[time-nuts] Need advice for multilateration setup

Robert Watzlavick rocket at watzlavick.com
Thu Mar 26 13:32:33 EDT 2015

Thanks for the suggestion. Does the DSSS make it easier to correlate between ground stations?  I'm not sure how to handle the phase offset on the 10 MHz ref clocks. 

> On Mar 26, 2015, at 07:25, Attila Kinali <attila at kinali.ch> wrote:
> On Wed, 25 Mar 2015 21:27:35 -0500
> Robert Watzlavick <rocket at watzlavick.com> wrote:
>> I'm working on a project that I could use some advice on and also might 
>> be of interest to the list.   If it's not appropriate for the list, my 
>> apologies.
> The gods have apporved of your request. You may speak now.
> ;-)
>> I want to develop a tracking system for an amateur rocket that can allow 
>> me to track the rocket even if onboard GPS is lost (as is typical during 
>> ascent and sometimes during descent) or if telemetry is lost.
> Given you can synchronize the clocks of the ground stations well
> enough, then the rest is "easy". Then you can get away with having
> a simple signal generator that only needs an XO. Or you can go
> for a TCXO to make your signal processing life easier.
> What you need to do, is actually the same as GPS does: Create a
> direct spread spectrum signal and track it on all ground stations.
> The DSSS has the advantage over the single pulse, that it's more
> resilient against noise and interference. The disadvantage is, that
> you have to have more complicated hardware. One viable way would be,
> that you have precisly synchronized sampling systems (e.g. SDR's like
> the bladeRF which can take an external clock) and then feed the data
> to a PC where you do the heavy lifting. Then you don't need to build
> custom hardware at least.
> Also, if the precision by the DSSS signal is not good enough, you can
> apply various tricks from the GPS world, like carrier phase tracking, etc.
>                Attila Kinali
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
>                 -- Miss Matheson, The Diamond Age, Neil Stephenson
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