[Ground-station] Balloon Launch - experiments?

[Bruce Perens]

I have been using Odroid rather than Raspberry Pi cor just that reason. Pi
has poor IO bandwidth.

If frequency precision is why you'd like an oxco, would a ground beacon
that is recorded provide enough?

On Sun, Apr 22, 2018, 19:53 Zach Leffke via Ground-Station
<ground-station at lists.openresearch.institute> wrote:

> I like this idea......it has elements of a couple projects that I've
> worked on in the last year or so.
>
> I just did similar math from a slightly different angle......
>
> 10 Msamp/sec complex capture (so 10 MHz of spectrum, using GNU Radio
> Complex datatype) at 64 bits per sample yields roughly 1.86 hours of record
> time on a 500 GB SSD......about perfect for this type of balloon
> flight.......go up, burst, come back down.  The recording could be
> triggered at a specific time or altitude to optimize the collect.
>
> I'd recommend the XU4 over the RPi as it has two USB 3.0 ports, one for a
> B200 mini, and one for an external USB3.0 SSD.  also its got a beefier
> processor and more RAM, better to keep up with the write speeds.
>
> A B200 mini is tiny and relatively cheap, though it would probably need a
> 10 MHz reference of some sort (could be a GPSDO, but would need to make
> sure the GPS works at altitude......standalone OCXO might be a better
> solution).  It also has a similar RF front end to the Astrod SDR (an ADXXXX
> whatever whatever, I can't remember off the top of my head, but same family
> at least).
>
> For the 2017 Eclipse experiment (recording satellite downlinks, looking
> for Scintillation effects due to the eclipse) I used a very similar setup
> to this and used a simple script to control the flowgraph recording....one
> minute on, one minute off.  I ended up with hours of 1 minute IQ recordings
> started at every odd minute.  Something like that could be used here, with
> the possibility of tweaking parameters between each recording (like
> stepping the USRP gain in 10dB increments each time, or possibly changing
> center freq).  Log files or the filename itself could be used to keep track
> of which IQ capture had what settings.
>
> Marc Franco has designed and I believe built some 5 GHz pre-amp prototypes
> for the uplink band...might be good to give them a test.
>
> Ground based 'reference beacons' might be useful/fun.  Maybe sending out
> CW at known center freqs at known power levels to give a reference to hunt
> for in the collects.
>
> Any ideas on antenna types?  patch array? horn? conical spiral? circular
> or linear (I vote circular on the balloon, pointed at Nadir)?
>
>
> This sounds like a perfect summer project for some of our undergrads!
>
> -Zach, KJ4QLP
>
> Research Associate
> Aerospace Systems Lab
> Ted & Karyn Hume Center for National Security & Technology
> Virginia Polytechnic Institute & State University
> Work Phone: 540-231-4174
> Cell Phone: 540-808-6305
>
> On 4/22/2018 1:20 AM, Phil Karn via Ground-Station wrote:
>
> On 4/20/18 10:07, Douglas Quagliana via Ground-Station wrote:
>
> I would like to suggest sending up a software defined radio that can
> recording on (and around) the proposed uplink frequencies.  It should
> sample at the highest sampling rate possible to capture the widest
> bandwidth possible into the recording.
>
> Let's see... what sample rate would fill a 256GB thumb drive during a
> typical 2 hour balloon flight?
>
> 256e9 bytes / 4 bytes/sample = 64 gigasamples assuming 16 bit complex
> samples. Over 2 hours that would be a sample rate of 64e9/7200 = 8.89
> megasamples/sec. I.e., we could collect 8+ megahertz of spectrum,
> depending on the anti-alias filters. You'd have to make sure that the
> drive can write continuously at that rate. A SSD might be necessary.
>
> Plenty for the 2m/70cm satellite subbands or for the entire 2m band, but
> not the entire 70cm band. It would be fun going through these recordings
> with my 'radio' program.
>
> Most latex weather balloons maintain a remarkably constant ascent rate
> of 1,000 fpm (5 m/s) and burst at 100,000-120,000' (30.5-36.5 km). Ergo
> the ascent time would be 100-120 minutes or from 1 hr 40 minutes to 2
> hr. The ascent is somewhat turbulent until the turbopause, then things
> usually smooth out in the stratosphere. At altitude it's positively
> serene until the balloon bursts. Then all hell breaks loose.
>
> This assumes hydrogen. Pretty much everybody uses it now since helium is
> getting scarce and bloody expensive. Treat it with respect and you'll
> have no problems.
>
> The descent by parachute usually takes about 30 minutes. Descent is VERY
> quick at first because of the thinner air (1% of surface density at 32.6
> km) but then slows as it descends into exponentially denser air.
> Descents are pretty violent due to turbulence (especially if the remains
> of the balloon are still attached) so it might not be worth collecting
> data on the way down since you're seeing much the same area anyway. It's
> easy to get sick watching HDTV of a descent on a large screen...
>
> Phil
>
>
>
>
>
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