[time-nuts] Lars GPSDO

[Bob kb8tq]

Hi

If you do decide to play with the AD5680, be careful of the “tone” on the output 
at about 180 Hz. You might also want to check the noise inside 100 Hz since the 
spec sheet is of no help there. If the 180 Hz is the third harmonic of something much 
larger at 60 Hz …. yikes …..  Since there don’t seem to be noise specs on the MCP4725,
who knows if things are getting better or worse. I’d bet better …..

That *is* a weird little package ….

Bob

> On Apr 5, 2019, at 3:27 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
> <Arduino GPSDO Schematic v4.pdf>_______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.