[time-nuts] FE 5680A GPSDO update

EWKehren at aol.com EWKehren at aol.com
Thu Jul 3 11:47:46 EDT 2014


First let me thank again Scott Newell for all the work he has  done. The 
links included in this post where made possible by Scott. All three  exceed 
the limit of time nuts but will give you a better understanding as to  what is 
going on. First removing the 10 K resistor changes the Rb frequency any  
where between 2 to 3.5 E-10 upward. It is a function of the temperature of the 
 device. In the first link you will see what happened right after removing 
the 10  K.
http://n5tnl.com/time/fe-5680a/gpsdo/JK5680A_Test35.xls  Allow me to explain
The first collum is time in seconds followed by time in hours. The third  
is phase input measured by the loop The loop will try to set it to 14080.  We 
call that the set point. The next column shows the delta to the set point  
followed by the control word send to the unit and its 2's compliment. 2's  
compliment since in this case it is mostly a very large negative number 
easier  to read. Finally the status word which shows a 1 saying it is unlocked 
followed  by a 0 other options are glitch hold and alpha. the third column 
shows which  mode. The way it is presently programmed it will advance to Mode 5 
and  alpha.  That would show up here as 15.
Before the modification this Rb showed when settled -124. The 1 pps comes  
from a $ 16 ublox M7 no sawtooth correction.. At about 18.5 hours the GPS 
filter  is activated with a 12 setting and you notice a dramatic change in the 
control  word. still has a few more steps. What you see is frequency 
correction do to  influences like GPS Rb and its temperature. Rb has only a 
heatsink, no  temperature control.
Next this mornings readings.  
http://n5tnl.com/time/fe-5680a/gpsdo/JK5680A_Test35c.xls.  This is more of the same but you see a dramatic change between 
day  (left) and night (right) allowing me to check when he is not  working.
Summarizing temperature control is not a requirement but the curve will  be 
flattened if the Rb is held at a constant temperature. Each digit is a 
change  of 6.8-13. but it is not directly correlated to the output frequency, 
what it  says it is the control word that according to the filter function 
tries to set  it exactly to 10 MHz. The plot that I attached so many times may 
contribute to  the frequency in 1 second increments that most likely is 
reduced by disabling  the heater current sensing but there may be other  sources.
That is why I feel strong about a clean up loop. Those happy with what  you 
see stop right now. Again thanks to Scott here is a link to the Auxillary  
board schematic. 
http://n5tnl.com/time/fe-5680a/gpsdo/AUXILLARYBOARDrevA27-04-2014.pdf   I did post a picture but to file limitation was not able to 
post  the schematic. It has room for power conditioning a PIC and two flexible 
outpu  circuits. First the PIC takes the output of the controller (attached) 
and  modifies it in such a way that it can drive a FTDI USB adapter to 
store the  output without PC requirement. The code is presently in PIC Basic 
would like to  find some one to write PIC code so we can use FTDI and a I2C 
display. Scott is  looking at it but if some one has the expertise would  help.
The outputs can be individually set to 5 or 10  MHz.
A third board is presently in the works by an other time nut. All boards  
will be in Gerber. He is working on a temperature control board. All boards 
are  5 X 5 cm.  What is missing is a clean up filter board. I am looking for  
someone that can do it in Gerber, please contact me off list. We have a 
circuit  but it is on expressPCB and should be modified for this  application.
I look at it the following way. More than half the cost of the kit  is 
taken  up by pay pal, shipping kitting etc. Boards are the smallest  cost part 
and going from one to 4 will only increase the kit cost by $ 5. In my  book a 
bargain. 
Comments are appreciated
Bert Kehren
Some may not get this post because AOL for instance flags it as  spam
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