[time-nuts] Lars GPSDO

[paul swed]

Jim
Your hitting the nail on the head with my questions.
Though I have quite a few GPSDOs, Berts results have my attention. I can
also tell that the solution you have should also be relatively low power
consumption. Lets see what his 24 hour test does.
That said changing to the DAC was a good idea, but that also changed the
software.
I agree on the SOT 23 technology. I have a microscope and can handle it
just barely.
There are smaller technologies like msop8s and hand soldering just doesn't
work. BGA's heck noooo.

Figuring out the offsets for a ocxo tends to be a challenge. Careful
measurements and behavior characterization since everything I ever pickup
is random flea market stuff.
Regards
Paul.

On Fri, Apr 5, 2019 at 4:00 PM Jim Harman <j99harman at gmail.com> wrote:

> Paul,
>
> Yes, I switched from Lars's PWM based DAC to the MCP4725, which is
> available on an inexpensive breakout board. I wanted to avoid the original
> design's sensitivity to the 5V supply voltage. My OCXO has a 4V reference
> output and I use that to power the DAC. I use a resistor network between
> the DAC and the VFC pin of the OCXO to shift the DC level and reduce the
> control range, effectively increasing the 12 bit resolution of the DAC. A
> change I am contemplating is to switch to an AD5680 18 bit DAC which looks
> ideal for this application, but I have been put off by the tiny SOT23
> package.
>
> A schematic is attached. Recent changes, not reflected in this schematic,
> are a circuit to linearize the diode-R-C integrator and also output buffers
> for the 10 MHz and 1 pps.
>
>
> On Fri, Apr 5, 2019 at 12:10 PM paul swed <paulswedb at gmail.com> wrote:
>
> > Jim
> > The whole gpsdo seems impressive and also seems to be performing well.
> > When I look at the Lars GPSDO what you have built doesn't quite seem to
> > match. Such as using a real DAC. Is this one of the variants that can
> > exist?
> > Regards
> > Paul
> > WB8TSL
> >
> >
> >
>
> --
>
> --Jim Harman
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