[time-nuts] Lars GPSDO

[Jim Harman]

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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