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.
-Bob
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