[time-nuts] GPS/UTC time

Bob Camp kb8tq at n1k.org
Sat Jul 4 09:20:26 EDT 2015


Hi


Unless your crystal has been cut for temperature sensing (AC or LC cut) you will have some
issues sensing temperature over a very wide region. 

Bob
> On Jul 4, 2015, at 12:45 AM, Brek Martin <bmar8190 at bigpond.net.au> wrote:
> 
> 
> 
> Hi Guys,
> 
> I feel like I missed “The Big Thing” in time keeping land. I should have watched my Ublox LEA-5T.
> What is the difference if it is in the reporting mode for GPS or UTC time?
> If they skip a second UTC, surely the GPS time isn’t run incorrectly forever.
> 
> I’m using the Ublox to synchronise a micro that is clocked with the 10Mz signal from and Rb module,
> and the micro controller keeps time from there. So I currently wouldn’t see a leap second unless I looked back at the GPS.
> 
> Another idea I had since making a copper thermal mass for the Rb module…

If you go back about 6 years ago in the archives, we went through all of the math on thermal mass as a regulator for this 
sort of thing. A search for “swimming pool full of mercury” may turn it up. Bottom line is that you need a *lot* of mass. A
fan / sensor / heatsink / controller combo is a much more effective solution. 

> A microcontroller clocked with the Rb module should be able to tell the temperature by counting the frequency
> of any other crystal generated clock in the circuit.. not necessarily just for the Rb thermal mass, but outside environment.
> Although the temperature has some effect on the Rb module frequency, it is less then the effect on Xtal frequency.

Unless your crystal has been cut for temperature sensing (AC or LC cut) you will have some
issues sensing temperature over a very wide region. Probably the best thing you can easily get
would be:

1) An SC cut run on the wrong mode.
2) An AT cut for an OCXO and used to sense in the vicinity of room.

Bob

> Cheers, Brek.
> 
> 
> ps. am I replying the way I’m supposed to with a new email and subject?
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