[time-nuts] Simple solution for disciplining OCXO with 1 PPS

djl djl at montana.com
Mon May 23 02:24:29 UTC 2016


I like the little boards at:
http://navspark.mybigcommerce.com/development-boards/
It's a GPS with a fully programmable 32-bit Arduino-compatible 
processor. $22
Crowdsourced about 3 yr ago, matured now. Various versions; you can even 
have Beidou :-).
Don


On 2016-05-22 19:45, Tom Van Baak wrote:
>> Can a pure analog design access the sawtooth correction?  My GPS
>> receivers send sawtooth as a digital message on a serial port.   I
>> don't know if saw tooth correction is required to meet his spec.
> 
> Hi Chris,
> 
> Many GPS/1PPS receivers don't output sawtooth information and yet they
> work really well. Sawtooth correction isn't necessary except for
> high-end GPSDO. The same is true for zero-D timing mode.
> 
> Examples include:
> https://www.adafruit.com/products/746
> https://www.parallax.com/product/28509
> as well as any number of equivalent GPS/1PPS boards at half the price
> on eBay. See also:
> http://www.leapsecond.com/pages/MG1613S/
> 
> In fact many simple GPSDO rely on sawtooth dither to improve their
> performance; that is, it's a feature to be exploited, not a bug to be
> corrected for.
> 
> A dirt cheap GPS receiver these days may have 1PPS error of 20 ns RMS.
> Over 1000 s integration that's 2e-11 in frequency stability; far
> better than the OP's modest target of 1e-10 at an hour.
> 
> Here's another thought. OP wants STS of stability of 1e-10 at an hour.
> No mention of accuracy, or long-term performance. So if stability is
> all that's needed I would just use a old 10811-class OCXO, perhaps one
> that's been running faithfully for a few weeks or months. That will
> get you 1e-10 at an hour without any GPS any antenna any analog any
> digital any complexity any tuning.
> 
> /tvb
> 
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