[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".
More information about the time-nuts