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

shalimr9 at gmail.com shalimr9 at gmail.com
Fri Dec 30 19:37:43 EST 2011


Bert,

Would you have time to generate a brief report of your DAC testing?

I for one am very interested.

I could publish it on my web site if you want.

Didier KO4BB

Sent from my BlackBerry Wireless thingy while I do other things...

-----Original Message-----
From: EWKehren at aol.com
Sender: time-nuts-bounces at febo.com
Date: Fri, 30 Dec 2011 17:48:24 
To: <time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.)

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.
Bert
 
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 
digital  
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  
you 
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 
but 
again finding them both in one chip is the problem. I have seen  OCXO and 
DAC 
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 
find.

Stanley  


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