[time-nuts] Lucent KS-24361, HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812A GPSDO system

Bob Camp kb8tq at n1k.org
Fri Oct 31 21:16:03 EDT 2014


One other possibility:

The GPS does a fast survey to get going. Then it starts a long / precision survey. It only stores the result if it finishes the precision survey. A good survey might be 10, 24, 48 or 72 hours….

Sure would be nice to have some basic info on these beasts ….


> On Oct 31, 2014, at 7:35 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> bob at evoria.net said:
>> I've noticed the same.  In looking at the Satstat program, it appears that
>> when you enter a location, that's only treated as a hint.  There is also a
>> value you can set to zero that supposedly tells it to come up with the last
>> hold value.  It didn't seem to work for me.  I've finally got my location
>> and power cords in more or less permanent locations, but things happen. 
>> And, I won't be getting a UPS for it for quite some time.  Maybe someone
>> else has the secret sauce. 
> There are several ideas tangled up in this area.
> If the GPS receiver has a recent enough almanac and you tell it the time 
> and/or location, it can get started much quicker.  The satellites broadcast 
> on a known frequency, but the Doppler pushes that a long distance relative to 
> the bandwidth.  The almanac and time+location lets it compute which 
> satellites are visible and the frequencies to listen on.  That shortens a 
> long search.
> Most/many GPS receivers have a watch crystal and clock and battery (or 
> supercap) for this purpose.
> GPSDOs are usually used at fixed locations.  If it saves the surveyed 
> location it can avoid another survey on power up.  You can save the surveyed 
> location in flash so a battery isn't required.
> Some GPSDOs automatically save the results of a survey.  Some don't.  The 
> Z3801A does an automatic save.  The TBolt requires a command to save it.
> It can also save the GPS-UTC offset so it can deliver correct time in UTC 
> without waiting to get that info from a satellite.
> -- 
> These are my opinions.  I hate spam.
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