[time-nuts] yet another GPSDO design, or so

Attila Kinali attila at kinali.ch
Sat Jun 26 19:11:19 UTC 2010


On Sat, 26 Jun 2010 12:38:29 -0600
Ed Palmer <ed_palmer at sasktel.net> wrote:

> Another GPS board with a 10 MHz output is the Navsync CW-12 module 
> (price ~US$85-90).

Hmm.. i didn't know about this one. Both seem to be comparable
from the specs, the LEA6-T being slightly better (well, the
design is newer, so that's to be expected).

As for the price. ublox is here, literally, sitting in the next
town and i'm in the fortunate position to get a LEA-6T out of
a bigger batch which makes it considerably cheaper than the CW-12.

>  I measured the 1 PPS output and found a Standard 
> Deviation of < 5 ns with a range of < 30 ns.  The 10 MHz output is kept 
> on frequency by occasionally adjusting the period of the 10 MHz output 
> by one cycle of the CPU clock (~8.3 ns = 120 MHz).  How often this 
> happens depends on the exact clock frequency of the particular unit.  On 
> mine it happens about 200 times per second.

Interesting information, thanks.
I know that the LEA6 has a TXCO that can be adjusted and the
timepulse output is generated from this source. What i dont know
is whether the TXCO is adjusted tracking the GPS signal or whether
it uses a similar "skip a cycle" technique like the CW-12.
Maybe i should drop ublox a mail and ask about that.

			Attila Kinali

If you want to walk fast, walk alone.
If you want to walk far, walk together.
		-- African proverb

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