[time-nuts] Dual Mixer update

[EWKehren at aol.com]

It is close to 18 month now that I first proposed a D/M for $200. Thanks to 
 the help of Corby, Richard, Brian, Bob and Hubert I think it is very close 
to  final release. The delay is mainly due to testing, not by the five 
mentioned  above but by others, that did get kits under the condition that they 
would  perform complete tests.
Corby focused on the Mixer board with excellent results and recommendations 
 with the final product now using AD 8007 and AD 8008 amplifiers for better 
 isolation. 1 E-13 at one second has been measured. To refresh every ones 
memory  it is a direct copy of the original NBS design with  newer components 
and  opto coupler in stead of transformer.
The counter went through two iterations and Richard was key with design  
support and PIC programming. A 100 MHz VCO/PLL was added in such a way that 
the  5/10 MHz reference can be used for counter frequency generation.
Hubert finally tested the complete system and that is why I am comfortable  
going forward.
Why did I not do the complete unit testing, my computer skills are  lacking!
Depending on the user the counter can get its power from the PC or the +-  
12 Volt needed by the D/M. When powered by the +-12 the opto Isolators can 
be  left out since the counter in turn is opto isolated on the output. 
Counter talks  to RS232 and USB. The counter in the one second mode has a 
resolution of 1E-15.  Obviously external counters can be used but at a total cost of 
$ 30 keeping ones  counter free for other tasks would make sense.
Cost of the system is mainly driven by board cost but with 20 board  sets 
the goal of $200 is attainable. Could not stay away from SMD parts  because 
some circuits are not available in DIL but there are only five on the  D/M 
and four on the counter. All but one are easy, the only challenge is the ADF  
4001 PLL but doable.
All info will be available to every one and I have no desire to get into  
the kit business but if only a small group is interested I will order boards 
and  critical components.
 
Right now I am looking for two time nuts that want to build a complete unit 
 and run tests with specific focus on the counter USB/R232 interface and  
adaptation of presently available plotting software. I would help with a 
parts  kit at cost. Please contact me direct and please only if you are willing 
and  able to get on it right now, the project could have been done eight 
month ago if  testing would have been done as promised. 
On a related subject Hubert and I are working on a slightly changed Austron 
 circuit that I previously posted, that will allow measuring delta between 
two  frequencies to 1 E-14 in one second, did get boards and will keep you 
updated on  progress.
Bert Kehren  Miami