[time-nuts] Thunderbolt? (re simple gpsdo.)

EWKehren at aol.com EWKehren at aol.com
Fri Dec 30 17:48:24 EST 2011

Over the last two years along with two list members that may want to pipe  
in, I have spend a large amount of time on D/A's and we went as far as  
developing a test board using the LTC 2440 and testing numerous D/A's taking in  
to consideration performance, solderability, cost, availability and the 
winner  is LTC 1655 by a long shot, is even available in a DIP with 16 bits 
more than  you need for any Rb and if you want 20 bits, dithering is an option. 
My testing  consistently shows with OCXO's aging that will in most cases 
allow operation of  an OCXO for 3 years with out intervention. To top it off 
the LTC1655 cost less  than $ 10. Testing the old AD 1861 was an eye opener 
but considering what its  purpose was and its time the best choice.
In a message dated 12/30/2011 4:24:37 P.M. Eastern Standard Time,  
timenuts at n4iqt.com writes:

The DAC  and it's voltage reference looks to be the weak link in the 
control and the "simple" goal. The CPU I mentioned before on closer look  
doesn't have a good DAC. The 20 bit TI DAC1220 looks better but not sure  
can find it in the same package as the CPU. The cheap Rb standards  with 
digital control would not need a DAC and maybe this points to a  simpler 
GPSDO that doesn't control the XO with analog but corrects it with  a DDS 
again finding them both in one chip is the problem. I have seen  OCXO and 
in the same package and even the DDS and OCXO combined but  they didn't fit 
the simple goal. Not even sure how good they were. I know  they are hard to 


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