[time-nuts] Low cost GPS gadgets for timing

[Eamon Skelton]

Hal Murray wrote:
>
> The problem is that most of the low-cost GPS toys use the SiRF chip set.  It 
> sucks for timing.  It looks like the NMEA sentences are sent from a timer 
> with 100 ms ticks.
>   http://www.megapathdsl.net/~hmurray/ntp/GPSSiRF-off.gif

A lot of SiRFstar III based devices have a 1pps pin, but you
might have to crack them open with a hammer to find it. Claimed
accuracy is 1 microsecond, but I find my cheap bluetooth GPS
receiver is always within a few tens of ns compared to a
Navsync CW12-TIM, Rockwell Jupiter and Garmin GPS 18.

I have read some words of wisdom on the web which say
that the SiRFstar III is not suitable for use in a
GPSDO, but I can't see any reason for this.

One thing to be aware of when you are searching for
the PPS output is that the PPS duration is only 1
microsecond which makes it difficult to spot on an
analogue scope.




-- 
Linux 2.6.26