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Re: [gpsd-dev] [Thumbgps-devel] PPS over USB

From: tz
Subject: Re: [gpsd-dev] [Thumbgps-devel] PPS over USB
Date: Wed, 2 May 2012 07:09:09 -0400

SkyTraq has a different version of the 638 (not just different firmware) that emits corrections to the pps edge to go to 10nS, and after a lock it will work down to 1 satellite and maintain accurate pps.

I don't know of any others that retain pps if they don't have a 3d lock.

The antenna is important but it won't overcome an obscured view of the sky - at best you will get multipath or other errors with the weak signals.

On May 1, 2012 11:33 PM, "Eric S. Raymond" <address@hidden> wrote:
Dave Taht <address@hidden>:
> I'm a little confused.
> There are two threads going by today. One is about a sirfIII and the
> other a ublox 6
> I have been assuming they are one and the same, but perhaps I'm confused.

You are.  The first set of prototypes, from UniTraq, were SiRF-III + CP2101.
These won't do - turns out the CP2101 driver can't wait on a handshake state
change because the vendor never released enough programnming information.

Gary is talking about the second set of prototypes, from NaviSys.
That's the uBlox + PL2303 device.  It works.  The next step is to
get them into volume production.

> Secondly an item that has not been looked into much is the quality of
> the antennas, or the quality of the clock source when only a single
> sat is available....

Quality of antenna will matter for the device's ability to function in
weak-signal conditions, e.g. indoors.  Clock time should be OK even with
a single sat - multiple birds are needed for the spherical trig to compute
position, but atomic time you get directly from each sat sample.

> Thirdly, wow.... when can I get one of these puppies to play with?

Gary has three.  He's keeping one and sending me the second.  Since OpenBSD
has no TICMIWAIT, Chris Kuethe is out of contention for the third and it
should logically go to you.
               <a href="" href="" target="_blank">">Eric S. Raymond</a>
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