[time-nuts] Looking for GPSDO for home use
Tom Van Baak
tvb at LeapSecond.com
Thu Apr 17 21:14:27 UTC 2014
> Having done extensive testing on the ublox 6M that you can buy with antenna
> for less than $ 23 new from DX.com I can say with certainty that the 1 Hz
> pulse is better than 1 E-9 accurate, closer to E-10. Depending on the
There are lots of cheap GPS/1PPS receivers out there these days. Having tested many GPS receivers myself, let me help you out. I understand the number $23. But the number "1 E-9" by itself means nothing. Like, are you talking time or frequency? There's a big difference.
Tell us if your number is timing accuracy or units of frequency accuracy or stability. Also either way, the measurement interval (or tau) is critical:
a) If it's timing, then the units are usually seconds; e.g., 1 ns, peak-to-peak, or rms or even something like TDEV(tau) -- and tau is important.
b) If it's frequency, then the units of absolute frequency accuracy or relative frequency stability; e.g., 0.01 Hz out of 10 MHz over some tau, or MDEV/ADEV(tau) -- and tau is critical.
I say this because:
a) If the 1e-9 or 1e-10 number you quote is rms time accuracy, then you have a GPS receiver better than what NIST or USNO has!
b) If the 1e-9 or 1e-10 number you quote is frequency stability over a day, then you have the worst GPS receiver we've ever seen!
So please clarify your units, or share raw data, or plots, or something. It's rather important.
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