[time-nuts] DMTD Question

EWKehren at aol.com EWKehren at aol.com
Mon Jan 25 13:56:39 UTC 2010


Bob, the mixer/Filter op amp schematic is a direct copy of the NBS unit  
with late model op amps, comparator and an opto coupler in stead of the  
transformer. Isolation amps are actually MINI CIRCUITS the next version will be  
op amps. I will ask Richard to release the counter schematic. Since there 
are  still changes I am reluctant to release partials.
Once a final version is complete, schematicsand PC board layouts will be  
available to every one, to do with as they choose. 
If you contact me directly I will send you a picture.
Bert 
 
 
In a message dated 1/25/2010 7:54:09 A.M. Eastern Standard Time,  
lists at cq.nu writes:

Hi

I think you will find that the SYPD-1 (or RPD-1) is the  better choice 
compared to the SRA-1.

Are the schematics out there for  the curious to look at?

Thanks!

Bob


On Jan 25, 2010,  at 7:01 AM, EWKehren at aol.com wrote:

> Allow me to add some comments  to this subject.
> Five month ago I set out to make a DMTD that would be  $ 200 max and be 
such 
> that any one can build it with readily  available parts. The unit also 
> includes  five counters yielding  a resolution of 1 E-15. Using five 
counters not 
> only  gives  Allan Variance but also frequency difference. The counter is 
> powered  by  the computer through USB and also transfers the data to the 
PC.  
> The counter  section is less than $30 of the total cost. The  cost goal 
has 
> been  reached. The counter does not have to be  used if one wants to use 
his 
> present  counter. The DM board does  have high speed opto couplers that 
allow 
> other  counters. Corby  is presently using that approach. Cost does not 
include 
> the   offset Osc. but a low cost solution is in the works, subject to  
>  evaluation.
> Corby Dawson and Richard McCorkle have been major  contributors.
> The goal is 1 E-13 and present tests show 3 E-13 right  out of the box. 
> Having Cesiums, Rubidiums and Xtal Osc. the best I  have is a FTS 1000  
> A-100 with 3.11 E-13 at one second. I also  think I will never have any  
thing 
> better than the FTS unit.  That is why my goal is 1 E-13.
> The present unit uses SYPD-1 as mixers  but Corby will test the unit  
with a 
> couple of HP10514A's to  evaluate the Mixer contribution.
> I realize I am offending some of the  purists on this site but I wanted 
to  
> keep cost down so I  squeezed both channels on a very compact board  
> (4.3X2.9) and  the counter is on a 4.3X2.3 board. How ever if we will  
not reach 1  
> E-13 with this approach I have a fallback using individual   boards for 
each 
> channel still meeting the cost goal. Other Mixers  will also be  
evaluated, 
> like the SRA1 since price and  availability of the HP10514A/B will not  
help the 
> cost  goal.
> 1 E-13 should satisfy 95% of time-nuts and at $200 including  PC  boards. 
> The second board with some changes hopefully will be  assembled this week 
 for 
> testing and based on its results a  third board will go  to ExpressPCB. 
> It is moving slower than  what I had hoped for, but 3 E-13 right out of 
the  
> box with no  special magnetic shielding or power supply decoupling gives 
me  
>  hope.
> PC boards will be the major cost factor, for my calculations I  assume in 
my 
> calculations that ten boards will be ordered at a  time.
> 
> Bert Kehren   Miami
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