[time-nuts] DMTD Question

David C. Partridge david.partridge at dsl.pipex.com
Mon Jan 25 13:21:57 UTC 2010


FWIW 100 boards will likely cost not a great deal more (say $5-20 depending
on board size than ten. 

Dave
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of EWKehren at aol.com
Sent: 25 January 2010 12:01
To: time-nuts at febo.com
Subject: [time-nuts] DMTD Question

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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