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

Hal Murray hmurray at megapathdsl.net
Fri Oct 31 19:35:14 EDT 2014


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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