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<p>To Bruce's point, the ground based reference would eliminate the
need for a freq reference onboard the payload. Would definitely
save on SWaP that way. <br>
</p>
<p>Would just have to make sure it has enough juice to be heard on
the payload. Geometry is also a major factor......particularly
with respect to antenna patterns. Depending on winds aloft,
antenna patterns, antenna pointing on the balloon/ground, and
expected travel of the payload, it might be worth having a few
beacons along the expected path of the balloon to make sure at
least one is always 'in view' of the payload that's nice and
strong. Also, if planning to 'scan' the rx freq (maybe top/bottom
halves of the 5 GHz uplink band?) then having multiple beacons on
different freqs on the ground could be useful.</p>
<p>Co-locating the beacons on chase vehicles (assumption is that
folks are chasing, probably via APRS) might simplify things a
bit. CW with callsigns to identify/differentiate between the
beacons......and since the vehicles are moving, probably want
ground recordings of the GPS coordinates of the beacons.<br>
</p>
<p>Many 'dimensions' to the tradeoff.....but overall, a bit more
complexity on the ground is probably worth the savings on SWaP on
the payload. Or if SWaP and the parts are available, might as
well use it to reduce complexity on the ground.<br>
</p>
<p><br>
</p>
<p>Also, FAA requirements need to be checked by someone.....its been
awhile since I've done one of these flights......I think I
remember something about a 6 pound limit (there is a density
requirement too...can't fly a 6 pound cannon ball). Also no
cordage with greater than 50lb test. I believe there is a
secondary cut down requirement as well (in case the balloon
doesn't pop and you hit equilibrium).</p>
<p><br>
</p>
<p>Fun Stuff!</p>
<p>-Zach<br>
</p>
<pre class="moz-signature" cols="72">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</pre>
<div class="moz-cite-prefix">On 4/22/2018 11:17 PM, Michelle
Thompson wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CACvjz2XP-Jv0n6Gznd7KJBUEYorB5ENozZj0Sec3JUV6CeeSmw@mail.gmail.com">I'll
be working at Kerry Banke's tomorrow on 10GHz and will run it by
him as well.
<div><br>
</div>
<div>We have almost all the elements on hand, including an odroid
with GNU Radio. </div>
<div><br>
</div>
<div>I can print an antenna if needed. </div>
<div><br>
</div>
<div>-mdt<br>
<br>
<div class="gmail_quote">
<div dir="ltr">On Sun, Apr 22, 2018, 20:12 Bruce Perens via
Ground-Station
<a class="moz-txt-link-rfc2396E" href="mailto:ground-station@lists.openresearch.institute"><ground-station@lists.openresearch.institute></a> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex"
id="gmail_block_quote0">I have been using Odroid rather than
Raspberry Pi cor just that reason. Pi has poor IO bandwidth.
<div><br>
</div>
<div>If frequency precision is why you'd like an oxco, would
a ground beacon that is recorded provide enough?</div>
<div><br>
<br>
<div class="gmail_quote">
<div dir="ltr">On Sun, Apr 22, 2018, 19:53 Zach Leffke
via Ground-Station
<a class="moz-txt-link-rfc2396E" href="mailto:ground-station@lists.openresearch.institute"><ground-station@lists.openresearch.institute></a>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>I like this idea......it has elements of a couple
projects that I've worked on in the last year or
so.<br>
</p>
<p>I just did similar math from a slightly different
angle......</p>
<p>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.<br>
</p>
<p>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.</p>
<p>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).<br>
</p>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<p>Any ideas on antenna types? patch array? horn?
conical spiral? circular or linear (I vote
circular on the balloon, pointed at Nadir)?<br>
</p>
<p><br>
</p>
<p>This sounds like a perfect summer project for
some of our undergrads!<br>
</p>
<p>-Zach, KJ4QLP<br>
</p>
<pre class="m_-8715101577330520922m_5315733742041589355moz-signature" cols="72">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</pre>
</div>
<div text="#000000" bgcolor="#FFFFFF">
<div
class="m_-8715101577330520922m_5315733742041589355moz-cite-prefix">On
4/22/2018 1:20 AM, Phil Karn via Ground-Station
wrote:<br>
</div>
<blockquote type="cite">
<pre>On 4/20/18 10:07, Douglas Quagliana via Ground-Station wrote:
</pre>
<blockquote type="cite">
<pre>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.
</pre>
</blockquote>
<pre>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
</pre>
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