[GPS_Standard] preferred GPS

[Martein Bakker]

I am using a Rockwell Jupiter TU30-D145 easily available on ebay. It is a 12 
channel receiver and has NMEA output when configured to do so. I do not know 
the specs of jitter of the 1PPS signal. I have been looking for a "Position 
hold" mode, but I have not found anything about it in the datasheet. Does 
anyone know if this unit has a position hold mode and how it can be 
activated?

Martein
pa3ake

----- Original Message ----- 
From: "Dave Platt" <dplatt at radagast.org>
To: "Bob Bownes" <bownes at gmail.com>
Cc: <gps_standard at mailman.qth.net>
Sent: Wednesday, June 02, 2010 7:53 PM
Subject: Re: [GPS_Standard] preferred GPS


> Bob Bownes wrote:
>> So, do folks have a preferred GPS module to discipline clocks? Clearly
>> some are better than others. I'd like one that will output in NMEA so
>> I can use it to drive some other things as well, but other than that,
>> it has become clear that the Rockwell MicroTrack TU00 just isn't going
>> to cut it as it only locks to 4 satellites, has quite a bit of jitter,
>> doesn't hold a very good 3D lock (+/-100m just isn't good enough for
>> me...)
>
> On the used / new-old-stock market, I'd suggest looking for one
> of the newer Motorola Oncore VP modules (the 8-satellite ones).
> They seem to have reasonably low (although not ideal) jitter,
> and support both NMEA and Motorola binary protocol.
>
> Motorola made some Oncore models optimized for timing purposes
> (I think the UT and UT+ were of this sort) but some of these
> don't speak NMEA.
>
> The one I'm using myself is an older VP, purchased as
> new old stock from Synergy Systems a few years ago... 6
> satellites, no NMEA.  I was concerned about the lack of
> NMEA support, but the "gpsd" daemon has recently been
> upgraded with a driver that understands Motorola binary
> packet protocol.  I had to hack the driver a bit to get
> it to work - as released it understands only the
> 8-satellite reports, and can't either request or parse
> the 6-satellite reports from the older VP receivers - but
> that wasn't hard to do.
>
> The newer VP/UT-family modules support a "site survey
> and automatic position hold" mode - they'll average
> out the positions they calculate for a day or so, then
> store the average in NVRAM and switch to position-hold
> mode.  This can improve the precision of the PPS
> timing pulses somewhat.  The older 6-channel VP modules
> do support position hold but don't have the automatic
> survey-and-average feature - the average or median
> position must be determined by external software and
> then programmed back into the NVRAM before position-hold
> mode can be used.
>
> Used/working Oncore modules are pretty easily available
> on eBay for a reasonable price, mostly from a number of
> well-stocked sellers in China.  My impression is that a
> bunch of older cellphone sites (which use GPS for
> timing synchronization) have been decommissioned or
> upgraded, and the GPS modules pulled for sale.  There
> are a bunch of Motorola UT+ modules available, for
> as low as $24 delivered.
>
> Newer modules... well, the more recent Oncore line
> has the M12+T, which seems to be optimized for timing
> purposes... I believe it's based on one of the SiRF
> chipsets.  Most newer modules are *not* 5-volt - they
> typically require 3 or 3.3 volts for power, and use
> this voltage for their I/O as well.  Dropping one of
> these into a design intended for a 5-volt module might
> not be the simplest approach.
>
> SparkFun has a whole bunch of modules, about which I
> know little... mostly 3- or 3.3 volt, most with their
> own internal antennas (which is probably not a good
> thing for this particular application).
>
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