Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!cs.utexas.edu!uunet!zephyr.ens.tek.com!tekcrl!tekfdi!videovax!bill From: bill@videovax.tv.Tek.com (William K. McFadden) Newsgroups: sci.electronics Subject: Re: NBS time broadcast Message-ID: <5504@videovax.tv.Tek.com> Date: 1 Aug 89 16:57:01 GMT References: <8720@kean.mun.ca> <5502@videovax.tv.Tek.com> <13107@nsc.nsc.com> Reply-To: bill@videovax.tv.tek.com (William K. McFadden) Distribution: na Organization: Tektronix TV Measurement Systems, Beaverton OR Lines: 69 In article <13107@nsc.nsc.com> woolsey@nsc.nsc.com.UUCP (Jeff Woolsey) writes: ->In article <5502@videovax.tv.Tek.com> bill@videovax.tv.tek.com (William K. McFadden) writes: ->>The clock's timebase is a 3.6 MHz 10 ppm crystal oscillator. It compares the ->>drift of this oscillator to the WWV tones and continually trims it with an ->>DAC-driven varactor. This makes the oscillator very accurate over the long ->>term. ->But obviously the oscillator isn't going to get any more accurate after ->the eighth time the clock sets itself. That can happen within an hour ->if you have a good signal. What I meant was that, integrated over a long period of time, the timebase is very accurate. This is because it is always playing "catchup" with WWV. (However, this is NOT true if the drift is large and the clock has to reset itself.) An analogy I like to think of is line frequency. The power line may be slightly off frequency at a particular moment, but over the long run it averages out. ->I have yet to see any such clock that does the DST correction properly, ->i.e. applies it at 2AM local time. All of the clocks I have seen ->simply apply the bit in the time code when they see it. At WWV, this ->bit is a toggle switch that the operator flips as close to 0000Z on the ->prescribed day as is possible. Sometimes they forget. That's true. Another nit I forgot to mention. Having it change in mid- afternoon is a bummer. ->>I have only a few complaints about the clock. First on the list would ->>have to be the RS-232 interface, .... ->>... the output levels are 0 volts and 5 volts. ->Indeed RS-232 standards are not met, but those aren't the actual output ->levels. Ground (pin 7) is at 5 volts, so that they can swing a 12V TxD ->line and it will go negative (relatively) more than 3 volts, so it is ->sort of within the realm of RS-232 operability. Your clock must be different than mine because mine puts out 0 and 5 volts. The schematic says so and an oscilloscope said so. I built my clock in 1985, so I'm not sure if yours is newer. Anyway, I'm glad they fixed this. (Maybe I can modify mine.) ->>The second problem is a couple of times it has set itself to the wrong ->>time. ->This is now a known problem, not limited to power-up. My clock did ->that a couple of times, and after some correspondence with Heathkit they ->sent me a replacement CPU (with a piggy-back 2716), and the problem has ->not recurred. At the same time, the 1-second delay in the ASCII time ->disappeared with this CPU. Was it free? I would like to get this if it doesn't cost an arm and a leg. Have any idea how they fixed it? ->>The third problem is there is no way to set the time manually. ->There is a way to set the time manually. Inside the clock there is a ->test switch which was used to calibrate the 1000/1200 Hz decoder. Push ->the switch a few more times and you get to read/advance the day of ->year, hour, minute, and perhaps second .... Sounds like another new feature. I don't remember my clock having it. (Of course, it could be my memory that's at fault, and not the clock! :-) I guess it's time to call Heathkit and ask about a software upgrade. -- Bill McFadden Tektronix, Inc. P.O. Box 500 MS 58-639 Beaverton, OR 97077 UUCP: bill@videovax.Tek.com, {hplabs,uw-beaver,decvax}!tektronix!videovax!bill GTE: (503) 627-6920 "The biggest difference between developing a missle component and a toy is the 'cost constraint.'" -- John Anderson, Engineer, TI