[time-nuts] advice: frequency calibration to 1 ppm possible without GPSDO?

Kasper Pedersen time-nuts at kasperkp.dk
Thu Feb 17 08:59:08 UTC 2011

On 02/17/2011 01:58 AM, beale wrote:
> Hello time enthusiasts!  I'm hoping for your advice on my (perhaps modest, by this list's standards) project.
> I would like to make a frequency calibration of a 10 MHz oscillator to 1 ppm (1E-6) or better, using some basic equipment. I do not have a GPSDO or any serious lab equipment, or budget for same as this is just a personal project. What I do have access to:

I did a piece of software to provide calibration to equipment-deficient 
microcontroller-hobbyist frequency counter builders (think 100ppm 
crystal from the bin) over ntp:

http://n1.taur.dk/nft/nft.pdf (usage guide with relevant screenshots, 
required reading)
http://n1.taur.dk/nft/nftsrc.zip (delphi source)

Depending on how you are connected, 0.1ppm is quite doable. Measure, 
adjust, measure 3 times to verify.

When you decide that this is too cumbersome and buy a GPS with pps 
output, you could make it self-adjusting:

/Kasper Pedersen

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