[time-nuts] Need advice for multilateration setup

Robert Watzlavick rocket at watzlavick.com
Thu Mar 26 22:43:32 EDT 2015

On 03/26/2015 01:56 PM, Jim Lux wrote:
> The key is that you don't need *real time* position.. a few seconds or 
> minutes delay is probably ok, right?
Seconds are probably ok, minutes might be a little long. PCs are pretty 
fast though these days for signal processing I would think.

> To compensate for the receiver variability, simultaneously transmit a 
> signal with a different PN code, at the same frequency (roughly) as 
> the rocket's transmitter..  The receiver will receive both, but the 
> signal from your ground reference transmitter isn't moving, so you can 
> use the "non-rocket" signal as a calibration reference.
Now I didn't think of that - so you're saying to send another signal 
from a central ground station to all the receivers and then have them 
use that as a relative reference?   Since I'll know where each ground 
station is, I should be able to subtract off the TOF so each station has 
a common reference point.  That's a pretty cool idea.

> What's your budget?
I was thinking in the $1k range so that would be about $200 per ground 
station.  A couple of controllers I was considering for the ground 
stations include the Netburner MOD54415 (same one I'm using for the 
flight computer) or the BeagleBone Black.  Both of those are under $100 
and have counter/timers onboard although I have to see what the max 
clock rate is.  As long as the channel-to-channel delay wan't too bad, I 
think using a 12-bit ADC to digitize the two signals would work because 
you can interpolate to get a higher-resolution zero crossing.


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