[time-nuts] 1PPS accuracy of commercial GPS receivers

[Philip Pemberton]

Just out of idle curiosity, is there any significant difference in 1PPS 
accuracy between different GPS modules?

I've got a pair of Trimble SVeeSix CM3 boards (firmware 4.13 if memory serves, 
have to be reflashed to change the comm protocol, which can be either TSIP or 
NMEA) and an Axiom Sandpiper (SiRFStar II, RAM only, no onboard NVM, SiRF 
Binary or NMEA switchable on-the-fly) which are specified at 1us and 40ns 
accuracy respectively. As a comparison point, I've also been looking at the 
Fastrax iTrax321 (IT321) which is a solder-down "micro-GPS" module based on 
the "20-channel" SiRFStar III and is -- like the Trimble -- specced at 1us 
accuracy. This is one of the newer SiRFStar III based design.

Am I missing something blindingly obvious here, or is there really that much 
spread in 1PPS accuracy on commercial receiver boards?

Is 1us jitter really that good for a GPS module?

Thanks,
-- 
Phil.
lists at philpem.me.uk
http://www.philpem.me.uk/