[time-nuts] Lars GPSDO

[Jim Harman]

I see the AD5680 uses a dithering approach to get the last 2 bits, so the
noise may be a problem. I suppose I could suppress it with  a LPF on the
DAC output. Also I have no way to measure the effect of any DAC noise on
the oscillator frequency, so for the time being I am blissfully ignorant.

I suppose I could AC couple a high gain amplifier to the DAC output and
measure the noise, or tune an FM receiver to the 9th harmonic of the 10 MHz
and listen for noise.

I have successfully hand soldered a 6 pin SOT-23 but the AD5680 is an 8 pin
chip and thus even more challenging, and breakout boards for them are hard
to find and/or expensive. I see Digi-Key has a service where you buy the
chip and they will deliver it soldered to a breakout board for a few $
extra. I may give that a try

On Fri, Apr 5, 2019 at 5:21 PM Bob kb8tq <kb8tq at n1k.org> wrote:

> 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
>
> --

--Jim Harman