/2 second. You're confusing accuracy and resolution. You're also ignoring the fact that the user can //see// when the minutes change. If you make sure the minutes change at the same time your reference clock changes, the clock's accuracy can be less than one second. I've also seen it in ham radio where the frequency really is around 14.200, but someone logs it as 14.203154 because that's what their (inacurate) receiver reads it as and in computers where someone thinks floating point numbers are integers. :-( I don't think most digital communications receivers display the frequency with a precision the LO is capable of. |
#60
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LED alarm clocks all lose accuracy over time
I've also seen it in ham radio where the frequency
really is around 14.200, but someone logs it as 14.203154 because that's what their (inaccurate) receiver reads it as, and in computers, where someone thinks floating point numbers are integers. I don't think most digital communications receivers display the frequency with a precision the LO is capable of. WHOOPS! That should have been "incapable of". |
#61
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LED alarm clocks all lose accuracy over time
William Sommerwerck wrote:
WHOOPS! That should have been "incapable of". Well, my 1980's Kenwood TS-430 is capable of tuning in 10Hz steps, and the modern high priced rigs in 1Hz steps. Geof. -- Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379 In 1969 the US could put a man on the moon, now teenagers just howl at it. :-( |
#62
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LED alarm clocks all lose accuracy over time
My 1980's Kenwood TS-430 is capable of tuning in 10Hz
steps, and the modern high-priced rigs in 1Hz steps. I'd like to make a joke about "high-priced [band]spread", but I will refrain. The former resolution would require the synthesizer's crystal to be accurate to about 1 part in 100,000, which is not out of the question. My Yaesu FTD-1000 is in storage. I don't remember its resolution, or the tolerance of its crystals. |
#63
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LED alarm clocks all lose accuracy over time
On Mon, 21 May 2012 00:00:49 -0700, isw wrote:
I don't understand why there would ever be a missed once-per-second pulse (assuming you know how to design digital stuff), but even so, the next time a NMEA sentence comes along (or whenever you decide to read the next one), you'd know you were off, and which way. The missing pulse problem is with the 1pps clock implementation, not the NEMA sentence reader. Clock slip with 1pps is very real. I can do it with my weather station if I transmit on my VHF HT within about 2ft. Maybe true, but I would have no easy way to determine if it needed to be resynced with the GPS clock. If it drifted off frequency for some reason, all my measurements would be off. But if it ran at the same rate as the GPS clock, then it wouldn't be drifting ... Only if the clock didn't miss a pulse. I think we have a problem here. You're mixing a NEMA sentence driven clock, with a 1pps conventional counting clock. The NEMA sentence device does NOT have a clock slip problem and does not need recalibration. The 1pps counting clock can easily lose count and offers no easy way to determine that the clock has slipped and that it requires recalibration. Setting the frequency to 1*10^-11 takes days to set, and the same time to reset. Might as well leave it on all the time. Well, of course it's on all the time; there's no other way to keep the oscillator stable. OK. Then forget about battery operation. But if your local notion of time (what the NTP folks call "epoch") tracks the data coming from the GPS, then it will eventually be within that error band. And if it stays on longer, it'll become ever more accurate (long-term). Overkill (except for leap seconds). I don't think anyone cares about sub-second accuracy in a home alarm clock. However, the last digit (seconds) should be accurate. Use whatever crystal you want/need to get the temperature/frequency curve you need. If I do that, the design becomes more difficult. For example, a higher freq/temp slope for the crystal will require more insulation. Crystals with such a slope tend to have large frequency drift during aging characteristics. Reverse slopes in the operating area will create some rather bizarre tuning characteristics. Pick an oven temperature range that gives the slope you need. Well, if I use an AT cut crystal at 80C, the slope is about 2ppm/C. At 10MHz, that's 5Hz/C. You could probably adjust the temperature over a 20C range (to avoid the dip in the AT curve at 75C) yielding a 100Hz range. Yep, that might work, but you'll need to reduce the oscillator thermal mass, and greatly increase the insulation. I don't see what's so hard about it. Pretend you're on a large boat, which has about a 3 minute delay between when you turn the rudder and when the vessel changes direction. Newton's 2nd law and hysteresis delay at its best. To speed up the turn, one tends to over shoot the rudder direction, and then bring it back to the correct orientation. To anyone lacking experience in piloting such an over-damped system, the path traveled will be rather erratic. See control system damping calculations. your manual oven corrections might be similarly erratic. It's not even clear to me why you even need a low-noise oscillator for a clock, assuming it's being disciplined by a more accurate "master" (the GPS time system). I don't need a low noise oscillator for an alarm clock. I mentioned the low noise in reference to by building a GPSDO, which will be used for everything from running my test equipment clock, to synchronizing transmitters. I don't see any reason to build multiple versions when one device will do it all. The 1/f phase noise of an oscillator is directly related to the power density of the device. That means using a moderately high current device at about 10% of its rated current. That's also why nobody uses low noise RF front end transistor for low noise oscillators. That leaves flicker noise, which reduced with lots of negative feedback. The short-term noise and the long-term stability are different. That's why super-precision sources use rubidium oscillators (low noise, poor drift), stabilized by cesium devices (higher noise, essentially zero long-term drift). True and thanks for recognizing that a rubidium source is not a primary frequency standard. The issue with noise is that it has an effect on accuracy in that one cannot measure the frequency to a resolution less than the noise. For example, if there is 1Hz of FM noise on the oscillator, the frequency cannot be measured to less than 1Hz. Of course, one could average the measurements, which only works if the noise spectra is symmetrical. Also, 1Hz of FM noise at the 10MHz clock reference, multiplied up to a 10GHz transmitter, is 1000Hz, which is audible and quite fatal to data. If you're building a clock, the noise and jitter aren't very important; long-term drift is. True. However, I'm building GPSDO, while you're building a GPS alarm clock. I agree that the requirements are quite different. Isaac -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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LED alarm clocks all lose accuracy over time
On Mon, 21 May 2012 05:31:07 -0400, JW wrote:
Incidentally, I'm building my own 10MHz GPSDO for running my test eqipment and ham junk. It's NOT a trivial or inexpensive exercise: http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm Too expensive. Get this while it lasts for $135: http://www.ebay.com/itm/TRIMBLE-GPS-...em27c728 a56b I almost went for one of those, but instead decided on this: http://www.ebay.com/itm/280655233263...3%26_rdc%3 D1 Try to find out which lamp they're using. Rubidium depletion is a major cause of failure. I had an old TFT reference osc crap out on me. The stupid lamp cost as much as the entire (used) unit. Some of the cheap lamps have as little as 0.1mg inside, while the one's that last almost forever have about 1mg. Not quite as accurate as the thunderbolt, but good enough for my bench. Yet another temptation to spend money... I would have no problem with using either of these as a reference. However, I have a unique problem. I have approximately 200ea Novatel Allstar 12 boards which are looking for a home. The grand plan is to build various projects (APRS tracker, GPSDO, GPS logger, test board, etc) around these boards and possibly sell the kits. Thanks. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#65
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LED alarm clocks all lose accuracy over time
Jim Yanik wrote:
"Ian Field" wrote in : "gregz" wrote in message -september .org... "N_Cook" wrote: Bill Proms wrote in message ... I have 3 Intelli-Time LED alarm clocks around the house, just like the one he http://www.acurite.com/clock/alarm-c...igital-alarm-c lock-13 027a2.html I initially bought these due to them keeping time when the power goes off and auto resetting for DST. There is a problem, however. Each of the clocks becomes inaccurate over time. If I set them all manually to the same time, within a few months, each one will be off by 3-5 minutes. So I ask, what is the problem and is there any way to repair it? Thanks in advance, Bill I've always put this down to hash on the mains being interpreted as extra cycles by the clock monitoring input. The supply companies contractually have to correct the mains frequency so an exact number of cycles per day (50/60)x60x60x24, but at any instant can be above or below the nominal frequency. I doubt if any use power line for sync. Most have battery backup. Crystals jump frequency from time to time. Even one I bought recently uses mains sync, but it has a battery & crystal divider backup to cover outages. The mains frequency varies depending on peak demand/off peak, but long term its average has less drift than the cheap crystal oscillator they're going to put in a radio alarm clock. radio alarm clock probably won't even use an xtal;like Jeff L. says,they may use a cheap RC osc. I note my MW oven clock that derives it's clock from line freq. has better stability than other "digital" clocks.(like my PC clock....) I wish the most recent MW oven I bought for our office worked like that. Its clock gains about one minute a day and I doubt that there's any syncing to the line frequency built in. It keeps far worse time than the $10 battery powered wall clocks we use around the office. Could be the problem is that the temperature of the electronics in that MW oven moves around quite a bit more than those in the clock on the wall next to it due to the high power loads when the oven is heating stuff. That could screw up a simple RC or even xtal oscillator, eh? OTOH the MW oven in our home's kitchen is always dead nuts on time, barring power failures, after which it needs resetting. Jeff Jeffry Wisnia (W1BSV + Brass Rat '57 EE) The speed of light is 1.8*10e12 furlongs per fortnight. (of course,I use an internet program to keep the PC clock fairly close. I used to use a program(Atomic Clock) that direct-dialed the Naval Observatory,but the long distance calls cost too much.) -- |
#66
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LED alarm clocks all lose accuracy over time
jeff_wisnia wrote:
I wish the most recent MW oven I bought for our office worked like that. Its clock gains about one minute a day and I doubt that there's any syncing to the line frequency built in. It keeps far worse time than the $10 battery powered wall clocks we use around the office. More likely it has one of those chips that detects if there is power line signal or battery backup and uses a built in crystal to keep time if the power line goes off. Unfortunately, at least one of the cheap Chinese versions is broken and uses the crystal all of the time. I have a clock like that. The crystals are spec'ed to run a microprocessor in the chip and not keep time. :-( Geoff. -- Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379 In 1969 the US could put a man on the moon, now teenagers just howl at it. :-( |
#67
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LED alarm clocks all lose accuracy over time
On Sun, 20 May 2012 17:25:54 +0000 (UTC), the renowned Cydrome Leader
wrote: gregz wrote: "William Sommerwerck" wrote: Many years ago I reviewed Heath's "Most-Accurate Clock" for one of Ed Dell's magazines. It used the Bureau of Standards' shortwave time signals. Sync was a bit touchy (I eventually replaced the carbon calibration pots with ceramic), but it otherwise worked very well. It even had an interface that allowed your computer to reset its clock each time the machine restarted. When I needed money a few years back, I sold it on eBay for something like $400, without anyone questioning the price. If Heath wants to come back as a kit company, it needs to design products that have no commercial equivalents. Heath had an fm tuner with direct frequency entry push button. I never saw another for home use, but there may have been another or commercial use. I think it was GE that had an alarm clock like that in the late 70s. It was actually pretty cool. It had a little keypad on it. I had one of those- nice. IIRC, the keys failed over time though. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
#68
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LED alarm clocks all lose accuracy over time
"Geoffrey S. Mendelson" wrote: Bill Proms wrote: As a possible replacement, I have considered an atomic LED clock, but these appear to be next to impossible to come by for some reason. I see LCD atomic clocks everywhere, but most or all have to have the backlight pressed to see the time in dim conditions. It's because the US is trying to get rid of those broadcasts. With GPS they are obsolete. Then why did they replace the WWVB towers & transmitters a couple years ago? They built a better antenna array, and raised the transmitter power so that it can be received in Florida on a $20 'Atomic clock'. Not only are they not looking to discontinue the service, but they are looking at a new modulation method to improve noise immunity. This web page from NIST says that there are about 50,000,000 radio controlled clocks using WWVB in the United States: http://www.nist.gov/pml/newsletter/radio.cfm -- You can't have a sense of humor, if you have no sense. |
#69
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LED alarm clocks all lose accuracy over time
Jeff Liebermann wrote: On Sun, 20 May 2012 00:41:44 -0700, isw wrote: The 1pps output can be used to run a digital clock, but I would hate to see the final cost. Why use the 1 pps? Any cheap GPS you get on eBay will output NMEA "sentences" in ASCII that tell you the precise time. Just use those. The NEMA sentences are not synchronized to GPS time and add delays in the decoding process. The time might be off a fraction of a secod. However, using the NEMA sentence is probably adequate for a consumer alarm clock. $GPZDA give the time as: $--ZDA,hhmmss.ss,xx,xx,xxxx,xx,xx hhmmss.ss = UTC xx = Day, 01 to 31 xx = Month, 01 to 12 xxxx = Year xx = Local zone description, 00 to +/- 13 hours xx = Local zone minutes description (same sign as hours) The 1pps output has the advantage of simplicity and easy of integration with existing digital clock designs. Say, $15 for the GPS, another $15 for an Arduino, $5 for an LCD, and whatever crystal you have on hand, stuck in a home-made oven. Maybe another $20 for all the "glue", and the rest, as they say, is just software. The cheapest GPS board or module that I could find is about $40. http://www.sparkfun.com/categories/4?sort_by=price_asc&per_page=50 Chips seem to run about $8/1000. Using your prices, a commercial digital alarm clock product would retail about $175-$200. Meanwhile, WWVB controlled "atomic" alarm clocks are selling for $15. This one decodes NEMA sentences, and has some compromises due to running on battery power: http://www.siliconchip.com.au/cms/A_111192/article.html To conserve the battery, the GPS module is only used to synchronise the clock every 44 hours and following synchronisation, the clock will either skip seconds or double-step to reach the correct time. After synchronisation the microcontroller is also able to calculate the inherent inaccuracy of its crystal oscillator and will compensate by occasionally skipping or double-stepping a second. This process can also compensate for aging of the crystal and will keep the clock accurate between synchronisations. http://geoffg.net/GPS_Synchronised_Clock.html http://www.siliconchip.com.au/cms/gallery/article.html?a=111709 $7.79 Trimble GPS module: http://www.ebay.com/itm/190626494449 $5.99 GPS antenna with MMCX connector: http://www.ebay.com/itm/170496886891 $32.00 for a GPS receiver & antenna module: http://www.ebay.com/itm/180815989220 Be VERY careful if you buy any Rockwell GPS receiver boards on Ebay. At least one seller is advertising a board with 10 KHz out then ship a different board, even though they have been sent the information by people who have tried to use them. -- You can't have a sense of humor, if you have no sense. |
#70
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LED alarm clocks all lose accuracy over time
N_Cook wrote: Confucius, he say, but even a stopped clock tells the right time twice a day Confucius was confused. -- You can't have a sense of humor, if you have no sense. |
#71
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LED alarm clocks all lose accuracy over time
In article ,
Jeff Liebermann wrote: On Mon, 21 May 2012 00:00:49 -0700, isw wrote: I don't understand why there would ever be a missed once-per-second pulse (assuming you know how to design digital stuff), but even so, the next time a NMEA sentence comes along (or whenever you decide to read the next one), you'd know you were off, and which way. The missing pulse problem is with the 1pps clock implementation, not the NEMA sentence reader. Clock slip with 1pps is very real. I can do it with my weather station if I transmit on my VHF HT within about 2ft. Maybe true, but I would have no easy way to determine if it needed to be resynced with the GPS clock. If it drifted off frequency for some reason, all my measurements would be off. But if it ran at the same rate as the GPS clock, then it wouldn't be drifting ... Only if the clock didn't miss a pulse. I think we have a problem here. You're mixing a NEMA sentence driven clock, with a 1pps conventional counting clock. The NEMA sentence device does NOT have a clock slip problem and does not need recalibration. The 1pps counting clock can easily lose count and offers no easy way to determine that the clock has slipped and that it requires recalibration. I'm proposing to build a time-of-the-year clock that uses a (say) 10 MHz oscillator for a timebase, with dividers (hardware or software) to provide all the various outputs. The time-of-year output is available to the frequency-controlling loop, which compares its value with what it gets from the NMEA sentences -- if the local clock is ahead, slow down the 10 MHz, and vice-versa. After a while, that oscillator is going to be dead on. Setting the frequency to 1*10^-11 takes days to set, and the same time to reset. Might as well leave it on all the time. Well, of course it's on all the time; there's no other way to keep the oscillator stable. OK. Then forget about battery operation. Using temperature to control frequency, probably; using other means, not much of a problem. A decent GPS chip set, a little CMOS computer, and an LCD for readout will come in at a small fraction of a watt. If you picked a better-than-average crystal, stability-wise, you could turn off everything but the oscillator for most of the time and still get exceptional long-term accuracy. I expect that some clever design could produce an "oven" that could be heated by a quarter-watt resistor glued to the crystal case, so even using the temperature-control-of-frequency method could still give you something that could operate all day on a battery. But if your local notion of time (what the NTP folks call "epoch") tracks the data coming from the GPS, then it will eventually be within that error band. And if it stays on longer, it'll become ever more accurate (long-term). Overkill (except for leap seconds). I don't think anyone cares about sub-second accuracy in a home alarm clock. However, the last digit (seconds) should be accurate. Right. But what they might care about is that the clock never drifts away from "real" time, no matter what the power line does. That, of course, is the appeal of all "radio clocks". Use whatever crystal you want/need to get the temperature/frequency curve you need. If I do that, the design becomes more difficult. For example, a higher freq/temp slope for the crystal will require more insulation. Not really. Remember, it's in a temperature-controlled oven. The temperature control loop will keep the crystal at whatever temperature is called for to keep the frequency at precisely 10.000... MHz. Crystals with such a slope tend to have large frequency drift during aging characteristics. Which will be compensated for continuously by the loop. Reverse slopes in the operating area will create some rather bizarre tuning characteristics. Well, don't operate it in that regime ... Pick an oven temperature range that gives the slope you need. Well, if I use an AT cut crystal at 80C, the slope is about 2ppm/C. At 10MHz, that's 5Hz/C. You could probably adjust the temperature over a 20C range (to avoid the dip in the AT curve at 75C) yielding a 100Hz range. Yep, that might work, but you'll need to reduce the oscillator thermal mass, and greatly increase the insulation. Nope. Very slow response times are no problem. The loop will eventually arrange things so that precisely ten million cycles will elapse per one second elapsed, over the long term. Still, small thermal mass is easy -- just pick a small crystal package, and heat that package directly with a small resistor or two. Insulation is cheap and a lot of it is not a problem. I'd use fairly long, very thin, stainless steel wires to connect the crystal (and those resistors) to the rest of the circuit, too. One major source of problems on high-stability oscillators is thermal or acoustical shock running right up the connecting wires directly to the quartz itself. I've seen ovenized oscillators that were disrupted every time the thermostat clicked, and not because of electrical transients. I don't see what's so hard about it. Pretend you're on a large boat, which has about a 3 minute delay between when you turn the rudder and when the vessel changes direction. Newton's 2nd law and hysteresis delay at its best. To speed up the turn, one tends to over shoot the rudder direction, and then bring it back to the correct orientation. To anyone lacking experience in piloting such an over-damped system, the path traveled will be rather erratic. See control system damping calculations. your manual oven corrections might be similarly erratic. I've done a few control loops, some of them a bit "peculiar". If you insist on having the fastest possible transition to the new heading to within some specified error band, then you're correct. It you're willing to do things a lot more slowly while still (eventually) arriving at the new heading, then the loop gets very simple. For the above problem, just put a really slow motor on the power steering for the rudder. It's not even clear to me why you even need a low-noise oscillator for a clock, assuming it's being disciplined by a more accurate "master" (the GPS time system). I don't need a low noise oscillator for an alarm clock. I mentioned the low noise in reference to by building a GPSDO, which will be used for everything from running my test equipment clock, to synchronizing transmitters. I don't see any reason to build multiple versions when one device will do it all. Consider the 10 MHz output from this sort of clock as the frequency reference for whatever sort of synthesizer you want. If the clock runs at the proper rate, the oscillator is at the specified frequency. After it's run for a while, the frequency will always be very, very close to exactly ten megahertz. The 1/f phase noise of an oscillator is directly related to the power density of the device. That means using a moderately high current device at about 10% of its rated current. That's also why nobody uses low noise RF front end transistor for low noise oscillators. That leaves flicker noise, which reduced with lots of negative feedback. The short-term noise and the long-term stability are different. That's why super-precision sources use rubidium oscillators (low noise, poor drift), stabilized by cesium devices (higher noise, essentially zero long-term drift). True and thanks for recognizing that a rubidium source is not a primary frequency standard. The issue with noise is that it has an effect on accuracy in that one cannot measure the frequency to a resolution less than the noise. For example, if there is 1Hz of FM noise on the oscillator, the frequency cannot be measured to less than 1Hz. Of course, one could average the measurements, which only works if the noise spectra is symmetrical. Also, 1Hz of FM noise at the 10MHz clock reference, multiplied up to a 10GHz transmitter, is 1000Hz, which is audible and quite fatal to data. One of the advantages of this sort of loop (thermally controlled) is that there is literally nothing in the circuit that prevents the noise from being as low as it can possibly be for whatever sort of oscillator you choose, while still constraining it to being very close to the design frequency. Isaac |
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LED alarm clocks all lose accuracy over time
Michael A. Terrell wrote:
"Geoffrey S. Mendelson" wrote: It's because the US is trying to get rid of those broadcasts. With GPS they are obsolete. Then why did they replace the WWVB towers & transmitters a couple years ago? They built a better antenna array, and raised the transmitter power so that it can be received in Florida on a $20 'Atomic clock'. They are playing "cheap catch up". The original plans were to build an east coast station, but they were unable to get any government installation to "host" it, (NIMBY) and lost the funding. Not only are they not looking to discontinue the service, but they are looking at a new modulation method to improve noise immunity. This web page from NIST says that there are about 50,000,000 radio controlled clocks using WWVB in the United States: The are using the improved modulation to keep relevant. In most large cities, the noise from computer and home electronic equipment, BPL (still very much in use but not for internet to customers), aDSL, etc has made it next to impossible to receive a signal. They exist today because people are willing to accept the poor service they get as it is the only game in town at that price tag. Most users never pay attention to how often they get sync, if ever. If they have to pay $100-$150 for a BPSK decoding clock, GPS or Wifi NTP clocks will seem a lot better deal. I'd love to know how they came up with the number of clocks in use. Anyone have an idea? Geoff. -- Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379 In 1969 the US could put a man on the moon, now teenagers just howl at it. :-( |
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LED alarm clocks all lose accuracy over time
On Tue, 22 May 2012 11:49:04 +0000 (UTC), "Geoffrey S. Mendelson"
wrote: The are using the improved modulation to keep relevant. In most large cities, the noise from computer and home electronic equipment, BPL (still very much in use but not for internet to customers), aDSL, etc has made it next to impossible to receive a signal. Many switching power supplies run at about 60KHz. I have one somewhere around my computer/TV pile, which kills WWVB reception if I get anywhere near it. They exist today because people are willing to accept the poor service they get as it is the only game in town at that price tag. Most users never pay attention to how often they get sync, if ever. Most WWVB devices have an indicator on the LCD display to show that the clock was recently synced with WWVB time. My weather stations and assorted digital clocks all have this feature. If they have to pay $100-$150 for a BPSK decoding clock, GPS or Wifi NTP clocks will seem a lot better deal. It's my understanding that only the modulation scheme will change, not the encoded data. A universal chip that works using both system should be possible without a major price jump. I'm a bit mystified with the "new type of PM receiving antenna" mentioned in: http://www.nist.gov/pml/newsletter/radio.cfm I didn't know that antennas were modulation specific. I'd love to know how they came up with the number of clocks in use. Anyone have an idea? Same as how they get wi-fi device numbers. Marketing research firms, that specialize in selling industry statistics and predictions, survey the chip manufacturers for how many chips they've sold. In this case, the leading manufactory is C-Max: http://www.c-max-time.com I suspect the largest numbers are in "atomic time" wris****ches. The accuracy of sales statistics are always questionable, but are usually accurate within an order of magnitude. The problem is while sales statistics are fairly simple to generate, devices in use are not. One could add up all the sales from the last 10 years, assume that few of the devices were trashed, and produce a very large number in use. Whether it has any value is very doubtful. Besides, sales statistics is what companies are willing to pay for, and that's what the marketing research firms tend to produce. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#74
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LED alarm clocks all lose accuracy over time
Jeff Liebermann wrote:
Many switching power supplies run at about 60KHz. I have one somewhere around my computer/TV pile, which kills WWVB reception if I get anywhere near it. Exactly, how many people have one? Most WWVB devices have an indicator on the LCD display to show that the clock was recently synced with WWVB time. My weather stations and assorted digital clocks all have this feature. What's recent? 1 minute? 1 Hour? 1 Day? a Week? It's my understanding that only the modulation scheme will change, not the encoded data. A universal chip that works using both system should be possible without a major price jump. Well no. The data is the same, but a new receiver needs to be used. The old one just did on/off for an AM pulse, the new one uses BPSK, which is two tone modulation. So not only does it have to decode the carrier being there at all, it has to decode two different tones. Then you have to decode the BPSK stream to get the data. This not a big deal, you could do it with a sound card and a microprocessor, but it's a different receiver design, and reprograming the microprocessor. The kind of thing that if you really were going to sell 50 million of them you could do it for a few dollars a chipset/board, which is probably what the current ones cost, but if you want to break even with 10,000 you have to sell them for at least $100, maybe more. It's like I saw an article about an Israeli startup that had sold 200,000 of their product. The article was entitled "sales of xxx disappointing". I guess they planned on selling a million of them. :-( I'm a bit mystified with the "new type of PM receiving antenna" mentioned in: http://www.nist.gov/pml/newsletter/radio.cfm I didn't know that antennas were modulation specific. Where have you been the last five years? I surprised that you have not been swamped with HDTV antennas. :-) I expect it's another gimick to say you need to buy a higher gain antenna, or that's why your device can't sync. I expect that everyone will need to buy 1/2 wavelength end fed wires. (for the humor impared, that's a joke, a wavelength is 5 kilometers). Geoff. -- Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379 In 1969 the US could put a man on the moon, now teenagers just howl at it. :-( |
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LED alarm clocks all lose accuracy over time
"Geoffrey S. Mendelson" wrote: Michael A. Terrell wrote: ? ? "Geoffrey S. Mendelson" wrote: ?? It's because the US is trying to get rid of those broadcasts. With GPS they ?? are obsolete. ? ? ? Then why did they replace the WWVB towers ? transmitters a couple ? years ago? They built a better antenna array, and raised the ? transmitter power so that it can be received in Florida on a $20 'Atomic ? clock'. They are playing "cheap catch up". The original plans were to build an east coast station, but they were unable to get any government installation to "host" it, (NIMBY) and lost the funding. So, they gave up and started the upgrade in the late '90s? ? Not only are they not looking to discontinue the service, but they ? are looking at a new modulation method to improve noise immunity. This ? web page from NIST says that there are about 50,000,000 radio controlled ? clocks using WWVB in the United States: The are using the improved modulation to keep relevant. In most large cities, the noise from computer and home electronic equipment, BPL (still very much in use but not for internet to customers), aDSL, etc has made it next to impossible to receive a signal. BPL isn't used around here. Progress Energy drives down the street and pings the transponders in their meters. The SW bands are fairly dead, these days. The SMPS in traffic lihts cause more noise than anything else, and appear to operate on the low end of the AM BCB, They exist today because people are willing to accept the poor service they get as it is the only game in town at that price tag. Most users never pay attention to how often they get sync, if ever. I am near Orlando, Florida and have no problem with my WWVB clocks. The one in this room is about ten feet from several computers & monitors, yet it matches the internet time on the screen. If they have to pay $100-$150 for a BPSK decoding clock, GPS or Wifi NTP clocks will seem a lot better deal. Who says they will cost that much? Custom ICs will make it into a single or two chip design. FQPSK would require a lot more processing, and the only place I used it was in the Microdyne DR2000 & RCB2000 telemetry recievers. Some people don't want to screw with wi-fi crap. There are times when every availible channel is full of noise I'd love to know how they came up with the number of clocks in use. Anyone have an idea? Geoff. -- Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379 In 1969 the US could put a man on the moon, now teenagers just howl at it. :-( -- You can't have a sense of humor, if you have no sense. |
#76
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LED alarm clocks all lose accuracy over time
"Geoffrey S. Mendelson" wrote: Well no. The data is the same, but a new receiver needs to be used. The old one just did on/off for an AM pulse, the new one uses BPSK, which is two tone modulation. So not only does it have to decode the carrier being there at all, it has to decode two different tones. The carrier was amplitude modulated by reducing the carrier level, not CW. The same carrier can be phase modulated and provide both data streams. -- You can't have a sense of humor, if you have no sense. |
#77
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LED alarm clocks all lose accuracy over time
On Tue, 22 May 2012 15:49:04 +0000 (UTC), "Geoffrey S. Mendelson"
wrote: Jeff Liebermann wrote: Many switching power supplies run at about 60KHz. I have one somewhere around my computer/TV pile, which kills WWVB reception if I get anywhere near it. Exactly, how many people have one? My guess(tm) is that it's the power supply in my DirecTV DVR. There are plenty of those out there. Most WWVB devices have an indicator on the LCD display to show that the clock was recently synced with WWVB time. My weather stations and assorted digital clocks all have this feature. What's recent? 1 minute? 1 Hour? 1 Day? a Week? The manual for the wx station says within 24 hrs. That makes sense as 60KHz skywave doesn't work too well until after about midnight. I suspect it's lucky to get one update per day. That should be sufficient to deal with any clock drift. When I was stupidly running it next to my computer/TV pile, it would never update. I vaguely recall that it drifted fast at about 5 minutes per month. Now that it gets updates, it's dead on. See: http://tf.nist.gov/general/pdf/1976.pdf Section 4, for recommended synchronization practices. It's my understanding that only the modulation scheme will change, not the encoded data. A universal chip that works using both system should be possible without a major price jump. Well no. The data is the same, but a new receiver needs to be used. The old one just did on/off for an AM pulse, the new one uses BPSK, which is two tone modulation. So not only does it have to decode the carrier being there at all, it has to decode two different tones. Nope. It's not two tone. It's a phase shift of the AM carrier, switching from 0 degrees to 180 degrees for 0/1. See video at: http://www.youtube.com/watch?v=mOjwxq5flTg I had thought that they were going to broadcast each separately, but apparently it's simply adding PSK to the existing AM carrier. Clever, methinks. Then you have to decode the BPSK stream to get the data. Yes, you have to modify the chip. However, it's really easy to build a BPSK to OOK (on off keying) converter, so an adapter is possible. This not a big deal, you could do it with a sound card and a microprocessor, but it's a different receiver design, and reprograming the microprocessor. While it's possible to demodulate a 60KHz carrier with a sound card, it would require a high end 192KHz card, and not a generic card that maxes out at 44KHz. The kind of thing that if you really were going to sell 50 million of them you could do it for a few dollars a chipset/board, which is probably what the current ones cost, but if you want to break even with 10,000 you have to sell them for at least $100, maybe more. Well, keep your eye on C-Max. When they produce a suitable BPSK chip, that should set the price point. It's this type of potentially high volume market that really attracts the chip vendors. It's like I saw an article about an Israeli startup that had sold 200,000 of their product. The article was entitled "sales of xxx disappointing". I guess they planned on selling a million of them. :-( Kinda like the Windoze Phone 7? http://www.dailytech.com/Ballmer+Admits+Windows+Phone+7+Sales+Are+Disappoin ting/article22747.htm It was really clever of MS to prematurely announce the WP8, and then leak that there's no upgrade path from the WP7 to the WP8. I'm a bit mystified with the "new type of PM receiving antenna" mentioned in: http://www.nist.gov/pml/newsletter/radio.cfm I didn't know that antennas were modulation specific. Where have you been the last five years? I surprised that you have not been swamped with HDTV antennas. :-) Sigh. I assumed that it was too early for the marketing hype in the "atomic clock" market. My apologies for being so naive. Incidentally, I designed stick-on metallic label, that you attach to your ordinary TV antenna, that turns it into an HDTV antenna. I expect it's another gimick to say you need to buy a higher gain antenna, or that's why your device can't sync. I expect that everyone will need to buy 1/2 wavelength end fed wires. (for the humor impared, that's a joke, a wavelength is 5 kilometers). Sorry, but zoning ordinances do not allow covering the neighborhood with giant antennas. The authorities claim that it attracts lightning, cosmic rays, and aliens from outer space. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#78
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LED alarm clocks all lose accuracy over time
On Tue, 22 May 2012 15:49:04 +0000 (UTC), "Geoffrey S. Mendelson"
wrote: Well no. The data is the same, but a new receiver needs to be used. The old one just did on/off for an AM pulse, the new one uses BPSK, which is two tone modulation. So not only does it have to decode the carrier being there at all, it has to decode two different tones. Ummm. No. BPSK is a variant of Manchester encoding. Binary Phase Shift Keying. Single frequency. Then you have to decode the BPSK stream to get the data. This not a big deal, you could do it with a sound card and a microprocessor, but it's a different receiver design, and reprograming the microprocessor. |
#79
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LED alarm clocks all lose accuracy over time
On Sat, 19 May 2012 16:17:37 +0000 (UTC), gregz
wrote: "N_Cook" wrote: Bill Proms wrote in message ... I have 3 Intelli-Time LED alarm clocks around the house, just like the one he http://www.acurite.com/clock/alarm-c...alarm-clock-13 027a2.html I initially bought these due to them keeping time when the power goes off and auto resetting for DST. There is a problem, however. Each of the clocks becomes inaccurate over time. If I set them all manually to the same time, within a few months, each one will be off by 3-5 minutes. So I ask, what is the problem and is there any way to repair it? Thanks in advance, Bill I've always put this down to hash on the mains being interpreted as extra cycles by the clock monitoring input. The supply companies contractually have to correct the mains frequency so an exact number of cycles per day (50/60)x60x60x24, but at any instant can be above or below the nominal frequency. I doubt if any use power line for sync. Most have battery backup. Crystals jump frequency from time to time. Greg I have an LED alarm clock that definitely uses the powerline frequency to keep time. I know this because I have a rotary phase converter to supply three phase power to my shop. When ever I use certain CNC machines with DC spindle drives the clock runs much faster. When I use machines with VFD spindle drives the clock gains only a little time and when powering only induction motors the clock is not affected at all. Looking at the power in the house with an oscilloscope a friend of mine who designs inverter power supplies showed me the noise on the powerline when the machines were running. It is a cheap clock though and is the only one that has this behavior. Eric |
#80
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LED alarm clocks all lose accuracy over time
On 05/19/12 12:51, Bill Proms wrote:
So I ask, what is the problem and is there any way to repair it? Thanks in advance, Bill Maybe you should switch to sundials, you ****ing peckerhead. |
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