[time-nuts] Rb lamp lifetime...

Yuri Ostry yuri at ostry.ru
Tue Nov 18 11:59:39 UTC 2008


Hello,

Sunday, November 2, 2008, 6:31:32, WB6BNQ wrote:

W> Hi Yuri,

W> Unless you need the longer term stability of an undisciplined Rb source, I think
W> you would be better served to get one of the “Timenuts group” Trimble Thunderbolt
W> GPS units to use as a home standard.  It is available via this page:

W> http://www.tapr.org/kits_thunder.html

W> and info about the unit is available at this URL:

W> http://www.leapsecond.com/tbolt-faq.htm

W> Add an external very high quality crystal oscillator locked to the Trimble and
W> you will have the same stability of a good Rb source.  Most would use a high
W> quality Rb source, undisciplined, as a tool for comparing or generating
W> specifications of crystal oscillators.

Unfortunately, I'm currently living in a place that have problems with
good location for GPS antenna. The best place available provides less than
40% of open sky view and a lot of buildings around, lots of reflected
signals. No access to roof, security is tightened heavily after 9/11
and terror acts in Moscow, so it is big problem to get access to
attics or cellars of residental buildings.

I curently have uBlox LEA-5S (SuperSense nav module) connected to this
antenna.... Not very promising... Fix is available about 70% of time
but drifting heavily (due to multipath?), often I see coordinates
about 400-500 m away from real location.

I have Motorola Oncore M12+T module as well (purchased it with
intention to build GPSDO controller), but (IMHO) it will be nearly
useless in such conditions with original W5OJM controller design.

I thinked about some FLL implementation where microcontroller
constantly monitor output of GPS for T-RAIM solution status and
discard measurement cycles that have T-RAIM alarms, restarting cycle
once T-RAIM reports good timing solution again... Will be fun project,
of course, but will take some time. And it will be a good reason to
familiarize myself with new 16-bit PIC24 series... Their cascadable up
to 32 bits timers/counters with input capture looks quite promising...

-- 
Best regards,
 Yuri, UA3ATQ/KI7XJ                 mailto:yuri at ostry.ru




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