[Ground-station] Balloon Launch - experiments?

[KENT BRITAIN]

The PCB 'Big Wheel' antennas are veterans of many balloon flights.
At the horizon they are linear horiz polarization.  But off axis they are 
elliptically polarized.  What band are you planning to use?
 

      From: Phil Karn <karn at ka9q.net>
 To: Michelle Thompson <mountain.michelle at gmail.com>; Zach Leffke <zleffke at vt.edu> 
Cc: KENT BRITAIN <wa5vjb at flash.net>; "ground-station at lists.openresearch.institute" <ground-station at lists.openresearch.institute>
 Sent: Monday, April 23, 2018 11:40 AM
 Subject: Re: [Ground-station] Balloon Launch - experiments?
   
On 4/23/18 08:45, Michelle Thompson wrote:

> 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. 

Balloon payloads do swing in pitch and yaw, but not that much.

cos(x) ~ 1 for small x.

The real problem is that the yaw is completely uncontrolled and can
change rapidly. Controlling this yaw is possible but difficult (I've
been thinking about it for a while). But simple knowledge of yaw might
suffice and would be much easier -- use an IMU with AHRS software.

This will require an omni antenna (with low gain), a steerable gain
antenna, or a set of directional antennas fixed to the payload and
selected electrically.

In the second category, the Qualcomm Omnitracs taco-shell antenna might
be a very workable design. The requirements are very similar:
azimuth-only control would be adequate, especially with a fan beam wide
in elevation. Vertical polarization would be fine. If a surplus
Omnitracs antenna could be modified, that would be ideal. Otherwise, the
rotating reflector could probably be 3D printed.

If an Omnitracs antenna could be modified for the payload, one could
also be used on the ground. The only drawback here is a wide fan beam in
elevation.

Phil




   
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