The digital frequency synthesizer used for tuning was not exactly well-designed, but the tuner and stereo decoder part (which is what most folks actually wanted an FM radio for) was a real POS.
Isaac
one
off
fails.
Confucius , he say, but even a stopped clock tells the right time twice a day
OT: Have you seen the recent thread on rec.antiques.radio+phono ?
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?
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.
The cheapest GPS board or module that I could find is about $40.
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:
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.
-- 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
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.
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 The big
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:
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.
Incidentally, some data on the accuracy of the 60Hz power line frequency:
-- 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
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:
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 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
isw wrote in news:isw-C3E189.00325620052012@[216.168.3.50]:
the time hysteresis would be too great for temp control of the oven.
-- Jim Yanik jyanik at localnet dot com
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.
According to the "Service Improvement Plans" , the east coast project has been abandoned, at least for the forseeable future. Funding for it was part of the 2009 stimulus bill, which, as much of the money in that bill, was never spent. Marshall Space Flight Center objected to the high power transmitter being built so close to its operation in Huntsville, AL.
-- Dave M A woman has the last word in any argument. Anything a man says after that is the beginning of a new argument.
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. :-(
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.
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.
No. AM transmissions were to continue, alternating with phase shift modulation.
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:
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:
It says accurate to 0.3 seconds.
More on such clocks:
-- 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
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.
I once had the older vacuum flourescent version. They changed to LEDs at one some point. I forgot how/why mine broke.
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
Then you need a slower filter. This sort of loop does not make sample-by-sample corrections; it zeroes long-term drift. Tweaking the frequency by altering the temperature will work fine for that. If your clock is drifting slow, tweak the temperature slightly in the proper direction and wait a few hours -- or a day or two. Check again, tweak again. Pretty soon, the corrections will become less and less frequent, and also smaller.
Think about it; it's exactly the same way you regulate a balance-wheel clock.
Isaac
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.
But if it ran at the same rate as the GPS clock, then it wouldn't be drifting ...
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).
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).
Yes, but if they're not even there to begin with, then they're pretty noiseless even without special measures ...
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
And his smarter cousin says "Quite true, but can you tell me when I should look at it to set my watch?"
Isaac
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