[time-nuts] GPS Control Loop

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25 years ago Brooks Shera developed a GPSDO that had a Frequency accuracy of 1 E-11. A year later in  1998 he published his work in July 11998 in QST. The total package included circuits,   PC board and in depth analysis of every part of his design including his filter.. I was one of the first buying the board, GPS receiver and working with an other Time Nut building a couple of units. Using my Tracor 527E,, HP5345A and aHP5061A Cs in parallel to an Austron Loran C system using multiple HP 10811's in all cases observed better than 1 E-11 frequency.  All 10811's had previously been tested to have an AV below E-12. Subsequent tests with Austron 1150 and Datum 1000 showed even better results. Over time Brooks added features but the design remained the same. His last effort was to make other DAC's available, but at that time his Cancer had spread to his brain.

Lets remember this was the time of S/A and it is safe to say GPS has improved by a factor of 100. DAC's compared to the Audio DAC are also improved by a factor 50.

Using later circuits we still use his design and Richard McCorkle did a PIC based on his Filter for us.

Very little else has changed. Reviewing commercial units like End Run short term is a function of the OCXO or Rb, long term GPS.

There was a time when Time Nuts had access to quality surplus OCXO's and Rb's at a 'reasonable" price, that tine is gone. Before the time I did get an OSA 8607 I did look at a Morion OCXO, their best with an AV of 2 E-13 at 1 second. The would not respond to my RFQ but thanks to a Time Nut that buys from them regular the answer was 6000 Euro and 1 year delivery after order!
To us Shera is the Gold Standard. worth a review for any one doing their own GPSDO, we are presently focusing on the best GPS receiver, my problem is Ublox 9T is not an option because at 80 I am not able to get safely on the roof. Hire some one is an option but liability may be a problem                                                                             Bert Kehren