[Ground-station] Balloon Launch - experiments?

[Michelle Thompson]

I'll be working at Kerry Banke's tomorrow on 10GHz and will run it by him
as well.

We have almost all the elements on hand, including an odroid with GNU
Radio.

I can print an antenna if needed.

-mdt

On Sun, Apr 22, 2018, 20:12 Bruce Perens via Ground-Station
<ground-station at lists.openresearch.institute> wrote:

> 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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