[time-nuts] KS-24361 REF-0 standalone
kb8tq at n1k.org
Sat Oct 3 09:47:00 EDT 2015
If indeed you are into a professional system, where holdover matters then
a lashup on a bunch of surplus gear likely isn’t going to measure up. Based
on about 10,000 previous posts on the list I’d say that holdover does not appear
to matter to Time Nuts. It would be difficult to find a thread where holdover performance
was the main topic. The focus (rightly) seems to be to keep the box locked to
GPS all the time. That approach (if you can do it) will always give you the best
The “not a T” uBlox units *do* put out “TRAIM" information in the words you
can get at. The data is valid and it can be used if you wish to put the unit
in holdover. I’m sure it works better with a well known position, but that it not
TRAIM was a really big deal back in the mid 90’s. That’s when Motorola put it on
the Oncore’s and did a lot of publicity on the topic. They saw it as a way to differentiate
their product in the marketplace. Much of our view of TRAIM is slanted by the
Motorola information on the topic.
Here’s one way to look at TRAIM:
If you are in position hold, you can get timing off of a single satellite. TRAIM
(just like any estimator) looks at the single input it has and says “that must be
correct”. Give it two inputs and it can look at the solution for each and decide if
they are close enough (your TRAIM threshold) to be correct. As you get up to 8 or
12 inputs, the right answer may be to throw away the single one that is (say) a microsecond
off from the rest. Somewhere between 3 satellites and 6 satellites, the “I need
a solid position” thing becomes less of a factor.
There are other ways to put the device into holdover. One is to simply look at the
number of satellites. If you are locked on to less than 4 sats, go into holdover. It’s not
elegant, but it does work. In the case of a lash up, just translate the “I have <= 3 sats” info into
“my TRAIM is junk”. Instant holdover.
> On Oct 2, 2015, at 10:44 PM, Bill Hawkins <bill at iaxs.net> wrote:
> Actually, the Lucent software uses RAIM, and reports the value in its
> status message. If the position appears to have drifted off, or there
> aren't enough satellites to calculate the position, the software
> declares the oscillators to be free-wheeling, an expression meaning that
> the oscillators are free from discipline and are now drifting.
> So yes, the positioning aspects matter.
> Disclaimer: I haven't studied RAIM (or TRAIM) enough to know exactly
> what goes on, but that's the behavior I've observed.
> Bill Hawkins
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Gregory
> Sent: Friday, October 02, 2015 6:07 PM
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] KS-24361 REF-0 standalone
> Dan -
> I have been following your experimentation with the surplus Lucent
> KS-24361 REF-0 module, to transform it into a standalone GPSDO.
> The original usage of the classic Oncore UT+ GPS receiver for KS-24361
> REF-1, by Symmetricom / Datum for Lucent, was deliberate.
> For usage at a cellular data/telecom site, the focus was on the timing
> and frequency discipline from the GPS satellite transmission, rather
> than the position or dead reckoning aspects -- used by smartphones,
> automobiles, and other GPS applications on the market.
> A couple of comments.
> While I can appreciate being economical (main criteria) and selecting
> the NEO-6M receiver, I believe that a u-Blox timing specific module
> (like LEA-6T) would be more desirable in this application.
> In addition, the u-Blox 6-series is the trailing edge of product support
> (market demand dictates its continuance), while the 7 and 8-series are
> their current modules (largely for the cellular / mobile industry
> (smartphones or cell sites themselves)
> u-Blox 6-series Timing Application Note (using the LEA-6T)
> IF you successfully adopt the u-Blox module to correctly "mimic" the
> Oncore UT+ GPS receiver command suite, THEN you open up a larger
> audience of "time-nuts" and Frequency Standard users (HP Z3801A
> frequency standard universe) as a receiver alternative.
> These users may desire a "newer" GPS receiver that has more channels
> (8-channel); latest generation receiver; access to the newest GPS
> TAPR might be interested in sponsoring, as a kit/module, if a wider
> audience existed.
> The Heol Designs N024 receiver (France) accomplished this replacement
> role for the Trimble ACE II/III GPS receiver used in the
> Symmetricom/Datum TymServe TS2100.
> Their solution resolved shortcomings in the mid-1990 Trimble receiver
> design and giving this Symmetricom NTP server, time IRIG-B time code
> generator, and 10 MHz reference appliance a new lease on life (no longer
> a door stop).
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