[time-nuts] LTE-Lite module

SAIDJACK at aol.com SAIDJACK at aol.com
Mon Oct 20 14:52:03 EDT 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  
comments.
 
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.

Thanks,
Said
 
 
 
 
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:

>  Hi
>
> We tend to focus on this or that enhanced feature in a  piece of code. It’
s
> fun to talk about. That’s not what keeps most  designs from doing what 
they
> should. By focusing on this rather than  the testing required, we set 
people
> 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 
pretty
> fast. Setting up for one  is not at all the same as setting up for the 
other.
>

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.

-- 
Brian Lloyd
Lloyd  Aviation
706 Flightline Drive
Spring Branch, TX  78070
brian at lloyd.aero
+1.210.802-8FLY  (1.210.802-8359)
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