In the UK, or in London at least, the mains frequency was maintained with a very accurate long term average, so that synchronous mains clocks just stayed correct.
Sometimes, after short power cuts, the frequency was increased to bring such clocks back to the correct time. Which was actually a bit of a nuiscance for us - we had clocks that weren't self starting (a reflection of the rareness of power outages in those days), so after a power cut, we'd set the clocks correctly and start them, only to find them gaining.
It seems a backward step that now, forty or so years later, household wall clocks are less accurate than they were back then.
Well, that's the basic receiver without that CPU. If you want to build a complete receiver, methinks this one:
is more appropriate. However it costs $71. The full development system, with software costs about $250. I was thinking that it might be best to have the PC do the processing, and use the cheaper receiver.
I don't know that much about the code used by WWVB. (I are not a programmist). I've gone as far as to disembowl an "atomic" clock (cheap LCD display), and sniff the time signals with a scope. It doesn't look too horrible. Some app notes on the CME8000 chip:
Software flow chart:
Also, the demo board app note was misnamed. Download the file and rename it with a .PDF extension. Then, it will be readable.
Start here:
Basically, you're building a clock, but instead of driving a display, you're converting the UTC to something the PC will digest. There are plenty of project on the internet, but none that I could find that included PC interface software.
PIC Based WWVB Decoder
Parallax Basic Stamp II Atomic Time Clock Receiver
Build a WWVB Radio Controlled Nixie Clock
Decoding WWVB from a Sony atomic time radio controlled clock
It's a very simple system that is well documented. It's simple and slow enough that anyone used to pulling apart data streams would be able to decode it with a Z80 derived embedded processor, the ARM chips in dead iPods, WiFi routers, etc would be "overkill".
Here in Jerusalem, we don't receive the signals of WWVB, or the German or UK equivalents here. Someone about 50 miles north and out of the mountains has a clock that syncs, but he never told me which station it uses (he may not know), or how often it syncs. This lead me to research how one would do the opposite, devise a local transmitter with an ethernet port on one end for NTP sync and a 60kHz transmitter to sync a clock on the other.
I gave up due to lack of a suitable design for the transmitter, no receiver and a lack of funds to obtain them. You probably could do it out of one of the Linux based routers, and blink one of the status LED's to generate the 50/60kHz signal.
I know by now you must be thinking "why would anyone even think of such a thing", but a discussion a few months ago about resurecting a Heathkit Most Accurate Clock, got me going. I think I also read a posting that the WWVB signals were being phased out.
Geoff.
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Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson.com N3OWJ/4X1GM
I did it 20 years ago with a VIC-20, in Commodore Basic.
You need a good antenna system to transmit on 50 or 60 KHz. Here is a sat photo of the WWVB antenna farm:
They replaced all the transmitters and towers at WWVB a few years ago to improve service. It now reaches Central Florida without a long wire antenna & tuner. Why would they spend millions and take a couple years to do the update if they were planning to shut it down?
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You can\'t have a sense of humor, if you have no sense!
Perhaps simple, not for me. I'm a lousy programmer and avoid programming as much as possible. However, taking a closer look, it does look rather simple.
See:
There's a list of other LF time xmissions. I wouldn't give up trying to hear various LF broadcasts. The problem is that they work best late at night. From Israel, I would not expect to hear them with an extremely short antenna. You may need to build a real LF antenna, with proper matching circuit, and possibly a FET RF amplifier. Maybe start with a loop antenna, which might be easier and grow as needed:
More on the C-Max receiver kit:
Building a store and forward repeater for WWVB (or the EU equivalent)
60Khz is a waste of time. The storage delay needed to regenerate the signal will result in the sync pulses arriving too late. However, a system that uses GPS, GLONASS, or Galileo as a reference, and generates a simulated time code format will work. The problem is that at 60Khz, the necessary antenna farm would be huge and the transmitters rather power hungry. WWVB runs at an EIRP of about 70kW.
Starting with NTP, GPS, or a Cesium or Rubidium clock will work. However, I don't know about the effectiveness of cramming it into the limited abilities of a commodity router. Methinks you would be better off with a SBC (single board computer) or common PC (ITX, Mini-ITX, etc).
Actually, a 60KHz xmitter is fairly easy to design. The problem is that all the components would be huge. There's also the not so easy problem of getting Ministry of Communications approval. It's not on the designated ham radio frequency list:
I'm sure that nearby users that went through the trouble of obtaining large antennas, will not be thrilled with your transmissions. Even a "local" transmitter can carry a substantial distance at 60KHz.
The GC-1000 used WWV at 5,10, and 15 MHz, all of which are still on the air. I'm not sure what a 60KHz system would do for you.
Repair your Heath kit GC-1000 Most Accurate Clock
I've given up asking "why". Some of the strange things I've seen on the internet defy logic and explanation.
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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
Do you really expect people to wear a watch when they sleep just to maintain accuracy? There's quite a difference in temperature between skin temp (about 37C) and room temperature (about 25C). The same for a computah. When turned off or in standby, the clock is slightly above room temperature. When running, it might be as warm as 75C.
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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
That's sort of what I was thinking of. Get the time from NTP, generate a fresh time code signal, which would not be accurate enough for someone who wanted truely accurate time code, but to keep a clock that displays to the minute, or even to the second on time, it would be good enough.
As for the transmitter, how much power do you need to transmit a signal from a time code generator to a receiver next to it, connected via a coax cable?
A microwatt? A milliwatt?
It depends. A cheap router, such as the Linksys WRTG-54L (note the L at the end it's the enhanced model that runs Linux) would do it. It sells new for not much money, will be obosolete as the 802.11N routers come into general useage, has an ARM processor, two ethernet interfaces (one connected to a
4 port hub), a WiFi radio and a bunch of status LEDs. The advantage of it is that there are several alternate Linux packages for it and you can easily compile your own programs, build your own "flash" (firmware image) and load it.
There are also distributions for other routers, I recently bought a $30 EDIMAX wired router that had a distribution for it.
If it is directly connected to the input of the receiver, it needs no license.
I also expect there are none. Around here the noise level is so high that they would never hear it until I got into the "real antenna" type system. A microwatt with true isotropic radiator antenna (a short wire) would not leave my apartment, let alone go anywhere. But if it is connected directly, then it is a moot point.
I was thinking of something simple, such as flashing the LED at 60kHz, and wrapping a pickup loop around it. That's about the same power level and frequency of a TV remote control and no one from the MOC has come and complained about any of the ones I have. I'm talking about the RF leakage from it, not the optical signal.
Not here. I have never heard them here, nor have I heard CHU (yes, I know it moved), any of the European stations, etc. I'm not talking about a cheap portable shortwave, I'm talking about a Kenwood R-5000 with a 75 foot random wire, or other equally as sensitive ham receivers either with a 20m resonant dipole or 1/4 wave vertical, or a 40m resonant dipole.
I'm not actually familar with the clock in question, the discussion (I think it was on this newsgroup) focused on them using WWVB (VLF) radios.
I'll agree with that.
Geoff.
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Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson.com N3OWJ/4X1GM
They will shut it down eventually because of the cost. NTP servers cost almost nothing, GPS is "free" because there are no incremental costs for providing the time signals.
Eventually someone will figure out that a 75kW transmitter has both a significant expense and a large "carbon footprint".
The upgrade was thought to be needed because of a satellite time system that was dropped due to GPS was thought to be unable to fit the needs of the common user. Now GPS units are almost throw away "toys", being used in almost every cell phone, and for all sorts of SATNAV devices.
Geoff.
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Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson.com N3OWJ/4X1GM
So Dave, do you happen to know if "New Tricks" is shot available light ? I was watching last week's episode that I had recorded, and that looked just like "The Bill" used to. Do you also happen to know how Euston Films shot "Minder" ? I watched an old episode of that on ITV4 tonight, and again, it had a lovely 'untouched' look. Was that actually film, naturally lit, or video ?
The receivers run on one or two AA cells for over a year. A GPS system would use a lot more than 75 KW to power an equal number of GPS based clocks.
Everything will die, some day including the earth itself.
Shutting down WWVB, with the large number of people using the 'Atomic clocks' that sync to it would cause a real stink. You can buy 'Atomic clocks' for under $20. Try replacing 75 cents worth of parts in a WWVB receiver & decoder with a GPS based clock for the same price.
VLF can be received under water, as well. Try using GPS for a submarine without surfacing, or raising a buoy with the antennas. Even better, try using that floating buoy in rough waters.
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You can\'t have a sense of humor, if you have no sense!
Yup, but the long-term average will be pretty good -- gain a little in the daytime, lose a bit at night (or the other way around; could be either one depending on how the circuit was set up).
Remember the old "Accutron" watches -- the ones with a tuning fork inside? You could adjust those by deciding which way to lay them on the table when you went to bed. "12 up" would run at a different rate than "12 down" because of the effects o gravity on the fork. Also, they ran noticeably fast on airplane trips, due to thinner air.
It would be *very good* because it would never drift. The rate (long-term) would be spot on, and the epoch (the name for "what time is it right now"?) would be only slightly in error.
You could synthesize the whole signal in software and drive a D-to-A converter to create the modulated carrier. Any commodity video D-A would be more than fast enough.
But very probably not, unless a very long antenna were attached to it.
Euston Films never used video. Suitable location equipment simply wasn't available in those days. They mostly used 16mm - with some 8mm if they wanted a particular effect.
I should make clear that making something look like it's shot by available light doesn't mean actually doing just that. Reflectors and flags etc are used to reduce the contrast to acceptable limits. To do it well can be more time consuming than actually lighting the thing. ;-) But things like Minder from Euston films were shot at breakneck speeds in normal film terms. ;-)
--
*If a pig loses its voice, is it disgruntled?
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
Maybe, if the wearer maintains a regular schedule. That's a fair assumption, until the wearer changes their usage pattern, such as going on a ski trip.
Also, please note that the original discussion was over the accuracy of a computah clock, not a wrist watch. Unless left on continuously, computers don't maintain a set schedule. Even so, their internal temperature is affected by the building environment.
I have a 1965 Accutron 214 Space View wrist watch in poor condition. The specs offered 1 or 2 seconds per day, but only for the first year. After about 30 years (the last time it ran) and zero service, my guess is that it was off about 60 seconds per day. I forgot if it was a gain or loss. The mercury battery leaked inside and it's unfortunately not currently running. (Yet another project).
You might also be refering to the problem caused by the original steel watch hands. When they were near the tuning fork coils, the frequency would lower slightly. The effect was not very big, but still and error.
The position problem is also not 12 o'clock up versus down. It's 12 o'clock verus 90 degree rotation which is 3 or 9 o'clock. The problem stems from the tuning fork being vertical or horizontal. The recommended solution is to lay the watch flat at night. I don't think it was ever a major problem, just an interesting curiousity for accuracy fanatics.
A more interesting problem was mechanical vibrations in the 360Hz range. (the frequency of the tuning fork). When my watch was working, it would tend to run quite fast if I was working near big synchronous or induction motors driven by 60Hz such as in my fathers clothing factory. It was not unusual to gain about a minute, after spending an hour pushing cloth through an industrial sewing machine (with my hands on the table). I suspect (guess) that vibration was also the problem in airplanes, not thin air.
Temperature is of course a problem:
--
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
How much accuracy are you looking for in a PC clock? I doubt that WWV will give you millisecond PC clock accuracy, but it's more than suitable for nailing it withing one second. Averaged over even a fairly short period of time, the 2.5/5/10/15/20Mhz frequencies are quite accurate. For re-synchronizing the clock, the time ticks are also sufficiently accurate:
WWV Frequency Accuracy As transmitted: 1 part in 100 billion As received: 1 part in 10 million
WWV Time Tick Accuracy As received: 1 millisecond plus propagation delay
WWVB Frequency Accuracy As transmitted: 1 part in 100 billion As received: 1 part in 100 billion
The major ionospheric multipath problem is the almost 180 degree phase reversals from constant path switching as the various incident and reflected signals fade in and out. Yeah, that's going to be a problem, but due to the limited accuracy required in a PC, it's not a big problem.
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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
NIST funding was increaded from $719 million to $819 million.
National Institute of Standards and Technology: The FY 2009 appropriation was $819.0 million. The Administration's request was $846.1 million, an increase of 3.3 percent or $27.1 million. The House bill provides $781.1 million, a cut of 4.6 percent or $37.9 million. The Senate Appropriations Committee bill would provide $878.8 million, an increase of 7.3 percent or $59.8 million.
Operating costs of the various standards stations and labs seems to so small as to not even be mentioned. I didn't see any mention of shutting down anything.
--
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
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