[time-nuts] removing sidereal correlation

Magnus Danielson magnus at rubidium.dyndns.org
Sun Apr 30 17:14:31 EDT 2017


Hi,

Upload rates have been important for GALILEO to distinguish itself from GPS.

As GPS has been looking into the future, they have asked about the 
bitstream rates and asked increased speed vs. improved redundancy. I 
think I recall going towards the later.

Cheers,
Magnus

On 04/30/2017 10:23 PM, Bob kb8tq wrote:
> Hi
>
> A *lot* of the upload and estimate processes have changed over the years. What was true
> at "maybe every 2 hours" four years ago might be wrong today. Oddly enough it *could* be
> wrong in either direction.  What they can’t change is the coarse resolution of the estimate.
> That’s embedded in the rather limited bit stream they have coming down from the sat’s.
>
> Bob
>
>> On Apr 30, 2017, at 2:08 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>>
>> Hi,
>>
>> Upload rate could be one. There is some systematics due to jumps from the old to new estimation. I think I recall a 2 h upload rate, but no guarantee for that number.
>>
>> Cheers,
>> Magnus
>>
>> On 04/30/2017 06:32 PM, Eric Scace wrote:
>>>   What other patterns, if any, are uncovered if one removes a smoothed sidereal variation?
>>>
>>> — Eric
>>>
>>>> Begin forwarded message:
>>>>
>>>> From: Jim Harman <j99harman at gmail.com>
>>>> Subject: Re: [time-nuts] Three-cornered hat on timelab?
>>>> Date: 2017 Apr 29 Sat at 10:14:58 EDT
>>>> To: Bob Stewart <bob at evoria.net>, Discussion of precise time and frequency measurement <time-nuts at febo.com>
>>>> Reply-To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
>>>>
>>>> On Thu, Apr 27, 2017 at 12:48 PM, Bob Stewart <bob at evoria.net> wrote:
>>>>
>>>>> So, back to my question:  Where are the large ionospheric phase moves?
>>>>> This question has been causing me doubt since I started on this project.
>>>>> Or don't I still have enough data collected for this to happen?
>>>>>
>>>>> Bob
>>>>>
>>>>
>>>> Bob, my test setup is a good deal simpler than yours, but attached is a
>>>> plot that I think shows the variations you are looking for quite clearly.
>>>> This is data from my homebrew GPSDO, which uses an Adafruit non-timing GPS
>>>> module and a run-of-the-mill surplus OCXO. The plot records the phase
>>>> comparator output over a period of about 1 week. The time constant of the
>>>> PLL is 1024 seconds and it is plotting the 5-minute average TIC values.
>>>>
>>>> The full horizontal scale is 24 hours.
>>>>
>>>> The vertical scale shows the data from several days with the traces for
>>>> successive days offset upwards by the equivalent of 40 nsec.
>>>>
>>>> As you can see there is pretty good correlation of the phase error from day
>>>> to day and the wiggles migrate to the left a little, corresponding to the
>>>> 23:56:04 siderial repeat time of the GPS constellation.This is with a
>>>> pretty good antenna location, under a shingle roof in the attic. I
>>>> calculate the day-to-day correlation at about 0.8.
>>>>
>>>> Making the time constant larger increases the variations somewhat, because
>>>> the loop does not adjust as much, and they definitely get worse if I use a
>>>> less optimal antenna location.
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>>
>>>> --Jim Harman
>>>> _______________________________________________
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>>>
>>>
>>>
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