[time-nuts] Fw: New to list and GPSDO questions

[Stanley]

As you drive down the road it is important that you do not over correct 
errors and look ahead and start turning before the car reaches the turn, 
your corrections have a delay in taking effect as well as a delay in knowing 
where on the road you are. You know where the car was but more important is 
where it will be when your correction takes effect.

Stanley

----- Original Message ----- 
From: "Chris Howard" <chris at elfpen.com>
To: <mccorkle at ptialaska.net>; "Discussion of precise time and frequency 
measurement" <time-nuts at febo.com>
Sent: Thursday, June 13, 2013 8:58 PM
Subject: Re: [time-nuts] Fw: New to list and GPSDO questions


>
> 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
>
>
>
>
>
> On 6/13/2013 5:51 PM, Richard H McCorkle wrote:
>> Hi Bob,
>>
>> The VE2ZAZ controller is a frequency locked loop that keeps the source
>> on frequency but over time the phase drifts, as past corrections are
>> not compensated for. When the system is stable every 16 seconds the
>> 16-bit counter rolls over 2441 times with an extra 26624 counts (6800
>> HEX). The previous count is subtracted from the current count, the
>> difference from 6800 HEX is used to update the EFC to correct the
>> frequency, and the current count is stored as the previous count for
>> the next sample. When the current difference is not exactly 6800 HEX
>> then a phase shift of 6.25ns has occurred over the sample period for
>> each count of the difference from 6800 HEX. The EFC corrects the
>> frequency to give the proper 6800 HEX over the following samples, but
>> the phase shift from the previous error during the correction period
>> remains.
>>   If you add a little code to provide a correction history you can
>> add phase correction to the VE2ZAZ controller as well. Once lock is
>> established store the sample count as a phase reference count. Add
>> 6800 HEX to the reference count every update and store the result as
>> the next reference value. Use the difference between the current and
>> previous samples from 6800 HEX to coarse correct the frequency as
>> currently done, but add the difference between the current count and
>> reference count to the EFC correction as a fine phase correction. If
>> hold or unlock occurs disable the phase correction routine until lock
>> is re-established. Then store a new reference and restart the phase
>> correction process. By updating the reference every update it provides
>> a phase history so the accumulated count error over time can be
>> removed and the phase of the source can be stabilized.
>>
>> Richard
>>
>>>
>>>
>>> Atilla,
>>>
>>> Isn't the VE2ZAZ circuit functionally equivalent to your example 3? 
>>> Granted, he's
>>> not picking the 10 millionth transition and checking its phase
>>> difference to the reference, but I've only got a 1PPS reference with a
>>> 1uS or so jitter from pulse to pulse.  Bert is averaging over 16
>>> seconds, and creating a PWM signal to drive an integrator (simulating a 
>>> DAC), which
>>> will drive a Trimble 34310-T.  And like I mentioned
>>> earlier, I just like the way Bert did it.  It has a kind of elegance
>>> that appeals to my inner hacker.  =)
>>>
>>>
>>> Bob - AE6RV
>>>
>>>
>>>
>>> ----- Original Message -----
>>>> From: Attila Kinali <attila at kinali.ch>
>>>> To: Bob Stewart <bob at evoria.net>; Discussion of precise time and 
>>>> frequency
>>>> measurement <time-nuts at febo.com>
>>>> Cc:
>>>> Sent: Thursday, June 13, 2013 3:39 PM
>>>> Subject: Re: [time-nuts] New to list and GPSDO questions
>>> snip
>>>> [3] Describes how to use a clock
>>>  synchronizer to build a GPSDO. Probably
>>>> not the easiest and not the cheapest way, but definitly one with a very
>>>> low parts count.
>>> snip
>>>> [3] The AD9548 as a GPS Disciplined Stratum 2 Clock, by Gentile, 2009
>>>> http://www.analog.com/static/imported-files/application_notes/AN-1002.pdf
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>>
>>
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>
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