[time-nuts] Did a member of time-nuts buy this?-

Mike Monett timenuts at binsamp.e4ward.com
Wed Dec 10 20:02:26 EST 2014

>> What does the temperature controller do that degrades the ADEV?
>> Can anything be done to modify it to improve the performance?

>On the lightweight Rb's they feed the correction into a DDS. The DDS
>steps are big enough to show up above the ADEV. You get a "hump" in
>the ADEV as a result. The solution is to disconnect the temperature
>sensor that feeds the correction circuit.

OK, Thanks

>>> Lots of details to take care of. If you get them all right,
>>> you'll beat any / all of the older Cs standards.

>> Is there a list anywhere of all the details that need to be
>> addressed?

>Well, there's this list :)

>The things that need to be done are a "that depends" based on the
>approach you take. A full listing of all you might do down all of
>the roads you could take would be a wall full of books.

Yes, I was afraid of that!

>> How about words or phrases that can be used to search google and
>> the archives?

>GPSDO is a good place to start.

I searched google with the following:

https://www.febo.com/pipermail/time-nuts/ gpsdo

This gave 68 hits. I then used

site:www.febo.com/pipermail/time-nuts/ gpsdo

This gave about 2,310 results. Going to page 2 reduced the count to 136.

I had previously downloaded the archives from 2004 to 2013. A Boyer-Moore
search gave the following:

  Files Searched : 63404
  Matches Found  : 6198
  Bytes Read     : 329,255,183
  Elapsed Time   : 31,350.793 ms

So it seems google is not very useful.

It would appear the best approach is to simply start reading the posts at
the beginning and save the interesting ones.

>>> One very cute addition would be to pull down the NIST GPS data
>>> and use it to correct your system on an hourly / daily basis. If
>>> you do that with common view satellites, you most certainly will
>>> beat a surplus grade Cs standard.

>> How can we do this?

>First step is to be able to extract timing data from individual
>sat's. Not all GPS modules do this correctly.

Can you tell me some of the ones that do?

>> The NIST archives state
>> "The archive is only updated once every 24 hours, so data are not
>> available for today's date.
>Thus the "daily" statement. There has been discussion on the list
>that interchange with other list members at a more rapid rate might
>make sense. Given the floor of most setups, daily updates are not a
>bad thing.

OK, that makes sense.

>> Data from the previous day are added to the archive at about 1600
>> UTC."

>> http://www.nist.gov/pml/div688/grp40/gpsarchive.cfm

>> Is there another page that has current data? If so, how do we
>> incorporate it into the GPSDO?

>1) Measure your local time offset by GPS sat number every hour and
>save the data.

>2) When NIST posts there data, pull it down.

>3) Compare your data to theirs

>4) Do a fit

>5) Feed that into your control loop equation.

There's another term I need to research!

>The missing element is the per sat data.


OK, so I figure out how to do this. How do I tell if this is making the
gpsdo more accurate? In other words, how do I get the ADEV without having
an H-Maser?

Thanks for your help!


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