Another day, another repost from another project I’m working on. This time, from White Star Balloons, the world’s lightest quad helix antenna.
After the scrub on the launch pad for flight attempt A, we went back to the books, to try and figure out what we could do to improve our odds the next time around. One of our biggest setbacks was the inability make an antenna suitable for our use: We needed an antenna tuned for 149 MHz, not needing a ground plane, weighing as little as possible.
After 4 tries, and some expensive test equipment, the end result was a Quadrifilar Helix antenna weighing only 80 grams!
Our ground test antenna was a 5/8ths wave whip antenna, which works well, but unfortunately needs a ground plane. Tests with both a quarter-wave dipole and a J-pole antenna were lackluster. Documentation from our satellite service provider implied that a quadrifilar helix antenna would provide the best coverage at all. While these antennas are pretty, their design and construction was voodoo magic at first.
Thanks to some design documentation here: http://jcoppens.com/ant/qfh/index.en.php and some help from the balloon community, we had some baselines for creating such an antenna. We still went through *quite* a few revisions. We went through 3 revisions that didn’t work, and one which works pretty darn well!
Here are the antennas which didn’t work: