[time-nuts] Voltage Standards

[SAIDJACK at aol.com]

Hi Brian, guys,
 
I think the original thread stated something like "how to use a GPSDO as a  
voltage reference".
 
To this I have a couple of suggestions for tinkering (not sure if this has  
been suggested before):
 
  1) Most OCXO's have an internal Zener reference voltage that is  located 
inside the oven, and thus extremely stable. This voltage is usually on  the 
center pin on a Eurocan OCXO, and it is meant to drive a pot that can be  used to 
trim the crystal frequency. Thus your GPSDO may just give you a  free ovenized 
Zener reference already.
 
The better the OCXO, the better the reference typically. Absolute voltage  
will be different from unit to unit though. High-end double oven units can be  
expected to have the best performance.
_____________________
 
   2) If we have a well aged GPSDO OCXO with extremely small  aging (such as 
the Jackson Labs Fury GPSDO unit in Mexico: 
_http://resco.ucol.mx/Fury/gpsstat.htm_ (http://resco.ucol.mx/Fury/gpsstat.htm) ,  and it does not jump (this 
one does from time to time), then the control voltage  of this OCXO can be used 
as a reference voltage with very high stability.
 
Number 2) would be generating a voltage directly from locking to a  frequency 
(UTC), so it would fulfill the premise of generating a voltage from a  
frequency :) This method only works if the OCXO has extremely small aging, the  
GPSDO has a very high resolution DAC (the Fury has 330nV lsb DAC resolution for  
example) and the OCXO does not jump. Some SC-cut OCXO's have close to zero 
aging  after months of operation, so maybe you are lucky to have one of these. 
 
You can see that the unit in Mexico typically has a DAC variation of  +/-20uV 
over the period of a day at 2.80055V, this includes the DAC/Reference  
stability errors of course, so the actual voltage variation may be less than  this.
 
Note that by locking to GPS, the method in 2) corrects for the temperature  
sensitivity of the external DAC and DAC reference!
 
The absolute OCXO EFC voltage is somewhat arbitrary of course, but the  
stability could be excellent depending on your OCXO aging.
 
Due to the OCXO aging affecting the measurement this may not be a perfect  
solution, but it does generate a voltage from a frequency, and many folks may  
have access to old OCXO's that do not age much at all anymore.
 
bye,
Said
 
 
In a message dated 11/29/2008 01:33:02 Pacific Standard Time,  
kirbybq at bellsouth.net writes:

Maybe we  should consider coming up with a standard voltage reference as 
a TAPR  project.  We have a lot of good brainpower out here and it seems 
a  lot of experience available.

Brian -  KD4FM