[time-nuts] New to list and GPSDO questions

[Chris Howard]

I like that explanation.  I think I get it.

I don't think it is likely to cause me any worry.

My actual measurement of ADEV on my VE2ZAZ device
gave me a 100,000s sigma of just under 1E-10
and that works for me (best is at 1000s, 4E-11).

Maybe the strength and the danger of the VE2ZAZ
design is the wide range of integration settings.
If I were to pick some very unfortunate settings,
maybe it would degrade overall performance in the
way you describe.

Thanks for taking the time to explain it to me.

Chris






On 6/13/2013 10:15 PM, Richard H McCorkle wrote:
> Chis,
> 
> Over time without phase correction the analogy would be more like
> zig to the right, correct to go straight, zig to the right, correct
> again, and keep repeating this sequence ad infinium as the source
> ages in predominantly one direction. Each time the phase shifts in
> the same direction and before long you are on a different road a
> full clock cycle to the right and continuing to shift in the same
> direction. The total number of clocks over the period has changed
> from the ideal even though the average frequency has been correct.
> So over the short-term the right number of cycles occur, but over
> the long term there is an increasing error from the ideal number
> of clock cycles as the period increases.
>   If all you need is a frequency that is stable over short periods
> then the phase is of no concern. But when using a scope or TIC to
> compare a device under test (DUT) to the reference to determine its
> Adev over longer periods then you need the phase of the reference
> to be constant over the maximum measurement period (typically 4-5
> days for a 1-day Adev value) to determine the DUT long-term drift.
>   By keeping track of the total accumulated count from an arbitrary
> starting point (i.e. when the reference sample is taken) and adding
> 6800 HEX each update the reference count would represent the ideal
> count after X updates if no drift had occurred. Comparing the
> current count to this ideal gives the total change since the
> arbitrary reference was first stored. By adding steering to keep
> the actual sample count at the ideal value then over the long-term
> there would be no drift as it would be corrected out. The actual
> phase to GPS isn't the important factor - the change in the phase
> over long periods (like a day or week) is as it represents an error
> in the total number of counts over that period and a reduction in
> the long-term stability.
> 
> Richard
> 
> 
>>
>> I'm with Bob in that I don't really understand this description.
>>
>> And what are we trying to be in phase with? the 1PPS?
>> Is it possible to reproduce the actual phase of the
>> clock in the GPS birds once it has been through my GPS
>> and come out as 1PPS?
>>
>> I picture the EFC steering the car straight down the road.
>> And you want to adjust not just the drift to the right but
>> steer back to the center of the lane.  I think I get
>> that part.  I don't get who is setting the lane
>> and why I should care.
>>
>> Do the statistics (ADEV, etc.) show that this is an improvement?
>> If I'm doing my slow zigzag down the center line or the
>> right shoulder, again, do I care?
>>
>> Chris
>> w0ep
>>
>>
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> 
> 
> 
>