[Ground-station] Balloon Launch - experiments?

[Michelle Thompson]

We are linear on the payload (4B, etc). Our dual band feed is linear.

There are some ambitious ideas for matching linear polarization (automated
closed loop) for something that is tumbling around like a balloon payload
probably would. Don't rule it out just because it sounds hard. We live in a
golden age.

Kent is right. There are some very generous uses of the word "circular" in
the ham antenna world. It just has to sort of work in many situations to be
successful, so that's when the development stopped and the building began.

Here, we can and should expect more from ourselves. A buildable higher
quality CP antenna would be a good contribution in and of itself.

However! Having said that.

We can take advantage of the opportunity to try out circular as well. In
between MATLAB and HFSS, both of which we have access to, I think we can
check any theoretical work.

We already know that we can print and make conductive nearly any surface at
5 and 10 GHz.



-Michelle W5NYV

"Potestatem obscuri lateris nescis."


On Sun, Apr 22, 2018 at 9:45 PM, Zach Leffke via Ground-Station <
ground-station at lists.openresearch.institute> wrote:

> What are you talking about Kent......you're a ham!
>
> I'd wager a dollar or two that YOU can build a CP antenna at 5.66GHz!
>
> hint hint........nudge nudge.........there's a particular need........and
> a member of the list with a particular capability.......
>
> :-)
>
>
> Assuming of course that we actually need CP on the payload....that was
> just a thought..........if not though and we are linear on the payload, and
> we have linear beacons on the ground......cross pol issues could arise with
> the changing geometry/attitude of the payload and we wouldn't know on the
> ground which way to 'twist' the beacon antenna......
>
>
> Though that brings up another idea.....................
>
> completely different idea.....slightly more advanced..........fly a B210
> with dual synchronized receive capability......each rx chain connected to
> its own linear antenna and the two antennas mounted 90 deg
> offset...........Each receive chain would dump IQ to its own capture file.
> With a reference beacon on the ground that could be used to calibrate out
> the random UHD phase offset that happens each time the flowgraph is
> started.......we could get all 4 polarizations.  Each receive chain would
> dump IQ to its own capture file.........and with the phase offset
> calibrated out from the ground beacon........could combine the two signals
> in software with +/- 90 deg offset to generate RHCP/LHCP in post processing.
>
> Net result.......would get half as much record time (or would need larger
> SSDs).....but would get 4 polarizations worth of collect / RF survey of the
> uplink band........
>
> The antennas would have to be more than just a pair of dipoles though
> right?  Axial ratio would degrade off nadir vector assuming the 'crossed
> dipole' is pointed at nadir.  Same goes for an eggbeater.......so not sure
> what the right elements would be for this......maybe the inverse
> idea.......a quadrafilar helix on each rx chain......one RHCP/one
> LHCP.......combined in software to produce H and V?  I think the QFHA
> maintain better circularity at the 'horizon' (90 deg off nadir)......but
> then someone would have to build two CP antennas.........
>
>
> That was really my last comment for the night.......fun stuff....but I
> need to go to bed!
>
> -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 4/23/2018 12:21 AM, KENT BRITAIN wrote:
>
> Good luck on the circular polarization.
>
> I have tested nearly 2000 antennas at various conferences with several
> hundred
> that were suppose to be Circular Polarized.   Only about 2 in 10 meet the
> minimal
> definition of CP.    Hams can't build CP Antennas!!!!
>
> Kent WA5VJB
>
> PS  Only about 1 Helix in 10 were CP.   Just because it has a spiral
> doesn't make it CP.
>
>
> ------------------------------
> *From:* Zach Leffke via Ground-Station <ground-station at lists.
> openresearch.institute> <ground-station at lists.openresearch.institute>
> *To:* Phil Karn <karn at ka9q.net> <karn at ka9q.net>; ground-station at lists.
> openresearch.institute
> *Sent:* Sunday, April 22, 2018 9:53 PM
> *Subject:* Re: [Ground-station] Balloon Launch - experiments?
>
> 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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