<html><head></head><body><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_239338">The PCB 'Big Wheel' antennas are veterans of many balloon flights.</div><div id="yui_3_16_0_ym19_1_1524415181240_239352"><br></div><div id="yui_3_16_0_ym19_1_1524415181240_239358">At the horizon they are linear horiz polarization. But off axis they are <br></div><div dir="ltr" id="yui_3_16_0_ym19_1_1524415181240_239359">elliptically polarized. What band are you planning to use?<br> </div><div id="yui_3_16_0_ym19_1_1524415181240_239337"><span></span></div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1524415181240_239336"><br><br></div><div class="yahoo_quoted" id="yui_3_16_0_ym19_1_1524415181240_239320" 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_239319"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;" id="yui_3_16_0_ym19_1_1524415181240_239318"> <div dir="ltr" id="yui_3_16_0_ym19_1_1524415181240_239317"> <font id="yui_3_16_0_ym19_1_1524415181240_239335" face="Arial" size="2"> <hr id="yui_3_16_0_ym19_1_1524415181240_239334" size="1"> <b><span style="font-weight:bold;">From:</span></b> Phil Karn <karn@ka9q.net><br> <b><span style="font-weight: bold;">To:</span></b> Michelle Thompson <mountain.michelle@gmail.com>; Zach Leffke <zleffke@vt.edu> <br><b><span style="font-weight: bold;">Cc:</span></b> KENT BRITAIN <wa5vjb@flash.net>; "ground-station@lists.openresearch.institute" <ground-station@lists.openresearch.institute><br> <b><span style="font-weight: bold;">Sent:</span></b> Monday, April 23, 2018 11:40 AM<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_239364"><br><div dir="ltr" id="yui_3_16_0_ym19_1_1524415181240_239363">On 4/23/18 08:45, Michelle Thompson wrote:<br clear="none"><br clear="none">> There are some ambitious ideas for matching linear polarization<br clear="none">> (automated closed loop) for something that is tumbling around like a<br clear="none">> balloon payload probably would. Don't rule it out just because it sounds<br clear="none">> hard. We live in a golden age. <br clear="none"><br clear="none">Balloon payloads do swing in pitch and yaw, but not that much.<br clear="none"><br clear="none">cos(x) ~ 1 for small x.<br clear="none"><br clear="none">The real problem is that the yaw is completely uncontrolled and can<br clear="none">change rapidly. Controlling this yaw is possible but difficult (I've<br clear="none">been thinking about it for a while). But simple knowledge of yaw might<br clear="none">suffice and would be much easier -- use an IMU with AHRS software.<br clear="none"><br clear="none">This will require an omni antenna (with low gain), a steerable gain<br clear="none">antenna, or a set of directional antennas fixed to the payload and<br clear="none">selected electrically.<br clear="none"><br clear="none">In the second category, the Qualcomm Omnitracs taco-shell antenna might<br clear="none">be a very workable design. The requirements are very similar:<br clear="none">azimuth-only control would be adequate, especially with a fan beam wide<br clear="none">in elevation. Vertical polarization would be fine. If a surplus<br clear="none">Omnitracs antenna could be modified, that would be ideal. Otherwise, the<br clear="none">rotating reflector could probably be 3D printed.<br clear="none"><br clear="none">If an Omnitracs antenna could be modified for the payload, one could<br clear="none">also be used on the ground. The only drawback here is a wide fan beam in<br clear="none">elevation.<div class="yqt0772347713" id="yqtfd11176"><br clear="none"><br clear="none">Phil<br clear="none"><br clear="none"><br clear="none"></div></div><br><br></div> </div> </div> </div></div></body></html>