[Ground-station] Balloon Launch - experiments?

[Phil Karn]

On 4/22/18 19:52, Zach Leffke wrote:

> 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.

64 bits/sample? That's what I use internally (two 32-bit floats) but it
seems pretty extravagant for a recording since the raw data is only 32
bits/sample.
> 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.

Fine, though cost is a moderate concern since there's a non-zero chance
of losing this thing. Like watching it splash down in the Salton Sea --
we've hit it twice in four tries so far.
>
> 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).

High altitude balloon people have a lot of experience picking GPS
receivers that work at altitude. A secondary consideration is
temperature, a unit mounted outside can easily freeze at -50C.

> Any ideas on antenna types?  patch array? horn? conical spiral? circular
> or linear (I vote circular on the balloon, pointed at Nadir)?

Depends on the pattern you want. Most of the earth you can see from a
balloon is not directly below you. (This is a way of saying that low
elevations are important if you want to cover everything within your
radio horizon.) It is difficult to make an omnidirectional antenna with
circular polarization. The one type I know of is the Lindenblad. It's
apparently popular with the FAA for ground VHF radio stations.

OTOH, maybe directionality could be useful if you use an array of
antennas and logging receivers pointing in different directions. An IMU
(perhaps backed up by a camera) can tell you where they're looking. Here
in Southern California, I'm sure the problem isn't too few signals, it's
too many...

Much
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 0xF14E4354ED463446.asc
Type: application/pgp-keys
Size: 3301 bytes
Desc: not available
URL: <http://lists.openresearch.institute/pipermail/ground-station-openresearch.institute/attachments/20180422/5ce1e5f6/attachment.key>