Guys, in order to entertain you a little bit during your hard work - here is an idea how to adjust gain and offset such it fits an OCXO's tuning range best..
![Cheesy :D](https://www.eevblog.com/forum/Smileys/default/xcheesy.gif.pagespeed.ic.KPzuH4J-TG.png)
The schematics:
1. at the input there is a resistive Divider (ie. it divides 1-5V DAC output to 100-500mV),
2. then an Adder (adds an Offset, ie. 6V for your OCXO) and
3. a "minus one" Multiplier (as the Adder does -1*(DAC+Offset) )
4. and finally the output goes to the OCXO's EFC input (the 100k there is the internal impedance of the OCXO).
With given values a DAC output of 1-5V divides to 100mV-500mV, adds approx 6V Offset (set via the pot trimmer) and the OCXO's EFC is then 100-500mV range around those 6V.
It needs a negative supply rail - that is pretty annoying..
![Face Palm :palm:](https://www.eevblog.com/forum/Smileys/default/xfacepalm.gif.pagespeed.ic.EBDwh1hCfo.png)
The below five colors are outputs for 1,2,3,4,5V input from the DAC.
You have to add a decoupling, use some better opamps (noise, offset, tempco), use stable and clean power supply.
Provided as-is, use at your own risk..
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/xsmiley.gif.pagespeed.ic.R8GFI-pF6f.png)