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

[Bob kb8tq]

Hi

There are a lot of plots out there looking at WWVB based devices. Since
there are a range of devices, there also is a range of performance. Accuracy
in the tenths to hundredths of a second is not uncommon depending on the
wall clock or module you are looking at. 

Propagation is a biggie with WWVB. The height of the ionosphere varies over
the day. That gives you a significant swing in “time of arrival” of the signal. 
This limits what you can get without going a bit crazy. The same changes also
impact signal levels and make reception a bit difficult in many areas on a 
24 hour a day basis.

The stock answer to all of this today is a GPS based device. Getting something
under a hundred nanoseconds out of one is pretty much a slam dunk. 

Bob

> On Aug 7, 2022, at 5:53 PM, Joe Duarte via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> 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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