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

[beale]

Hi Kasper,

Thank you, your nft program looks very interesting! It turns out the local ISP that provides my DSL, sonic.net runs a GPS-driven NTP server and I have a pretty low and stable latency, so this may work well.  To measure a relative frequency offset, I presume that what limits accuracy is the total length of time of the test. So with a stable latency, I should not need to poll the server very often.

Meanwhile I have a M12+ timing GPS and antenna on order, and am assembling some glue logic, case, 3.0V power supply etc. I may not ever manage a long-term GPS installation, since my apartment is surrounded by tall obstructions, and my workplace has metallized-film window panes which block all GPS signals, and no roof access.  It has a big open parking lot, though... I imagine using a car-mount GPS setup and sending a 1 Hz or 100 Hz LED or laser pulse up through the window to a telescope / photodetector at my workbench on the 2nd floor.... or maybe sending a frequency-locked 10 kHz tone through a FM wireless mic system would be adequate.

-John Beale

> 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   
> /Kasper Pedersen