[time-nuts] Deriving PPS from hockey-puck G-Mouse GPS receiver to lock an oscillator

Steve Rooke sar10538 at gmail.com
Mon Dec 29 13:46:23 UTC 2008


I bought a job lot of Polstar G-Mouse receivers to play with. These
use the Sony CXD2951GA-4 chipset which has a PPS output but this is
not made available at the end of the cable unfortunately. The units
themselves are fully waterproof so they are happy to sit through all
kinds of weather outside and cling like limpets to a metal surface
even with the gusty winds we have been experiencing here. Now I have
looked at the output of these which from a reset state run at 4800bd
and produce the requisite NMEA 0183 protocol as expected. Looking at
the TTL output on a scope there is a burst of data, at 4800bd, each
second with a reasonable gap between each burst. Each packet of data
starts with a $GPGGA message and time-stamping these shows they seem
to occur at 1 second intervals. What I was thinking about building was
a small circuit which would switch on the start of the data block and
then time out at the end of the block thereby producing a 1Hz signal,
albeit not 50% duty cycle, which could possibly be used to lock a ocxo
via a phase-frequency detector, like a MC4044, and a low pass filter.
Has anyone looked at this before and, perhaps discarded it or
whatever? Yes, I know it is no substitute for a Thunderbolt but I
don't have one of those yet and this may be a cheap and cheerful way
to sync to GPS.

Be gentle Bruce :-)

73, Steve
-- 
Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW
Omnium finis imminet



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