[time-nuts] LTE-Lite module

Bob Camp kb8tq at n1k.org
Mon Oct 20 17:58:22 EDT 2014


Hi

The problem is that there are no “magic coefficients”. What you run depends very much on the exact OCXO you have, the environment you run it in, and the result you are after. 

For instance, Bert is after frequency stability. Tom is after the right time. Each of them will have very different coefficients for the same oscillator. 

My Morion OCXO has a floor of 2x10^-12, Bert has some that are 10X better than that (maybe). His coefficients and mine will be very different. 

I had an antenna outdoors. It got many sat’s all the time. Now I have one indoors. It’s not getting lots of sats all the time. My old coefficients are not going to be my new coefficients. 

No magic bullet, you have to do the work. 

Bob

> On Oct 20, 2014, at 1:20 PM, Brian Lloyd <brian at lloyd.aero> wrote:
> 
> 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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