[time-nuts] Cheap stable frequency sources

[Magnus Danielson]

On 09/23/2010 06:27 AM, Hal Murray wrote:
>
>> You’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 shouldn’t drift out of spec.
>
> diurnal
>
> 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
> stable.

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.

Cheers,
Magnus