[time-nuts] Cheap stable frequency sources
magnus at rubidium.dyndns.org
Thu Sep 23 21:45:45 UTC 2010
On 09/23/2010 06:27 AM, Hal Murray wrote:
>> Youâ€™d probably want to inhibit the circuit during the two periods between
>> dawn and dusk to avoid what I believe is called the diurineal (sp) shift.
>> In that small amount of time the Rb oscillator shouldnâ€™t drift out of spec.
> I think it's more complicated than that. The problem is that the ionosphere
> layer changes height from day to night. While it's changing, there is a
> slight Doppler shift. If all you want is frequency, both day and night are
Daytime involves much more changes than night-time.
> The catch is that there will be a phase/time shift between day and night. So
> if you mask out a few hours around sunrise and sunset, you will be modulating
> your oscillator with a square wave with a frequency of 1 cycle per day.
> If you can coast for 24 hours, it might work to only unmask during the night
> or during the day. (whichever works better at your location)
You can run interleaved measurements of day and night-time such that
unregulated time becomes less. Trouble is, other effects will work with
the same period.
More information about the time-nuts