[time-nuts] GPSDO Alternatives

EWKehren at aol.com EWKehren at aol.com
Fri Dec 7 22:38:35 UTC 2012

Attached is my latest ExpresPCB layout of a GPSDO. A clear  understanding 
of the GPS limitations, a goal as to what I want to control ,focus  on 
attainability, reproducibility KISS, cost and tests of partials on  development 
boards and what you see if you download the ExpessPCB software is on  the 
right the saw tooth correction, in the middle the analog board with opto  
isolation to prevent ground loop and on the right the actual GPSDO.  This  
particular unit also allows you to link a 20 Hz offset FRS-C (part of my dual  
mixer) to my house reference. Total material cost depending how many boards  one 
buys is below $ 40. I will include this particular board along with other  
designs on my next order and subsequently cut with a sheer.
The board on the right could be used by itself with minor  modifications to 
directly drive a FE 5680 if some one would step up to the task.  Total cost 
below $ 15. I use the analog board, which by the way is the most  expensive 
since it has a LTC 1655 and REF 02.
No dither 16 bits, dither 18 bits and depending on loop time,  clock 
frequency range starting at 3 E-9 and resolution up to 6  E-16.
Again I am only interested in to controlling a Rb which gives  me way more 
flexibility, the Rb's are either modified with a 10811 or in  one case with 
the M1000 and in the case of the FE 5680 a MV89 with a separate  analog loop.
And in all cases the RB is temperature  controlled.
All this based on over 10 years of work with the Shera  controller, 
exclusively controlling Rb's.
Bert Kehren
One more thought you may want to look at a 1 $ gate array for  all your 
timing issues. Simplifies the work dramatically. With the long loop  times 
associated with Rb and high sample rate, 100 psec. are no  problem.
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