For generating pseudonoise, NOAA helpfully posted some Matlab code:

The "bigger" sample I took is only 196MB in raw I/Q sign/mag binary
format.  But that turns into 3.1GB in complex 32-bit floats.  I tried
compressing a few different ways:

3.1G gpslog_big-outside.floats
196M gpslog_big-outside.raw
181M gpslog_big-outside.raw.gz  # gzip --best
181M gpslog_big-outside.raw.7z  # 7z -mx=9
179M gpslog_big-outside.raw.bz2 # bzip2 --best

Compressing by almost 10% is pretty surprising to me.  It doesn't seem
like the fixed frequency spurs (at DC and -400kHz) would be enough to
account for this.  Maybe some of the aliasing artifacts could be

I don't have a good place to post this file at the moment.
Recommendations?  I'll have it with me on a thumbdrive for the capstones
Thursday, Friday hackday and Sunday lab hours.


On Wed, 2015-06-03 at 12:14 -0700, Jamey Sharp wrote:
> On Jun 3, 2015 7:44 AM, "Kenny" <> wrote:
> >   + The STM32 which controls the MAX2769 (GPS baseband receiver) now
> > dynamically configures the MAX according to instructions received by
> > debug scripts so we can test all the configurations we want without
> > reprogramming the STM32 each time.
> I was skeptical about whether this would be worth the engineering
> effort, but Theo's time spent building it already paid for itself last
> night. Excellent idea.
> >   + Kenny joined the party to help transmit a sweeping sine wave +/-
> > 2MHz around GPS baseband using HackRF.  Samples received from the
> > MAX2769, converted and viewed in baudline showed the same sweeping
> sine
> > wave (with noise and other artifacts).  This turned out to be a good
> way
> > to test poorly documented configuration settings and lay to rest
> > bit-order questions.
> I disagree. It was a *great* way to test. ;-) We now have confidence
> about the meaning of most of the MAX2769 registers, and we know the
> entire signal path on the jGPSv3 board is functioning!
> I have two next steps in mind for testing:
> First, someone (Nathan or me probably) should generate one GPS
> satellite's pseudonoise sequence in a file. We should test feeding it
> into soft-correlator first, which ought to report a strong signal from
> that satellite at 0 Doppler shift. Then we should feed the same signal
> through HackRF, record it with jGPSv3, and try feeding *that* to the
> correlator. If that doesn't work, I don't know what's wrong; bad noise
> maybe? If it does work, we can also try simulating some Doppler shifts
> and adding varying amounts of noise in GNU Radio.
> After that: don't we know some folks who make GPS satellite
> simulators? We're ready to ask them for help.
> In parallel, I think it's time to do the other engineering tasks we
> need: send the COTS GPS data to Ethernet simultaneously with the MAX
> samples; log it all to disk on the FC; stream the COTS data to the
> ground; and log it all to SDCard on the STM if we're going to do that.
> I suspect that's mostly on Theo's plate, but anyone who's interested
> in the microcontroller firmware or flight computer software could
> help.
> >   + Jamey said we could fly with this configuration and probably
> figure
> > out how to tease satellites out of the logged data later.
> I won't swear there's anything to tease out. I just think at this
> point we've mitigated most of the risks of hardware problems. So if we
> decided to fly with the hardware in this state, I'd feel pretty
> comfortable that we'd done our due diligence toward getting useful
> science out of the flight. And I think I should shift to focusing on
> roll control and overall system engineering details.
> >   + For fun, Kenny collected a larger sample outside from the
> MAX2769, ...
> Could you post that larger sample somewhere? How big is it? And out of
> curiosity, do any of the general purpose compression algorithms (gzip,
> bzip2, etc) manage to compress it at all? (If they do we've probably
> screwed something up, so that would be good to know.)
> Maybe we can try feeding the sample into the GNSS-SDR code we looked
> at last fall, as another check. I think that's a good task for K if he
> has time; he had that code running successfully IIRC.
> Jamey

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