Stratum one autonomy and assumptions about GPS

[Achim Gratz]

Hal Murray writes:
> esr at thyrsus.com said:
>> I have a USB thermometer on order, they're cheap.  Might I suggest you get
>> one and repeat this experiment, actually plotting your temperature
>> variation? 
>
> Most CPU chips include a temperature sensor.
>
> For Linux PCs, you need the coretemp module loaded.  The lm-sensors package 
> does that.
>
> You can get it by either parsing the output of the sensors command or by 
> looking in things like
>   /sys/devices/platform/coretemp.0/hwmon/hwmon0/temp2_input

I've checked the loopstat data from last week and both my rasPi get
steered less than +-1ppm from their baseline of -6ppm and -9ppm with a
temperature swing of about 4K over the day.  I can see when the sun was
hitting the roof and when I've had open windows, so I'm pretty certain
this is real.  You'd need a thermometer that does at least have
repeatability down to 0.25K to get something useful out of the
temperature data.

If you can get repeatability down to 10mK, then it'd probably be
possible to forward-compensate the temperature effects to below 5ppb,
giving you holdover capability for around 5 hours.


Regards,
Achim.
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