[time-nuts] GPSDO on the cheap

M. Simon msimon6808 at yahoo.com
Thu Dec 6 18:45:48 UTC 2012

I would use a digital pot for coarse setting. Or a manual trimpot. That way your control signal "holds" even if your comparison goes away or if for some reason your loop comes out of lock. Something like that also reduces the noise contribution of the DAC.  



Date: Thu, 6 Dec 2012 01:17:52 -0800
From: Chris Albertson <albertson.chris at gmail.com>
To: Discussion of precise time and frequency measurement
    <time-nuts at febo.com>
Subject: Re: [time-nuts] GPSDO Alternatives
    <CABbxVHs_XiBAX15h27c38L4gEvmMGNzWO+9Fw2J-BQG9k5Z_jQ at mail.gmail.com>
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Don't need anything so complex.   A GPSDO depend on an OCXO that is VERY
stable.  It can be controlled with a very low bandwidth analog signal.

The output from a OCXO is divided down and then the phase of the divided
down 10MHz RF is compared to the PPS and you don't need to even know the
how far apart they are.  All you need to know is "led or lag"  just a one
bit answer.   An XOR gate or a flip flop can tell you that.

If you want to get more fancy you can connect a few temperature sensors to
the Arduino's ADC lines and push those over the USB port along with other
statistics.   Youcan also do things like control the time constants the
software uses via USB also.  But you don't need this.   It can be added
later or not.


Engineering is the art of making what you want from what you can get at a profit.

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