[time-nuts] Re: Power and heat re: Heathkit WWV clock / where are the good oscillators?

[Joe Duarte]

Thanks all. That Dallas Semiconductor model looks a lot better than I've
been seeing. The DS RTC on the Beagle or Canaduino boards I've seen off
some of your websites were using a lower DS model number, maybe 3107 or
some such. The Microcrystal models look good too – I just learned about
that company last week, even went to their site, but must not have
processed the specs. Maybe I looked at lesser part numbers.

Around the same year that Heathkit designed and launched the GC-1000, I
discovered that the British magazine *Radio & Electronics World* published
a guide to build your own MSF-synced clock (MSF is 60 KHz like WWVB). Their
design seems much cleaner than the Heathkit monstrosity – it might be
because they use a Zilog Z80 instead of microcontrollers. In 1982 they
released the first design guide, and in April 1983 they updated it as the
"Rewbichron 2". See here:
https://worldradiohistory.com/Radio_and_Electronics-World.htm

The antennas alone make WWVB seem like a better choice than WWV – little
ferrites vs. a giant loop.

I wish I understood the disciplining better. I still don't grok PLLs. I
don't understand what exactly the Heathkit does to its oscillator, and how
long the benefits last without a sync. The descriptions of GPSDO make it
sound like it's not real disciplining, just software correction. If
disciplining is just software then I assume I can find code. I wonder if
the high accuracy watch movements all use aged crystals.

Cheers,

Joe

On Sun, Aug 7, 2022, 17:21 Bob kb8tq via time-nuts <time-nuts at lists.febo.com>
wrote:

> Hi
>
> Backing up a bit:
>
> Any oscillator ( RTC or not ) is going to age. As it ages, the rate it
> looses
> or gains time speeds up. A device that is dead on today might well age
> a ppm ( or more ….) per year.
>
> Oscillators all are going to have a temperature spec. That’s going to apply
> over some range of temperatures *and* up to some (often unstated) rate
> of change.
>
> You then have a set accuracy. When the device leaves the factory, it’s
> within tolerance of “dead on”. That might be 0.1 ppm, it could easily
> be something else. Solder the device into a board via a typical reflow
> process and it’s not set where the factory put it any more …
>
> Past that, you have all of the other nasty little factors. Supply voltage
> moves things around. Shock / vibration / acceleration move things.
> On a module that is not hermetic, humidity will get into the act. How much
> do any of these contribute? That depends ….. could be tenths of a ppm.
>
> The accuracy of any oscillator at any point will be driven by the sum of
> all this “stuff”. The bold print number in that flashy ad likely puts one
> of
> the numbers in focus and pretty much ignores the rest ( …. in a constant
> environment ….). Parsing all the advertising talk often is more than a bit
> difficult.
>
> Do most oscillators do pretty well? Sure they do. This or that goes one
> way today and the other way tomorrow. Net at the end of the week is some
> sort of cancelation. If the aging spec is a max, you can bet that most will
> do better than that limit. However if you have to be *sure* the device
> will
> do this or that  ….. hmmm …..
>
> If you make wrist watches, the most common solution to this is to set them
> so they typically go a bit fast. Apparently folks don’t seem to mind
> arriving
> a bit early. They get bothered when they show up late. Back in the day,
> that set target was 10 seconds a month. These days, it’s not quite that
> much.
>
> Fun !!
>
> Bob
>
> > On Aug 7, 2022, at 1:56 PM, Hal Murray via time-nuts <
> time-nuts at lists.febo.com> wrote:
> >
> >
> > Azelio Boriani said:
> >> The Swiss MicroCrystal claims +/- 1ppm accuracy and +/- 0.09 seconds
> per day
> >> for their RTC modules. <https://www.microcrystal.com/en/products/
> >> real-time-clock-rtc-modules/>
> >
> > Note that the slots in that table with 1ppm are for 25C.
> >
> > I looked at the data sheet for the top slot: 2.5ppm over -40 to +85C.
> >
> > There is a graph for the temperature of the crystal that goes to over
> 100 ppm
> > so I assume there is some trickery to add/drop pulses.  That is probably
> OK if
> > you are driving a watch but may be "interesting" in other applications.
> >
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
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