[time-nuts] KS-24361 REF-0 standalone

Bob Camp kb8tq at n1k.org
Fri Oct 2 20:32:11 EDT 2015


Given that eBay is awash in various older uBlox devices at really low prices, going for the > $200 a unit single piece price of the LEA-8T seems a bit much. You get all of the core timing functions in the “not T” parts (including sawtooth data). The main thing you get with the 7’s (vs the 5 and 6) is the ability to switch over to Glonass. With the 8’s you get the ability to run Glonass plus GPS at the same time. In both cases, you get nothing from the Glonass constellation that’s worth the switch. In a timing application you likely would run “pure GPS”. 

The net effect is that you only loose the position hold mode with the “not T” devices. With a reasonable antenna location the timing performance of these units is actually quite good in “not hold” mode. If you are combining one with a $25 REF-0, then a $20 GPS makes a lot of sense.  You *might* be giving up 5 ns to 10 ns a day of wander due to position issues. 

Even with the location hold, you still have about 10 to 30 ns of daily wander from ionosphere issues. Your money probably would be better spent on an L1/L2 GPS that takes this out rather than on a position hold device. eBay has these sort of devices for (almost) the same sort of money as the LEA-8T single. 


> On Oct 2, 2015, at 7:06 PM, Gregory Beat <w9gb at icloud.com> wrote:
> 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)
> https://www.u-blox.com/sites/default/files/products/documents/Timing_AppNote_%28GPS.G6-X-11007%29.pdf
> 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.
> http://www.realhamradio.com/GPS_Frequency_Standard.htm
> These users may desire a "newer" GPS receiver that has more channels (8-channel); latest generation receiver; access to the newest GPS constellations.
> 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).
> http://www.heoldesign.com/index.php?module=products&action=catalog&cat=14&id=54
> w9gb
> Sent from iPad Air
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