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.
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
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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'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 don't think most digital communications receivers display the frequency with a precision the LO is capable of.
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.
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.
OK. Then forget about battery operation.
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.
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.
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.
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 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.
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.
True. However, I'm building GPSDO, while you're building a GPS alarm clock. I agree that the requirements are quite different.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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.
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 jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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.
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.
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Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379
In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(
I had one of those- nice. IIRC, the keys failed over time though.
Best regards, Spehro Pefhany
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"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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:
formatting link
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You can't have a sense of humor, if you have no sense.
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.
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You can't have a sense of humor, if you have no sense.
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.
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.
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".
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.
Which will be compensated for continuously by the loop.
Well, don't operate it in that regime ...
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'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.
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.
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.
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.
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.
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Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379
In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(
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.
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.
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:
I didn't know that antennas were modulation specific.
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:
I suspect the largest numbers are in "atomic time" wristwatches.
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 jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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. :-(
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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