[time-nuts] Need advice for multilateration setup

Attila Kinali attila at kinali.ch
Thu Mar 26 08:25:03 EDT 2015

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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