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<p>What are you talking about Kent......you're a ham! <br>
</p>
<p>I'd wager a dollar or two that YOU can build a CP antenna at
5.66GHz!</p>
<p>hint hint........nudge nudge.........there's a particular
need........and a member of the list with a particular
capability.......</p>
<p>:-)</p>
<p><br>
</p>
<p>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......</p>
<p><br>
</p>
<p>Though that brings up another idea.....................<br>
</p>
<p>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.</p>
<p>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........</p>
<p>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......... <br>
</p>
<p><br>
</p>
<p>That was really my last comment for the night.......fun
stuff....but I need to go to bed!<br>
</p>
<p>-Zach, KJ4QLP<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 4/23/2018 12:21 AM, KENT BRITAIN
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:1725588749.2586376.1524457309194@mail.yahoo.com">
<div style="color:#000; background-color:#fff;
font-family:Helvetica Neue, Helvetica, Arial, Lucida Grande,
sans-serif;font-size:16px">
<div id="yui_3_16_0_ym19_1_1524415181240_61778">Good luck on the
circular polarization.</div>
<div id="yui_3_16_0_ym19_1_1524415181240_61777"><br>
</div>
<div id="yui_3_16_0_ym19_1_1524415181240_61776">I have tested
nearly 2000 antennas at various conferences with several
hundred</div>
<div dir="ltr" id="yui_3_16_0_ym19_1_1524415181240_61775">that
were suppose to be Circular Polarized. Only about 2 in 10
meet the minimal</div>
<div dir="ltr" id="yui_3_16_0_ym19_1_1524415181240_61738">definition
of CP. Hams can't build CP Antennas!!!!</div>
<div dir="ltr" id="yui_3_16_0_ym19_1_1524415181240_61780"><br>
</div>
<div dir="ltr" id="yui_3_16_0_ym19_1_1524415181240_61781">Kent
WA5VJB</div>
<div dir="ltr" id="yui_3_16_0_ym19_1_1524415181240_61833"><br>
</div>
<div dir="ltr" id="yui_3_16_0_ym19_1_1524415181240_61860">PS
Only about 1 Helix in 10 were CP. Just because it has a
spiral doesn't make it CP.<br>
</div>
<div id="yui_3_16_0_ym19_1_1524415181240_61737"><span></span></div>
<div class="qtdSeparateBR"
id="yui_3_16_0_ym19_1_1524415181240_61736"><br>
<br>
</div>
<div class="yahoo_quoted"
id="yui_3_16_0_ym19_1_1524415181240_61657" style="display:
block;">
<div style="font-family: Helvetica Neue, Helvetica, Arial,
Lucida Grande, sans-serif; font-size: 16px;"
id="yui_3_16_0_ym19_1_1524415181240_61656">
<div style="font-family: HelveticaNeue, Helvetica Neue,
Helvetica, Arial, Lucida Grande, sans-serif; font-size:
16px;" id="yui_3_16_0_ym19_1_1524415181240_61655">
<div dir="ltr" id="yui_3_16_0_ym19_1_1524415181240_61690">
<font id="yui_3_16_0_ym19_1_1524415181240_61735"
size="2" face="Arial">
<hr id="yui_3_16_0_ym19_1_1524415181240_61757"
size="1"> <b><span style="font-weight:bold;">From:</span></b>
Zach Leffke via Ground-Station
<a class="moz-txt-link-rfc2396E" href="mailto:ground-station@lists.openresearch.institute"><ground-station@lists.openresearch.institute></a><br>
<b><span style="font-weight: bold;">To:</span></b>
Phil Karn <a class="moz-txt-link-rfc2396E" href="mailto:karn@ka9q.net"><karn@ka9q.net></a>;
<a class="moz-txt-link-abbreviated" href="mailto:ground-station@lists.openresearch.institute">ground-station@lists.openresearch.institute</a> <br>
<b><span style="font-weight: bold;">Sent:</span></b>
Sunday, April 22, 2018 9:53 PM<br>
<b><span style="font-weight: bold;">Subject:</span></b>
Re: [Ground-station] Balloon Launch - experiments?<br>
</font> </div>
<div class="y_msg_container"
id="yui_3_16_0_ym19_1_1524415181240_61654"><br>
<div id="yiv4921132858">
<div id="yui_3_16_0_ym19_1_1524415181240_61653">
<div id="yui_3_16_0_ym19_1_1524415181240_61671">I
like this idea......it has elements of a couple
projects that I've worked on in the last year or
so.<br clear="none">
</div>
<div id="yui_3_16_0_ym19_1_1524415181240_61661">I
just did similar math from a slightly different
angle......</div>
<div id="yui_3_16_0_ym19_1_1524415181240_61652">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
clear="none">
</div>
<div id="yui_3_16_0_ym19_1_1524415181240_61734">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.</div>
<div>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 clear="none">
</div>
<div id="yui_3_16_0_ym19_1_1524415181240_61754">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.</div>
<div>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.</div>
<div>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.</div>
<div>Any ideas on antenna types? patch array? horn?
conical spiral? circular or linear (I vote
circular on the balloon, pointed at Nadir)?<br
clear="none">
</div>
<div><br clear="none">
</div>
<div>This sounds like a perfect summer project for
some of our undergrads!<br clear="none">
</div>
<div>-Zach, KJ4QLP<br clear="none">
</div>
<pre class="yiv4921132858moz-signature">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="yiv4921132858yqt2465690583"
id="yiv4921132858yqtfd27628">
<div class="yiv4921132858moz-cite-prefix">On
4/22/2018 1:20 AM, Phil Karn via Ground-Station
wrote:<br clear="none">
</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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class="yiv4921132858mimeAttachmentHeader"></fieldset>
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