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

["Ron Frazier (NTP)" <timekeepingntplist@techstarship.com>]

On 5/1/2012 11:33 PM, Eric S. Raymond wrote:
> Dave Taht<dave.taht@gmail.com>:
>    
>> 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.
>    

Hi guys,

Just wondering.  On the USB + PPS + PL2303 concept, has the long term 
variation that has been observed in NMEA data in other similar units 
without PPS been accounted for?  I have personally observed a variation 
in NMEA data on my Globalsat Sirf III USB device of up to +/- 70 ms over 
several days.  Will having the PPS coming though USB solve that problem?

Sincerely,

Ron


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Ron Frazier
timekeepingdude AT techstarship.com