[time-nuts] LTE-Lite module
SAIDJACK at aol.com
SAIDJACK at aol.com
Mon Oct 20 18:52:03 UTC 2014
Hi Brian, Bob, Charles, et. al.
Bob has a great point about the difference between a one-off in a basement
lab, and a commercial product that has to work under any circumstances,
wether flying at 50,000 feet at -56C, or in an urban canyon, or under whatever
other stress could be thrown at it. In fact the testing and fine tuning
does take 90% of a product design cycle.
That said here is the ADEV plot from my overnight test with the DOCXO. No
This was done without any loop adjustment whatsoever, same board and
software that drives the on-board TCXO. I will let the result speak for itself,
save to say the loop, the DAC, the DAC reference, and the GPS with a proper
OCXO can achieve performance at a level approaching two orders of
magnitude better than our spec which is 1ppb for this particular product.
PLEASE(!) do not send me emails once you get your board and plug in your
own OCXO and don't see similar performance for whatever reasons. There is not
much we can do about that, other than say our product meets
specifications. On the other hand if you connect a really good OCXO you may even get
better performance than I got, but who knows.
In a message dated 10/20/2014 10:21:15 Pacific Daylight Time,
brian at lloyd.aero writes:
On Mon, Oct 20, 2014 at 6:48 AM, Bob Camp <kb8tq at n1k.org> wrote:
> We tend to focus on this or that enhanced feature in a piece of code. It’
> fun to talk about. That’s not what keeps most designs from doing what
> should. By focusing on this rather than the testing required, we set
> up to fail. If you start off the project believing you mostly need fancy
> code when you mostly need long term testing instead, you hit a wall
> fast. Setting up for one is not at all the same as setting up for the
Sounds to me like the hardware and code are pretty straight-forward. The
difference comes from the terms and coefficients in the PLL loop filter and
those need to be optimized for each OCXO. There appear to be here a handful
of people who have a pretty good idea of what those coefficients should be
for various well-known OCXOs out there.
So why not do the GPSD hardware, software, and then provide the
coefficients that will get a handful of the more popular OCXOs available
out there to within a decade of optimum, certainly closer than what one
would be talking about by just bolting x-random OCXO onto an LTE-lite? I
suspect there would be a market in the time-nut world for such a critter.
706 Flightline Drive
Spring Branch, TX 78070
brian at lloyd.aero
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