[time-nuts] Rb lamp lifetime...

[WB6BNQ]

Yuri Ostry wrote:

> 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

Hi Yuri,

Someone correct me if I am wrong, but I think the M12+ is like the UT+ and uses one
bird, at a time in the time mode, to do the timing process after you got a position
fix.  If that is true then maybe it will yeild a better result ?  I think it would be
worth a try.  So, put the Shera controller together with your M12+ and see what happens.

I am wondering if limiting the antenna's view would help with the multipath ?  For
instance, what happens if you build a cone shaped skirt that is pretty tall such that it
prevents a majority of the side view energy from reaching the antenna ?

Worst case, you could use the M12+/Shera arrangement with a Rb unit and go to a park or
other open space for a day, or if camping is available, maybe a weekend camping trip
would be in order.  Then compare the Rb oscillator, setting it if need be, and then take
it home.  Not an ideal solution, but with the much better holdover of the Rb source you
would, maybe, at least have perhaps a few parts in 10E-10th for a month or so before
having to do it again.

Bill....WB6BNQ