[time-nuts] Dual Mixer/DMTD

EWKehren at aol.com EWKehren at aol.com
Fri Oct 2 13:08:34 UTC 2009

A couple of months ago I did announce that I plan to build a dual Mixer  
based on the NBS design with minor updates and add a counter section. All with 
a  cost goal of $ 200. Having all parts in house the goal has been reached 
when  boards get ordered in quantity ten. Thanks to inputs from Bruce 
Griffiths, Corby  Dawson and Richard McCorkle I do have prototypes and am in the 
testing phase.  Richard has written the code for the processors and the 
counter board is  assembled along with the simulator to be send this weekend to 
Richard to allow  him to test his code. The Dual Mixer will be assembled and 
tested this weekend  and will go next week to Corby to see how good it 
performs with his Maser and  compare to his NBS unit.
What makes this unit different is that it has five counters running at  100 
MHz giving at 1 Hz a resolution of 1 part E 15. The counters talk through a 
 RS 232 interface to a computer. This will not only give Allan Variances 
but also  show the frequency difference with the same resolution at a 1 Hz 
rate or if  the offset Osc. is 10 Hz ten times a second. There are also outputs 
for  those that want to use their present counters for Allan Variance. 
Right now the  PC interface is RS 232 but long term I would like to see USB, 
because the  counter uses so little power it could be powered by the PC. 
Isolation to  the Dual Mixer is through high speed Opto couplers.
 Long term I would like to encourage some one to design a two line  display 
that shows Allan Variance and frequency difference and also records the  
information on a USB stick. That would allow total isolation from power since 
it  could run on one 12 Volt battery.
What is next. 
Once Richard has checked his programs and Corby has checked the Dual Mixer  
I will incorporate any changes in the boards order and test one more set 
and  then make all information available to all. Richard has also graciously  
agreed to make his code available. In the meantime I have two extra boards 
and  part kits for some that are also willing to make a contribution to the  
project and I am not talking about money but further the project. Once 
finished  I will also have a few more kits available since with the exception of 
the  boards I purchase enough for ten units. The next board order (after 
check out)  will make it ten. I also have six HP 10811 that have been checked 
to 20 Hz  offset making them usable at 10 Hz offset at 5 MHz!
If every thing works as planned, my goal is to have every thing released by 
 1 November. Cross your fingers.
The Dual Mixer is 4.2" by 2.8" fitting into a standard German 72x111x20  
metal box for shielding. the counter is 4.8"x2.2". 
Bert Kehren

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