On 01/17/2011 02:29 AM, jimlux wrote:
On 1/16/11 5:19 PM, Magnus Danielson wrote:
On 01/16/2011 09:12 PM, Brooke Clarke wrote:
Hi Pete:
The SiGe receiver IC is not much use by itself since you need to
literally be a rocket scientist in order to process its output data.
The GPS1A, with open source software is interesting, but again you need
to be a rocket scientist to modify the code.
I haven't launched or made any part (to the best of my knowledge) of any
rocket. Yet again I've been able to write software which can
post-process the data originating from this device.
Real time processing of it would be challenging, but I haven't spent
quality time on THAT problem.
real time processing of *anything* is challenging, even if it's only
updating once an hour. I write this because updating once an hour
implies you are probably looking at data spanning months, and keeping a
program or set of programs reliably running without a hiccup for months
is non-trivial. Sure, we've all got anecdotes of "my machine only needed
to be rebooted 6 months ago", but there's a difference between seeing
that in the past, and guaranteeing it for the future.
The real-time processing is a bit challenging since one has to
orchestrate the rather high sample rate processing. Also, since I didn't
spend any time on efficiency at all. Being able to lock up and start
decode the stream was a great step in the right direction before I got
distracted. It only use 2 out of 8 bits in the byte-stream.
Hooking in a 10 MHz and PPS/time-tag and correlate them to the received
signal would be an easy hack. What to do with the other 4 bits remains
to figure out... hooking up a PIC for a PICDIV to do 1 kHz frame
reference and PPS would be a possibility.
Anyway, it could probably be figured out if only spending some time on
the data flow and front-end.
I implemented FFT based acquire method, tracking loops for carrier and
code, message decoding etc. It doesn't take a rocket scientist to do
this, but having a few books at hand and ICD-GPS-200... but I was
recording data onto file and then processing from that.
So, it is definitely possible to cook up yourself. I would not say that
my code is particularly wonderful in any sense. There is quite a bit of
coding before you can lock up, and many false starts. Actually doing the
FFT lock-up is recommended. It's not that hard really.
Cheers,
Magnus
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
