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

[Richard H McCorkle]

Hi Bob,
Any user of a Brooks Shera controller will tell you that phase errors
can be recovered using a jittery 1PPS reference. While the 1PPS may
jitter (+/- 42ns in a UT+ GPS) the jitter averages out to zero error
over time. The Shera controller uses the phase difference between the
1PPS and divided by 16 source to drive the EFC to maintain a constant
phase difference. The Shera design updates every 30 seconds and in
mode 1 the phase error from setpoint is sent directly to a DAC to
correct the frequency. Shera adds a selectable filter before the DAC
to reduce the EFC noise and increase the correction stability. More
samples averaged over a longer period increases the stability, but
smaller corrections are applied over a longer period to make the
phase (frequency) correction.

Richard



> Hi Richard,
>
> As time goes by, I'll reread your post until I understand it.  I'm a newbie, but
> It's hard to believe that there is enough information in a jittery 1PPS reference
> pulse to be able to recover phase errors.
>
> Bob
>
>
>
> ----- Original Message -----
>> From: Richard H McCorkle <mccorkle at ptialaska.net>
>> 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 5:51 PM
>> Subject: Re: [time-nuts] Fw:  New to list and GPSDO questions
>>
>> 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.
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